Attachment 261675 Details for Bug 148610 – patch for landing

[patch] patch for landing

blah.patch (text/plain), 230.96 KB, created by Filip Pizlo on 2015-09-21 12:09:40 PDT

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Creator: Filip Pizlo

Created: 2015-09-21 12:09:40 PDT

Size: 230.96 KB

patch

obsolete

>Index: Source/JavaScriptCore/ChangeLog
>===================================================================
>--- Source/JavaScriptCore/ChangeLog	(revision 190059)
>+++ Source/JavaScriptCore/ChangeLog	(working copy)
>@@ -1,3 +1,333 @@
>+2015-09-17  Filip Pizlo  <fpizlo@apple.com>
>+
>+        JSC should infer property types
>+        https://bugs.webkit.org/show_bug.cgi?id=148610
>+
>+        Reviewed by Geoffrey Garen.
>+
>+        This change brings recursive type inference to JavaScript object properties in JSC. We check that a
>+        value being stored into a property obeys a property's type before we do the store. If it doesn't,
>+        we broaden the property's type to include the new value. If optimized code was relying on the old
>+        type, we deoptimize that code.
>+
>+        The type system that this supports includes important primitive types like Int32 and Boolean. But
>+        it goes further and also includes a type kind called ObjectWithStructure, which means that we
>+        expect the property to always point to objects with a particular structure. This only works for
>+        leaf structures (i.e. structures that have a valid transition watchpoint set). Invalidation of the
>+        transition set causes the property type to become Object (meaning an object with any structure).
>+        This capability gives us recursive type inference. It's possible for an expression like "o.f.g.h"
>+        to execute without any type checks if .f and .g are both ObjectWithStructure.
>+
>+        The type inference of a property is tracked by an InferredType instance, which is a JSCell. This
>+        means that it manages its own memory. That's convenient. For example, when the DFG is interested in
>+        one of these, it can just list the InferredType as a weak reference in addition to setting a
>+        watchpoint. This ensures that even if the InferredType is dropped by the owning structure, the DFG
>+        won't read a dangling pointer. A mapping from property name to InferredType is implemented by
>+        InferredTypeTable, which is also a JSCell. Each Structure may point to some InferredTypeTable.
>+
>+        This feature causes programs to be happier (run faster without otherwise doing bad things like
>+        using lots of memory) when four conditions hold:
>+
>+        1) A property converges to one of the types that we support.
>+        2) The property is loaded from more frequently than it is stored to.
>+        3) The stores are all cached, so that we statically emit a type check.
>+        4) We don't allocate a lot of meta-data for the property's type.
>+
>+        We maximize the likelihood of (1) by having a rich type system. But having a rich type system means
>+        that a reflective put to a property has to have a large switch over the inferred type to decide how
>+        to do the type check. That's why we need (3). We ensure (3) by having every reflective property
>+        store (i.e. putDirectInternal in any context that isn't PutById) force the inferred type to become
>+        Top. We don't really worry about ensuring (2); this is statistically true for most programs
>+        already.
>+
>+        Probably the most subtle trickery goes into (4). Logically we'd like to say that each
>+        (Structure, Property) maps to its own InferredType. If structure S1 has a transition edge to S2,
>+        then we could ensure that the InferredType I1 where (S1, Property)->I1 has a data flow constraint
>+        to I2 where (S2, Property)->I2. That would work, but it would involve a lot of memory. And when I1
>+        gets invalidated in some way, it would have to tell I2 about it, and then I2 might tell other
>+        InferredType objects downstream. That's madness. So, the first major compromise that we make here
>+        is to say that if some property has some InferredType at some Structure, then anytime we
>+        transition from that Structure, the new Structure shares the same InferredType for that property.
>+        This unifies the type of the property over the entire transition tree starting at the Structure at
>+        which the property was added. But this would still mean that each Structure would have its own
>+        InferredTypeTable. We don't want that because experience with PropertyTable shows that this can be
>+        a major memory hog. So, we don't create an InferredTypeTable until someone adds a property that is
>+        subject to type inference (i.e. it was added non-reflectively), and we share that InferredTypeTable
>+        with the entire structure transition tree rooted at the Structure that had the first inferred
>+        property. We also drop the InferredTypeTable anytime that we do a dictionary transition, and we
>+        don't allow further property type inference if a structure had ever been a dictionary.
>+
>+        This is a 3% speed-up on Octane and a 12% speed-up on Kraken on my setup. It's not a significant
>+        slow-down on any benchmark I ran.
>+
>+        * CMakeLists.txt:
>+        * JavaScriptCore.vcxproj/JavaScriptCore.vcxproj:
>+        * JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters:
>+        * JavaScriptCore.xcodeproj/project.pbxproj:
>+        * assembler/MacroAssemblerARM64.h:
>+        (JSC::MacroAssemblerARM64::branchTest64):
>+        * assembler/MacroAssemblerX86_64.h:
>+        (JSC::MacroAssemblerX86_64::branchTest64):
>+        (JSC::MacroAssemblerX86_64::test64):
>+        * bytecode/PolymorphicAccess.cpp:
>+        (JSC::AccessCase::generate):
>+        * bytecode/PutByIdFlags.cpp:
>+        (WTF::printInternal):
>+        * bytecode/PutByIdFlags.h:
>+        (JSC::encodeStructureID):
>+        (JSC::decodeStructureID):
>+        * bytecode/PutByIdStatus.cpp:
>+        (JSC::PutByIdStatus::computeFromLLInt):
>+        (JSC::PutByIdStatus::computeFor):
>+        (JSC::PutByIdStatus::computeForStubInfo):
>+        * bytecode/PutByIdVariant.cpp:
>+        (JSC::PutByIdVariant::operator=):
>+        (JSC::PutByIdVariant::replace):
>+        (JSC::PutByIdVariant::transition):
>+        (JSC::PutByIdVariant::setter):
>+        (JSC::PutByIdVariant::attemptToMerge):
>+        (JSC::PutByIdVariant::dumpInContext):
>+        * bytecode/PutByIdVariant.h:
>+        (JSC::PutByIdVariant::newStructure):
>+        (JSC::PutByIdVariant::requiredType):
>+        * bytecode/UnlinkedCodeBlock.h:
>+        (JSC::UnlinkedInstruction::UnlinkedInstruction):
>+        * bytecode/Watchpoint.h:
>+        (JSC::InlineWatchpointSet::touch):
>+        (JSC::InlineWatchpointSet::isBeingWatched):
>+        * bytecompiler/BytecodeGenerator.cpp:
>+        (JSC::BytecodeGenerator::addConstantValue):
>+        (JSC::BytecodeGenerator::emitPutById):
>+        (JSC::BytecodeGenerator::emitDirectPutById):
>+        * dfg/DFGAbstractInterpreter.h:
>+        (JSC::DFG::AbstractInterpreter::filter):
>+        (JSC::DFG::AbstractInterpreter::filterByValue):
>+        * dfg/DFGAbstractInterpreterInlines.h:
>+        (JSC::DFG::AbstractInterpreter<AbstractStateType>::executeEffects):
>+        (JSC::DFG::AbstractInterpreter<AbstractStateType>::filter):
>+        * dfg/DFGAbstractValue.cpp:
>+        (JSC::DFG::AbstractValue::setType):
>+        (JSC::DFG::AbstractValue::set):
>+        (JSC::DFG::AbstractValue::fixTypeForRepresentation):
>+        (JSC::DFG::AbstractValue::mergeOSREntryValue):
>+        (JSC::DFG::AbstractValue::isType):
>+        (JSC::DFG::AbstractValue::filter):
>+        (JSC::DFG::AbstractValue::filterValueByType):
>+        * dfg/DFGAbstractValue.h:
>+        (JSC::DFG::AbstractValue::setType):
>+        (JSC::DFG::AbstractValue::isType):
>+        (JSC::DFG::AbstractValue::validate):
>+        * dfg/DFGByteCodeParser.cpp:
>+        (JSC::DFG::ByteCodeParser::handleConstantInternalFunction):
>+        (JSC::DFG::ByteCodeParser::handleGetByOffset):
>+        (JSC::DFG::ByteCodeParser::handlePutByOffset):
>+        (JSC::DFG::ByteCodeParser::load):
>+        (JSC::DFG::ByteCodeParser::store):
>+        (JSC::DFG::ByteCodeParser::handleGetById):
>+        (JSC::DFG::ByteCodeParser::handlePutById):
>+        * dfg/DFGClobbersExitState.cpp:
>+        (JSC::DFG::clobbersExitState):
>+        * dfg/DFGConstantFoldingPhase.cpp:
>+        (JSC::DFG::ConstantFoldingPhase::foldConstants):
>+        (JSC::DFG::ConstantFoldingPhase::emitGetByOffset):
>+        (JSC::DFG::ConstantFoldingPhase::emitPutByOffset):
>+        (JSC::DFG::ConstantFoldingPhase::addBaseCheck):
>+        * dfg/DFGDesiredInferredType.h: Added.
>+        (JSC::DFG::DesiredInferredType::DesiredInferredType):
>+        (JSC::DFG::DesiredInferredType::operator bool):
>+        (JSC::DFG::DesiredInferredType::object):
>+        (JSC::DFG::DesiredInferredType::expected):
>+        (JSC::DFG::DesiredInferredType::isStillValid):
>+        (JSC::DFG::DesiredInferredType::add):
>+        (JSC::DFG::DesiredInferredType::operator==):
>+        (JSC::DFG::DesiredInferredType::operator!=):
>+        (JSC::DFG::DesiredInferredType::isHashTableDeletedValue):
>+        (JSC::DFG::DesiredInferredType::hash):
>+        (JSC::DFG::DesiredInferredType::dumpInContext):
>+        (JSC::DFG::DesiredInferredType::dump):
>+        (JSC::DFG::DesiredInferredTypeHash::hash):
>+        (JSC::DFG::DesiredInferredTypeHash::equal):
>+        * dfg/DFGDesiredWatchpoints.cpp:
>+        (JSC::DFG::AdaptiveStructureWatchpointAdaptor::add):
>+        (JSC::DFG::InferredTypeAdaptor::add):
>+        (JSC::DFG::DesiredWatchpoints::DesiredWatchpoints):
>+        (JSC::DFG::DesiredWatchpoints::~DesiredWatchpoints):
>+        (JSC::DFG::DesiredWatchpoints::addLazily):
>+        (JSC::DFG::DesiredWatchpoints::consider):
>+        (JSC::DFG::DesiredWatchpoints::reallyAdd):
>+        (JSC::DFG::DesiredWatchpoints::areStillValid):
>+        (JSC::DFG::DesiredWatchpoints::dumpInContext):
>+        * dfg/DFGDesiredWatchpoints.h:
>+        (JSC::DFG::AdaptiveStructureWatchpointAdaptor::dumpInContext):
>+        (JSC::DFG::InferredTypeAdaptor::hasBeenInvalidated):
>+        (JSC::DFG::InferredTypeAdaptor::dumpInContext):
>+        (JSC::DFG::DesiredWatchpoints::isWatched):
>+        * dfg/DFGFixupPhase.cpp:
>+        (JSC::DFG::FixupPhase::fixupNode):
>+        * dfg/DFGGraph.cpp:
>+        (JSC::DFG::Graph::dump):
>+        (JSC::DFG::Graph::isSafeToLoad):
>+        (JSC::DFG::Graph::inferredTypeFor):
>+        (JSC::DFG::Graph::livenessFor):
>+        (JSC::DFG::Graph::tryGetConstantProperty):
>+        (JSC::DFG::Graph::inferredValueForProperty):
>+        (JSC::DFG::Graph::tryGetConstantClosureVar):
>+        * dfg/DFGGraph.h:
>+        (JSC::DFG::Graph::registerInferredType):
>+        (JSC::DFG::Graph::inferredTypeForProperty):
>+        * dfg/DFGInferredTypeCheck.cpp: Added.
>+        (JSC::DFG::insertInferredTypeCheck):
>+        * dfg/DFGInferredTypeCheck.h: Added.
>+        * dfg/DFGNode.h:
>+        * dfg/DFGObjectAllocationSinkingPhase.cpp:
>+        * dfg/DFGPropertyTypeKey.h: Added.
>+        (JSC::DFG::PropertyTypeKey::PropertyTypeKey):
>+        (JSC::DFG::PropertyTypeKey::operator bool):
>+        (JSC::DFG::PropertyTypeKey::structure):
>+        (JSC::DFG::PropertyTypeKey::uid):
>+        (JSC::DFG::PropertyTypeKey::operator==):
>+        (JSC::DFG::PropertyTypeKey::operator!=):
>+        (JSC::DFG::PropertyTypeKey::hash):
>+        (JSC::DFG::PropertyTypeKey::isHashTableDeletedValue):
>+        (JSC::DFG::PropertyTypeKey::dumpInContext):
>+        (JSC::DFG::PropertyTypeKey::dump):
>+        (JSC::DFG::PropertyTypeKey::deletedUID):
>+        (JSC::DFG::PropertyTypeKeyHash::hash):
>+        (JSC::DFG::PropertyTypeKeyHash::equal):
>+        * dfg/DFGSafeToExecute.h:
>+        (JSC::DFG::SafeToExecuteEdge::operator()):
>+        (JSC::DFG::safeToExecute):
>+        * dfg/DFGSpeculativeJIT.cpp:
>+        (JSC::DFG::SpeculativeJIT::compileTypeOf):
>+        (JSC::DFG::SpeculativeJIT::compileCheckStructure):
>+        (JSC::DFG::SpeculativeJIT::compileAllocatePropertyStorage):
>+        (JSC::DFG::SpeculativeJIT::speculateCell):
>+        (JSC::DFG::SpeculativeJIT::speculateCellOrOther):
>+        (JSC::DFG::SpeculativeJIT::speculateObject):
>+        (JSC::DFG::SpeculativeJIT::speculate):
>+        * dfg/DFGSpeculativeJIT.h:
>+        * dfg/DFGSpeculativeJIT32_64.cpp:
>+        (JSC::DFG::SpeculativeJIT::compile):
>+        * dfg/DFGSpeculativeJIT64.cpp:
>+        (JSC::DFG::SpeculativeJIT::compile):
>+        * dfg/DFGStoreBarrierInsertionPhase.cpp:
>+        * dfg/DFGStructureAbstractValue.h:
>+        (JSC::DFG::StructureAbstractValue::at):
>+        (JSC::DFG::StructureAbstractValue::operator[]):
>+        (JSC::DFG::StructureAbstractValue::onlyStructure):
>+        (JSC::DFG::StructureAbstractValue::forEach):
>+        * dfg/DFGUseKind.cpp:
>+        (WTF::printInternal):
>+        * dfg/DFGUseKind.h:
>+        (JSC::DFG::typeFilterFor):
>+        * dfg/DFGValidate.cpp:
>+        (JSC::DFG::Validate::validate):
>+        * ftl/FTLCapabilities.cpp:
>+        (JSC::FTL::canCompile):
>+        * ftl/FTLLowerDFGToLLVM.cpp:
>+        (JSC::FTL::DFG::LowerDFGToLLVM::compileCheckStructure):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::compileCheckCell):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::compileMultiPutByOffset):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::numberOrNotCellToInt32):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::checkInferredType):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::loadProperty):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::speculate):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::speculateCell):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::speculateCellOrOther):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::speculateMachineInt):
>+        (JSC::FTL::DFG::LowerDFGToLLVM::appendOSRExit):
>+        * jit/AssemblyHelpers.cpp:
>+        (JSC::AssemblyHelpers::decodedCodeMapFor):
>+        (JSC::AssemblyHelpers::branchIfNotType):
>+        (JSC::AssemblyHelpers::purifyNaN):
>+        * jit/AssemblyHelpers.h:
>+        (JSC::AssemblyHelpers::branchIfEqual):
>+        (JSC::AssemblyHelpers::branchIfNotCell):
>+        (JSC::AssemblyHelpers::branchIfCell):
>+        (JSC::AssemblyHelpers::branchIfNotOther):
>+        (JSC::AssemblyHelpers::branchIfInt32):
>+        (JSC::AssemblyHelpers::branchIfNotInt32):
>+        (JSC::AssemblyHelpers::branchIfNumber):
>+        (JSC::AssemblyHelpers::branchIfNotNumber):
>+        (JSC::AssemblyHelpers::branchIfEmpty):
>+        (JSC::AssemblyHelpers::branchStructure):
>+        * jit/Repatch.cpp:
>+        (JSC::tryCachePutByID):
>+        * llint/LLIntSlowPaths.cpp:
>+        (JSC::LLInt::LLINT_SLOW_PATH_DECL):
>+        * llint/LowLevelInterpreter.asm:
>+        * llint/LowLevelInterpreter32_64.asm:
>+        * llint/LowLevelInterpreter64.asm:
>+        * runtime/InferredType.cpp: Added.
>+        (JSC::InferredType::create):
>+        (JSC::InferredType::destroy):
>+        (JSC::InferredType::createStructure):
>+        (JSC::InferredType::visitChildren):
>+        (JSC::InferredType::kindForFlags):
>+        (JSC::InferredType::Descriptor::forValue):
>+        (JSC::InferredType::Descriptor::forFlags):
>+        (JSC::InferredType::Descriptor::putByIdFlags):
>+        (JSC::InferredType::Descriptor::merge):
>+        (JSC::InferredType::Descriptor::removeStructure):
>+        (JSC::InferredType::Descriptor::subsumes):
>+        (JSC::InferredType::Descriptor::dumpInContext):
>+        (JSC::InferredType::Descriptor::dump):
>+        (JSC::InferredType::InferredType):
>+        (JSC::InferredType::~InferredType):
>+        (JSC::InferredType::canWatch):
>+        (JSC::InferredType::addWatchpoint):
>+        (JSC::InferredType::dump):
>+        (JSC::InferredType::willStoreValueSlow):
>+        (JSC::InferredType::makeTopSlow):
>+        (JSC::InferredType::set):
>+        (JSC::InferredType::removeStructure):
>+        (JSC::InferredType::InferredStructureWatchpoint::fireInternal):
>+        (JSC::InferredType::InferredStructureFinalizer::finalizeUnconditionally):
>+        (JSC::InferredType::InferredStructure::InferredStructure):
>+        (WTF::printInternal):
>+        * runtime/InferredType.h: Added.
>+        * runtime/InferredTypeTable.cpp: Added.
>+        (JSC::InferredTypeTable::create):
>+        (JSC::InferredTypeTable::destroy):
>+        (JSC::InferredTypeTable::createStructure):
>+        (JSC::InferredTypeTable::visitChildren):
>+        (JSC::InferredTypeTable::get):
>+        (JSC::InferredTypeTable::willStoreValue):
>+        (JSC::InferredTypeTable::makeTop):
>+        (JSC::InferredTypeTable::InferredTypeTable):
>+        (JSC::InferredTypeTable::~InferredTypeTable):
>+        * runtime/InferredTypeTable.h: Added.
>+        * runtime/JSObject.h:
>+        (JSC::JSObject::putDirectInternal):
>+        (JSC::JSObject::putDirectWithoutTransition):
>+        * runtime/Structure.cpp:
>+        (JSC::Structure::materializePropertyMap):
>+        (JSC::Structure::addPropertyTransition):
>+        (JSC::Structure::removePropertyTransition):
>+        (JSC::Structure::startWatchingInternalProperties):
>+        (JSC::Structure::willStoreValueSlow):
>+        (JSC::Structure::visitChildren):
>+        (JSC::Structure::prototypeChainMayInterceptStoreTo):
>+        * runtime/Structure.h:
>+        (JSC::PropertyMapEntry::PropertyMapEntry):
>+        * runtime/StructureInlines.h:
>+        (JSC::Structure::get):
>+        * runtime/VM.cpp:
>+        (JSC::VM::VM):
>+        * runtime/VM.h:
>+        * tests/stress/prop-type-boolean-then-string.js: Added.
>+        * tests/stress/prop-type-int32-then-string.js: Added.
>+        * tests/stress/prop-type-number-then-string.js: Added.
>+        * tests/stress/prop-type-object-or-other-then-string.js: Added.
>+        * tests/stress/prop-type-object-then-string.js: Added.
>+        * tests/stress/prop-type-other-then-string.js: Added.
>+        * tests/stress/prop-type-string-then-object.js: Added.
>+        * tests/stress/prop-type-struct-or-other-then-string.js: Added.
>+        * tests/stress/prop-type-struct-then-object.js: Added.
>+        * tests/stress/prop-type-struct-then-object-opt.js: Added.
>+        * tests/stress/prop-type-struct-then-object-opt-fold.js: Added.
>+        * tests/stress/prop-type-struct-then-object-opt-multi.js: Added.
>+
> 2015-09-20  Sukolsak Sakshuwong  <sukolsak@gmail.com>
> 
>         Implement SetLocal and SetGlobal expressions in WebAssembly
>Index: Source/JavaScriptCore/CMakeLists.txt
>===================================================================
>--- Source/JavaScriptCore/CMakeLists.txt	(revision 190059)
>+++ Source/JavaScriptCore/CMakeLists.txt	(working copy)
>@@ -192,6 +192,7 @@ set(JavaScriptCore_SOURCES
>     dfg/DFGGraphSafepoint.cpp
>     dfg/DFGHeapLocation.cpp
>     dfg/DFGInPlaceAbstractState.cpp
>+    dfg/DFGInferredTypeCheck.cpp
>     dfg/DFGInsertionSet.cpp
>     dfg/DFGIntegerCheckCombiningPhase.cpp
>     dfg/DFGIntegerRangeOptimizationPhase.cpp
>@@ -501,6 +502,8 @@ set(JavaScriptCore_RUNTIME_SOURCES
>     runtime/Identifier.cpp
>     runtime/IndexingType.cpp
>     runtime/InferredValue.cpp
>+    runtime/InferredType.cpp
>+    runtime/InferredTypeTable.cpp
>     runtime/InitializeThreading.cpp
>     runtime/InspectorInstrumentationObject.cpp
>     runtime/InternalFunction.cpp
>Index: Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj
>===================================================================
>--- Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj	(revision 190059)
>+++ Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj	(working copy)
>@@ -428,6 +428,7 @@
>     <ClCompile Include="..\dfg\DFGGraphSafepoint.cpp" />
>     <ClCompile Include="..\dfg\DFGHeapLocation.cpp" />
>     <ClCompile Include="..\dfg\DFGInPlaceAbstractState.cpp" />
>+    <ClCompile Include="..\dfg\DFGInferredTypeCheck.cpp" />
>     <ClCompile Include="..\dfg\DFGInsertionSet.cpp" />
>     <ClCompile Include="..\dfg\DFGIntegerCheckCombiningPhase.cpp" />
>     <ClCompile Include="..\dfg\DFGIntegerRangeOptimizationPhase.cpp" />
>@@ -750,6 +751,8 @@
>     <ClCompile Include="..\runtime\Identifier.cpp" />
>     <ClCompile Include="..\runtime\IndexingType.cpp" />
>     <ClCompile Include="..\runtime\InferredValue.cpp" />
>+    <ClCompile Include="..\runtime\InferredType.cpp" />
>+    <ClCompile Include="..\runtime\InferredTypeTable.cpp" />
>     <ClCompile Include="..\runtime\InitializeThreading.cpp" />
>     <ClCompile Include="..\runtime\InspectorInstrumentationObject.cpp" />
>     <ClCompile Include="..\runtime\InternalFunction.cpp" />
>@@ -1137,6 +1140,7 @@
>     <ClInclude Include="..\dfg\DFGCSEPhase.h" />
>     <ClInclude Include="..\dfg\DFGDCEPhase.h" />
>     <ClInclude Include="..\dfg\DFGDesiredIdentifiers.h" />
>+    <ClInclude Include="..\dfg\DFGDesiredInferredType.h" />
>     <ClInclude Include="..\dfg\DFGDesiredTransitions.h" />
>     <ClInclude Include="..\dfg\DFGDesiredWatchpoints.h" />
>     <ClInclude Include="..\dfg\DFGDesiredWeakReferences.h" />
>@@ -1166,6 +1170,7 @@
>     <ClInclude Include="..\dfg\DFGGraphSafepoint.h" />
>     <ClInclude Include="..\dfg\DFGHeapLocation.h" />
>     <ClInclude Include="..\dfg\DFGInPlaceAbstractState.h" />
>+    <ClInclude Include="..\dfg\DFGInferredTypeCheck.h" />
>     <ClInclude Include="..\dfg\DFGInsertionSet.h" />
>     <ClInclude Include="..\dfg\DFGIntegerCheckCombiningPhase.h" />
>     <ClInclude Include="..\dfg\DFGIntegerRangeOptimizationPhase.h" />
>@@ -1217,6 +1222,7 @@
>     <ClInclude Include="..\dfg\DFGPredictionInjectionPhase.h" />
>     <ClInclude Include="..\dfg\DFGPredictionPropagationPhase.h" />
>     <ClInclude Include="..\dfg\DFGPromotedHeapLocation.h" />
>+    <ClInclude Include="..\dfg\DFGPropertyTypeKey.h" />
>     <ClInclude Include="..\dfg\DFGPureValue.h" />
>     <ClInclude Include="..\dfg\DFGPutStackSinkingPhase.h" />
>     <ClInclude Include="..\dfg\DFGRegisterBank.h" />
>@@ -1591,6 +1597,8 @@
>     <ClInclude Include="..\runtime\IndexingHeaderInlines.h" />
>     <ClInclude Include="..\runtime\IndexingType.h" />
>     <ClInclude Include="..\runtime\InferredValue.h" />
>+    <ClInclude Include="..\runtime\InferredType.h" />
>+    <ClInclude Include="..\runtime\InferredTypeTable.h" />
>     <ClInclude Include="..\runtime\InitializeThreading.h" />
>     <ClInclude Include="..\runtime\Int16Array.h" />
>     <ClInclude Include="..\runtime\Int32Array.h" />
>Index: Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters
>===================================================================
>--- Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters	(revision 190059)
>+++ Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters	(working copy)
>@@ -1269,6 +1269,9 @@
>     <ClCompile Include="..\dfg\DFGInPlaceAbstractState.cpp">
>       <Filter>dfg</Filter>
>     </ClCompile>
>+    <ClCompile Include="..\dfg\DFGInferredTypeCheck.cpp">
>+      <Filter>dfg</Filter>
>+    </ClCompile>
>     <ClCompile Include="..\dfg\DFGInvalidationPointInjectionPhase.cpp">
>       <Filter>dfg</Filter>
>     </ClCompile>
>@@ -1866,6 +1869,8 @@
>     <ClCompile Include="..\runtime\DirectArguments.cpp" />
>     <ClCompile Include="..\runtime\DirectArgumentsOffset.cpp" />
>     <ClCompile Include="..\runtime\InferredValue.cpp" />
>+    <ClCompile Include="..\runtime\InferredType.cpp" />
>+    <ClCompile Include="..\runtime\InferredTypeTable.cpp" />
>     <ClCompile Include="..\runtime\ScopeOffset.cpp" />
>     <ClCompile Include="..\runtime\ScopedArguments.cpp" />
>     <ClCompile Include="..\runtime\ScopedArgumentsTable.cpp" />
>@@ -3676,6 +3681,9 @@
>     <ClInclude Include="..\dfg\DFGDesiredIdentifiers.h">
>       <Filter>dfg</Filter>
>     </ClInclude>
>+    <ClInclude Include="..\dfg\DFGDesiredInferredType.h">
>+      <Filter>dfg</Filter>
>+    </ClInclude>
>     <ClInclude Include="..\dfg\DFGDesiredTransitions.h">
>       <Filter>dfg</Filter>
>     </ClInclude>
>@@ -3742,6 +3750,9 @@
>     <ClInclude Include="..\dfg\DFGInPlaceAbstractState.h">
>       <Filter>dfg</Filter>
>     </ClInclude>
>+    <ClInclude Include="..\dfg\DFGInferredTypeCheck.h">
>+      <Filter>dfg</Filter>
>+    </ClInclude>
>     <ClInclude Include="..\dfg\DFGInvalidationPointInjectionPhase.h">
>       <Filter>dfg</Filter>
>     </ClInclude>
>@@ -4424,6 +4435,9 @@
>     <ClInclude Include="..\dfg\DFGPromotedHeapLocation.h">
>       <Filter>dfg</Filter>
>     </ClInclude>
>+    <ClInclude Include="..\dfg\DFGPropertyTypeKey.h">
>+      <Filter>dfg</Filter>
>+    </ClInclude>
>     <ClInclude Include="..\ftl\FTLExitPropertyValue.h">
>       <Filter>ftl</Filter>
>     </ClInclude>
>@@ -4467,6 +4481,8 @@
>     <ClInclude Include="..\runtime\GenericArgumentsInlines.h" />
>     <ClInclude Include="..\runtime\GenericOffset.h" />
>     <ClInclude Include="..\runtime\InferredValue.h" />
>+    <ClInclude Include="..\runtime\InferredType.h" />
>+    <ClInclude Include="..\runtime\InferredTypeTable.h" />
>     <ClInclude Include="..\runtime\ScopeOffset.h" />
>     <ClInclude Include="..\runtime\ScopedArguments.h" />
>     <ClInclude Include="..\runtime\ScopedArgumentsTable.h" />
>Index: Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
>===================================================================
>--- Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj	(revision 190059)
>+++ Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj	(working copy)
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>@@ -4671,8 +4687,8 @@
> 				BC02E98B0E183E38000F9297 /* ErrorInstance.h */,
> 				BC02E9060E1839DB000F9297 /* ErrorPrototype.cpp */,
> 				BC02E9070E1839DB000F9297 /* ErrorPrototype.h */,
>-				FE1C0FFC1B193E9800B53FCA /* Exception.h */,
> 				FE1C0FFE1B194FD100B53FCA /* Exception.cpp */,
>+				FE1C0FFC1B193E9800B53FCA /* Exception.h */,
> 				0F12DE0D1979D5FD0006FF4E /* ExceptionFuzz.cpp */,
> 				0F12DE0E1979D5FD0006FF4E /* ExceptionFuzz.h */,
> 				1429D8770ED21ACD00B89619 /* ExceptionHelpers.cpp */,
>@@ -4706,6 +4722,10 @@
> 				0FB7F38E15ED8E3800F167B2 /* IndexingHeaderInlines.h */,
> 				0F13E04C16164A1B00DC8DE7 /* IndexingType.cpp */,
> 				0FB7F38F15ED8E3800F167B2 /* IndexingType.h */,
>+				0F0A75201B94BFA900110660 /* InferredType.cpp */,
>+				0F0A75211B94BFA900110660 /* InferredType.h */,
>+				0FFC920F1B94D4DF0071DD66 /* InferredTypeTable.cpp */,
>+				0FFC92101B94D4DF0071DD66 /* InferredTypeTable.h */,
> 				0FF8BDE81AD4CF7100DFE884 /* InferredValue.cpp */,
> 				0FF8BDE91AD4CF7100DFE884 /* InferredValue.h */,
> 				E178636C0D9BEEC300D74E75 /* InitializeThreading.cpp */,
>@@ -4756,10 +4776,10 @@
> 				0F2B66BC17B6B5AB00A7AE3F /* JSArrayBufferViewInlines.h */,
> 				A7BDAEC417F4EA1400F6140C /* JSArrayIterator.cpp */,
> 				A7BDAEC517F4EA1400F6140C /* JSArrayIterator.h */,
>-				86FA9E8F142BBB2D001773B7 /* JSBoundFunction.cpp */,
>-				86FA9E90142BBB2E001773B7 /* JSBoundFunction.h */,
> 				8B0F424B1ABD6DE2003917EA /* JSArrowFunction.cpp */,
> 				8B0F424A1ABD6D2F003917EA /* JSArrowFunction.h */,
>+				86FA9E8F142BBB2D001773B7 /* JSBoundFunction.cpp */,
>+				86FA9E90142BBB2E001773B7 /* JSBoundFunction.h */,
> 				657CF45619BF6662004ACBF2 /* JSCallee.cpp */,
> 				657CF45719BF6662004ACBF2 /* JSCallee.h */,
> 				BC7F8FBA0E19D1EF008632C0 /* JSCell.cpp */,
>@@ -5062,9 +5082,9 @@
> 				0FE050241AA9095600D33B33 /* VarOffset.h */,
> 				E18E3A570DF9278C00D90B34 /* VM.cpp */,
> 				E18E3A560DF9278C00D90B34 /* VM.h */,
>-				FE90BB3A1B7CF64E006B3F03 /* VMInlines.h */,
> 				FE5932A5183C5A2600A1ECCC /* VMEntryScope.cpp */,
> 				FE5932A6183C5A2600A1ECCC /* VMEntryScope.h */,
>+				FE90BB3A1B7CF64E006B3F03 /* VMInlines.h */,
> 				FED94F2B171E3E2300BE77A4 /* Watchdog.cpp */,
> 				FED94F2C171E3E2300BE77A4 /* Watchdog.h */,
> 				14BFCE6810CDB1FC00364CCE /* WeakGCMap.h */,
>@@ -5216,6 +5236,7 @@
> 				0F2FC77116E12F6F0038D976 /* DFGDCEPhase.h */,
> 				0F8F2B97172F04FD007DBDA5 /* DFGDesiredIdentifiers.cpp */,
> 				0F8F2B98172F04FD007DBDA5 /* DFGDesiredIdentifiers.h */,
>+				0FFC92131B94E83E0071DD66 /* DFGDesiredInferredType.h */,
> 				C2C0F7CB17BBFC5B00464FE4 /* DFGDesiredTransitions.cpp */,
> 				C2C0F7CC17BBFC5B00464FE4 /* DFGDesiredTransitions.h */,
> 				0FE853491723CDA500B618F5 /* DFGDesiredWatchpoints.cpp */,
>@@ -5262,6 +5283,8 @@
> 				0F2FCCF318A60070001A27F8 /* DFGGraphSafepoint.h */,
> 				0FB1765C196B8F9E0091052A /* DFGHeapLocation.cpp */,
> 				0FB1765D196B8F9E0091052A /* DFGHeapLocation.h */,
>+				0FC841661BA8C3210061837D /* DFGInferredTypeCheck.cpp */,
>+				0FC841671BA8C3210061837D /* DFGInferredTypeCheck.h */,
> 				0FB14E201812570B009B6B4D /* DFGInlineCacheWrapper.h */,
> 				0FB14E2218130955009B6B4D /* DFGInlineCacheWrapperInlines.h */,
> 				A704D90017A0BAA8006BA554 /* DFGInPlaceAbstractState.cpp */,
>@@ -5294,10 +5317,10 @@
> 				0FB4B51D16B62772003F696B /* DFGLongLivedState.h */,
> 				A767B5B317A0B9650063D940 /* DFGLoopPreHeaderCreationPhase.cpp */,
> 				A767B5B417A0B9650063D940 /* DFGLoopPreHeaderCreationPhase.h */,
>-				0F5874EB194FEB1200AAB2C1 /* DFGMayExit.cpp */,
>-				0F5874EC194FEB1200AAB2C1 /* DFGMayExit.h */,
> 				79F8FC1C1B9FED0F00CA66AB /* DFGMaximalFlushInsertionPhase.cpp */,
> 				79F8FC1D1B9FED0F00CA66AB /* DFGMaximalFlushInsertionPhase.h */,
>+				0F5874EB194FEB1200AAB2C1 /* DFGMayExit.cpp */,
>+				0F5874EC194FEB1200AAB2C1 /* DFGMayExit.h */,
> 				0F1725FE1B48719A00AC3A55 /* DFGMinifiedGraph.cpp */,
> 				0F2BDC3D1522801700CD8910 /* DFGMinifiedGraph.h */,
> 				0FB4B51016B3A964003F696B /* DFGMinifiedID.h */,
>@@ -5365,6 +5388,7 @@
> 				0F3E01A919D353A500F61B7F /* DFGPrePostNumbering.h */,
> 				0F2B9CE019D0BA7D00B1D1B5 /* DFGPromotedHeapLocation.cpp */,
> 				0F2B9CE119D0BA7D00B1D1B5 /* DFGPromotedHeapLocation.h */,
>+				0FFC92151B94FB3E0071DD66 /* DFGPropertyTypeKey.h */,
> 				0FB1765E196B8F9E0091052A /* DFGPureValue.cpp */,
> 				0FB1765F196B8F9E0091052A /* DFGPureValue.h */,
> 				0F3A1BF71A9ECB7D000DE01A /* DFGPutStackSinkingPhase.cpp */,
>@@ -5957,6 +5981,7 @@
> 				FE5068651AE246390009DAB7 /* DeferredSourceDump.h in Headers */,
> 				C442CB251A6CDB8C005D3D7C /* JSInputs.json in Headers */,
> 				FE1C0FFD1B193E9800B53FCA /* Exception.h in Headers */,
>+				0FFC92141B94E83E0071DD66 /* DFGDesiredInferredType.h in Headers */,
> 				79EE0C001B4AFB85000385C9 /* VariableEnvironment.h in Headers */,
> 				52678F911A04177C006A306D /* ControlFlowProfiler.h in Headers */,
> 				52678F8F1A031009006A306D /* BasicBlockLocation.h in Headers */,
>@@ -6071,6 +6096,7 @@
> 				0FBD7E691447999600481315 /* CodeOrigin.h in Headers */,
> 				7B0247591B868EB700542440 /* WASMFunctionSyntaxChecker.h in Headers */,
> 				0F21C27D14BE727A00ADC64B /* CodeSpecializationKind.h in Headers */,
>+				0F0A75231B94BFA900110660 /* InferredType.h in Headers */,
> 				0F0B83A714BCF50700885B4F /* CodeType.h in Headers */,
> 				BC18C3F30E16F5CD00B34460 /* CommonIdentifiers.h in Headers */,
> 				709FB86C1AE335C60039D069 /* WeakSetPrototype.h in Headers */,
>@@ -6351,12 +6377,14 @@
> 				0F25F1B4181635F300522F39 /* FTLSlowPathCallKey.h in Headers */,
> 				0F9D339B1803ADB70073C2BC /* FTLStackMaps.h in Headers */,
> 				0FEA0A12170513DB00BB722C /* FTLState.h in Headers */,
>+				0FC841691BA8C3210061837D /* DFGInferredTypeCheck.h in Headers */,
> 				A7FCC26D17A0B6AA00786D1A /* FTLSwitchCase.h in Headers */,
> 				0F235BE217178E1C00690C7F /* FTLThunks.h in Headers */,
> 				0FEA0A201708B00700BB722C /* FTLTypedPointer.h in Headers */,
> 				0F6B1CC61862C47800845D97 /* FTLUnwindInfo.h in Headers */,
> 				0FDB2CCA173DA523007B3C1B /* FTLValueFromBlock.h in Headers */,
> 				0FE7211E193B9C590031F6ED /* DFGTransition.h in Headers */,
>+				0FFC92121B94D4DF0071DD66 /* InferredTypeTable.h in Headers */,
> 				0F5A6284188C98D40072C9DF /* FTLValueRange.h in Headers */,
> 				0F0332C618B53FA9005F979A /* FTLWeight.h in Headers */,
> 				0F0332C818B546EC005F979A /* FTLWeightedTarget.h in Headers */,
>@@ -6521,6 +6549,7 @@
> 				BC18C41F0E16F5CD00B34460 /* JSFunction.h in Headers */,
> 				A72028BA1797603D0098028C /* JSFunctionInlines.h in Headers */,
> 				0F2B66F117B6B5AB00A7AE3F /* JSGenericTypedArrayView.h in Headers */,
>+				0FFC92161B94FB3E0071DD66 /* DFGPropertyTypeKey.h in Headers */,
> 				0F2B66F217B6B5AB00A7AE3F /* JSGenericTypedArrayViewConstructor.h in Headers */,
> 				0F2B66F317B6B5AB00A7AE3F /* JSGenericTypedArrayViewConstructorInlines.h in Headers */,
> 				0F2B66F417B6B5AB00A7AE3F /* JSGenericTypedArrayViewInlines.h in Headers */,
>@@ -7463,6 +7492,7 @@
> 				1428082E107EC0570013E7B2 /* ConstructData.cpp in Sources */,
> 				A57D23F11891B5B40031C7FA /* ContentSearchUtilities.cpp in Sources */,
> 				C240305514B404E60079EB64 /* CopiedSpace.cpp in Sources */,
>+				0FFC92111B94D4DF0071DD66 /* InferredTypeTable.cpp in Sources */,
> 				2AACE63C18CA5A0300ED0191 /* GCActivityCallback.cpp in Sources */,
> 				C2239D1716262BDD005AC5FD /* CopyVisitor.cpp in Sources */,
> 				0F2B66DE17B6B5AB00A7AE3F /* DataView.cpp in Sources */,
>@@ -7847,6 +7877,7 @@
> 				0FF054F91AC35B4400E5BE57 /* ExecutableAllocationFuzz.cpp in Sources */,
> 				86E3C61A167BABEE006D760A /* JSValue.mm in Sources */,
> 				0FF8BDEA1AD4CF7100DFE884 /* InferredValue.cpp in Sources */,
>+				0FC841681BA8C3210061837D /* DFGInferredTypeCheck.cpp in Sources */,
> 				0F8F14351ADF090100ED792C /* DFGMovHintRemovalPhase.cpp in Sources */,
> 				14BD5A320A3E91F600BAF59C /* JSValueRef.cpp in Sources */,
> 				147F39D7107EC37600427A48 /* JSEnvironmentRecord.cpp in Sources */,
>@@ -7881,6 +7912,7 @@
> 				86C568E011A213EE0007F7F0 /* MacroAssemblerARM.cpp in Sources */,
> 				E33F50741B8421C000413856 /* JSInternalPromisePrototype.cpp in Sources */,
> 				A729009C17976C6000317298 /* MacroAssemblerARMv7.cpp in Sources */,
>+				0F0A75221B94BFA900110660 /* InferredType.cpp in Sources */,
> 				A53CE08518BC1A5600BEDF76 /* ConsolePrototype.cpp in Sources */,
> 				A7A4AE0817973B26005612B1 /* MacroAssemblerX86Common.cpp in Sources */,
> 				A5B6A74D18C6DBA600F11E91 /* ConsoleClient.cpp in Sources */,
>Index: Source/JavaScriptCore/assembler/MacroAssemblerARM64.h
>===================================================================
>--- Source/JavaScriptCore/assembler/MacroAssemblerARM64.h	(revision 190059)
>+++ Source/JavaScriptCore/assembler/MacroAssemblerARM64.h	(working copy)
>@@ -1,5 +1,5 @@
> /*
>- * Copyright (C) 2012, 2014 Apple Inc. All rights reserved.
>+ * Copyright (C) 2012, 2014, 2015 Apple Inc. All rights reserved.
>  *
>  * Redistribution and use in source and binary forms, with or without
>  * modification, are permitted provided that the following conditions
>@@ -1853,6 +1853,12 @@ public:
>         return Jump(makeBranch(cond));
>     }
> 
>+    Jump branchTest64(ResultCondition cond, RegisterID reg, TrustedImm64 mask)
>+    {
>+        move(mask, getCachedDataTempRegisterIDAndInvalidate());
>+        return branchTest64(cond, reg, dataTempRegister);
>+    }
>+
>     Jump branchTest64(ResultCondition cond, Address address, RegisterID mask)
>     {
>         load64(address, getCachedDataTempRegisterIDAndInvalidate());
>Index: Source/JavaScriptCore/assembler/MacroAssemblerX86_64.h
>===================================================================
>--- Source/JavaScriptCore/assembler/MacroAssemblerX86_64.h	(revision 190059)
>+++ Source/JavaScriptCore/assembler/MacroAssemblerX86_64.h	(working copy)
>@@ -605,6 +605,12 @@ public:
>         return Jump(m_assembler.jCC(x86Condition(cond)));
>     }
> 
>+    Jump branchTest64(ResultCondition cond, RegisterID reg, TrustedImm64 mask)
>+    {
>+        move(mask, scratchRegister);
>+        return branchTest64(cond, reg, scratchRegister);
>+    }
>+
>     void test64(ResultCondition cond, RegisterID reg, TrustedImm32 mask, RegisterID dest)
>     {
>         if (mask.m_value == -1)
>Index: Source/JavaScriptCore/bytecode/PolymorphicAccess.cpp
>===================================================================
>--- Source/JavaScriptCore/bytecode/PolymorphicAccess.cpp	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/PolymorphicAccess.cpp	(working copy)
>@@ -691,6 +691,15 @@ void AccessCase::generate(AccessGenerati
>     }
> 
>     case Replace: {
>+        if (InferredType* type = structure()->inferredTypeFor(ident.impl())) {
>+            if (verbose)
>+                dataLog("Have type: ", type->descriptor(), "\n");
>+            state.failAndRepatch.append(
>+                jit.branchIfNotType(
>+                    valueRegs, scratchGPR, type->descriptor(), CCallHelpers::DoNotHaveTagRegisters));
>+        } else if (verbose)
>+            dataLog("Don't have type.\n");
>+        
>         if (isInlineOffset(m_offset)) {
>             jit.storeValue(
>                 valueRegs,
>@@ -714,6 +723,15 @@ void AccessCase::generate(AccessGenerati
>         RELEASE_ASSERT(GPRInfo::numberOfRegisters >= 6 || !structure()->outOfLineCapacity() || structure()->outOfLineCapacity() == newStructure()->outOfLineCapacity());
>         RELEASE_ASSERT(!structure()->couldHaveIndexingHeader());
> 
>+        if (InferredType* type = newStructure()->inferredTypeFor(ident.impl())) {
>+            if (verbose)
>+                dataLog("Have type: ", type->descriptor(), "\n");
>+            state.failAndRepatch.append(
>+                jit.branchIfNotType(
>+                    valueRegs, scratchGPR, type->descriptor(), CCallHelpers::DoNotHaveTagRegisters));
>+        } else if (verbose)
>+            dataLog("Don't have type.\n");
>+        
>         CCallHelpers::JumpList slowPath;
> 
>         ScratchRegisterAllocator allocator(stubInfo.patch.usedRegisters);
>Index: Source/JavaScriptCore/bytecode/PutByIdFlags.cpp
>===================================================================
>--- Source/JavaScriptCore/bytecode/PutByIdFlags.cpp	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/PutByIdFlags.cpp	(working copy)
>@@ -26,6 +26,7 @@
> #include "config.h"
> #include "PutByIdFlags.h"
> 
>+#include "InferredType.h"
> #include <wtf/CommaPrinter.h>
> #include <wtf/PrintStream.h>
> #include <wtf/StringPrintStream.h>
>@@ -35,16 +36,14 @@ namespace WTF {
> using namespace JSC;
> 
> void printInternal(PrintStream& out, PutByIdFlags flags) {
>-    StringPrintStream stringOut;
>     CommaPrinter comma("|");
>     if (flags & PutByIdIsDirect)
>-        stringOut.print(comma, "IsDirect");
>+        out.print(comma, "IsDirect");
> 
>-    CString string = stringOut.toCString();
>-    if (!string.length())
>-        out.print("None");
>-    else
>-        out.print(string);
>+    InferredType::Kind kind = InferredType::kindForFlags(flags);
>+    out.print(comma, kind);
>+    if (InferredType::hasStructure(kind))
>+        out.print(":", bitwise_cast<int32_t>(decodeStructureID(flags)));
> }
> 
> } // namespace WTF
>Index: Source/JavaScriptCore/bytecode/PutByIdFlags.h
>===================================================================
>--- Source/JavaScriptCore/bytecode/PutByIdFlags.h	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/PutByIdFlags.h	(working copy)
>@@ -26,13 +26,70 @@
> #ifndef PutByIdFlags_h
> #define PutByIdFlags_h
> 
>+#include "StructureIDTable.h"
>+
> namespace JSC {
> 
>-enum PutByIdFlags {
>+enum PutByIdFlags : intptr_t {
>     PutByIdNone = 0,
>-    PutByIdIsDirect = 1
>+
>+    // This flag indicates that the put_by_id is direct. That means that we store the property without
>+    // checking if the prototype chain has a setter.
>+    PutByIdIsDirect = 0x1,
>+    PutByIdPersistentFlagsMask = 0x1,
>+
>+    // NOTE: The values below must be in sync with what is in LowLevelInterpreter.asm.
>+
>+    // Determining the required inferred type involves first checking the primary type mask, and then
>+    // using that to figure out the meaning of the secondary mask:
>+    // switch (flags & PutByIdPrimaryTypeMask) {
>+    // case PutByIdPrimaryTypeSecondary:
>+    //     switch (flags & PutByIdSecondaryTypeMask) {
>+    //     ...
>+    //     }
>+    //     break;
>+    // case PutByIdPrimaryTypeObjectWithStructure:
>+    // case PutByIdPrimaryTypeObjectWithStructureOrOther:
>+    //     StructureID structureID = decodeStructureID(flags);
>+    //     break;
>+    // }
>+    PutByIdPrimaryTypeMask = 0x6,
>+    PutByIdPrimaryTypeSecondary = 0x0, // Need to check the secondary type mask for the type.
>+    PutByIdPrimaryTypeObjectWithStructure = 0x2, // Secondary type has structure ID.
>+    PutByIdPrimaryTypeObjectWithStructureOrOther = 0x4, // Secondary type has structure ID.
>+
>+    PutByIdSecondaryTypeMask = -0x8,
>+    PutByIdSecondaryTypeBottom = 0x0,
>+    PutByIdSecondaryTypeBoolean = 0x8,
>+    PutByIdSecondaryTypeOther = 0x10,
>+    PutByIdSecondaryTypeInt32 = 0x18,
>+    PutByIdSecondaryTypeNumber = 0x20,
>+    PutByIdSecondaryTypeString = 0x28,
>+    PutByIdSecondaryTypeObject = 0x30,
>+    PutByIdSecondaryTypeObjectOrOther = 0x38,
>+    PutByIdSecondaryTypeTop = 0x40
> };
> 
>+inline PutByIdFlags encodeStructureID(StructureID id)
>+{
>+#if USE(JSVALUE64)
>+    return static_cast<PutByIdFlags>(static_cast<PutByIdFlags>(id) << 3);
>+#else
>+    PutByIdFlags result = bitwise_cast<PutByIdFlags>(id);
>+    ASSERT(!(result & ~PutByIdSecondaryTypeMask));
>+    return result;
>+#endif
>+}
>+
>+inline StructureID decodeStructureID(PutByIdFlags flags)
>+{
>+#if USE(JSVALUE64)
>+    return static_cast<StructureID>(flags >> 3);
>+#else
>+    return bitwise_cast<StructureID>(flags & PutByIdSecondaryTypeMask);
>+#endif
>+}
>+
> } // namespace JSC
> 
> namespace WTF {
>Index: Source/JavaScriptCore/bytecode/PutByIdStatus.cpp
>===================================================================
>--- Source/JavaScriptCore/bytecode/PutByIdStatus.cpp	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/PutByIdStatus.cpp	(working copy)
>@@ -83,7 +83,7 @@ PutByIdStatus PutByIdStatus::computeFrom
>         if (!isValidOffset(offset))
>             return PutByIdStatus(NoInformation);
>         
>-        return PutByIdVariant::replace(structure, offset);
>+        return PutByIdVariant::replace(structure, offset, structure->inferredTypeDescriptorFor(uid));
>     }
> 
>     Structure* newStructure = vm.heap.structureIDTable().get(newStructureID);
>@@ -103,7 +103,8 @@ PutByIdStatus PutByIdStatus::computeFrom
>             return PutByIdStatus(NoInformation);
>     }
>     
>-    return PutByIdVariant::transition(structure, newStructure, conditionSet, offset);
>+    return PutByIdVariant::transition(
>+        structure, newStructure, conditionSet, offset, newStructure->inferredTypeDescriptorFor(uid));
> }
> 
> PutByIdStatus PutByIdStatus::computeFor(CodeBlock* profiledBlock, StubInfoMap& map, unsigned bytecodeIndex, UniquedStringImpl* uid)
>@@ -162,7 +163,7 @@ PutByIdStatus PutByIdStatus::computeForS
>             stubInfo->u.byIdSelf.baseObjectStructure->getConcurrently(uid);
>         if (isValidOffset(offset)) {
>             return PutByIdVariant::replace(
>-                stubInfo->u.byIdSelf.baseObjectStructure.get(), offset);
>+                stubInfo->u.byIdSelf.baseObjectStructure.get(), offset, InferredType::Top);
>         }
>         return PutByIdStatus(TakesSlowPath);
>     }
>@@ -193,7 +194,8 @@ PutByIdStatus PutByIdStatus::computeForS
>                 PropertyOffset offset = structure->getConcurrently(uid);
>                 if (!isValidOffset(offset))
>                     return PutByIdStatus(slowPathState);
>-                variant = PutByIdVariant::replace(structure, offset);
>+                variant = PutByIdVariant::replace(
>+                    structure, offset, structure->inferredTypeDescriptorFor(uid));
>                 break;
>             }
>                 
>@@ -206,7 +208,8 @@ PutByIdStatus PutByIdStatus::computeForS
>                 if (!conditionSet.structuresEnsureValidity())
>                     return PutByIdStatus(slowPathState);
>                 variant = PutByIdVariant::transition(
>-                    access.structure(), access.newStructure(), conditionSet, offset);
>+                    access.structure(), access.newStructure(), conditionSet, offset,
>+                    access.newStructure()->inferredTypeDescriptorFor(uid));
>                 break;
>             }
>                 
>@@ -329,8 +332,10 @@ PutByIdStatus PutByIdStatus::computeFor(
>                 // So, better leave this alone and take slow path.
>                 return PutByIdStatus(TakesSlowPath);
>             }
>-            
>-            if (!result.appendVariant(PutByIdVariant::replace(structure, offset)))
>+
>+            PutByIdVariant variant =
>+                PutByIdVariant::replace(structure, offset, structure->inferredTypeDescriptorFor(uid));
>+            if (!result.appendVariant(variant))
>                 return PutByIdStatus(TakesSlowPath);
>             continue;
>         }
>@@ -356,13 +361,16 @@ PutByIdStatus PutByIdStatus::computeFor(
>         }
>     
>         // We only optimize if there is already a structure that the transition is cached to.
>-        Structure* transition = Structure::addPropertyTransitionToExistingStructureConcurrently(structure, uid, 0, offset);
>+        Structure* transition =
>+            Structure::addPropertyTransitionToExistingStructureConcurrently(structure, uid, 0, offset);
>         if (!transition)
>             return PutByIdStatus(TakesSlowPath);
>         ASSERT(isValidOffset(offset));
>     
>         bool didAppend = result.appendVariant(
>-            PutByIdVariant::transition(structure, transition, conditionSet, offset));
>+            PutByIdVariant::transition(
>+                structure, transition, conditionSet, offset,
>+                transition->inferredTypeDescriptorFor(uid)));
>         if (!didAppend)
>             return PutByIdStatus(TakesSlowPath);
>     }
>Index: Source/JavaScriptCore/bytecode/PutByIdVariant.cpp
>===================================================================
>--- Source/JavaScriptCore/bytecode/PutByIdVariant.cpp	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/PutByIdVariant.cpp	(working copy)
>@@ -45,6 +45,7 @@ PutByIdVariant& PutByIdVariant::operator
>     m_newStructure = other.m_newStructure;
>     m_conditionSet = other.m_conditionSet;
>     m_offset = other.m_offset;
>+    m_requiredType = other.m_requiredType;
>     if (other.m_callLinkStatus)
>         m_callLinkStatus = std::make_unique<CallLinkStatus>(*other.m_callLinkStatus);
>     else
>@@ -52,18 +53,21 @@ PutByIdVariant& PutByIdVariant::operator
>     return *this;
> }
> 
>-PutByIdVariant PutByIdVariant::replace(const StructureSet& structure, PropertyOffset offset)
>+PutByIdVariant PutByIdVariant::replace(
>+    const StructureSet& structure, PropertyOffset offset, const InferredType::Descriptor& requiredType)
> {
>     PutByIdVariant result;
>     result.m_kind = Replace;
>     result.m_oldStructure = structure;
>     result.m_offset = offset;
>+    result.m_requiredType = requiredType;
>     return result;
> }
> 
> PutByIdVariant PutByIdVariant::transition(
>     const StructureSet& oldStructure, Structure* newStructure,
>-    const ObjectPropertyConditionSet& conditionSet, PropertyOffset offset)
>+    const ObjectPropertyConditionSet& conditionSet, PropertyOffset offset,
>+    const InferredType::Descriptor& requiredType)
> {
>     PutByIdVariant result;
>     result.m_kind = Transition;
>@@ -71,6 +75,7 @@ PutByIdVariant PutByIdVariant::transitio
>     result.m_newStructure = newStructure;
>     result.m_conditionSet = conditionSet;
>     result.m_offset = offset;
>+    result.m_requiredType = requiredType;
>     return result;
> }
> 
>@@ -85,6 +90,7 @@ PutByIdVariant PutByIdVariant::setter(
>     result.m_conditionSet = conditionSet;
>     result.m_offset = offset;
>     result.m_callLinkStatus = WTF::move(callLinkStatus);
>+    result.m_requiredType = InferredType::Top;
>     return result;
> }
> 
>@@ -134,9 +140,12 @@ bool PutByIdVariant::attemptToMerge(cons
> {
>     if (m_offset != other.m_offset)
>         return false;
>+
>+    if (m_requiredType != other.m_requiredType)
>+        return false;
>     
>     switch (m_kind) {
>-    case Replace:
>+    case Replace: {
>         switch (other.m_kind) {
>         case Replace: {
>             ASSERT(m_conditionSet.isEmpty());
>@@ -158,6 +167,7 @@ bool PutByIdVariant::attemptToMerge(cons
>         default:
>             return false;
>         }
>+    }
>         
>     case Transition:
>         switch (other.m_kind) {
>@@ -210,14 +220,16 @@ void PutByIdVariant::dumpInContext(Print
>         
>     case Replace:
>         out.print(
>-            "<Replace: ", inContext(structure(), context), ", offset = ", offset(), ">");
>+            "<Replace: ", inContext(structure(), context), ", offset = ", offset(), ", ",
>+            inContext(requiredType(), context), ">");
>         return;
>         
>     case Transition:
>         out.print(
>             "<Transition: ", inContext(oldStructure(), context), " -> ",
>             pointerDumpInContext(newStructure(), context), ", [",
>-            inContext(m_conditionSet, context), "], offset = ", offset(), ">");
>+            inContext(m_conditionSet, context), "], offset = ", offset(), ", ",
>+            inContext(requiredType(), context), ">");
>         return;
>         
>     case Setter:
>Index: Source/JavaScriptCore/bytecode/PutByIdVariant.h
>===================================================================
>--- Source/JavaScriptCore/bytecode/PutByIdVariant.h	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/PutByIdVariant.h	(working copy)
>@@ -53,11 +53,11 @@ public:
>     PutByIdVariant(const PutByIdVariant&);
>     PutByIdVariant& operator=(const PutByIdVariant&);
> 
>-    static PutByIdVariant replace(const StructureSet&, PropertyOffset);
>+    static PutByIdVariant replace(const StructureSet&, PropertyOffset, const InferredType::Descriptor&);
>     
>     static PutByIdVariant transition(
>         const StructureSet& oldStructure, Structure* newStructure,
>-        const ObjectPropertyConditionSet&, PropertyOffset);
>+        const ObjectPropertyConditionSet&, PropertyOffset, const InferredType::Descriptor&);
>     
>     static PutByIdVariant setter(
>         const StructureSet&, PropertyOffset, const ObjectPropertyConditionSet&,
>@@ -99,6 +99,11 @@ public:
>         return m_newStructure;
>     }
> 
>+    InferredType::Descriptor requiredType() const
>+    {
>+        return m_requiredType;
>+    }
>+
>     bool writesStructures() const;
>     bool reallocatesStorage() const;
>     bool makesCalls() const;
>@@ -130,6 +135,7 @@ private:
>     Structure* m_newStructure;
>     ObjectPropertyConditionSet m_conditionSet;
>     PropertyOffset m_offset;
>+    InferredType::Descriptor m_requiredType;
>     std::unique_ptr<CallLinkStatus> m_callLinkStatus;
> };
> 
>Index: Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.h
>===================================================================
>--- Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.h	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.h	(working copy)
>@@ -36,7 +36,6 @@
> #include "JSCell.h"
> #include "JSString.h"
> #include "ParserModes.h"
>-#include "PutByIdFlags.h"
> #include "RegExp.h"
> #include "SpecialPointer.h"
> #include "UnlinkedFunctionExecutable.h"
>@@ -98,12 +97,10 @@ struct UnlinkedInstruction {
>     UnlinkedInstruction() { u.operand = 0; }
>     UnlinkedInstruction(OpcodeID opcode) { u.opcode = opcode; }
>     UnlinkedInstruction(int operand) { u.operand = operand; }
>-    UnlinkedInstruction(PutByIdFlags flags) { u.putByIdFlags = flags; }
>     union {
>         OpcodeID opcode;
>         int32_t operand;
>         unsigned index;
>-        PutByIdFlags putByIdFlags;
>     } u;
> };
> 
>Index: Source/JavaScriptCore/bytecode/Watchpoint.h
>===================================================================
>--- Source/JavaScriptCore/bytecode/Watchpoint.h	(revision 190059)
>+++ Source/JavaScriptCore/bytecode/Watchpoint.h	(working copy)
>@@ -336,7 +336,39 @@ public:
>     {
>         touch(StringFireDetail(reason));
>     }
>-    
>+
>+    // Note that for any watchpoint that is visible from the DFG, it would be incorrect to write code like:
>+    //
>+    // if (w.isBeingWatched())
>+    //     w.fireAll()
>+    //
>+    // Concurrently to this, the DFG could do:
>+    //
>+    // if (w.isStillValid())
>+    //     perform optimizations;
>+    // if (!w.isStillValid())
>+    //     retry compilation;
>+    //
>+    // Note that the DFG algorithm is widespread, and sound, because fireAll() and invalidate() will leave
>+    // the watchpoint in a !isStillValid() state. Hence, if fireAll() or invalidate() interleaved between
>+    // the first isStillValid() check and the second one, then it would simply cause the DFG to retry
>+    // compilation later.
>+    //
>+    // But, if you change some piece of state that the DFG might optimize for, but invalidate the
>+    // watchpoint by doing:
>+    //
>+    // if (w.isBeingWatched())
>+    //     w.fireAll()
>+    //
>+    // then the DFG would never know that you invalidated state between the two checks.
>+    //
>+    // There are two ways to work around this:
>+    //
>+    // - Call fireAll() without a isBeingWatched() check. Then, the DFG will know that the watchpoint has
>+    //   been invalidated when it does its second check.
>+    //
>+    // - Do not expose the watchpoint set to the DFG directly, and have your own way of validating whether
>+    //   the assumptions that the DFG thread used are still valid when the DFG code is installed.
>     bool isBeingWatched() const
>     {
>         if (isFat())
>Index: Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp
>===================================================================
>--- Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp	(revision 190059)
>+++ Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp	(working copy)
>@@ -2114,7 +2114,7 @@ RegisterID* BytecodeGenerator::emitPutBy
>     instructions().append(0); // offset
>     instructions().append(0); // new structure
>     instructions().append(0); // structure chain
>-    instructions().append(PutByIdNone); // is not direct
>+    instructions().append(static_cast<int>(PutByIdNone)); // is not direct
> 
>     return value;
> }
>@@ -2136,7 +2136,7 @@ RegisterID* BytecodeGenerator::emitDirec
>     instructions().append(0); // offset
>     instructions().append(0); // new structure
>     instructions().append(0); // structure chain (unused if direct)
>-    instructions().append((putType == PropertyNode::KnownDirect || property != m_vm->propertyNames->underscoreProto) ? PutByIdIsDirect : PutByIdNone);
>+    instructions().append(static_cast<int>((putType == PropertyNode::KnownDirect || property != m_vm->propertyNames->underscoreProto) ? PutByIdIsDirect : PutByIdNone));
>     return value;
> }
> 
>Index: Source/JavaScriptCore/dfg/DFGAbstractInterpreter.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGAbstractInterpreter.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGAbstractInterpreter.h	(working copy)
>@@ -116,9 +116,9 @@ public:
>     void dump(PrintStream& out);
>     
>     template<typename T>
>-    FiltrationResult filter(T node, const StructureSet& set)
>+    FiltrationResult filter(T node, const StructureSet& set, SpeculatedType admittedTypes = SpecNone)
>     {
>-        return filter(forNode(node), set);
>+        return filter(forNode(node), set, admittedTypes);
>     }
>     
>     template<typename T>
>@@ -139,7 +139,7 @@ public:
>         return filterByValue(forNode(node), value);
>     }
>     
>-    FiltrationResult filter(AbstractValue&, const StructureSet&);
>+    FiltrationResult filter(AbstractValue&, const StructureSet&, SpeculatedType admittedTypes = SpecNone);
>     FiltrationResult filterArrayModes(AbstractValue&, ArrayModes);
>     FiltrationResult filter(AbstractValue&, SpeculatedType);
>     FiltrationResult filterByValue(AbstractValue&, FrozenValue);
>Index: Source/JavaScriptCore/dfg/DFGAbstractInterpreterInlines.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGAbstractInterpreterInlines.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGAbstractInterpreterInlines.h	(working copy)
>@@ -1829,10 +1829,10 @@ bool AbstractInterpreter<AbstractStateTy
>         }
>         
>         AbstractValue& value = forNode(node->child1());
>-        if (!value.m_structure.isTop() && !value.m_structure.isClobbered()
>+        if (value.m_structure.isFinite()
>             && (node->child1().useKind() == CellUse || !(value.m_type & ~SpecCell))) {
>-            GetByIdStatus status = GetByIdStatus::computeFor(
>-                value.m_structure.set(), m_graph.identifiers()[node->identifierNumber()]);
>+            UniquedStringImpl* uid = m_graph.identifiers()[node->identifierNumber()];
>+            GetByIdStatus status = GetByIdStatus::computeFor(value.m_structure.set(), uid);
>             if (status.isSimple()) {
>                 // Figure out what the result is going to be - is it TOP, a constant, or maybe
>                 // something more subtle?
>@@ -1841,22 +1841,12 @@ bool AbstractInterpreter<AbstractStateTy
>                     // This thing won't give us a variant that involves prototypes. If it did, we'd
>                     // have more work to do here.
>                     DFG_ASSERT(m_graph, node, status[i].conditionSet().isEmpty());
>-                    
>-                    JSValue constantResult =
>-                        m_graph.tryGetConstantProperty(value, status[i].offset());
>-                    if (!constantResult) {
>-                        result.makeHeapTop();
>-                        break;
>-                    }
>-                    
>-                    AbstractValue thisResult;
>-                    thisResult.set(
>-                        m_graph, *m_graph.freeze(constantResult),
>-                        m_state.structureClobberState());
>-                    result.merge(thisResult);
>+
>+                    result.merge(
>+                        m_graph.inferredValueForProperty(
>+                            value, uid, status[i].offset(), m_state.structureClobberState()));
>                 }
>-                if (status.numVariants() == 1 || isFTL(m_graph.m_plan.mode))
>-                    m_state.setFoundConstants(true);
>+                m_state.setFoundConstants(true);
>                 forNode(node) = result;
>                 break;
>             }
>@@ -1880,7 +1870,6 @@ bool AbstractInterpreter<AbstractStateTy
>         
>     case CheckStructure: {
>         AbstractValue& value = forNode(node->child1());
>-        ASSERT(!(value.m_type & ~SpecCell)); // Edge filtering should have already ensured this.
> 
>         StructureSet& set = node->structureSet();
>         
>@@ -1888,12 +1877,24 @@ bool AbstractInterpreter<AbstractStateTy
>         // that includes the set we're testing. In that case we could make the structure check
>         // more efficient. We currently don't.
>         
>-        if (value.m_structure.isSubsetOf(set)) {
>+        if (value.m_structure.isSubsetOf(set))
>             m_state.setFoundConstants(true);
>+
>+        SpeculatedType admittedTypes = SpecNone;
>+        switch (node->child1().useKind()) {
>+        case CellUse:
>+        case KnownCellUse:
>+            admittedTypes = SpecNone;
>+            break;
>+        case CellOrOtherUse:
>+            admittedTypes = SpecOther;
>+            break;
>+        default:
>+            DFG_CRASH(m_graph, node, "Bad use kind");
>             break;
>         }
>-
>-        filter(value, set);
>+        
>+        filter(value, set, admittedTypes);
>         break;
>     }
>         
>@@ -2084,13 +2085,29 @@ bool AbstractInterpreter<AbstractStateTy
>         
>     case GetByOffset: {
>         StorageAccessData& data = node->storageAccessData();
>-        JSValue result = m_graph.tryGetConstantProperty(forNode(node->child2()), data.offset);
>-        if (result) {
>-            setConstant(node, *m_graph.freeze(result));
>-            break;
>-        }
>-        
>-        forNode(node).makeHeapTop();
>+        UniquedStringImpl* uid = m_graph.identifiers()[data.identifierNumber];
>+
>+        // FIXME: The part of this that handles inferred property types relies on AI knowing the structure
>+        // right now. That's probably not optimal. In some cases, we may perform an optimization (usually
>+        // by something other than AI, maybe by CSE for example) that obscures AI's view of the structure
>+        // at the point where GetByOffset runs. Currently, when that happens, we'll have to rely entirely
>+        // on the type that ByteCodeParser was able to prove.
>+        AbstractValue value = m_graph.inferredValueForProperty(
>+            forNode(node->child2()), uid, data.offset, m_state.structureClobberState());
>+
>+        // It's possible that the type that ByteCodeParser came up with is better.
>+        AbstractValue typeFromParsing;
>+        typeFromParsing.set(m_graph, data.inferredType, m_state.structureClobberState());
>+        value.filter(typeFromParsing);
>+
>+        // If we decide that there does not exist any value that this can return, then it's probably
>+        // because the compilation was already invalidated.
>+        if (value.isClear())
>+            m_state.setIsValid(false);
>+
>+        forNode(node) = value;
>+        if (value.m_value)
>+            m_state.setFoundConstants(true);
>         break;
>     }
>         
>@@ -2120,6 +2137,8 @@ bool AbstractInterpreter<AbstractStateTy
>         // because of the effect on compile times, but this node is FTL-only.
>         m_state.setFoundConstants(true);
>         
>+        UniquedStringImpl* uid = m_graph.identifiers()[node->multiGetByOffsetData().identifierNumber];
>+
>         AbstractValue base = forNode(node->child1());
>         StructureSet baseSet;
>         AbstractValue result;
>@@ -2129,18 +2148,29 @@ bool AbstractInterpreter<AbstractStateTy
>             if (set.isEmpty())
>                 continue;
>             baseSet.merge(set);
>-            
>-            if (getCase.method().kind() != GetByOffsetMethod::Constant) {
>-                result.makeHeapTop();
>-                continue;
>+
>+            switch (getCase.method().kind()) {
>+            case GetByOffsetMethod::Constant: {
>+                AbstractValue thisResult;
>+                thisResult.set(
>+                    m_graph,
>+                    *getCase.method().constant(),
>+                    m_state.structureClobberState());
>+                result.merge(thisResult);
>+                break;
>             }
>-            
>-            AbstractValue thisResult;
>-            thisResult.set(
>-                m_graph,
>-                *getCase.method().constant(),
>-                m_state.structureClobberState());
>-            result.merge(thisResult);
>+
>+            case GetByOffsetMethod::Load: {
>+                result.merge(
>+                    m_graph.inferredValueForProperty(
>+                        set, uid, m_state.structureClobberState()));
>+                break;
>+            }
>+
>+            default: {
>+                result.makeHeapTop();
>+                break;
>+            } }
>         }
>         
>         if (forNode(node->child1()).changeStructure(m_graph, baseSet) == Contradiction)
>@@ -2163,6 +2193,8 @@ bool AbstractInterpreter<AbstractStateTy
>         m_state.setFoundConstants(true);
>         
>         AbstractValue base = forNode(node->child1());
>+        AbstractValue originalValue = forNode(node->child2());
>+        AbstractValue resultingValue;
>         
>         for (unsigned i = node->multiPutByOffsetData().variants.size(); i--;) {
>             const PutByIdVariant& variant = node->multiPutByOffsetData().variants[i];
>@@ -2170,6 +2202,11 @@ bool AbstractInterpreter<AbstractStateTy
>             thisSet.filter(base);
>             if (thisSet.isEmpty())
>                 continue;
>+
>+            AbstractValue thisValue = originalValue;
>+            thisValue.filter(m_graph, variant.requiredType());
>+            resultingValue.merge(thisValue);
>+            
>             if (variant.kind() == PutByIdVariant::Transition) {
>                 if (thisSet.onlyStructure() != variant.newStructure()) {
>                     transitions.append(
>@@ -2185,6 +2222,9 @@ bool AbstractInterpreter<AbstractStateTy
>         observeTransitions(clobberLimit, transitions);
>         if (forNode(node->child1()).changeStructure(m_graph, newSet) == Contradiction)
>             m_state.setIsValid(false);
>+        forNode(node->child2()) = resultingValue;
>+        if (!!originalValue && !resultingValue)
>+            m_state.setIsValid(false);
>         break;
>     }
>         
>@@ -2264,13 +2304,13 @@ bool AbstractInterpreter<AbstractStateTy
>     case PutByIdFlush:
>     case PutByIdDirect: {
>         AbstractValue& value = forNode(node->child1());
>-        if (!value.m_structure.isTop() && !value.m_structure.isClobbered()) {
>+        if (value.m_structure.isFinite()) {
>             PutByIdStatus status = PutByIdStatus::computeFor(
>                 m_graph.globalObjectFor(node->origin.semantic),
>                 value.m_structure.set(),
>                 m_graph.identifiers()[node->identifierNumber()],
>                 node->op() == PutByIdDirect);
>-            
>+
>             if (status.isSimple()) {
>                 StructureSet newSet;
>                 TransitionVector transitions;
>@@ -2615,9 +2655,9 @@ void AbstractInterpreter<AbstractStateTy
> 
> template<typename AbstractStateType>
> FiltrationResult AbstractInterpreter<AbstractStateType>::filter(
>-    AbstractValue& value, const StructureSet& set)
>+    AbstractValue& value, const StructureSet& set, SpeculatedType admittedTypes)
> {
>-    if (value.filter(m_graph, set) == FiltrationOK)
>+    if (value.filter(m_graph, set, admittedTypes) == FiltrationOK)
>         return FiltrationOK;
>     m_state.setIsValid(false);
>     return Contradiction;
>Index: Source/JavaScriptCore/dfg/DFGAbstractValue.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGAbstractValue.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGAbstractValue.cpp	(working copy)
>@@ -117,6 +117,56 @@ void AbstractValue::setType(Graph& graph
>     checkConsistency();
> }
> 
>+void AbstractValue::set(Graph& graph, const InferredType::Descriptor& descriptor)
>+{
>+    switch (descriptor.kind()) {
>+    case InferredType::Bottom:
>+        clear();
>+        return;
>+    case InferredType::Boolean:
>+        setType(SpecBoolean);
>+        return;
>+    case InferredType::Other:
>+        setType(SpecOther);
>+        return;
>+    case InferredType::Int32:
>+        setType(SpecInt32);
>+        return;
>+    case InferredType::Number:
>+        setType(SpecBytecodeNumber);
>+        return;
>+    case InferredType::String:
>+        set(graph, graph.m_vm.stringStructure.get());
>+        return;
>+    case InferredType::ObjectWithStructure:
>+        set(graph, descriptor.structure());
>+        return;
>+    case InferredType::ObjectWithStructureOrOther:
>+        set(graph, descriptor.structure());
>+        merge(SpecOther);
>+        return;
>+    case InferredType::Object:
>+        setType(graph, SpecObject);
>+        return;
>+    case InferredType::ObjectOrOther:
>+        setType(graph, SpecObject | SpecOther);
>+        return;
>+    case InferredType::Top:
>+        makeHeapTop();
>+        return;
>+    }
>+
>+    RELEASE_ASSERT_NOT_REACHED();
>+}
>+
>+void AbstractValue::set(
>+    Graph& graph, const InferredType::Descriptor& descriptor, StructureClobberState clobberState)
>+{
>+    set(graph, descriptor);
>+    if (clobberState == StructuresAreClobbered)
>+        clobberStructures();
>+}
>+
> void AbstractValue::fixTypeForRepresentation(Graph& graph, NodeFlags representation, Node* node)
> {
>     if (representation == NodeResultDouble) {
>@@ -189,8 +239,22 @@ bool AbstractValue::mergeOSREntryValue(G
>     return oldMe != *this;
> }
> 
>-FiltrationResult AbstractValue::filter(Graph& graph, const StructureSet& other)
>+bool AbstractValue::isType(Graph& graph, const InferredType::Descriptor& inferredType) const
> {
>+    AbstractValue typeValue;
>+    typeValue.set(graph, inferredType);
>+
>+    AbstractValue mergedValue = *this;
>+    mergedValue.merge(typeValue);
>+
>+    return mergedValue == typeValue;
>+}
>+
>+FiltrationResult AbstractValue::filter(
>+    Graph& graph, const StructureSet& other, SpeculatedType admittedTypes)
>+{
>+    ASSERT(!(admittedTypes & SpecCell));
>+    
>     if (isClear())
>         return FiltrationOK;
>     
>@@ -198,7 +262,7 @@ FiltrationResult AbstractValue::filter(G
>     // having structures, array modes, or a specific value.
>     // https://bugs.webkit.org/show_bug.cgi?id=109663
>     
>-    m_type &= other.speculationFromStructures();
>+    m_type &= other.speculationFromStructures() | admittedTypes;
>     m_arrayModes &= other.arrayModesFromStructures();
>     m_structure.filter(other);
>     
>@@ -315,6 +379,13 @@ FiltrationResult AbstractValue::filter(c
>     return Contradiction;
> }
> 
>+FiltrationResult AbstractValue::filter(Graph& graph, const InferredType::Descriptor& descriptor)
>+{
>+    AbstractValue filterValue;
>+    filterValue.set(graph, descriptor);
>+    return filter(filterValue);
>+}
>+
> void AbstractValue::filterValueByType()
> {
>     // We could go further, and ensure that if the futurePossibleStructure contravenes
>Index: Source/JavaScriptCore/dfg/DFGAbstractValue.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGAbstractValue.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGAbstractValue.h	(working copy)
>@@ -34,6 +34,7 @@
> #include "DFGNodeFlags.h"
> #include "DFGStructureAbstractValue.h"
> #include "DFGStructureClobberState.h"
>+#include "InferredType.h"
> #include "JSCell.h"
> #include "SpeculatedType.h"
> #include "DumpContext.h"
>@@ -214,7 +215,10 @@ struct AbstractValue {
>         m_value = JSValue();
>         checkConsistency();
>     }
>-    
>+
>+    void set(Graph&, const InferredType::Descriptor&);
>+    void set(Graph&, const InferredType::Descriptor&, StructureClobberState);
>+
>     void fixTypeForRepresentation(Graph&, NodeFlags representation, Node* = nullptr);
>     void fixTypeForRepresentation(Graph&, Node*);
>     
>@@ -280,17 +284,27 @@ struct AbstractValue {
>     {
>         return !(m_type & ~desiredType);
>     }
>+
>+    bool isType(Graph&, const InferredType::Descriptor&) const;
>+
>+    // Filters the value using the given structure set. If the admittedTypes argument is not passed, this
>+    // implicitly filters by the types implied by the structure set, which are usually a subset of
>+    // SpecCell. Hence, after this call, the value will no longer have any non-cell members. But, you can
>+    // use admittedTypes to preserve some non-cell types. Note that it's wrong for admittedTypes to overlap
>+    // with SpecCell.
>+    FiltrationResult filter(Graph&, const StructureSet&, SpeculatedType admittedTypes = SpecNone);
>     
>-    FiltrationResult filter(Graph&, const StructureSet&);
>     FiltrationResult filterArrayModes(ArrayModes);
>     FiltrationResult filter(SpeculatedType);
>     FiltrationResult filterByValue(const FrozenValue& value);
>     FiltrationResult filter(const AbstractValue&);
>+
>+    FiltrationResult filter(Graph&, const InferredType::Descriptor&);
>     
>     FiltrationResult changeStructure(Graph&, const StructureSet&);
>     
>     bool contains(Structure*) const;
>-    
>+
>     bool validate(JSValue value) const
>     {
>         if (isHeapTop())
>Index: Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp	(working copy)
>@@ -206,9 +206,8 @@ private:
>     bool handleTypedArrayConstructor(int resultOperand, InternalFunction*, int registerOffset, int argumentCountIncludingThis, TypedArrayType, const ChecksFunctor& insertChecks);
>     template<typename ChecksFunctor>
>     bool handleConstantInternalFunction(int resultOperand, InternalFunction*, int registerOffset, int argumentCountIncludingThis, CodeSpecializationKind, const ChecksFunctor& insertChecks);
>-    Node* handlePutByOffset(Node* base, unsigned identifier, PropertyOffset, Node* value);
>-    Node* handleGetByOffset(SpeculatedType, Node* base, unsigned identifierNumber, PropertyOffset, NodeType = GetByOffset);
>-    Node* handleGetByOffset(SpeculatedType, Node* base, UniquedStringImpl*, PropertyOffset, NodeType = GetByOffset);
>+    Node* handlePutByOffset(Node* base, unsigned identifier, PropertyOffset, const InferredType::Descriptor&, Node* value);
>+    Node* handleGetByOffset(SpeculatedType, Node* base, unsigned identifierNumber, PropertyOffset, const InferredType::Descriptor&, NodeType = GetByOffset);
> 
>     // Create a presence ObjectPropertyCondition based on some known offset and structure set. Does not
>     // check the validity of the condition, but it may return a null one if it encounters a contradiction.
>@@ -2306,7 +2305,9 @@ bool ByteCodeParser::handleConstantInter
>     return false;
> }
> 
>-Node* ByteCodeParser::handleGetByOffset(SpeculatedType prediction, Node* base, unsigned identifierNumber, PropertyOffset offset, NodeType op)
>+Node* ByteCodeParser::handleGetByOffset(
>+    SpeculatedType prediction, Node* base, unsigned identifierNumber, PropertyOffset offset,
>+    const InferredType::Descriptor& inferredType, NodeType op)
> {
>     Node* propertyStorage;
>     if (isInlineOffset(offset))
>@@ -2317,13 +2318,17 @@ Node* ByteCodeParser::handleGetByOffset(
>     StorageAccessData* data = m_graph.m_storageAccessData.add();
>     data->offset = offset;
>     data->identifierNumber = identifierNumber;
>+    data->inferredType = inferredType;
>+    m_graph.registerInferredType(inferredType);
>     
>     Node* getByOffset = addToGraph(op, OpInfo(data), OpInfo(prediction), propertyStorage, base);
> 
>     return getByOffset;
> }
> 
>-Node* ByteCodeParser::handlePutByOffset(Node* base, unsigned identifier, PropertyOffset offset, Node* value)
>+Node* ByteCodeParser::handlePutByOffset(
>+    Node* base, unsigned identifier, PropertyOffset offset, const InferredType::Descriptor& inferredType,
>+    Node* value)
> {
>     Node* propertyStorage;
>     if (isInlineOffset(offset))
>@@ -2334,6 +2339,8 @@ Node* ByteCodeParser::handlePutByOffset(
>     StorageAccessData* data = m_graph.m_storageAccessData.add();
>     data->offset = offset;
>     data->identifierNumber = identifier;
>+    data->inferredType = inferredType;
>+    m_graph.registerInferredType(inferredType);
>     
>     Node* result = addToGraph(PutByOffset, OpInfo(data), propertyStorage, base, value);
>     
>@@ -2448,7 +2455,8 @@ Node* ByteCodeParser::load(
>         return addToGraph(JSConstant, OpInfo(method.constant()));
>     case GetByOffsetMethod::LoadFromPrototype: {
>         Node* baseNode = addToGraph(JSConstant, OpInfo(method.prototype()));
>-        return handleGetByOffset(prediction, baseNode, identifierNumber, method.offset(), op);
>+        return handleGetByOffset(
>+            prediction, baseNode, identifierNumber, method.offset(), InferredType::Top, op);
>     }
>     case GetByOffsetMethod::Load:
>         // Will never see this from planLoad().
>@@ -2554,13 +2562,13 @@ Node* ByteCodeParser::load(
>     
>     bool needStructureCheck = true;
>     
>+    UniquedStringImpl* uid = m_graph.identifiers()[identifierNumber];
>+    
>     if (JSObject* knownBase = base->dynamicCastConstant<JSObject*>()) {
>         // Try to optimize away the structure check. Note that it's not worth doing anything about this
>         // if the base's structure is watched.
>         Structure* structure = base->constant()->structure();
>         if (!structure->dfgShouldWatch()) {
>-            UniquedStringImpl* uid = m_graph.identifiers()[identifierNumber];
>-            
>             if (!variant.conditionSet().isEmpty()) {
>                 // This means that we're loading from a prototype. We expect the base not to have the
>                 // property. We can only use ObjectPropertyCondition if all of the structures in the
>@@ -2625,9 +2633,18 @@ Node* ByteCodeParser::load(
>             if (constant)
>                 return weakJSConstant(constant);
>         }
>+
>+        InferredType::Descriptor inferredType;
>+        if (needStructureCheck) {
>+            for (Structure* structure : variant.structureSet()) {
>+                InferredType::Descriptor thisType = m_graph.inferredTypeForProperty(structure, uid);
>+                inferredType.merge(thisType);
>+            }
>+        } else
>+            inferredType = InferredType::Top;
>         
>         loadedValue = handleGetByOffset(
>-            loadPrediction, base, identifierNumber, variant.offset(), loadOp);
>+            loadPrediction, base, identifierNumber, variant.offset(), inferredType, loadOp);
>     }
> 
>     return loadedValue;
>@@ -2638,7 +2655,7 @@ Node* ByteCodeParser::store(Node* base, 
>     RELEASE_ASSERT(variant.kind() == PutByIdVariant::Replace);
> 
>     checkPresenceLike(base, m_graph.identifiers()[identifier], variant.offset(), variant.structure());
>-    return handlePutByOffset(base, identifier, variant.offset(), value);
>+    return handlePutByOffset(base, identifier, variant.offset(), variant.requiredType(), value);
> }
> 
> void ByteCodeParser::handleGetById(
>@@ -2797,6 +2814,9 @@ void ByteCodeParser::handlePutById(
>         
>         if (m_graph.compilation())
>             m_graph.compilation()->noticeInlinedPutById();
>+
>+        for (const PutByIdVariant& variant : putByIdStatus.variants())
>+            m_graph.registerInferredType(variant.requiredType());
>         
>         MultiPutByOffsetData* data = m_graph.m_multiPutByOffsetData.add();
>         data->variants = putByIdStatus.variants();
>@@ -2853,6 +2873,8 @@ void ByteCodeParser::handlePutById(
>         StorageAccessData* data = m_graph.m_storageAccessData.add();
>         data->offset = variant.offset();
>         data->identifierNumber = identifierNumber;
>+        data->inferredType = variant.requiredType();
>+        m_graph.registerInferredType(data->inferredType);
>         
>         addToGraph(
>             PutByOffset,
>Index: Source/JavaScriptCore/dfg/DFGClobbersExitState.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGClobbersExitState.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGClobbersExitState.cpp	(working copy)
>@@ -64,6 +64,8 @@ bool clobbersExitState(Graph& graph, Nod
>     case PhantomCreateActivation:
>     case MaterializeCreateActivation:
>     case CountExecution:
>+    case AllocatePropertyStorage:
>+    case ReallocatePropertyStorage:
>         // These do clobber memory, but nothing that is observable. It may be nice to separate the
>         // heaps into those that are observable and those that aren't, but we don't do that right now.
>         // FIXME: https://bugs.webkit.org/show_bug.cgi?id=148440
>Index: Source/JavaScriptCore/dfg/DFGConstantFoldingPhase.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGConstantFoldingPhase.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGConstantFoldingPhase.cpp	(working copy)
>@@ -33,6 +33,7 @@
> #include "DFGBasicBlock.h"
> #include "DFGGraph.h"
> #include "DFGInPlaceAbstractState.h"
>+#include "DFGInferredTypeCheck.h"
> #include "DFGInsertionSet.h"
> #include "DFGPhase.h"
> #include "GetByIdStatus.h"
>@@ -373,7 +374,8 @@ private:
>                         && variant.oldStructure().onlyStructure() == variant.newStructure()) {
>                         variant = PutByIdVariant::replace(
>                             variant.oldStructure(),
>-                            variant.offset());
>+                            variant.offset(),
>+                            variant.requiredType());
>                         changed = true;
>                     }
>                 }
>@@ -448,6 +450,7 @@ private:
>                 ASSERT(childEdge.useKind() == CellUse);
>                 
>                 AbstractValue baseValue = m_state.forNode(child);
>+                AbstractValue valueValue = m_state.forNode(node->child2());
> 
>                 m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
>                 alreadyHandled = true; // Don't allow the default constant folder to do things to this.
>@@ -463,7 +466,7 @@ private:
>                 
>                 if (!status.isSimple())
>                     break;
>-                
>+
>                 ASSERT(status.numVariants());
>                 
>                 if (status.numVariants() > 1 && !isFTL(m_graph.m_plan.mode))
>@@ -640,7 +643,9 @@ private:
>         emitGetByOffset(indexInBlock, node, childEdge, identifierNumber, variant.offset());
>     }
>     
>-    void emitGetByOffset(unsigned indexInBlock, Node* node, Edge childEdge, unsigned identifierNumber, PropertyOffset offset)
>+    void emitGetByOffset(
>+        unsigned indexInBlock, Node* node, Edge childEdge, unsigned identifierNumber,
>+        PropertyOffset offset, const InferredType::Descriptor& inferredType = InferredType::Top)
>     {
>         childEdge.setUseKind(KnownCellUse);
>         
>@@ -656,6 +661,7 @@ private:
>         StorageAccessData& data = *m_graph.m_storageAccessData.add();
>         data.offset = offset;
>         data.identifierNumber = identifierNumber;
>+        data.inferredType = inferredType;
>         
>         node->convertToGetByOffset(data, propertyStorage);
>     }
>@@ -664,8 +670,10 @@ private:
>     {
>         NodeOrigin origin = node->origin;
>         Edge childEdge = node->child1();
>-        
>+
>         addBaseCheck(indexInBlock, node, baseValue, variant.oldStructure());
>+        insertInferredTypeCheck(
>+            m_insertionSet, indexInBlock, origin, node->child2().node(), variant.requiredType());
> 
>         node->child1().setUseKind(KnownCellUse);
>         childEdge.setUseKind(KnownCellUse);
>@@ -730,6 +738,7 @@ private:
>             // Arises when we prune MultiGetByOffset. We could have a
>             // MultiGetByOffset with a single variant that checks for structure S,
>             // and the input has structures S and T, for example.
>+            ASSERT(node->child1());
>             m_insertionSet.insertNode(
>                 indexInBlock, SpecNone, CheckStructure, node->origin,
>                 OpInfo(m_graph.addStructureSet(set)), node->child1());
>Index: Source/JavaScriptCore/dfg/DFGDesiredInferredType.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGDesiredInferredType.h	(revision 0)
>+++ Source/JavaScriptCore/dfg/DFGDesiredInferredType.h	(working copy)
>@@ -0,0 +1,132 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
>+ */
>+
>+#ifndef DFGDesiredInferredType_h
>+#define DFGDesiredInferredType_h
>+
>+#if ENABLE(DFG_JIT)
>+
>+#include "InferredType.h"
>+#include <wtf/HashMap.h>
>+
>+namespace JSC { namespace DFG {
>+
>+// This documents the DFG's expectation for an InferredType: specifically, that we want it to have a live
>+// InferredType object and that this object has the type that we originally saw.
>+
>+class DesiredInferredType {
>+public:
>+    DesiredInferredType()
>+        : m_object(nullptr)
>+    {
>+    }
>+    
>+    DesiredInferredType(InferredType* object, const InferredType::Descriptor& expected)
>+        : m_object(object)
>+        , m_expected(expected)
>+    {
>+    }
>+
>+    DesiredInferredType(WTF::HashTableDeletedValueType)
>+        : m_object(nullptr)
>+        , m_expected(InferredType::Top)
>+    {
>+    }
>+
>+    explicit operator bool() const { return m_object && m_expected; }
>+
>+    InferredType* object() const { return m_object; }
>+    InferredType::Descriptor expected() const { return m_expected; }
>+
>+    bool isStillValid() const
>+    {
>+        return m_object->canWatch(m_expected);
>+    }
>+
>+    void add(Watchpoint* watchpoint) const
>+    {
>+        m_object->addWatchpoint(watchpoint);
>+    }
>+
>+    bool operator==(const DesiredInferredType& other) const
>+    {
>+        return m_object == other.m_object
>+            && m_expected == other.m_expected;
>+    }
>+
>+    bool operator!=(const DesiredInferredType& other) const
>+    {
>+        return !(*this == other);
>+    }
>+
>+    bool isHashTableDeletedValue() const
>+    {
>+        return !m_object && m_expected == InferredType::Top;
>+    }
>+
>+    unsigned hash() const
>+    {
>+        return WTF::PtrHash<InferredType*>::hash(m_object) + m_expected.hash() * 7;
>+    }
>+
>+    void dumpInContext(PrintStream& out, DumpContext* context) const
>+    {
>+        out.print(inContext(m_expected, context), " for ", RawPointer(m_object));
>+    }
>+
>+    void dump(PrintStream& out) const
>+    {
>+        dumpInContext(out, nullptr);
>+    }
>+
>+private:
>+    InferredType* m_object;
>+    InferredType::Descriptor m_expected;
>+};
>+
>+struct DesiredInferredTypeHash {
>+    static unsigned hash(const DesiredInferredType& key) { return key.hash(); }
>+    static bool equal(const DesiredInferredType& a, const DesiredInferredType& b) { return a == b; }
>+    static const bool safeToCompareToEmptyOrDeleted = true;
>+};
>+
>+} } // namespace JSC::DFG
>+
>+namespace WTF {
>+
>+template<typename T> struct DefaultHash;
>+template<> struct DefaultHash<JSC::DFG::DesiredInferredType> {
>+    typedef JSC::DFG::DesiredInferredTypeHash Hash;
>+};
>+
>+template<typename T> struct HashTraits;
>+template<> struct HashTraits<JSC::DFG::DesiredInferredType> : SimpleClassHashTraits<JSC::DFG::DesiredInferredType> { };
>+
>+} // namespace WTF
>+
>+#endif // ENABLE(DFG_JIT)
>+
>+#endif // DFGDesiredInferredType_h
>+
>Index: Source/JavaScriptCore/dfg/DFGDesiredWatchpoints.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGDesiredWatchpoints.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGDesiredWatchpoints.cpp	(working copy)
>@@ -65,6 +65,11 @@ void AdaptiveStructureWatchpointAdaptor:
>     }
> }
> 
>+void InferredTypeAdaptor::add(CodeBlock* codeBlock, const DesiredInferredType& key, CommonData& common)
>+{
>+    key.add(common.watchpoints.add(codeBlock));
>+}
>+
> DesiredWatchpoints::DesiredWatchpoints() { }
> DesiredWatchpoints::~DesiredWatchpoints() { }
> 
>@@ -93,6 +98,11 @@ void DesiredWatchpoints::addLazily(const
>     m_adaptiveStructureSets.addLazily(key);
> }
> 
>+void DesiredWatchpoints::addLazily(const DesiredInferredType& key)
>+{
>+    m_inferredTypes.addLazily(key);
>+}
>+
> bool DesiredWatchpoints::consider(Structure* structure)
> {
>     if (!structure->dfgShouldWatch())
>@@ -108,6 +118,7 @@ void DesiredWatchpoints::reallyAdd(CodeB
>     m_inferredValues.reallyAdd(codeBlock, commonData);
>     m_bufferViews.reallyAdd(codeBlock, commonData);
>     m_adaptiveStructureSets.reallyAdd(codeBlock, commonData);
>+    m_inferredTypes.reallyAdd(codeBlock, commonData);
> }
> 
> bool DesiredWatchpoints::areStillValid() const
>@@ -116,7 +127,8 @@ bool DesiredWatchpoints::areStillValid()
>         && m_inlineSets.areStillValid()
>         && m_inferredValues.areStillValid()
>         && m_bufferViews.areStillValid()
>-        && m_adaptiveStructureSets.areStillValid();
>+        && m_adaptiveStructureSets.areStillValid()
>+        && m_inferredTypes.areStillValid();
> }
> 
> void DesiredWatchpoints::dumpInContext(PrintStream& out, DumpContext* context) const
>@@ -127,6 +139,7 @@ void DesiredWatchpoints::dumpInContext(P
>     out.print("    Inferred values: ", inContext(m_inferredValues, context), "\n");
>     out.print("    Buffer views: ", inContext(m_bufferViews, context), "\n");
>     out.print("    Object property conditions: ", inContext(m_adaptiveStructureSets, context), "\n");
>+    out.print("    Inferred types: ", inContext(m_inferredTypes, context), "\n");
> }
> 
> } } // namespace JSC::DFG
>Index: Source/JavaScriptCore/dfg/DFGDesiredWatchpoints.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGDesiredWatchpoints.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGDesiredWatchpoints.h	(working copy)
>@@ -30,6 +30,7 @@
> 
> #include "CodeOrigin.h"
> #include "DFGCommonData.h"
>+#include "DFGDesiredInferredType.h"
> #include "InferredValue.h"
> #include "JSArrayBufferView.h"
> #include "ObjectPropertyCondition.h"
>@@ -91,6 +92,18 @@ struct AdaptiveStructureWatchpointAdapto
>     }
> };
> 
>+struct InferredTypeAdaptor {
>+    static void add(CodeBlock*, const DesiredInferredType&, CommonData&);
>+    static bool hasBeenInvalidated(const DesiredInferredType& key)
>+    {
>+        return !key.isStillValid();
>+    }
>+    static void dumpInContext(PrintStream& out, const DesiredInferredType& key, DumpContext* context)
>+    {
>+        out.print(inContext(key, context));
>+    }
>+};
>+
> template<typename WatchpointSetType, typename Adaptor = SetPointerAdaptor<WatchpointSetType>>
> class GenericDesiredWatchpoints {
> #if !ASSERT_DISABLED
>@@ -159,6 +172,10 @@ public:
>     // It's recommended that you don't call this directly. Use Graph::watchCondition(), which does
>     // the required GC magic as well as some other bookkeeping.
>     void addLazily(const ObjectPropertyCondition&);
>+
>+    // It's recommended that you don't call this directly. Use Graph::inferredTypeFor(), which does
>+    // the required GC magic.
>+    void addLazily(const DesiredInferredType&);
>     
>     bool consider(Structure*);
>     
>@@ -186,6 +203,10 @@ public:
>     {
>         return m_adaptiveStructureSets.isWatched(key);
>     }
>+    bool isWatched(const DesiredInferredType& key)
>+    {
>+        return m_inferredTypes.isWatched(key);
>+    }
> 
>     void dumpInContext(PrintStream&, DumpContext*) const;
>     void dump(PrintStream&) const;
>@@ -196,6 +217,7 @@ private:
>     GenericDesiredWatchpoints<InferredValue*, InferredValueAdaptor> m_inferredValues;
>     GenericDesiredWatchpoints<JSArrayBufferView*, ArrayBufferViewWatchpointAdaptor> m_bufferViews;
>     GenericDesiredWatchpoints<ObjectPropertyCondition, AdaptiveStructureWatchpointAdaptor> m_adaptiveStructureSets;
>+    GenericDesiredWatchpoints<DesiredInferredType, InferredTypeAdaptor> m_inferredTypes;
> };
> 
> } } // namespace JSC::DFG
>Index: Source/JavaScriptCore/dfg/DFGFixupPhase.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGFixupPhase.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGFixupPhase.cpp	(working copy)
>@@ -30,6 +30,7 @@
> 
> #include "ArrayPrototype.h"
> #include "DFGGraph.h"
>+#include "DFGInferredTypeCheck.h"
> #include "DFGInsertionSet.h"
> #include "DFGPhase.h"
> #include "DFGPredictionPropagationPhase.h"
>@@ -1092,6 +1093,9 @@ private:
>             if (!node->child1()->hasStorageResult())
>                 fixEdge<KnownCellUse>(node->child1());
>             fixEdge<KnownCellUse>(node->child2());
>+            insertInferredTypeCheck(
>+                m_insertionSet, m_indexInBlock, node->origin, node->child3().node(),
>+                node->storageAccessData().inferredType);
>             speculateForBarrier(node->child3());
>             break;
>         }
>Index: Source/JavaScriptCore/dfg/DFGGraph.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGGraph.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGGraph.cpp	(working copy)
>@@ -261,12 +261,16 @@ void Graph::dump(PrintStream& out, const
>         StorageAccessData& storageAccessData = node->storageAccessData();
>         out.print(comma, "id", storageAccessData.identifierNumber, "{", identifiers()[storageAccessData.identifierNumber], "}");
>         out.print(", ", static_cast<ptrdiff_t>(storageAccessData.offset));
>+        out.print(", inferredType = ", inContext(storageAccessData.inferredType, context));
>     }
>     if (node->hasMultiGetByOffsetData()) {
>         MultiGetByOffsetData& data = node->multiGetByOffsetData();
>         out.print(comma, "id", data.identifierNumber, "{", identifiers()[data.identifierNumber], "}");
>-        for (unsigned i = 0; i < data.cases.size(); ++i)
>+        for (unsigned i = 0; i < data.cases.size(); ++i) {
>             out.print(comma, inContext(data.cases[i], context));
>+            if (data.cases[i].method().kind() == GetByOffsetMethod::Load)
>+                out.print(" (inferred value = ", inContext(inferredValueForProperty(data.cases[i].set(), identifiers()[data.identifierNumber]), context), ")");
>+        }
>     }
>     if (node->hasMultiPutByOffsetData()) {
>         MultiPutByOffsetData& data = node->multiPutByOffsetData();
>@@ -887,6 +891,38 @@ bool Graph::isSafeToLoad(JSObject* base,
>     return m_safeToLoad.contains(std::make_pair(base, offset));
> }
> 
>+InferredType::Descriptor Graph::inferredTypeFor(const PropertyTypeKey& key)
>+{
>+    assertIsRegistered(key.structure());
>+    
>+    auto iter = m_inferredTypes.find(key);
>+    if (iter != m_inferredTypes.end())
>+        return iter->value;
>+
>+    InferredType* typeObject = key.structure()->inferredTypeFor(key.uid());
>+    if (!typeObject) {
>+        m_inferredTypes.add(key, InferredType::Top);
>+        return InferredType::Top;
>+    }
>+
>+    InferredType::Descriptor typeDescriptor = typeObject->descriptor();
>+    if (typeDescriptor.kind() == InferredType::Top) {
>+        m_inferredTypes.add(key, InferredType::Top);
>+        return InferredType::Top;
>+    }
>+    
>+    m_inferredTypes.add(key, typeDescriptor);
>+
>+    m_plan.weakReferences.addLazily(typeObject);
>+    registerInferredType(typeDescriptor);
>+
>+    // Note that we may already be watching this desired inferred type, because multiple structures may
>+    // point to the same InferredType instance.
>+    m_plan.watchpoints.addLazily(DesiredInferredType(typeObject, typeDescriptor));
>+
>+    return typeDescriptor;
>+}
>+
> FullBytecodeLiveness& Graph::livenessFor(CodeBlock* codeBlock)
> {
>     HashMap<CodeBlock*, std::unique_ptr<FullBytecodeLiveness>>::iterator iter = m_bytecodeLiveness.find(codeBlock);
>@@ -1061,7 +1097,7 @@ JSValue Graph::tryGetConstantProperty(JS
> JSValue Graph::tryGetConstantProperty(
>     JSValue base, const StructureAbstractValue& structure, PropertyOffset offset)
> {
>-    if (structure.isTop() || structure.isClobbered()) {
>+    if (structure.isInfinite()) {
>         // FIXME: If we just converted the offset to a uid, we could do ObjectPropertyCondition
>         // watching to constant-fold the property.
>         // https://bugs.webkit.org/show_bug.cgi?id=147271
>@@ -1076,6 +1112,37 @@ JSValue Graph::tryGetConstantProperty(co
>     return tryGetConstantProperty(base.m_value, base.m_structure, offset);
> }
> 
>+AbstractValue Graph::inferredValueForProperty(
>+    const StructureSet& base, UniquedStringImpl* uid, StructureClobberState clobberState)
>+{
>+    AbstractValue result;
>+    base.forEach(
>+        [&] (Structure* structure) {
>+            AbstractValue value;
>+            value.set(*this, inferredTypeForProperty(structure, uid));
>+            result.merge(value);
>+        });
>+    if (clobberState == StructuresAreClobbered)
>+        result.clobberStructures();
>+    return result;
>+}
>+
>+AbstractValue Graph::inferredValueForProperty(
>+    const AbstractValue& base, UniquedStringImpl* uid, PropertyOffset offset,
>+    StructureClobberState clobberState)
>+{
>+    if (JSValue value = tryGetConstantProperty(base, offset)) {
>+        AbstractValue result;
>+        result.set(*this, *freeze(value), clobberState);
>+        return result;
>+    }
>+
>+    if (base.m_structure.isFinite())
>+        return inferredValueForProperty(base.m_structure.set(), uid, clobberState);
>+
>+    return AbstractValue::heapTop();
>+}
>+
> JSValue Graph::tryGetConstantClosureVar(JSValue base, ScopeOffset offset)
> {
>     // This has an awesome concurrency story. See comment for GetGlobalVar in ByteCodeParser.
>Index: Source/JavaScriptCore/dfg/DFGGraph.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGGraph.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGGraph.h	(working copy)
>@@ -41,6 +41,7 @@
> #include "DFGNodeAllocator.h"
> #include "DFGPlan.h"
> #include "DFGPrePostNumbering.h"
>+#include "DFGPropertyTypeKey.h"
> #include "DFGScannable.h"
> #include "FullBytecodeLiveness.h"
> #include "JSStack.h"
>@@ -675,6 +676,27 @@ public:
>     // Checks if it's known that loading from the given object at the given offset is fine. This is
>     // computed by tracking which conditions we track with watchCondition().
>     bool isSafeToLoad(JSObject* base, PropertyOffset);
>+
>+    void registerInferredType(const InferredType::Descriptor& type)
>+    {
>+        if (type.structure())
>+            registerStructure(type.structure());
>+    }
>+
>+    // Tells us what inferred type we are able to prove the property to have now and in the future.
>+    InferredType::Descriptor inferredTypeFor(const PropertyTypeKey&);
>+    InferredType::Descriptor inferredTypeForProperty(Structure* structure, UniquedStringImpl* uid)
>+    {
>+        return inferredTypeFor(PropertyTypeKey(structure, uid));
>+    }
>+
>+    AbstractValue inferredValueForProperty(
>+        const StructureSet& base, UniquedStringImpl* uid, StructureClobberState = StructuresAreWatched);
>+
>+    // This uses either constant property inference or property type inference to derive a good abstract
>+    // value for some property accessed with the given abstract value base.
>+    AbstractValue inferredValueForProperty(
>+        const AbstractValue& base, UniquedStringImpl* uid, PropertyOffset, StructureClobberState);
>     
>     FullBytecodeLiveness& livenessFor(CodeBlock*);
>     FullBytecodeLiveness& livenessFor(InlineCallFrame*);
>@@ -856,6 +878,7 @@ public:
>     HashMap<CodeBlock*, std::unique_ptr<FullBytecodeLiveness>> m_bytecodeLiveness;
>     HashMap<CodeBlock*, std::unique_ptr<BytecodeKills>> m_bytecodeKills;
>     HashSet<std::pair<JSObject*, PropertyOffset>> m_safeToLoad;
>+    HashMap<PropertyTypeKey, InferredType::Descriptor> m_inferredTypes;
>     Dominators m_dominators;
>     PrePostNumbering m_prePostNumbering;
>     NaturalLoops m_naturalLoops;
>Index: Source/JavaScriptCore/dfg/DFGInferredTypeCheck.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGInferredTypeCheck.cpp	(revision 0)
>+++ Source/JavaScriptCore/dfg/DFGInferredTypeCheck.cpp	(working copy)
>@@ -0,0 +1,98 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "DFGInferredTypeCheck.h"
>+
>+#if ENABLE(DFG_JIT)
>+
>+#include "JSCInlines.h"
>+
>+namespace JSC { namespace DFG {
>+
>+void insertInferredTypeCheck(
>+    InsertionSet& insertionSet, unsigned nodeIndex, NodeOrigin origin, Node* baseNode,
>+    const InferredType::Descriptor& type)
>+{
>+    insertionSet.graph().registerInferredType(type);
>+    
>+    switch (type.kind()) {
>+    case InferredType::Bottom:
>+        insertionSet.insertNode(nodeIndex, SpecNone, ForceOSRExit, origin);
>+        return;
>+
>+    case InferredType::Boolean:
>+        insertionSet.insertNode(nodeIndex, SpecNone, Check, origin, Edge(baseNode, BooleanUse));
>+        return;
>+
>+    case InferredType::Other:
>+        insertionSet.insertNode(nodeIndex, SpecNone, Check, origin, Edge(baseNode, OtherUse));
>+        return;
>+
>+    case InferredType::Int32:
>+        insertionSet.insertNode(nodeIndex, SpecNone, Check, origin, Edge(baseNode, Int32Use));
>+        return;
>+
>+    case InferredType::Number:
>+        insertionSet.insertNode(nodeIndex, SpecNone, Check, origin, Edge(baseNode, NumberUse));
>+        return;
>+
>+    case InferredType::String:
>+        insertionSet.insertNode(nodeIndex, SpecNone, Check, origin, Edge(baseNode, StringUse));
>+        return;
>+
>+    case InferredType::ObjectWithStructure:
>+        insertionSet.insertNode(
>+            nodeIndex, SpecNone, CheckStructure, origin,
>+            OpInfo(insertionSet.graph().addStructureSet(type.structure())),
>+            Edge(baseNode, CellUse));
>+        return;
>+
>+    case InferredType::ObjectWithStructureOrOther:
>+        insertionSet.insertNode(
>+            nodeIndex, SpecNone, CheckStructure, origin,
>+            OpInfo(insertionSet.graph().addStructureSet(type.structure())),
>+            Edge(baseNode, CellOrOtherUse));
>+        return;
>+
>+    case InferredType::Object:
>+        insertionSet.insertNode(nodeIndex, SpecNone, Check, origin, Edge(baseNode, ObjectUse));
>+        return;
>+
>+    case InferredType::ObjectOrOther:
>+        insertionSet.insertNode(nodeIndex, SpecNone, Check, origin, Edge(baseNode, ObjectOrOtherUse));
>+        return;
>+
>+    case InferredType::Top:
>+        return;
>+    }
>+
>+    DFG_CRASH(insertionSet.graph(), baseNode, "Bad inferred type");
>+}
>+
>+} } // namespace JSC::DFG
>+
>+#endif // ENABLE(DFG_JIT)
>+
>Index: Source/JavaScriptCore/dfg/DFGInferredTypeCheck.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGInferredTypeCheck.h	(revision 0)
>+++ Source/JavaScriptCore/dfg/DFGInferredTypeCheck.h	(working copy)
>@@ -0,0 +1,45 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#ifndef DFGInferredTypeCheck_h
>+#define DFGInferredTypeCheck_h
>+
>+#if ENABLE(DFG_JIT)
>+
>+#include "DFGInsertionSet.h"
>+#include "InferredType.h"
>+
>+namespace JSC { namespace DFG {
>+
>+// Inserts a type check that ensures that baseNode has the given inferred type.
>+void insertInferredTypeCheck(
>+    InsertionSet&, unsigned nodeIndex, NodeOrigin, Node* baseNode, const InferredType::Descriptor&);
>+
>+} } // namespace JSC::DFG
>+
>+#endif // ENABLE(DFG_JIT)
>+
>+#endif // DFGInferredTypeCheck_h
>+
>Index: Source/JavaScriptCore/dfg/DFGNode.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGNode.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGNode.h	(working copy)
>@@ -64,6 +64,11 @@ struct BasicBlock;
> struct StorageAccessData {
>     PropertyOffset offset;
>     unsigned identifierNumber;
>+
>+    // This needs to know the inferred type. For puts, this is necessary because we need to remember
>+    // what check is needed. For gets, this is necessary because otherwise AI might forget what type is
>+    // guaranteed.
>+    InferredType::Descriptor inferredType;
> };
> 
> struct MultiPutByOffsetData {
>Index: Source/JavaScriptCore/dfg/DFGObjectAllocationSinkingPhase.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGObjectAllocationSinkingPhase.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGObjectAllocationSinkingPhase.cpp	(working copy)
>@@ -2135,14 +2135,20 @@ private:
>                 for (Structure* structure : structures) {
>                     PropertyOffset offset = structure->getConcurrently(uid);
>                     if (offset != currentOffset) {
>+                        // Because our analysis treats MultiPutByOffset like an escape, we only have to
>+                        // deal with storing results that would have been previously stored by PutByOffset
>+                        // nodes. Those nodes were guarded by the appropriate type checks. This means that
>+                        // at this point, we can simply trust that the incoming value has the right type
>+                        // for whatever structure we are using.
>                         data->variants.append(
>-                            PutByIdVariant::replace(currentSet, currentOffset));
>+                            PutByIdVariant::replace(currentSet, currentOffset, InferredType::Top));
>                         currentOffset = offset;
>                         currentSet.clear();
>                     }
>                     currentSet.add(structure);
>                 }
>-                data->variants.append(PutByIdVariant::replace(currentSet, currentOffset));
>+                data->variants.append(
>+                    PutByIdVariant::replace(currentSet, currentOffset, InferredType::Top));
>             }
> 
>             return m_graph.addNode(
>Index: Source/JavaScriptCore/dfg/DFGPropertyTypeKey.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGPropertyTypeKey.h	(revision 0)
>+++ Source/JavaScriptCore/dfg/DFGPropertyTypeKey.h	(working copy)
>@@ -0,0 +1,129 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
>+ */
>+
>+#ifndef DFGPropertyTypeKey_h
>+#define DFGPropertyTypeKey_h
>+
>+#if ENABLE(DFG_JIT)
>+
>+#include "Structure.h"
>+#include <wtf/HashMap.h>
>+
>+namespace JSC { namespace DFG {
>+
>+// This object is a key for finding a property's type. It's a tuple of Structure* and UniquedStringImpl*.
>+
>+class PropertyTypeKey {
>+public:
>+    PropertyTypeKey()
>+        : m_structure(nullptr)
>+        , m_uid(nullptr)
>+    {
>+    }
>+
>+    PropertyTypeKey(Structure* structure, UniquedStringImpl* uid)
>+        : m_structure(structure)
>+        , m_uid(uid)
>+    {
>+    }
>+
>+    PropertyTypeKey(WTF::HashTableDeletedValueType)
>+        : m_structure(nullptr)
>+        , m_uid(deletedUID())
>+    {
>+    }
>+
>+    explicit operator bool() const { return m_structure && m_uid; }
>+
>+    Structure* structure() const { return m_structure; }
>+    UniquedStringImpl* uid() const { return m_uid; }
>+
>+    bool operator==(const PropertyTypeKey& other) const
>+    {
>+        return m_structure == other.m_structure
>+            && m_uid == other.m_uid;
>+    }
>+
>+    bool operator!=(const PropertyTypeKey& other) const
>+    {
>+        return !(*this == other);
>+    }
>+
>+    unsigned hash() const
>+    {
>+        return WTF::PtrHash<Structure*>::hash(m_structure) + WTF::PtrHash<UniquedStringImpl*>::hash(m_uid);
>+    }
>+
>+    bool isHashTableDeletedValue() const
>+    {
>+        return !m_structure && m_uid == deletedUID();
>+    }
>+
>+    void dumpInContext(PrintStream& out, DumpContext* context) const
>+    {
>+        out.print(pointerDumpInContext(m_structure, context), "+", m_uid);
>+    }
>+
>+    void dump(PrintStream& out) const
>+    {
>+        dumpInContext(out, nullptr);
>+    }
>+
>+private:
>+    static UniquedStringImpl* deletedUID()
>+    {
>+        return bitwise_cast<UniquedStringImpl*>(static_cast<intptr_t>(1));
>+    }
>+    
>+    Structure* m_structure;
>+    UniquedStringImpl* m_uid;
>+};
>+
>+struct PropertyTypeKeyHash {
>+    static unsigned hash(const PropertyTypeKey& key) { return key.hash(); }
>+    static bool equal(const PropertyTypeKey& a, const PropertyTypeKey& b) { return a == b; }
>+    static const bool safeToCompareToEmptyOrDeleted = true;
>+};
>+
>+} } // namespace JSC::DFG
>+
>+namespace WTF {
>+
>+template<typename T> struct DefaultHash;
>+template<> struct DefaultHash<JSC::DFG::PropertyTypeKey> {
>+    typedef JSC::DFG::PropertyTypeKeyHash Hash;
>+};
>+
>+template<typename T> struct HashTraits;
>+template<> struct HashTraits<JSC::DFG::PropertyTypeKey> : SimpleClassHashTraits<JSC::DFG::PropertyTypeKey> {
>+    static const bool emptyValueIsZero = false;
>+};
>+
>+} // namespace WTF
>+
>+#endif // ENABLE(DFG_JIT)
>+
>+#endif // DFGPropertyTypeKey_h
>+
>Index: Source/JavaScriptCore/dfg/DFGSafeToExecute.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGSafeToExecute.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGSafeToExecute.h	(working copy)
>@@ -53,6 +53,7 @@ public:
>         case RealNumberUse:
>         case BooleanUse:
>         case CellUse:
>+        case CellOrOtherUse:
>         case ObjectUse:
>         case FunctionUse:
>         case FinalObjectUse:
>@@ -127,6 +128,9 @@ bool safeToExecute(AbstractStateType& st
>     if (!safeToExecuteEdge.result())
>         return false;
> 
>+    // NOTE: This tends to lie when it comes to effectful nodes, because it knows that they aren't going to
>+    // get hoisted anyway.
>+
>     switch (node->op()) {
>     case JSConstant:
>     case DoubleConstant:
>Index: Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp	(working copy)
>@@ -3901,36 +3901,7 @@ void SpeculativeJIT::compile(Node* node)
>     }
>         
>     case CheckStructure: {
>-        SpeculateCellOperand base(this, node->child1());
>-        
>-        ASSERT(node->structureSet().size());
>-        
>-        if (node->structureSet().size() == 1) {
>-            speculationCheck(
>-                BadCache, JSValueSource::unboxedCell(base.gpr()), 0,
>-                m_jit.branchWeakPtr(
>-                    JITCompiler::NotEqual,
>-                    JITCompiler::Address(base.gpr(), JSCell::structureIDOffset()),
>-                    node->structureSet()[0]));
>-        } else {
>-            GPRTemporary structure(this);
>-            
>-            m_jit.loadPtr(JITCompiler::Address(base.gpr(), JSCell::structureIDOffset()), structure.gpr());
>-            
>-            JITCompiler::JumpList done;
>-            
>-            for (size_t i = 0; i < node->structureSet().size() - 1; ++i)
>-                done.append(m_jit.branchWeakPtr(JITCompiler::Equal, structure.gpr(), node->structureSet()[i]));
>-            
>-            speculationCheck(
>-                BadCache, JSValueSource::unboxedCell(base.gpr()), 0,
>-                m_jit.branchWeakPtr(
>-                    JITCompiler::NotEqual, structure.gpr(), node->structureSet().last()));
>-            
>-            done.link(&m_jit);
>-        }
>-        
>-        noResult(node);
>+        compileCheckStructure(node);
>         break;
>     }
>         
>Index: Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp	(working copy)
>@@ -3916,38 +3916,7 @@ void SpeculativeJIT::compile(Node* node)
>     }
>         
>     case CheckStructure: {
>-        SpeculateCellOperand base(this, node->child1());
>-        
>-        ASSERT(node->structureSet().size());
>-        
>-        ExitKind exitKind;
>-        if (node->child1()->hasConstant())
>-            exitKind = BadConstantCache;
>-        else
>-            exitKind = BadCache;
>-        
>-        if (node->structureSet().size() == 1) {
>-            speculationCheck(
>-                exitKind, JSValueSource::unboxedCell(base.gpr()), 0,
>-                m_jit.branchWeakStructure(
>-                    JITCompiler::NotEqual,
>-                    JITCompiler::Address(base.gpr(), JSCell::structureIDOffset()),
>-                    node->structureSet()[0]));
>-        } else {
>-            JITCompiler::JumpList done;
>-            
>-            for (size_t i = 0; i < node->structureSet().size() - 1; ++i)
>-                done.append(m_jit.branchWeakStructure(JITCompiler::Equal, MacroAssembler::Address(base.gpr(), JSCell::structureIDOffset()), node->structureSet()[i]));
>-            
>-            speculationCheck(
>-                exitKind, JSValueSource::unboxedCell(base.gpr()), 0,
>-                m_jit.branchWeakStructure(
>-                    JITCompiler::NotEqual, MacroAssembler::Address(base.gpr(), JSCell::structureIDOffset()), node->structureSet().last()));
>-            
>-            done.link(&m_jit);
>-        }
>-        
>-        noResult(node);
>+        compileCheckStructure(node);
>         break;
>     }
>         
>Index: Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp	(working copy)
>@@ -5232,6 +5232,81 @@ void SpeculativeJIT::compileTypeOf(Node*
>     cellResult(resultGPR, node);
> }
> 
>+void SpeculativeJIT::compileCheckStructure(Node* node, GPRReg cellGPR, GPRReg tempGPR)
>+{
>+    ASSERT(node->structureSet().size());
>+    
>+    if (node->structureSet().size() == 1) {
>+        speculationCheck(
>+            BadCache, JSValueSource::unboxedCell(cellGPR), 0,
>+            m_jit.branchWeakStructure(
>+                JITCompiler::NotEqual,
>+                JITCompiler::Address(cellGPR, JSCell::structureIDOffset()),
>+                node->structureSet()[0]));
>+    } else {
>+        std::unique_ptr<GPRTemporary> structure;
>+        GPRReg structureGPR;
>+        
>+        if (tempGPR == InvalidGPRReg) {
>+            structure = std::make_unique<GPRTemporary>(this);
>+            structureGPR = structure->gpr();
>+        } else
>+            structureGPR = tempGPR;
>+        
>+        m_jit.load32(JITCompiler::Address(cellGPR, JSCell::structureIDOffset()), structureGPR);
>+        
>+        JITCompiler::JumpList done;
>+        
>+        for (size_t i = 0; i < node->structureSet().size() - 1; ++i) {
>+            done.append(
>+                m_jit.branchWeakStructure(JITCompiler::Equal, structureGPR, node->structureSet()[i]));
>+        }
>+        
>+        speculationCheck(
>+            BadCache, JSValueSource::unboxedCell(cellGPR), 0,
>+            m_jit.branchWeakStructure(
>+                JITCompiler::NotEqual, structureGPR, node->structureSet().last()));
>+        
>+        done.link(&m_jit);
>+    }
>+}
>+
>+void SpeculativeJIT::compileCheckStructure(Node* node)
>+{
>+    switch (node->child1().useKind()) {
>+    case CellUse:
>+    case KnownCellUse: {
>+        SpeculateCellOperand cell(this, node->child1());
>+        compileCheckStructure(node, cell.gpr(), InvalidGPRReg);
>+        noResult(node);
>+        return;
>+    }
>+
>+    case CellOrOtherUse: {
>+        JSValueOperand value(this, node->child1(), ManualOperandSpeculation);
>+        GPRTemporary temp(this);
>+
>+        JSValueRegs valueRegs = value.jsValueRegs();
>+        GPRReg tempGPR = temp.gpr();
>+
>+        JITCompiler::Jump cell = m_jit.branchIfCell(valueRegs);
>+        DFG_TYPE_CHECK(
>+            valueRegs, node->child1(), SpecCell | SpecOther,
>+            m_jit.branchIfNotOther(valueRegs, tempGPR));
>+        JITCompiler::Jump done = m_jit.jump();
>+        cell.link(&m_jit);
>+        compileCheckStructure(node, valueRegs.payloadGPR(), tempGPR);
>+        done.link(&m_jit);
>+        noResult(node);
>+        return;
>+    }
>+
>+    default:
>+        DFG_CRASH(m_jit.graph(), node, "Bad use kind");
>+        return;
>+    }
>+}
>+
> void SpeculativeJIT::compileAllocatePropertyStorage(Node* node)
> {
>     if (node->transition()->previous->couldHaveIndexingHeader()) {
>@@ -5636,6 +5711,22 @@ void SpeculativeJIT::speculateCell(Edge 
>     (SpeculateCellOperand(this, edge)).gpr();
> }
> 
>+void SpeculativeJIT::speculateCellOrOther(Edge edge)
>+{
>+    if (!needsTypeCheck(edge, SpecCell | SpecOther))
>+        return;
>+    
>+    JSValueOperand operand(this, edge, ManualOperandSpeculation);
>+    GPRTemporary temp(this);
>+    GPRReg tempGPR = temp.gpr();
>+
>+    MacroAssembler::Jump ok = m_jit.branchIfCell(operand.jsValueRegs());
>+    DFG_TYPE_CHECK(
>+        operand.jsValueRegs(), edge, SpecCell | SpecOther,
>+        m_jit.branchIfNotOther(operand.jsValueRegs(), tempGPR));
>+    ok.link(&m_jit);
>+}
>+
> void SpeculativeJIT::speculateObject(Edge edge)
> {
>     if (!needsTypeCheck(edge, SpecObject))
>@@ -5916,6 +6007,9 @@ void SpeculativeJIT::speculate(Node*, Ed
>     case CellUse:
>         speculateCell(edge);
>         break;
>+    case CellOrOtherUse:
>+        speculateCellOrOther(edge);
>+        break;
>     case ObjectUse:
>         speculateObject(edge);
>         break;
>Index: Source/JavaScriptCore/dfg/DFGSpeculativeJIT.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGSpeculativeJIT.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGSpeculativeJIT.h	(working copy)
>@@ -2215,6 +2215,8 @@ public:
>     void compileIsObjectOrNull(Node*);
>     void compileIsFunction(Node*);
>     void compileTypeOf(Node*);
>+    void compileCheckStructure(Node*, GPRReg cellGPR, GPRReg tempGPR);
>+    void compileCheckStructure(Node*);
>     
>     void moveTrueTo(GPRReg);
>     void moveFalseTo(GPRReg);
>@@ -2374,6 +2376,7 @@ public:
>     void speculateDoubleRepReal(Edge);
>     void speculateBoolean(Edge);
>     void speculateCell(Edge);
>+    void speculateCellOrOther(Edge);
>     void speculateObject(Edge);
>     void speculateFunction(Edge);
>     void speculateFinalObject(Edge);
>Index: Source/JavaScriptCore/dfg/DFGStoreBarrierInsertionPhase.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGStoreBarrierInsertionPhase.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGStoreBarrierInsertionPhase.cpp	(working copy)
>@@ -314,7 +314,7 @@ private:
>             case AllocatePropertyStorage:
>             case ReallocatePropertyStorage:
>                 // These allocate but then run their own barrier.
>-                insertBarrierWithInvalidExit(m_nodeIndex + 1, Edge(m_node->child1().node(), KnownCellUse));
>+                insertBarrier(m_nodeIndex + 1, Edge(m_node->child1().node(), KnownCellUse));
>                 m_node->setEpoch(Epoch());
>                 break;
>                 
>@@ -481,11 +481,6 @@ private:
>         insertBarrier(m_nodeIndex, base);
>     }
> 
>-    void insertBarrierWithInvalidExit(unsigned nodeIndex, Edge base)
>-    {
>-        insertBarrier(nodeIndex, base, false);
>-    }
>-
>     void insertBarrier(unsigned nodeIndex, Edge base, bool exitOK = true)
>     {
>         // If we're in global mode, we should only insert the barriers once we have converged.
>Index: Source/JavaScriptCore/dfg/DFGStructureAbstractValue.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGStructureAbstractValue.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGStructureAbstractValue.h	(working copy)
>@@ -192,7 +192,7 @@ public:
>     }
>     
>     Structure* operator[](size_t i) const { return at(i); }
>-    
>+
>     // In most cases, what you really want to do is verify whether the set is top or clobbered, and
>     // if not, enumerate the set of structures. Use this only in cases where the singleton case is
>     // meaningfully special, like for transitions.
>@@ -202,6 +202,13 @@ public:
>             return nullptr;
>         return m_set.onlyStructure();
>     }
>+
>+    template<typename Functor>
>+    void forEach(const Functor& functor) const
>+    {
>+        ASSERT(!isTop());
>+        m_set.forEach(functor);
>+    }
>     
>     void dumpInContext(PrintStream&, DumpContext*) const;
>     void dump(PrintStream&) const;
>Index: Source/JavaScriptCore/dfg/DFGUseKind.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGUseKind.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGUseKind.cpp	(working copy)
>@@ -79,6 +79,9 @@ void printInternal(PrintStream& out, Use
>     case KnownCellUse:
>         out.print("KnownCell");
>         return;
>+    case CellOrOtherUse:
>+        out.print("CellOrOther");
>+        return;
>     case ObjectUse:
>         out.print("Object");
>         return;
>Index: Source/JavaScriptCore/dfg/DFGUseKind.h
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGUseKind.h	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGUseKind.h	(working copy)
>@@ -51,6 +51,7 @@ enum UseKind {
>     KnownBooleanUse,
>     CellUse,
>     KnownCellUse,
>+    CellOrOtherUse,
>     ObjectUse,
>     FunctionUse,
>     FinalObjectUse,
>@@ -108,6 +109,8 @@ inline SpeculatedType typeFilterFor(UseK
>     case CellUse:
>     case KnownCellUse:
>         return SpecCell;
>+    case CellOrOtherUse:
>+        return SpecCell | SpecOther;
>     case ObjectUse:
>         return SpecObject;
>     case FunctionUse:
>Index: Source/JavaScriptCore/dfg/DFGValidate.cpp
>===================================================================
>--- Source/JavaScriptCore/dfg/DFGValidate.cpp	(revision 190059)
>+++ Source/JavaScriptCore/dfg/DFGValidate.cpp	(working copy)
>@@ -263,6 +263,9 @@ public:
>                     VALIDATE((node), !!node->child1());
>                     VALIDATE((node), !!node->child2());
>                     break;
>+                case CheckStructure:
>+                    VALIDATE((node), !!node->child1());
>+                    break;
>                 case PutStructure:
>                     VALIDATE((node), !node->transition()->previous->dfgShouldWatch());
>                     break;
>Index: Source/JavaScriptCore/ftl/FTLCapabilities.cpp
>===================================================================
>--- Source/JavaScriptCore/ftl/FTLCapabilities.cpp	(revision 190059)
>+++ Source/JavaScriptCore/ftl/FTLCapabilities.cpp	(working copy)
>@@ -418,6 +418,7 @@ CapabilityLevel canCompile(Graph& graph)
>                 case KnownBooleanUse:
>                 case CellUse:
>                 case KnownCellUse:
>+                case CellOrOtherUse:
>                 case ObjectUse:
>                 case FunctionUse:
>                 case ObjectOrOtherUse:
>Index: Source/JavaScriptCore/ftl/FTLLowerDFGToLLVM.cpp
>===================================================================
>--- Source/JavaScriptCore/ftl/FTLLowerDFGToLLVM.cpp	(revision 190059)
>+++ Source/JavaScriptCore/ftl/FTLLowerDFGToLLVM.cpp	(working copy)
>@@ -2026,21 +2026,57 @@ private:
>     
>     void compileCheckStructure()
>     {
>-        LValue cell = lowCell(m_node->child1());
>-        
>         ExitKind exitKind;
>         if (m_node->child1()->hasConstant())
>             exitKind = BadConstantCache;
>         else
>             exitKind = BadCache;
>-        
>-        LValue structureID = m_out.load32(cell, m_heaps.JSCell_structureID);
>-        
>-        checkStructure(
>-            structureID, jsValueValue(cell), exitKind, m_node->structureSet(),
>-            [this] (Structure* structure) {
>-                return weakStructureID(structure);
>-            });
>+
>+        switch (m_node->child1().useKind()) {
>+        case CellUse:
>+        case KnownCellUse: {
>+            LValue cell = lowCell(m_node->child1());
>+            
>+            checkStructure(
>+                m_out.load32(cell, m_heaps.JSCell_structureID), jsValueValue(cell),
>+                exitKind, m_node->structureSet(),
>+                [&] (Structure* structure) {
>+                    return weakStructureID(structure);
>+                });
>+            return;
>+        }
>+
>+        case CellOrOtherUse: {
>+            LValue value = lowJSValue(m_node->child1(), ManualOperandSpeculation);
>+
>+            LBasicBlock cellCase = FTL_NEW_BLOCK(m_out, ("CheckStructure CellOrOtherUse cell case"));
>+            LBasicBlock notCellCase = FTL_NEW_BLOCK(m_out, ("CheckStructure CellOrOtherUse not cell case"));
>+            LBasicBlock continuation = FTL_NEW_BLOCK(m_out, ("CheckStructure CellOrOtherUse continuation"));
>+
>+            m_out.branch(
>+                isCell(value, provenType(m_node->child1())), unsure(cellCase), unsure(notCellCase));
>+
>+            LBasicBlock lastNext = m_out.appendTo(cellCase, notCellCase);
>+            checkStructure(
>+                m_out.load32(value, m_heaps.JSCell_structureID), jsValueValue(value),
>+                exitKind, m_node->structureSet(),
>+                [&] (Structure* structure) {
>+                    return weakStructureID(structure);
>+                });
>+            m_out.jump(continuation);
>+
>+            m_out.appendTo(notCellCase, continuation);
>+            FTL_TYPE_CHECK(jsValueValue(value), m_node->child1(), SpecCell | SpecOther, isNotOther(value));
>+            m_out.jump(continuation);
>+
>+            m_out.appendTo(continuation, lastNext);
>+            return;
>+        }
>+
>+        default:
>+            DFG_CRASH(m_graph, m_node, "Bad use kind");
>+            return;
>+        }
>     }
>     
>     void compileCheckCell()
>@@ -4022,6 +4058,8 @@ private:
>             m_out.appendTo(blocks[i], i + 1 < data.variants.size() ? blocks[i + 1] : exit);
>             
>             PutByIdVariant variant = data.variants[i];
>+
>+            checkInferredType(m_node->child2(), value, variant.requiredType());
>             
>             LValue storage;
>             if (variant.kind() == PutByIdVariant::Replace) {
>@@ -5674,6 +5712,135 @@ private:
>         m_out.appendTo(continuation, lastNext);
>         return m_out.phi(m_out.int32, results);
>     }
>+
>+    void checkInferredType(Edge edge, LValue value, const InferredType::Descriptor& type)
>+    {
>+        // This cannot use FTL_TYPE_CHECK or typeCheck() because it is called partially, as in a node like:
>+        //
>+        //     MultiPutByOffset(...)
>+        //
>+        // may be lowered to:
>+        //
>+        //     switch (object->structure) {
>+        //     case 42:
>+        //         checkInferredType(..., type1);
>+        //         ...
>+        //         break;
>+        //     case 43:
>+        //         checkInferredType(..., type2);
>+        //         ...
>+        //         break;
>+        //     }
>+        //
>+        // where type1 and type2 are different. Using typeCheck() would mean that the edge would be
>+        // filtered by type1 & type2, instead of type1 | type2.
>+        
>+        switch (type.kind()) {
>+        case InferredType::Bottom:
>+            speculate(BadType, jsValueValue(value), edge.node(), m_out.booleanTrue);
>+            return;
>+
>+        case InferredType::Boolean:
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotBoolean(value, provenType(edge)));
>+            return;
>+
>+        case InferredType::Other:
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotOther(value, provenType(edge)));
>+            return;
>+
>+        case InferredType::Int32:
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotInt32(value, provenType(edge)));
>+            return;
>+
>+        case InferredType::Number:
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotNumber(value, provenType(edge)));
>+            return;
>+
>+        case InferredType::String:
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotCell(value, provenType(edge)));
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotString(value, provenType(edge)));
>+            return;
>+
>+        case InferredType::ObjectWithStructure:
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotCell(value, provenType(edge)));
>+            if (!abstractValue(edge).m_structure.isSubsetOf(StructureSet(type.structure()))) {
>+                speculate(
>+                    BadType, jsValueValue(value), edge.node(),
>+                    m_out.notEqual(
>+                        m_out.load32(value, m_heaps.JSCell_structureID),
>+                        weakStructureID(type.structure())));
>+            }
>+            return;
>+
>+        case InferredType::ObjectWithStructureOrOther: {
>+            LBasicBlock cellCase = FTL_NEW_BLOCK(m_out, ("checkInferredType ObjectWithStructureOrOther cell case"));
>+            LBasicBlock notCellCase = FTL_NEW_BLOCK(m_out, ("checkInferredType ObjectWithStructureOrOther not cell case"));
>+            LBasicBlock continuation = FTL_NEW_BLOCK(m_out, ("checkInferredType ObjectWithStructureOrOther continuation"));
>+
>+            m_out.branch(isCell(value, provenType(edge)), unsure(cellCase), unsure(notCellCase));
>+
>+            LBasicBlock lastNext = m_out.appendTo(cellCase, notCellCase);
>+
>+            if (!abstractValue(edge).m_structure.isSubsetOf(StructureSet(type.structure()))) {
>+                speculate(
>+                    BadType, jsValueValue(value), edge.node(),
>+                    m_out.notEqual(
>+                        m_out.load32(value, m_heaps.JSCell_structureID),
>+                        weakStructureID(type.structure())));
>+            }
>+
>+            m_out.jump(continuation);
>+
>+            m_out.appendTo(notCellCase, continuation);
>+
>+            speculate(
>+                BadType, jsValueValue(value), edge.node(),
>+                isNotOther(value, provenType(edge) & ~SpecCell));
>+
>+            m_out.jump(continuation);
>+
>+            m_out.appendTo(continuation, lastNext);
>+            return;
>+        }
>+
>+        case InferredType::Object:
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotCell(value, provenType(edge)));
>+            speculate(BadType, jsValueValue(value), edge.node(), isNotObject(value, provenType(edge)));
>+            return;
>+
>+        case InferredType::ObjectOrOther: {
>+            LBasicBlock cellCase = FTL_NEW_BLOCK(m_out, ("checkInferredType ObjectOrOther cell case"));
>+            LBasicBlock notCellCase = FTL_NEW_BLOCK(m_out, ("checkInferredType ObjectOrOther not cell case"));
>+            LBasicBlock continuation = FTL_NEW_BLOCK(m_out, ("checkInferredType ObjectOrOther continuation"));
>+
>+            m_out.branch(isCell(value, provenType(edge)), unsure(cellCase), unsure(notCellCase));
>+
>+            LBasicBlock lastNext = m_out.appendTo(cellCase, notCellCase);
>+
>+            speculate(
>+                BadType, jsValueValue(value), edge.node(),
>+                isNotObject(value, provenType(edge) & SpecCell));
>+
>+            m_out.jump(continuation);
>+
>+            m_out.appendTo(notCellCase, continuation);
>+
>+            speculate(
>+                BadType, jsValueValue(value), edge.node(),
>+                isNotOther(value, provenType(edge) & ~SpecCell));
>+
>+            m_out.jump(continuation);
>+
>+            m_out.appendTo(continuation, lastNext);
>+            return;
>+        }
>+
>+        case InferredType::Top:
>+            return;
>+        }
>+
>+        DFG_CRASH(m_graph, m_node, "Bad inferred type");
>+    }
>     
>     LValue loadProperty(LValue storage, unsigned identifierNumber, PropertyOffset offset)
>     {
>@@ -7514,6 +7681,9 @@ private:
>         case CellUse:
>             speculateCell(edge);
>             break;
>+        case CellOrOtherUse:
>+            speculateCellOrOther(edge);
>+            break;
>         case KnownCellUse:
>             ASSERT(!m_interpreter.needsTypeCheck(edge));
>             break;
>@@ -7594,6 +7764,22 @@ private:
>         lowCell(edge);
>     }
>     
>+    void speculateCellOrOther(Edge edge)
>+    {
>+        LValue value = lowJSValue(edge, ManualOperandSpeculation);
>+
>+        LBasicBlock isNotCell = FTL_NEW_BLOCK(m_out, ("Speculate CellOrOther not cell"));
>+        LBasicBlock continuation = FTL_NEW_BLOCK(m_out, ("Speculate CellOrOther continuation"));
>+
>+        m_out.branch(isCell(value, provenType(edge)), unsure(continuation), unsure(isNotCell));
>+
>+        LBasicBlock lastNext = m_out.appendTo(isNotCell, continuation);
>+        FTL_TYPE_CHECK(jsValueValue(value), edge, SpecCell | SpecOther, isNotOther(value));
>+        m_out.jump(continuation);
>+
>+        m_out.appendTo(continuation, lastNext);
>+    }
>+    
>     void speculateMachineInt(Edge edge)
>     {
>         if (!m_interpreter.needsTypeCheck(edge))
>@@ -8127,6 +8313,9 @@ private:
>             }
>         }
> 
>+        if (failCondition == m_out.booleanFalse)
>+            return;
>+
>         ASSERT(m_ftlState.jitCode->osrExit.size() == m_ftlState.finalizer->osrExit.size());
>         
>         m_ftlState.jitCode->osrExit.append(OSRExit(
>@@ -8135,9 +8324,14 @@ private:
>             availabilityMap().m_locals.numberOfArguments(),
>             availabilityMap().m_locals.numberOfLocals()));
>         m_ftlState.finalizer->osrExit.append(OSRExitCompilationInfo());
>-        
>+
>         OSRExit& exit = m_ftlState.jitCode->osrExit.last();
> 
>+        if (failCondition == m_out.booleanTrue) {
>+            emitOSRExitCall(exit, lowValue);
>+            return;
>+        }
>+
>         LBasicBlock lastNext = nullptr;
>         LBasicBlock continuation = nullptr;
>         
>Index: Source/JavaScriptCore/jit/AssemblyHelpers.cpp
>===================================================================
>--- Source/JavaScriptCore/jit/AssemblyHelpers.cpp	(revision 190059)
>+++ Source/JavaScriptCore/jit/AssemblyHelpers.cpp	(working copy)
>@@ -55,6 +55,78 @@ Vector<BytecodeAndMachineOffset>& Assemb
>     return result.iterator->value;
> }
> 
>+AssemblyHelpers::JumpList AssemblyHelpers::branchIfNotType(
>+    JSValueRegs regs, GPRReg tempGPR, const InferredType::Descriptor& descriptor, TagRegistersMode mode)
>+{
>+    AssemblyHelpers::JumpList result;
>+
>+    switch (descriptor.kind()) {
>+    case InferredType::Bottom:
>+        result.append(jump());
>+        break;
>+
>+    case InferredType::Boolean:
>+        result.append(branchIfNotBoolean(regs, tempGPR));
>+        break;
>+
>+    case InferredType::Other:
>+        result.append(branchIfNotOther(regs, tempGPR));
>+        break;
>+
>+    case InferredType::Int32:
>+        result.append(branchIfNotInt32(regs, mode));
>+        break;
>+
>+    case InferredType::Number:
>+        result.append(branchIfNotNumber(regs, tempGPR, mode));
>+        break;
>+
>+    case InferredType::String:
>+        result.append(branchIfNotCell(regs, mode));
>+        result.append(branchIfNotString(regs.payloadGPR()));
>+        break;
>+
>+    case InferredType::ObjectWithStructure:
>+        result.append(branchIfNotCell(regs, mode));
>+        result.append(
>+            branchStructure(
>+                NotEqual,
>+                Address(regs.payloadGPR(), JSCell::structureIDOffset()),
>+                descriptor.structure()));
>+        break;
>+
>+    case InferredType::ObjectWithStructureOrOther: {
>+        Jump ok = branchIfOther(regs, tempGPR);
>+        result.append(branchIfNotCell(regs, mode));
>+        result.append(
>+            branchStructure(
>+                NotEqual,
>+                Address(regs.payloadGPR(), JSCell::structureIDOffset()),
>+                descriptor.structure()));
>+        ok.link(this);
>+        break;
>+    }
>+
>+    case InferredType::Object:
>+        result.append(branchIfNotCell(regs, mode));
>+        result.append(branchIfNotObject(regs.payloadGPR()));
>+        break;
>+
>+    case InferredType::ObjectOrOther: {
>+        Jump ok = branchIfOther(regs, tempGPR);
>+        result.append(branchIfNotCell(regs, mode));
>+        result.append(branchIfNotObject(regs.payloadGPR()));
>+        ok.link(this);
>+        break;
>+    }
>+
>+    case InferredType::Top:
>+        break;
>+    }
>+
>+    return result;
>+}
>+
> void AssemblyHelpers::purifyNaN(FPRReg fpr)
> {
>     MacroAssembler::Jump notNaN = branchDouble(DoubleEqual, fpr, fpr);
>Index: Source/JavaScriptCore/jit/AssemblyHelpers.h
>===================================================================
>--- Source/JavaScriptCore/jit/AssemblyHelpers.h	(revision 190059)
>+++ Source/JavaScriptCore/jit/AssemblyHelpers.h	(working copy)
>@@ -555,37 +555,48 @@ public:
> #endif
>     }
> 
>-    Jump branchIfNotCell(GPRReg reg)
>+    enum TagRegistersMode {
>+        DoNotHaveTagRegisters,
>+        HaveTagRegisters
>+    };
>+
>+    Jump branchIfNotCell(GPRReg reg, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>-        return branchTest64(MacroAssembler::NonZero, reg, GPRInfo::tagMaskRegister);
>+        if (mode == HaveTagRegisters)
>+            return branchTest64(NonZero, reg, GPRInfo::tagMaskRegister);
>+        return branchTest64(NonZero, reg, TrustedImm64(TagMask));
> #else
>+        UNUSED_PARAM(mode);
>         return branch32(MacroAssembler::NotEqual, reg, TrustedImm32(JSValue::CellTag));
> #endif
>     }
>-    Jump branchIfNotCell(JSValueRegs regs)
>+    Jump branchIfNotCell(JSValueRegs regs, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>-        return branchIfNotCell(regs.gpr());
>+        return branchIfNotCell(regs.gpr(), mode);
> #else
>-        return branchIfNotCell(regs.tagGPR());
>+        return branchIfNotCell(regs.tagGPR(), mode);
> #endif
>     }
>     
>-    Jump branchIfCell(GPRReg reg)
>+    Jump branchIfCell(GPRReg reg, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>-        return branchTest64(MacroAssembler::Zero, reg, GPRInfo::tagMaskRegister);
>+        if (mode == HaveTagRegisters)
>+            return branchTest64(Zero, reg, GPRInfo::tagMaskRegister);
>+        return branchTest64(Zero, reg, TrustedImm64(TagMask));
> #else
>+        UNUSED_PARAM(mode);
>         return branch32(MacroAssembler::Equal, reg, TrustedImm32(JSValue::CellTag));
> #endif
>     }
>-    Jump branchIfCell(JSValueRegs regs)
>+    Jump branchIfCell(JSValueRegs regs, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>-        return branchIfCell(regs.gpr());
>+        return branchIfCell(regs.gpr(), mode);
> #else
>-        return branchIfCell(regs.tagGPR());
>+        return branchIfCell(regs.tagGPR(), mode);
> #endif
>     }
>     
>@@ -613,43 +624,55 @@ public:
> #endif
>     }
>     
>-    Jump branchIfInt32(JSValueRegs regs)
>+    Jump branchIfInt32(JSValueRegs regs, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>-        return branch64(AboveOrEqual, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        if (mode == HaveTagRegisters)
>+            return branch64(AboveOrEqual, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        return branch64(AboveOrEqual, regs.gpr(), TrustedImm64(TagTypeNumber));
> #else
>+        UNUSED_PARAM(mode);
>         return branch32(Equal, regs.tagGPR(), TrustedImm32(JSValue::Int32Tag));
> #endif
>     }
>     
>-    Jump branchIfNotInt32(JSValueRegs regs)
>+    Jump branchIfNotInt32(JSValueRegs regs, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>-        return branch64(Below, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        if (mode == HaveTagRegisters)
>+            return branch64(Below, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        return branch64(Below, regs.gpr(), TrustedImm64(TagTypeNumber));
> #else
>+        UNUSED_PARAM(mode);
>         return branch32(NotEqual, regs.tagGPR(), TrustedImm32(JSValue::Int32Tag));
> #endif
>     }
> 
>     // Note that the tempGPR is not used in 64-bit mode.
>-    Jump branchIfNumber(JSValueRegs regs, GPRReg tempGPR)
>+    Jump branchIfNumber(JSValueRegs regs, GPRReg tempGPR, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>         UNUSED_PARAM(tempGPR);
>-        return branchTest64(NonZero, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        if (mode == HaveTagRegisters)
>+            return branchTest64(NonZero, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        return branchTest64(NonZero, regs.gpr(), TrustedImm64(TagTypeNumber));
> #else
>+        UNUSED_PARAM(mode);
>         add32(TrustedImm32(1), regs.tagGPR(), tempGPR);
>         return branch32(Below, tempGPR, TrustedImm32(JSValue::LowestTag + 1));
> #endif
>     }
>     
>     // Note that the tempGPR is not used in 64-bit mode.
>-    Jump branchIfNotNumber(JSValueRegs regs, GPRReg tempGPR)
>+    Jump branchIfNotNumber(JSValueRegs regs, GPRReg tempGPR, TagRegistersMode mode = HaveTagRegisters)
>     {
> #if USE(JSVALUE64)
>         UNUSED_PARAM(tempGPR);
>-        return branchTest64(Zero, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        if (mode == HaveTagRegisters)
>+            return branchTest64(Zero, regs.gpr(), GPRInfo::tagTypeNumberRegister);
>+        return branchTest64(Zero, regs.gpr(), TrustedImm64(TagTypeNumber));
> #else
>+        UNUSED_PARAM(mode);
>         add32(TrustedImm32(1), regs.tagGPR(), tempGPR);
>         return branch32(AboveOrEqual, tempGPR, TrustedImm32(JSValue::LowestTag + 1));
> #endif
>@@ -719,6 +742,9 @@ public:
> #endif
>     }
> 
>+    JumpList branchIfNotType(
>+        JSValueRegs, GPRReg tempGPR, const InferredType::Descriptor&, TagRegistersMode);
>+
>     template<typename T>
>     Jump branchStructure(RelationalCondition condition, T leftHandSide, Structure* structure)
>     {
>Index: Source/JavaScriptCore/jit/Repatch.cpp
>===================================================================
>--- Source/JavaScriptCore/jit/Repatch.cpp	(revision 190059)
>+++ Source/JavaScriptCore/jit/Repatch.cpp	(working copy)
>@@ -378,7 +378,8 @@ static InlineCacheAction tryCachePutByID
>             ptrdiff_t offsetToPatchedStorage = offsetRelativeToPatchedStorage(slot.cachedOffset());
>             if (stubInfo.cacheType == CacheType::Unset
>                 && MacroAssembler::isPtrAlignedAddressOffset(offsetToPatchedStorage)
>-                && !structure->needImpurePropertyWatchpoint()) {
>+                && !structure->needImpurePropertyWatchpoint()
>+                && !structure->inferredTypeFor(ident.impl())) {
> 
>                 repatchByIdSelfAccess(
>                     codeBlock, stubInfo, structure, slot.cachedOffset(),
>Index: Source/JavaScriptCore/llint/LLIntSlowPaths.cpp
>===================================================================
>--- Source/JavaScriptCore/llint/LLIntSlowPaths.cpp	(revision 190059)
>+++ Source/JavaScriptCore/llint/LLIntSlowPaths.cpp	(working copy)
>@@ -631,6 +631,8 @@ LLINT_SLOW_PATH_DECL(slow_path_put_by_id
>         pc[5].u.pointer = nullptr; // offset
>         pc[6].u.pointer = nullptr; // new structure
>         pc[7].u.pointer = nullptr; // structure chain
>+        pc[8].u.putByIdFlags =
>+            static_cast<PutByIdFlags>(pc[8].u.putByIdFlags & PutByIdPersistentFlagsMask);
>         
>         JSCell* baseCell = baseValue.asCell();
>         Structure* structure = baseCell->structure();
>@@ -658,12 +660,18 @@ LLINT_SLOW_PATH_DECL(slow_path_put_by_id
>                             pc[7].u.structureChain.set(
>                                 vm, codeBlock->ownerExecutable(), chain);
>                         }
>+                        pc[8].u.putByIdFlags = static_cast<PutByIdFlags>(
>+                            pc[8].u.putByIdFlags |
>+                            structure->inferredTypeDescriptorFor(ident.impl()).putByIdFlags());
>                     }
>                 }
>             } else {
>                 structure->didCachePropertyReplacement(vm, slot.cachedOffset());
>                 pc[4].u.structureID = structure->id();
>                 pc[5].u.operand = slot.cachedOffset();
>+                pc[8].u.putByIdFlags = static_cast<PutByIdFlags>(
>+                    pc[8].u.putByIdFlags |
>+                    structure->inferredTypeDescriptorFor(ident.impl()).putByIdFlags());
>             }
>         }
>     }
>Index: Source/JavaScriptCore/llint/LowLevelInterpreter32_64.asm
>===================================================================
>--- Source/JavaScriptCore/llint/LowLevelInterpreter32_64.asm	(revision 190059)
>+++ Source/JavaScriptCore/llint/LowLevelInterpreter32_64.asm	(working copy)
>@@ -1391,17 +1391,91 @@ _llint_op_put_by_id:
>     # At this point, we have:
>     # t2 -> currentStructureID
>     # t0 -> object base
>+    # We will lose currentStructureID in the shenanigans below.
> 
>+    loadi 12[PC], t1
>+    loadConstantOrVariable(t1, t2, t3)
>+    loadi 32[PC], t1
>+
>+    # At this point, we have:
>+    # t0 -> object base
>+    # t1 -> put by id flags
>+    # t2 -> value tag
>+    # t3 -> value payload
>+
>+    btinz t1, PutByIdPrimaryTypeMask, .opPutByIdTypeCheckObjectWithStructureOrOther
>+
>+    # We have one of the non-structure type checks. Find out which one.
>+    andi PutByIdSecondaryTypeMask, t1
>+    bilt t1, PutByIdSecondaryTypeString, .opPutByIdTypeCheckLessThanString
>+
>+    # We are one of the following: String, Object, ObjectOrOther, Top
>+    bilt t1, PutByIdSecondaryTypeObjectOrOther, .opPutByIdTypeCheckLessThanObjectOrOther
>+
>+    # We are either ObjectOrOther or Top.
>+    bieq t1, PutByIdSecondaryTypeTop, .opPutByIdDoneCheckingTypes
>+
>+    # Check if we are ObjectOrOther.
>+    bieq t2, CellTag, .opPutByIdTypeCheckObject
>+.opPutByIdTypeCheckOther:
>+    bieq t2, NullTag, .opPutByIdDoneCheckingTypes
>+    bieq t2, UndefinedTag, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckLessThanObjectOrOther:
>+    # We are either String or Object.
>+    bineq t2, CellTag, .opPutByIdSlow
>+    bieq t1, PutByIdSecondaryTypeObject, .opPutByIdTypeCheckObject
>+    bbeq JSCell::m_type[t3], StringType, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+.opPutByIdTypeCheckObject:
>+    bbaeq JSCell::m_type[t3], ObjectType, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckLessThanString:
>+    # We are one of the following: Bottom, Boolean, Other, Int32, Number.
>+    bilt t1, PutByIdSecondaryTypeInt32, .opPutByIdTypeCheckLessThanInt32
>+
>+    # We are either Int32 or Number.
>+    bieq t1, PutByIdSecondaryTypeNumber, .opPutByIdTypeCheckNumber
>+
>+    bieq t2, Int32Tag, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckNumber:
>+    bib t2, LowestTag + 1, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckLessThanInt32:
>+    # We are one of the following: Bottom, Boolean, Other
>+    bineq t1, PutByIdSecondaryTypeBoolean, .opPutByIdTypeCheckBottomOrOther
>+    bieq t2, BooleanTag, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckBottomOrOther:
>+    bieq t1, PutByIdSecondaryTypeOther, .opPutByIdTypeCheckOther
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckObjectWithStructureOrOther:
>+    bieq t2, CellTag, .opPutByIdTypeCheckObjectWithStructure
>+    btinz t1, PutByIdPrimaryTypeObjectWithStructureOrOther, .opPutByIdTypeCheckOther
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckObjectWithStructure:
>+    andi PutByIdSecondaryTypeMask, t1
>+    bineq t1, JSCell::m_structureID[t3], .opPutByIdSlow
>+
>+.opPutByIdDoneCheckingTypes:
>     loadi 24[PC], t1
> 
>     btiz t1, .opPutByIdNotTransition
> 
>-    # This is the transition case. t1 holds the new Structure*. t2 holds the old Structure*.
>-    # If we have a chain, we need to check it. t0 is the base. We may clobber t1 to use it as
>-    # scratch.
>+    # This is the transition case. t1 holds the new Structure*. If we have a chain, we need to
>+    # check it. t0 is the base. We may clobber t1 to use it as scratch.
>     loadp 28[PC], t3
>     btpz t3, .opPutByIdTransitionDirect
> 
>+    loadi 16[PC], t2 # Need old structure again.
>     loadp StructureChain::m_vector[t3], t3
>     assert(macro (ok) btpnz t3, ok end)
> 
>Index: Source/JavaScriptCore/llint/LowLevelInterpreter64.asm
>===================================================================
>--- Source/JavaScriptCore/llint/LowLevelInterpreter64.asm	(revision 190059)
>+++ Source/JavaScriptCore/llint/LowLevelInterpreter64.asm	(working copy)
>@@ -1266,14 +1266,88 @@ _llint_op_put_by_id:
>     writeBarrierOnOperands(1, 3)
>     loadisFromInstruction(1, t3)
>     loadConstantOrVariableCell(t3, t0, .opPutByIdSlow)
>-    loadi JSCell::m_structureID[t0], t2
>-    loadisFromInstruction(4, t1)
>-    bineq t2, t1, .opPutByIdSlow
>+    loadisFromInstruction(4, t2)
>+    bineq t2, JSCell::m_structureID[t0], .opPutByIdSlow
> 
>     # At this point, we have:
>-    # t1, t2 -> current structure ID
>+    # t2 -> current structure ID
>     # t0 -> object base
> 
>+    loadisFromInstruction(3, t1)
>+    loadConstantOrVariable(t1, t3)
>+
>+    loadpFromInstruction(8, t1)
>+
>+    # At this point, we have:
>+    # t0 -> object base
>+    # t1 -> put by id flags
>+    # t2 -> current structure ID
>+    # t3 -> value to put
>+
>+    btpnz t1, PutByIdPrimaryTypeMask, .opPutByIdTypeCheckObjectWithStructureOrOther
>+
>+    # We have one of the non-structure type checks. Find out which one.
>+    andp PutByIdSecondaryTypeMask, t1
>+    bplt t1, PutByIdSecondaryTypeString, .opPutByIdTypeCheckLessThanString
>+
>+    # We are one of the following: String, Object, ObjectOrOther, Top
>+    bplt t1, PutByIdSecondaryTypeObjectOrOther, .opPutByIdTypeCheckLessThanObjectOrOther
>+
>+    # We are either ObjectOrOther or Top.
>+    bpeq t1, PutByIdSecondaryTypeTop, .opPutByIdDoneCheckingTypes
>+
>+    # Check if we are ObjectOrOther.
>+    btqz t3, tagMask, .opPutByIdTypeCheckObject
>+.opPutByIdTypeCheckOther:
>+    andq ~TagBitUndefined, t3
>+    bqeq t3, ValueNull, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckLessThanObjectOrOther:
>+    # We are either String or Object.
>+    btqnz t3, tagMask, .opPutByIdSlow
>+    bpeq t1, PutByIdSecondaryTypeObject, .opPutByIdTypeCheckObject
>+    bbeq JSCell::m_type[t3], StringType, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+.opPutByIdTypeCheckObject:
>+    bbaeq JSCell::m_type[t3], ObjectType, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckLessThanString:
>+    # We are one of the following: Bottom, Boolean, Other, Int32, Number
>+    bplt t1, PutByIdSecondaryTypeInt32, .opPutByIdTypeCheckLessThanInt32
>+
>+    # We are either Int32 or Number.
>+    bpeq t1, PutByIdSecondaryTypeNumber, .opPutByIdTypeCheckNumber
>+
>+    bqaeq t3, tagTypeNumber, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckNumber:
>+    btqnz t3, tagTypeNumber, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckLessThanInt32:
>+    # We are one of the following: Bottom, Boolean, Other.
>+    bpneq t1, PutByIdSecondaryTypeBoolean, .opPutByIdTypeCheckBottomOrOther
>+    xorq ValueFalse, t3
>+    btqz t3, ~1, .opPutByIdDoneCheckingTypes
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckBottomOrOther:
>+    bpeq t1, PutByIdSecondaryTypeOther, .opPutByIdTypeCheckOther
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckObjectWithStructureOrOther:
>+    btqz t3, tagMask, .opPutByIdTypeCheckObjectWithStructure
>+    btpnz t1, PutByIdPrimaryTypeObjectWithStructureOrOther, .opPutByIdTypeCheckOther
>+    jmp .opPutByIdSlow
>+
>+.opPutByIdTypeCheckObjectWithStructure:
>+    urshiftp 3, t1
>+    bineq t1, JSCell::m_structureID[t3], .opPutByIdSlow
>+
>+.opPutByIdDoneCheckingTypes:
>     loadisFromInstruction(6, t1)
>     
>     btiz t1, .opPutByIdNotTransition
>Index: Source/JavaScriptCore/llint/LowLevelInterpreter.asm
>===================================================================
>--- Source/JavaScriptCore/llint/LowLevelInterpreter.asm	(revision 190059)
>+++ Source/JavaScriptCore/llint/LowLevelInterpreter.asm	(working copy)
>@@ -204,6 +204,22 @@ else
>     const LowestTag = DeletedValueTag
> end
> 
>+# NOTE: The values below must be in sync with what is in PutByIdFlags.h.
>+const PutByIdPrimaryTypeMask = 0x6
>+const PutByIdPrimaryTypeSecondary = 0x0
>+const PutByIdPrimaryTypeObjectWithStructure = 0x2
>+const PutByIdPrimaryTypeObjectWithStructureOrOther = 0x4
>+const PutByIdSecondaryTypeMask = -0x8
>+const PutByIdSecondaryTypeBottom = 0x0
>+const PutByIdSecondaryTypeBoolean = 0x8
>+const PutByIdSecondaryTypeOther = 0x10
>+const PutByIdSecondaryTypeInt32 = 0x18
>+const PutByIdSecondaryTypeNumber = 0x20
>+const PutByIdSecondaryTypeString = 0x28
>+const PutByIdSecondaryTypeObject = 0x30
>+const PutByIdSecondaryTypeObjectOrOther = 0x38
>+const PutByIdSecondaryTypeTop = 0x40
>+
> const CallOpCodeSize = 9
> 
> if X86_64 or ARM64 or C_LOOP
>Index: Source/JavaScriptCore/runtime/Executable.h
>===================================================================
>--- Source/JavaScriptCore/runtime/Executable.h	(revision 190059)
>+++ Source/JavaScriptCore/runtime/Executable.h	(working copy)
>@@ -31,7 +31,6 @@
> #include "CodeBlockHash.h"
> #include "CodeSpecializationKind.h"
> #include "CompilationResult.h"
>-#include "DFGPlan.h"
> #include "ExecutableInfo.h"
> #include "HandlerInfo.h"
> #include "InferredValue.h"
>Index: Source/JavaScriptCore/runtime/InferredType.cpp
>===================================================================
>--- Source/JavaScriptCore/runtime/InferredType.cpp	(revision 0)
>+++ Source/JavaScriptCore/runtime/InferredType.cpp	(working copy)
>@@ -0,0 +1,565 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
>+ */
>+
>+#include "config.h"
>+#include "InferredType.h"
>+
>+#include "JSCInlines.h"
>+
>+namespace JSC {
>+
>+namespace {
>+
>+class InferredTypeFireDetail : public FireDetail {
>+public:
>+    InferredTypeFireDetail(
>+        InferredType* inferredType, UniquedStringImpl* uid,
>+        const InferredType::Descriptor& oldDescriptor, const InferredType::Descriptor& newDescriptor,
>+        JSValue offendingValue)
>+        : m_inferredType(inferredType)
>+        , m_uid(uid)
>+        , m_oldDescriptor(oldDescriptor)
>+        , m_newDescriptor(newDescriptor)
>+        , m_offendingValue(offendingValue)
>+    {
>+    }
>+
>+protected:
>+    void dump(PrintStream& out) const override
>+    {
>+        out.print(
>+            "Inferred type changed on ", RawPointer(m_inferredType), " for property ", m_uid, ": "
>+            "old type was ", m_oldDescriptor, " while desired type is ", m_newDescriptor);
>+        if (m_offendingValue)
>+            out.print(" due to ", m_offendingValue);
>+    }
>+
>+private:
>+    InferredType* m_inferredType;
>+    RefPtr<UniquedStringImpl> m_uid;
>+    InferredType::Descriptor m_oldDescriptor;
>+    InferredType::Descriptor m_newDescriptor;
>+    JSValue m_offendingValue;
>+};
>+
>+} // anonymous namespace
>+
>+const ClassInfo InferredType::s_info = { "InferredType", 0, 0, CREATE_METHOD_TABLE(InferredType) };
>+
>+InferredType* InferredType::create(VM& vm)
>+{
>+    InferredType* result = new (NotNull, allocateCell<InferredType>(vm.heap)) InferredType(vm);
>+    result->finishCreation(vm);
>+    return result;
>+}
>+
>+void InferredType::destroy(JSCell* cell)
>+{
>+    InferredType* inferredType = static_cast<InferredType*>(cell);
>+    inferredType->InferredType::~InferredType();
>+}
>+
>+Structure* InferredType::createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>+{
>+    return Structure::create(vm, globalObject, prototype, TypeInfo(CellType, StructureFlags), info());
>+}
>+
>+void InferredType::visitChildren(JSCell* cell, SlotVisitor& visitor)
>+{
>+    InferredType* inferredType = jsCast<InferredType*>(cell);
>+
>+    if (inferredType->m_structure)
>+        visitor.addUnconditionalFinalizer(&inferredType->m_structure->m_finalizer);
>+}
>+
>+InferredType::Kind InferredType::kindForFlags(PutByIdFlags flags)
>+{
>+    switch (flags & PutByIdPrimaryTypeMask) {
>+    case PutByIdPrimaryTypeSecondary:
>+        switch (flags & PutByIdSecondaryTypeMask) {
>+        case PutByIdSecondaryTypeBottom:
>+            return Bottom;
>+        case PutByIdSecondaryTypeBoolean:
>+            return Boolean;
>+        case PutByIdSecondaryTypeOther:
>+            return Other;
>+        case PutByIdSecondaryTypeInt32:
>+            return Int32;
>+        case PutByIdSecondaryTypeNumber:
>+            return Number;
>+        case PutByIdSecondaryTypeString:
>+            return String;
>+        case PutByIdSecondaryTypeObject:
>+            return Object;
>+        case PutByIdSecondaryTypeObjectOrOther:
>+            return ObjectOrOther;
>+        case PutByIdSecondaryTypeTop:
>+            return Top;
>+        default:
>+            RELEASE_ASSERT_NOT_REACHED();
>+            return Bottom;
>+        }
>+    case PutByIdPrimaryTypeObjectWithStructure:
>+        return ObjectWithStructure;
>+    case PutByIdPrimaryTypeObjectWithStructureOrOther:
>+        return ObjectWithStructureOrOther;
>+    default:
>+        RELEASE_ASSERT_NOT_REACHED();
>+        return Bottom;
>+    }
>+}
>+
>+InferredType::Descriptor InferredType::Descriptor::forValue(JSValue value)
>+{
>+    if (value.isBoolean())
>+        return Boolean;
>+    if (value.isUndefinedOrNull())
>+        return Other;
>+    if (value.isInt32())
>+        return Int32;
>+    if (value.isNumber())
>+        return Number;
>+    if (value.isCell()) {
>+        JSCell* cell = value.asCell();
>+        if (cell->isString())
>+            return String;
>+        if (cell->isObject()) {
>+            if (cell->structure()->transitionWatchpointSetIsStillValid())
>+                return Descriptor(ObjectWithStructure, cell->structure());
>+            return Object;
>+        }
>+    }
>+    return Top;
>+}
>+
>+InferredType::Descriptor InferredType::Descriptor::forFlags(VM& vm, PutByIdFlags flags)
>+{
>+    Kind kind = kindForFlags(flags);
>+    Structure* structure;
>+    if (hasStructure(kind))
>+        structure = vm.heap.structureIDTable().get(decodeStructureID(flags));
>+    else
>+        structure = nullptr;
>+    return Descriptor(kind, structure);
>+}
>+
>+PutByIdFlags InferredType::Descriptor::putByIdFlags() const
>+{
>+    switch (m_kind) {
>+    case Bottom:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeBottom);
>+    case Boolean:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeBoolean);
>+    case Other:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeOther);
>+    case Int32:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeInt32);
>+    case Number:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeNumber);
>+    case String:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeString);
>+    case Object:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeObject);
>+    case ObjectOrOther:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeObjectOrOther);
>+    case Top:
>+        return static_cast<PutByIdFlags>(PutByIdPrimaryTypeSecondary | PutByIdSecondaryTypeTop);
>+    case ObjectWithStructure:
>+        return static_cast<PutByIdFlags>(
>+            PutByIdPrimaryTypeObjectWithStructure | encodeStructureID(m_structure->id()));
>+    case ObjectWithStructureOrOther:
>+        return static_cast<PutByIdFlags>(
>+            PutByIdPrimaryTypeObjectWithStructureOrOther | encodeStructureID(m_structure->id()));
>+    }
>+    RELEASE_ASSERT_NOT_REACHED();
>+    return PutByIdNone;
>+}
>+
>+void InferredType::Descriptor::merge(const Descriptor& other)
>+{
>+    // Filter out common things to simplify the switch statement below.
>+    if (*this == other)
>+        return;
>+    if (other.m_kind == Bottom)
>+        return;
>+
>+    switch (m_kind) {
>+    case Bottom:
>+        *this = other;
>+        return;
>+    case Boolean:
>+    case String:
>+        *this = Top;
>+        return;
>+    case Other:
>+        switch (other.m_kind) {
>+        case ObjectWithStructure:
>+        case ObjectWithStructureOrOther:
>+            *this = Descriptor(ObjectWithStructureOrOther, other.structure());
>+            return;
>+        case Object:
>+        case ObjectOrOther:
>+            *this = ObjectOrOther;
>+            return;
>+        default:
>+            *this = Top;
>+            return;
>+        }
>+    case Int32:
>+        switch (other.m_kind) {
>+        case Number:
>+            *this = Number;
>+            return;
>+        default:
>+            *this = Top;
>+            return;
>+        }
>+    case Number:
>+        switch (other.m_kind) {
>+        case Int32:
>+            return;
>+        default:
>+            *this = Top;
>+            return;
>+        }
>+    case ObjectWithStructure:
>+        switch (other.m_kind) {
>+        case ObjectWithStructure: // If we see this here, then we know that the structures didn't match.
>+        case Object:
>+            *this = Object;
>+            return;
>+        case ObjectWithStructureOrOther:
>+            if (m_structure == other.m_structure) {
>+                *this = other;
>+                return;
>+            }
>+            *this = ObjectOrOther;
>+            return;
>+        case ObjectOrOther:
>+            *this = ObjectOrOther;
>+            return;
>+        case Other:
>+            m_kind = ObjectWithStructureOrOther;
>+            return;
>+        default:
>+            *this = Top;
>+            return;
>+        }
>+    case ObjectWithStructureOrOther:
>+        switch (other.m_kind) {
>+        case ObjectWithStructure:
>+            if (m_structure == other.m_structure)
>+                return;
>+            *this = ObjectOrOther;
>+            return;
>+        case Object:
>+        case ObjectWithStructureOrOther: // If we see this here, then we know that the structures didn't match.
>+        case ObjectOrOther:
>+            *this = ObjectOrOther;
>+            return;
>+        case Other:
>+            return;
>+        default:
>+            *this = Top;
>+            return;
>+        }
>+    case Object:
>+        switch (other.m_kind) {
>+        case ObjectWithStructure:
>+            return;
>+        case ObjectWithStructureOrOther:
>+        case ObjectOrOther:
>+        case Other:
>+            *this = ObjectOrOther;
>+            return;
>+        default:
>+            *this = Top;
>+            return;
>+        }
>+    case ObjectOrOther:
>+        switch (other.m_kind) {
>+        case ObjectWithStructure:
>+        case ObjectWithStructureOrOther:
>+        case Object:
>+        case Other:
>+            return;
>+        default:
>+            *this = Top;
>+            return;
>+        }
>+    case Top:
>+        return;
>+    }
>+
>+    RELEASE_ASSERT_NOT_REACHED();
>+}
>+
>+void InferredType::Descriptor::removeStructure()
>+{
>+    switch (m_kind) {
>+    case ObjectWithStructure:
>+        *this = Object;
>+        return;
>+    case ObjectWithStructureOrOther:
>+        *this = ObjectOrOther;
>+        return;
>+    default:
>+        return;
>+    }
>+}
>+
>+bool InferredType::Descriptor::subsumes(const Descriptor& other) const
>+{
>+    Descriptor merged = *this;
>+    merged.merge(other);
>+    return *this == merged;
>+}
>+
>+void InferredType::Descriptor::dumpInContext(PrintStream& out, DumpContext* context) const
>+{
>+    out.print(m_kind);
>+    if (m_structure)
>+        out.print(":", inContext(*m_structure, context));
>+}
>+
>+void InferredType::Descriptor::dump(PrintStream& out) const
>+{
>+    dumpInContext(out, nullptr);
>+}
>+
>+InferredType::InferredType(VM& vm)
>+    : Base(vm, vm.inferredTypeStructure.get())
>+    , m_watchpointSet(ClearWatchpoint)
>+{
>+}
>+
>+InferredType::~InferredType()
>+{
>+}
>+
>+bool InferredType::canWatch(const ConcurrentJITLocker& locker, const Descriptor& expected)
>+{
>+    if (expected.kind() == Top)
>+        return false;
>+    
>+    return descriptor(locker) == expected;
>+}
>+
>+bool InferredType::canWatch(const Descriptor& expected)
>+{
>+    ConcurrentJITLocker locker(m_lock);
>+    return canWatch(locker, expected);
>+}
>+
>+void InferredType::addWatchpoint(const ConcurrentJITLocker& locker, Watchpoint* watchpoint)
>+{
>+    RELEASE_ASSERT(descriptor(locker).kind() != Top);
>+
>+    m_watchpointSet.add(watchpoint);
>+}
>+
>+void InferredType::addWatchpoint(Watchpoint* watchpoint)
>+{
>+    ConcurrentJITLocker locker(m_lock);
>+    addWatchpoint(locker, watchpoint);
>+}
>+
>+void InferredType::dump(PrintStream& out) const
>+{
>+    out.print(RawPointer(this), ":", descriptor());
>+}
>+
>+bool InferredType::willStoreValueSlow(VM& vm, PropertyName propertyName, JSValue value)
>+{
>+    ConcurrentJITLocker locker(m_lock);
>+    Descriptor myType = descriptor(locker);
>+    Descriptor otherType = Descriptor::forValue(value);
>+
>+    myType.merge(otherType);
>+
>+    ASSERT(descriptor(locker) != myType); // The type must have changed if we're on the slow path.
>+
>+    set(locker, vm, propertyName, value, myType);
>+
>+    return kind(locker) != Top;
>+}
>+
>+void InferredType::makeTopSlow(VM& vm, PropertyName propertyName)
>+{
>+    ConcurrentJITLocker locker(m_lock);
>+    set(locker, vm, propertyName, JSValue(), Top);
>+}
>+
>+void InferredType::set(
>+    const ConcurrentJITLocker& locker, VM& vm, PropertyName propertyName, JSValue offendingValue,
>+    Descriptor newDescriptor)
>+{
>+    // We will trigger write barriers while holding our lock. Currently, write barriers don't GC, but that
>+    // could change. If it does, we don't want to deadlock. Note that we could have used
>+    // GCSafeConcurrentJITLocker in the caller, but the caller is on a fast path so maybe that wouldn't be
>+    // a good idea.
>+    DeferGCForAWhile deferGC(vm.heap);
>+    
>+    // Be defensive: if we're not really changing the type, then we don't have to do anything.
>+    if (descriptor(locker) == newDescriptor)
>+        return;
>+
>+    // The new descriptor must be more general than the previous one.
>+    ASSERT(newDescriptor.subsumes(descriptor(locker)));
>+
>+    // If the new descriptors have different structures, then it can only be because one is null.
>+    if (descriptor(locker).structure() != newDescriptor.structure())
>+        ASSERT(!descriptor(locker).structure() || !newDescriptor.structure());
>+
>+    // We are changing the type, so make sure that if anyone was watching, they find out about it now. If
>+    // anyone is watching, we make sure to go to Top so that we don't do this sort of thing again.
>+    if (m_watchpointSet.state() != ClearWatchpoint) {
>+        // We cannot have been invalidated, since if we were, then we'd already be at Top.
>+        ASSERT(m_watchpointSet.state() != IsInvalidated);
>+
>+        InferredTypeFireDetail detail(
>+            this, propertyName.uid(), descriptor(locker), newDescriptor, offendingValue);
>+        
>+        // We're about to do expensive things because some compiler thread decided to watch this type and
>+        // then the type changed. Assume that this property is crazy, and don't ever do any more things for
>+        // it.
>+        newDescriptor = Top;
>+
>+        m_watchpointSet.fireAll(detail);
>+    }
>+
>+    // Remove the old InferredStructure object if we no longer need it.
>+    if (!newDescriptor.structure())
>+        m_structure = nullptr;
>+
>+    // Add a new InferredStructure object if we need one now.
>+    if (newDescriptor.structure()) {
>+        if (m_structure) {
>+            // We should agree on the structures if we get here.
>+            ASSERT(newDescriptor.structure() == m_structure->structure());
>+        } else {
>+            m_structure = std::make_unique<InferredStructure>(vm, this, newDescriptor.structure());
>+            newDescriptor.structure()->addTransitionWatchpoint(&m_structure->m_watchpoint);
>+        }
>+    }
>+
>+    // Finally, set the descriptor kind.
>+    m_kind = newDescriptor.kind();
>+
>+    // Assert that we did things.
>+    ASSERT(descriptor(locker) == newDescriptor);
>+}
>+
>+void InferredType::removeStructure()
>+{
>+    // FIXME: Find an elegant and cheap way to thread information about why we got here into the fire
>+    // detail in set().
>+    
>+    VM& vm = *Heap::heap(this)->vm();
>+
>+    ConcurrentJITLocker locker(m_lock);
>+    
>+    Descriptor newDescriptor = descriptor(locker);
>+    newDescriptor.removeStructure();
>+    
>+    set(locker, vm, PropertyName(nullptr), JSValue(), newDescriptor);
>+}
>+
>+void InferredType::InferredStructureWatchpoint::fireInternal(const FireDetail&)
>+{
>+    InferredStructure* inferredStructure =
>+        bitwise_cast<InferredStructure*>(
>+            bitwise_cast<char*>(this) - OBJECT_OFFSETOF(InferredStructure, m_watchpoint));
>+
>+    inferredStructure->m_parent->removeStructure();
>+}
>+
>+void InferredType::InferredStructureFinalizer::finalizeUnconditionally()
>+{
>+    InferredStructure* inferredStructure =
>+        bitwise_cast<InferredStructure*>(
>+            bitwise_cast<char*>(this) - OBJECT_OFFSETOF(InferredStructure, m_finalizer));
>+
>+    ASSERT(Heap::isMarked(inferredStructure->m_parent));
>+    
>+    if (!Heap::isMarked(inferredStructure->m_structure.get()))
>+        inferredStructure->m_parent->removeStructure();
>+}
>+
>+InferredType::InferredStructure::InferredStructure(VM& vm, InferredType* parent, Structure* structure)
>+    : m_parent(parent)
>+    , m_structure(vm, parent, structure)
>+{
>+}
>+
>+} // namespace JSC
>+
>+namespace WTF {
>+
>+using namespace JSC;
>+
>+void printInternal(PrintStream& out, InferredType::Kind kind)
>+{
>+    switch (kind) {
>+    case InferredType::Bottom:
>+        out.print("Bottom");
>+        return;
>+    case InferredType::Boolean:
>+        out.print("Boolean");
>+        return;
>+    case InferredType::Other:
>+        out.print("Other");
>+        return;
>+    case InferredType::Int32:
>+        out.print("Int32");
>+        return;
>+    case InferredType::Number:
>+        out.print("Number");
>+        return;
>+    case InferredType::String:
>+        out.print("String");
>+        return;
>+    case InferredType::ObjectWithStructure:
>+        out.print("ObjectWithStructure");
>+        return;
>+    case InferredType::ObjectWithStructureOrOther:
>+        out.print("ObjectWithStructureOrOther");
>+        return;
>+    case InferredType::Object:
>+        out.print("Object");
>+        return;
>+    case InferredType::ObjectOrOther:
>+        out.print("ObjectOrOther");
>+        return;
>+    case InferredType::Top:
>+        out.print("Top");
>+        return;
>+    }
>+
>+    RELEASE_ASSERT_NOT_REACHED();
>+}
>+
>+} // namespace WTF
>+
>Index: Source/JavaScriptCore/runtime/InferredType.h
>===================================================================
>--- Source/JavaScriptCore/runtime/InferredType.h	(revision 0)
>+++ Source/JavaScriptCore/runtime/InferredType.h	(working copy)
>@@ -0,0 +1,286 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
>+ */
>+
>+#ifndef InferredType_h
>+#define InferredType_h
>+
>+#include "ConcurrentJITLock.h"
>+#include "JSCell.h"
>+#include "PropertyName.h"
>+#include "PutByIdFlags.h"
>+#include "Watchpoint.h"
>+
>+namespace JSC {
>+
>+// This is an object used for the inference of the types of object properties.
>+
>+class InferredType final : public JSCell {
>+public:
>+    typedef JSCell Base;
>+
>+    static InferredType* create(VM&);
>+
>+    static const bool needsDestruction = true;
>+    static void destroy(JSCell*);
>+
>+    static const unsigned StructureFlags = StructureIsImmortal | Base::StructureFlags;
>+    
>+    static Structure* createStructure(VM&, JSGlobalObject*, JSValue prototype);
>+
>+    static void visitChildren(JSCell*, SlotVisitor&);
>+
>+    DECLARE_INFO;
>+
>+    enum Kind : uint8_t {
>+        Bottom,
>+        Boolean,
>+        Other,
>+        Int32,
>+        Number,
>+        String,
>+        ObjectWithStructure,
>+        ObjectWithStructureOrOther,
>+        Object,
>+        ObjectOrOther,
>+        Top
>+    };
>+
>+    static Kind kindForFlags(PutByIdFlags);
>+    
>+    static bool hasStructure(Kind kind)
>+    {
>+        switch (kind) {
>+        case ObjectWithStructure:
>+        case ObjectWithStructureOrOther:
>+            return true;
>+        default:
>+            return false;
>+        }
>+    }
>+
>+    class Descriptor {
>+    public:
>+        Descriptor()
>+            : m_kind(Bottom)
>+            , m_structure(nullptr)
>+        {
>+        }
>+
>+        Descriptor(Kind kind, Structure* structure = nullptr)
>+            : m_kind(kind)
>+            , m_structure(structure)
>+        {
>+            if (hasStructure(kind))
>+                ASSERT(structure);
>+        }
>+
>+        static Descriptor forValue(JSValue);
>+
>+        static Descriptor forFlags(VM&, PutByIdFlags);
>+
>+        explicit operator bool() const
>+        {
>+            return m_kind != Bottom || m_structure;
>+        }
>+
>+        Kind kind() const { return m_kind; }
>+        Structure* structure() const { return m_structure; }
>+
>+        PutByIdFlags putByIdFlags() const;
>+
>+        ALWAYS_INLINE bool includesValue(JSValue value)
>+        {
>+            switch (m_kind) {
>+            case Bottom:
>+                return false;
>+            case Boolean:
>+                return value.isBoolean();
>+            case Other:
>+                return value.isUndefinedOrNull();
>+            case Int32:
>+                return value.isInt32();
>+            case Number:
>+                return value.isNumber();
>+            case String:
>+                return value.isString();
>+            case ObjectWithStructure:
>+                return value.isCell() && value.asCell()->structure() == m_structure;
>+            case ObjectWithStructureOrOther:
>+                return value.isUndefinedOrNull()
>+                    || (value.isCell() && value.asCell()->structure() == m_structure);
>+            case Object:
>+                return value.isObject();
>+            case ObjectOrOther:
>+                return value.isUndefinedOrNull() || value.isObject();
>+            case Top:
>+                return true;
>+            }
>+
>+            RELEASE_ASSERT_NOT_REACHED();
>+        }
>+
>+        bool operator==(const Descriptor& other) const
>+        {
>+            return m_kind == other.m_kind
>+                && m_structure == other.m_structure;
>+        }
>+
>+        bool operator!=(const Descriptor& other) const
>+        {
>+            return !(*this == other);
>+        }
>+
>+        unsigned hash() const
>+        {
>+            return WTF::PtrHash<Structure*>::hash(m_structure) ^ static_cast<unsigned>(m_kind);
>+        }
>+    
>+        void merge(const Descriptor&);
>+        void removeStructure();
>+
>+        // Returns true if this descriptor is more general than the other one.
>+        bool subsumes(const Descriptor&) const;
>+
>+        void dumpInContext(PrintStream&, DumpContext*) const;
>+        void dump(PrintStream&) const;
>+
>+    private:
>+        Kind m_kind;
>+        Structure* m_structure;
>+    };
>+
>+    ConcurrentJITLock& lock() const { return m_lock; }
>+
>+    Descriptor descriptorMainThread() const
>+    {
>+        return Descriptor(m_kind, m_structure ? m_structure->structure() : nullptr);
>+    }
>+    
>+    Descriptor descriptor(const ConcurrentJITLocker&) const
>+    {
>+        return descriptorMainThread();
>+    }
>+    Descriptor descriptor() const
>+    {
>+        ConcurrentJITLocker locker(m_lock);
>+        return descriptor(locker);
>+    }
>+    
>+    Kind kind(const ConcurrentJITLocker& locker) const { return descriptor(locker).kind(); }
>+
>+    bool isTop() const { return m_kind == Top; }
>+    bool isRelevant() const { return m_kind != Top; }
>+
>+    // Returns true if the InferredType is still relevant after the store. It's not relevant if it's Top.
>+    ALWAYS_INLINE bool willStoreValue(VM& vm, PropertyName propertyName, JSValue value)
>+    {
>+        Descriptor currentDescriptor = descriptorMainThread();
>+        if (currentDescriptor.includesValue(value))
>+            return currentDescriptor.kind() != Top;
>+        return willStoreValueSlow(vm, propertyName, value);
>+    }
>+
>+    // Immediately makes this type irrelevant.
>+    void makeTop(VM& vm, PropertyName propertyName)
>+    {
>+        if (isTop())
>+            return;
>+        makeTopSlow(vm, propertyName);
>+    }
>+
>+    // Returns true if it currently makes sense to watch this InferredType for this descriptor. Note that
>+    // this will always return false for Top.
>+    bool canWatch(const ConcurrentJITLocker& locker, const Descriptor&);
>+    bool canWatch(const Descriptor&);
>+    
>+    void addWatchpoint(const ConcurrentJITLocker& locker, Watchpoint*);
>+    void addWatchpoint(Watchpoint*);
>+
>+    void dump(PrintStream&) const;
>+
>+private:
>+    InferredType(VM&);
>+    ~InferredType();
>+
>+    bool willStoreValueSlow(VM&, PropertyName, JSValue);
>+    void makeTopSlow(VM&, PropertyName);
>+    void set(const ConcurrentJITLocker&, VM&, PropertyName, JSValue, Descriptor);
>+    void removeStructure();
>+
>+    mutable ConcurrentJITLock m_lock;
>+    
>+    Kind m_kind { Bottom };
>+
>+    class InferredStructureWatchpoint : public Watchpoint {
>+    public:
>+        InferredStructureWatchpoint() { }
>+    protected:
>+        void fireInternal(const FireDetail&) override;
>+    };
>+
>+    class InferredStructureFinalizer : public UnconditionalFinalizer {
>+    public:
>+        InferredStructureFinalizer() { }
>+    protected:
>+        void finalizeUnconditionally() override;
>+    };
>+
>+    class InferredStructure {
>+        WTF_MAKE_FAST_ALLOCATED;
>+    public:
>+        InferredStructure(VM&, InferredType* parent, Structure*);
>+
>+        Structure* structure() const { return m_structure.get(); };
>+
>+    private:
>+        friend class InferredType;
>+        friend class InferredStructureWatchpoint;
>+        friend class InferredStructureFinalizer;
>+        
>+        InferredType* m_parent;
>+        WriteBarrier<Structure> m_structure;
>+
>+        InferredStructureWatchpoint m_watchpoint;
>+        InferredStructureFinalizer m_finalizer;
>+    };
>+
>+    std::unique_ptr<InferredStructure> m_structure;
>+
>+    // NOTE: If this is being watched, we transform to Top because that implies that it wouldn't be
>+    // profitable to watch it again. Also, this set is initialized clear, and is never exposed to the DFG
>+    // thread. The DFG will use the InferredType as the thing that it watches.
>+    InlineWatchpointSet m_watchpointSet;
>+};
>+
>+} // namespace JSC
>+
>+namespace WTF {
>+
>+void printInternal(PrintStream&, JSC::InferredType::Kind);
>+
>+} // namespace WTF
>+
>+#endif // InferredType_h
>+
>Index: Source/JavaScriptCore/runtime/InferredTypeTable.cpp
>===================================================================
>--- Source/JavaScriptCore/runtime/InferredTypeTable.cpp	(revision 0)
>+++ Source/JavaScriptCore/runtime/InferredTypeTable.cpp	(working copy)
>@@ -0,0 +1,166 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
>+ */
>+
>+#include "config.h"
>+#include "InferredTypeTable.h"
>+
>+#include "JSCInlines.h"
>+
>+namespace JSC {
>+
>+const ClassInfo InferredTypeTable::s_info = { "InferredTypeTable", 0, 0, CREATE_METHOD_TABLE(InferredTypeTable) };
>+
>+InferredTypeTable* InferredTypeTable::create(VM& vm)
>+{
>+    InferredTypeTable* result = new (NotNull, allocateCell<InferredTypeTable>(vm.heap)) InferredTypeTable(vm);
>+    result->finishCreation(vm);
>+    return result;
>+}
>+
>+void InferredTypeTable::destroy(JSCell* cell)
>+{
>+    InferredTypeTable* inferredTypeTable = static_cast<InferredTypeTable*>(cell);
>+    inferredTypeTable->InferredTypeTable::~InferredTypeTable();
>+}
>+
>+Structure* InferredTypeTable::createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>+{
>+    return Structure::create(vm, globalObject, prototype, TypeInfo(CellType, StructureFlags), info());
>+}
>+
>+void InferredTypeTable::visitChildren(JSCell* cell, SlotVisitor& visitor)
>+{
>+    InferredTypeTable* inferredTypeTable = jsCast<InferredTypeTable*>(cell);
>+
>+    ConcurrentJITLocker locker(inferredTypeTable->m_lock);
>+    
>+    for (auto& entry : inferredTypeTable->m_table) {
>+        if (!entry.value)
>+            continue;
>+        if (entry.value->isRelevant())
>+            visitor.append(&entry.value);
>+        else
>+            entry.value.clear();
>+    }
>+}
>+
>+InferredType* InferredTypeTable::get(const ConcurrentJITLocker&, UniquedStringImpl* uid)
>+{
>+    auto iter = m_table.find(uid);
>+    if (iter == m_table.end() || !iter->value)
>+        return nullptr;
>+
>+    // Take this opportunity to prune invalidated types.
>+    if (!iter->value->isRelevant()) {
>+        iter->value.clear();
>+        return nullptr;
>+    }
>+
>+    return iter->value.get();
>+}
>+
>+InferredType* InferredTypeTable::get(UniquedStringImpl* uid)
>+{
>+    ConcurrentJITLocker locker(m_lock);
>+    return get(locker, uid);
>+}
>+
>+InferredType* InferredTypeTable::get(PropertyName propertyName)
>+{
>+    return get(propertyName.uid());
>+}
>+
>+bool InferredTypeTable::willStoreValue(
>+    VM& vm, PropertyName propertyName, JSValue value, StoredPropertyAge age)
>+{
>+    // The algorithm here relies on the fact that only one thread modifies the hash map.
>+    
>+    if (age == OldProperty) {
>+        TableType::iterator iter = m_table.find(propertyName.uid());
>+        if (iter == m_table.end() || !iter->value)
>+            return false; // Absence on replace => top.
>+        
>+        if (iter->value->willStoreValue(vm, propertyName, value))
>+            return true;
>+        
>+        iter->value.clear();
>+        return false;
>+    }
>+
>+    TableType::AddResult result;
>+    {
>+        ConcurrentJITLocker locker(m_lock);
>+        result = m_table.add(propertyName.uid(), WriteBarrier<InferredType>());
>+    }
>+    if (result.isNewEntry) {
>+        InferredType* inferredType = InferredType::create(vm);
>+        WTF::storeStoreFence();
>+        result.iterator->value.set(vm, this, inferredType);
>+    } else if (!result.iterator->value)
>+        return false;
>+    
>+    if (result.iterator->value->willStoreValue(vm, propertyName, value))
>+        return true;
>+    
>+    result.iterator->value.clear();
>+    return false;
>+}
>+
>+void InferredTypeTable::makeTop(VM& vm, PropertyName propertyName, StoredPropertyAge age)
>+{
>+    // The algorithm here relies on the fact that only one thread modifies the hash map.
>+    if (age == OldProperty) {
>+        TableType::iterator iter = m_table.find(propertyName.uid());
>+        if (iter == m_table.end() || !iter->value)
>+            return; // Absence on replace => top.
>+
>+        iter->value->makeTop(vm, propertyName);
>+        iter->value.clear();
>+        return;
>+    }
>+
>+    TableType::AddResult result;
>+    {
>+        ConcurrentJITLocker locker(m_lock);
>+        result = m_table.add(propertyName.uid(), WriteBarrier<InferredType>());
>+    }
>+    if (!result.iterator->value)
>+        return;
>+    
>+    result.iterator->value->makeTop(vm, propertyName);
>+    result.iterator->value.clear();
>+}
>+
>+InferredTypeTable::InferredTypeTable(VM& vm)
>+    : Base(vm, vm.inferredTypeTableStructure.get())
>+{
>+}
>+
>+InferredTypeTable::~InferredTypeTable()
>+{
>+}
>+
>+} // namespace JSC
>+
>Index: Source/JavaScriptCore/runtime/InferredTypeTable.h
>===================================================================
>--- Source/JavaScriptCore/runtime/InferredTypeTable.h	(revision 0)
>+++ Source/JavaScriptCore/runtime/InferredTypeTable.h	(working copy)
>@@ -0,0 +1,114 @@
>+/*
>+ * Copyright (C) 2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
>+ */
>+
>+#ifndef InferredTypeTable_h
>+#define InferredTypeTable_h
>+
>+#include "Identifier.h"
>+#include "InferredType.h"
>+#include "JSCell.h"
>+
>+namespace JSC {
>+
>+// A table of inferred types for some structure. This is a JSCell because that simplifies the Structure
>+// destructor and makes lifetime easier to manage. For example, since it's a cell, we know that this thing
>+// cannot be deleted while the DFG is running. This is separate from PropertyTable because most properties
>+// will not have an InferredType, since most properties are in dictionaries (if you think of "a property"
>+// as being "a property in some Structure"). Also, this will happily conflate the types of properties from
>+// different structures even if the structures represent disjoint sets of objects.
>+
>+class InferredTypeTable final : public JSCell {
>+public:
>+    typedef JSCell Base;
>+
>+    static InferredTypeTable* create(VM&);
>+
>+    static const bool needsDestruction = true;
>+    static void destroy(JSCell*);
>+
>+    static const unsigned StructureFlags = StructureIsImmortal | Base::StructureFlags;
>+    
>+    static Structure* createStructure(VM&, JSGlobalObject*, JSValue prototype);
>+
>+    static void visitChildren(JSCell*, SlotVisitor&);
>+
>+    DECLARE_INFO;
>+
>+    ConcurrentJITLock& lock() { return m_lock; }
>+
>+    bool isEmpty() const { return m_table.isEmpty(); }
>+
>+    // Get the current inferred type. Returns nullptr for both Top and Bottom. Null means Bottom if the
>+    // owning Structure doesn't know about the property.
>+    InferredType* get(const ConcurrentJITLocker&, UniquedStringImpl*);
>+    InferredType* get(UniquedStringImpl*);
>+    InferredType* get(PropertyName);
>+
>+    enum StoredPropertyAge {
>+        NewProperty,
>+        OldProperty
>+    };
>+    
>+    // Returns true if the InferredType for this property is still relevant after the store. It's not
>+    // relevant if it's Top. Note that this table will internally prune Top entries.
>+    bool willStoreValue(VM&, PropertyName, JSValue, StoredPropertyAge);
>+
>+    // Invalidates the type for the property. Useful if we detect a store in a reflective context.
>+    void makeTop(VM&, PropertyName, StoredPropertyAge);
>+
>+private:
>+    InferredTypeTable(VM&);
>+    ~InferredTypeTable();
>+
>+    // Bottom: absence from table.
>+    // Top: null value in table, !value->isRelevant(), or absence from table.
>+    //
>+    // We know how to determine if absence from the table is bottom or top depending on whether the
>+    // property is present in the owning structure. Hence, depending on the structure, absence may have
>+    // different meanings. The way that this class determines if the owning structure knows of the property
>+    // is that we differentiate between actions: replace or transition. If we're adding a new property
>+    // (transition), then absence means bottom. If we're storing to an existing property (replace), then
>+    // absence means top. To make this work, we have to watch out for the case where two structures, S1 and
>+    // S2, share the same InferredTypeTable and neither of them initially know about property P. S1 may
>+    // want to add P without a type, while S2 may want to add P with a type. If S1 added P and used absence
>+    // to indicate Top, then S2 would use that absence to mean Bottom and would end up creating a non-Top
>+    // entry in the table. Then S1 would forget that it wanted Top, and would use S2's type. Clearly,
>+    // that's bad. We avoid such confusion by ensuring that a transition always adds an entry. Hence,
>+    // absence-means-bottom only comes into play for properties added before the InferredTypeTable was
>+    // created.
>+    typedef HashMap<RefPtr<UniquedStringImpl>, WriteBarrier<InferredType>, IdentifierRepHash, HashTraits<UniquedStringImpl*>> TableType;
>+    
>+    TableType m_table;
>+
>+    // We only grab this lock when we're doing modifications on the main thread, or reads on the compiler
>+    // thread. The compiler thread is not allowed to do modifications.
>+    ConcurrentJITLock m_lock;
>+};
>+
>+} // namespace JSC
>+
>+#endif // InferredTypeTable_h
>+
>+
>Index: Source/JavaScriptCore/runtime/JSObject.h
>===================================================================
>--- Source/JavaScriptCore/runtime/JSObject.h	(revision 190059)
>+++ Source/JavaScriptCore/runtime/JSObject.h	(working copy)
>@@ -1189,6 +1189,8 @@ inline bool JSObject::putDirectInternal(
> 
>     Structure* structure = this->structure(vm);
>     if (structure->isDictionary()) {
>+        ASSERT(!structure->hasInferredTypes());
>+        
>         unsigned currentAttributes;
>         PropertyOffset offset = structure->get(vm, propertyName, currentAttributes);
>         if (offset != invalidOffset) {
>@@ -1227,29 +1229,40 @@ inline bool JSObject::putDirectInternal(
> 
>     PropertyOffset offset;
>     size_t currentCapacity = this->structure()->outOfLineCapacity();
>-    if (Structure* structure = Structure::addPropertyTransitionToExistingStructure(this->structure(), propertyName, attributes, offset)) {
>+    Structure* newStructure = Structure::addPropertyTransitionToExistingStructure(
>+        structure, propertyName, attributes, offset);
>+    if (newStructure) {
>+        newStructure->willStoreValueForTransition(
>+            vm, propertyName, value, slot.context() == PutPropertySlot::PutById);
>+        
>         DeferGC deferGC(vm.heap);
>         Butterfly* newButterfly = butterfly();
>-        if (currentCapacity != structure->outOfLineCapacity()) {
>-            ASSERT(structure != this->structure());
>-            newButterfly = growOutOfLineStorage(vm, currentCapacity, structure->outOfLineCapacity());
>+        if (currentCapacity != newStructure->outOfLineCapacity()) {
>+            ASSERT(newStructure != this->structure());
>+            newButterfly = growOutOfLineStorage(vm, currentCapacity, newStructure->outOfLineCapacity());
>         }
> 
>         validateOffset(offset);
>-        ASSERT(structure->isValidOffset(offset));
>-        setStructureAndButterfly(vm, structure, newButterfly);
>+        ASSERT(newStructure->isValidOffset(offset));
>+        setStructureAndButterfly(vm, newStructure, newButterfly);
>         putDirect(vm, offset, value);
>         slot.setNewProperty(this, offset);
>         return true;
>     }
> 
>     unsigned currentAttributes;
>-    offset = structure->get(vm, propertyName, currentAttributes);
>+    bool hasInferredType;
>+    offset = structure->get(vm, propertyName, currentAttributes, hasInferredType);
>     if (offset != invalidOffset) {
>         if ((mode == PutModePut) && currentAttributes & ReadOnly)
>             return false;
> 
>         structure->didReplaceProperty(offset);
>+        if (UNLIKELY(hasInferredType)) {
>+            structure->willStoreValueForReplace(
>+                vm, propertyName, value, slot.context() == PutPropertySlot::PutById);
>+        }
>+
>         slot.setExistingProperty(this, offset);
>         putDirect(vm, offset, value);
> 
>@@ -1268,16 +1281,19 @@ inline bool JSObject::putDirectInternal(
>     // we want.
>     DeferredStructureTransitionWatchpointFire deferredWatchpointFire;
>     
>-    structure = Structure::addPropertyTransition(vm, structure, propertyName, attributes, offset, slot.context(), &deferredWatchpointFire);
>+    newStructure = Structure::addPropertyTransition(
>+        vm, structure, propertyName, attributes, offset, slot.context(), &deferredWatchpointFire);
>+    newStructure->willStoreValueForTransition(
>+        vm, propertyName, value, slot.context() == PutPropertySlot::PutById);
>     
>     validateOffset(offset);
>-    ASSERT(structure->isValidOffset(offset));
>-    setStructureAndReallocateStorageIfNecessary(vm, structure);
>+    ASSERT(newStructure->isValidOffset(offset));
>+    setStructureAndReallocateStorageIfNecessary(vm, newStructure);
> 
>     putDirect(vm, offset, value);
>     slot.setNewProperty(this, offset);
>     if (attributes & ReadOnly)
>-        structure->setContainsReadOnlyProperties();
>+        newStructure->setContainsReadOnlyProperties();
>     return true;
> }
> 
>@@ -1335,8 +1351,11 @@ inline void JSObject::putDirectWithoutTr
>     Butterfly* newButterfly = m_butterfly.get();
>     if (structure()->putWillGrowOutOfLineStorage())
>         newButterfly = growOutOfLineStorage(vm, structure()->outOfLineCapacity(), structure()->suggestedNewOutOfLineStorageCapacity());
>-    PropertyOffset offset = structure()->addPropertyWithoutTransition(vm, propertyName, attributes);
>-    setStructureAndButterfly(vm, structure(), newButterfly);
>+    Structure* structure = this->structure();
>+    PropertyOffset offset = structure->addPropertyWithoutTransition(vm, propertyName, attributes);
>+    bool shouldOptimize = false;
>+    structure->willStoreValueForTransition(vm, propertyName, value, shouldOptimize);
>+    setStructureAndButterfly(vm, structure, newButterfly);
>     putDirect(vm, offset, value);
> }
> 
>Index: Source/JavaScriptCore/runtime/Structure.cpp
>===================================================================
>--- Source/JavaScriptCore/runtime/Structure.cpp	(revision 190059)
>+++ Source/JavaScriptCore/runtime/Structure.cpp	(working copy)
>@@ -350,11 +350,15 @@ void Structure::materializePropertyMap(V
>     else
>         propertyTable().set(vm, this, table);
> 
>+    InferredTypeTable* typeTable = m_inferredTypeTable.get();
>+
>     for (size_t i = structures.size(); i--;) {
>         structure = structures[i];
>         if (!structure->m_nameInPrevious)
>             continue;
>         PropertyMapEntry entry(structure->m_nameInPrevious.get(), structure->m_offset, structure->attributesInPrevious());
>+        if (typeTable && typeTable->get(structure->m_nameInPrevious.get()))
>+            entry.hasInferredType = true;
>         propertyTable()->add(entry, m_offset, PropertyTable::PropertyOffsetMustNotChange);
>     }
>     
>@@ -464,6 +468,7 @@ Structure* Structure::addPropertyTransit
>     transition->setAttributesInPrevious(attributes);
>     transition->propertyTable().set(vm, transition, structure->takePropertyTableOrCloneIfPinned(vm));
>     transition->m_offset = structure->m_offset;
>+    transition->m_inferredTypeTable.setMayBeNull(vm, transition, structure->m_inferredTypeTable.get());
> 
>     offset = transition->add(vm, propertyName, attributes);
> 
>@@ -479,6 +484,24 @@ Structure* Structure::addPropertyTransit
> 
> Structure* Structure::removePropertyTransition(VM& vm, Structure* structure, PropertyName propertyName, PropertyOffset& offset)
> {
>+    // NOTE: There are some good reasons why this goes directly to uncacheable dictionary rather than
>+    // caching the removal. We can fix all of these things, but we must remember to do so, if we ever try
>+    // to optimize this case.
>+    //
>+    // - Cached transitions usually steal the property table, and assume that this is possible because they
>+    //   can just rebuild the table by looking at past transitions. That code assumes that the table only
>+    //   grew and never shrank. To support removals, we'd have to change the property table materialization
>+    //   code to handle deletions. Also, we have logic to get the list of properties on a structure that
>+    //   lacks a property table by just looking back through the set of transitions since the last
>+    //   structure that had a pinned table. That logic would also have to be changed to handle cached
>+    //   removals.
>+    //
>+    // - InferredTypeTable assumes that removal has never happened. This is important since if we could
>+    //   remove a property and then re-add it later, then the "absence means top" optimization wouldn't
>+    //   work anymore, unless removal also either poisoned type inference (by doing something equivalent to
>+    //   hasBeenDictionary) or by strongly marking the entry as Top by ensuring that it is not absent, but
>+    //   instead, has a null entry.
>+    
>     ASSERT(!structure->isUncacheableDictionary());
> 
>     Structure* transition = toUncacheableDictionaryTransition(vm, structure);
>@@ -841,6 +864,43 @@ void Structure::startWatchingInternalPro
>     setDidWatchInternalProperties(true);
> }
> 
>+void Structure::willStoreValueSlow(
>+    VM& vm, PropertyName propertyName, JSValue value, bool shouldOptimize,
>+    InferredTypeTable::StoredPropertyAge age)
>+{
>+    ASSERT(!isCompilationThread());
>+    ASSERT(structure()->classInfo() == info());
>+    ASSERT(!hasBeenDictionary());
>+
>+    // Create the inferred type table before doing anything else, so that we don't GC after we have already
>+    // grabbed a pointer into the property map.
>+    InferredTypeTable* table = m_inferredTypeTable.get();
>+    if (!table) {
>+        table = InferredTypeTable::create(vm);
>+        WTF::storeStoreFence();
>+        m_inferredTypeTable.set(vm, this, table);
>+    }
>+
>+    // This only works if we've got a property table.
>+    PropertyTable* propertyTable;
>+    materializePropertyMapIfNecessary(vm, propertyTable);
>+
>+    // We must be calling this after having created the given property or confirmed that it was present
>+    // already, so we must have a property table now.
>+    ASSERT(propertyTable);
>+
>+    // ... and the property must be present.
>+    PropertyMapEntry* entry = propertyTable->get(propertyName.uid());
>+    ASSERT(entry);
>+
>+    if (shouldOptimize)
>+        entry->hasInferredType = table->willStoreValue(vm, propertyName, value, age);
>+    else {
>+        table->makeTop(vm, propertyName, age);
>+        entry->hasInferredType = false;
>+    }
>+}
>+
> #if DUMP_PROPERTYMAP_STATS
> 
> PropertyMapHashTableStats* propertyMapHashTableStats = 0;
>@@ -1058,6 +1118,8 @@ void Structure::visitChildren(JSCell* ce
>         visitor.append(&thisObject->m_propertyTableUnsafe);
>     } else if (thisObject->m_propertyTableUnsafe)
>         thisObject->m_propertyTableUnsafe.clear();
>+
>+    visitor.append(&thisObject->m_inferredTypeTable);
> }
> 
> bool Structure::prototypeChainMayInterceptStoreTo(VM& vm, PropertyName propertyName)
>Index: Source/JavaScriptCore/runtime/Structure.h
>===================================================================
>--- Source/JavaScriptCore/runtime/Structure.h	(revision 190059)
>+++ Source/JavaScriptCore/runtime/Structure.h	(working copy)
>@@ -29,6 +29,7 @@
> #include "ClassInfo.h"
> #include "ConcurrentJITLock.h"
> #include "IndexingType.h"
>+#include "InferredTypeTable.h"
> #include "JSCJSValue.h"
> #include "JSCell.h"
> #include "JSType.h"
>@@ -81,11 +82,13 @@ struct PropertyMapEntry {
>     UniquedStringImpl* key;
>     PropertyOffset offset;
>     uint8_t attributes;
>+    bool hasInferredType; // This caches whether or not a property has an inferred type in the inferred type table, and is used for a fast check in JSObject::putDirectInternal().
> 
>     PropertyMapEntry()
>         : key(nullptr)
>         , offset(invalidOffset)
>         , attributes(0)
>+        , hasInferredType(false)
>     {
>     }
>     
>@@ -93,6 +96,7 @@ struct PropertyMapEntry {
>         : key(key)
>         , offset(offset)
>         , attributes(attributes)
>+        , hasInferredType(false)
>     {
>         ASSERT(this->attributes == attributes);
>     }
>@@ -323,6 +327,7 @@ public:
> 
>     PropertyOffset get(VM&, PropertyName);
>     PropertyOffset get(VM&, PropertyName, unsigned& attributes);
>+    PropertyOffset get(VM&, PropertyName, unsigned& attributes, bool& hasInferredType);
> 
>     // This is a somewhat internalish method. It will call your functor while possibly holding the
>     // Structure's lock. There is no guarantee whether the lock is held or not in any particular
>@@ -481,6 +486,40 @@ public:
>             structure->startWatchingInternalPropertiesIfNecessary(vm);
>     }
> 
>+    bool hasInferredTypes() const
>+    {
>+        return !!m_inferredTypeTable;
>+    }
>+
>+    InferredType* inferredTypeFor(UniquedStringImpl* uid)
>+    {
>+        if (InferredTypeTable* table = m_inferredTypeTable.get())
>+            return table->get(uid);
>+        return nullptr;
>+    }
>+
>+    InferredType::Descriptor inferredTypeDescriptorFor(UniquedStringImpl* uid)
>+    {
>+        if (InferredType* result = inferredTypeFor(uid))
>+            return result->descriptor();
>+        return InferredType::Top;
>+    }
>+
>+    ALWAYS_INLINE void willStoreValueForTransition(
>+        VM& vm, PropertyName propertyName, JSValue value, bool shouldOptimize)
>+    {
>+        if (hasBeenDictionary() || (!shouldOptimize && !m_inferredTypeTable))
>+            return;
>+        willStoreValueSlow(vm, propertyName, value, shouldOptimize, InferredTypeTable::NewProperty);
>+    }
>+    ALWAYS_INLINE void willStoreValueForReplace(
>+        VM& vm, PropertyName propertyName, JSValue value, bool shouldOptimize)
>+    {
>+        if (hasBeenDictionary())
>+            return;
>+        willStoreValueSlow(vm, propertyName, value, shouldOptimize, InferredTypeTable::OldProperty);
>+    }
>+
>     PassRefPtr<StructureShape> toStructureShape(JSValue);
>     
>     // Determines if the two structures match enough that this one could be used for allocations
>@@ -632,6 +671,9 @@ private:
>     
>     void startWatchingInternalProperties(VM&);
> 
>+    JS_EXPORT_PRIVATE void willStoreValueSlow(
>+        VM&, PropertyName, JSValue, bool, InferredTypeTable::StoredPropertyAge);
>+
>     static const int s_maxTransitionLength = 64;
>     static const int s_maxTransitionLengthForNonEvalPutById = 512;
> 
>@@ -655,6 +697,8 @@ private:
>     // Should be accessed through propertyTable(). During GC, it may be set to 0 by another thread.
>     WriteBarrier<PropertyTable> m_propertyTableUnsafe;
> 
>+    WriteBarrier<InferredTypeTable> m_inferredTypeTable;
>+
>     mutable InlineWatchpointSet m_transitionWatchpointSet;
> 
>     COMPILE_ASSERT(firstOutOfLineOffset < 256, firstOutOfLineOffset_fits);
>Index: Source/JavaScriptCore/runtime/StructureInlines.h
>===================================================================
>--- Source/JavaScriptCore/runtime/StructureInlines.h	(revision 190059)
>+++ Source/JavaScriptCore/runtime/StructureInlines.h	(working copy)
>@@ -1,5 +1,5 @@
> /*
>- * Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
>+ * Copyright (C) 2013-2015 Apple Inc. All rights reserved.
>  *
>  * Redistribution and use in source and binary forms, with or without
>  * modification, are permitted provided that the following conditions
>@@ -75,19 +75,19 @@ inline Structure* Structure::storedProto
> 
> ALWAYS_INLINE PropertyOffset Structure::get(VM& vm, PropertyName propertyName)
> {
>-    ASSERT(!isCompilationThread());
>-    ASSERT(structure()->classInfo() == info());
>-    PropertyTable* propertyTable;
>-    materializePropertyMapIfNecessary(vm, propertyTable);
>-    if (!propertyTable)
>-        return invalidOffset;
>-
>-    PropertyMapEntry* entry = propertyTable->get(propertyName.uid());
>-    return entry ? entry->offset : invalidOffset;
>+    unsigned attributes;
>+    bool hasInferredType;
>+    return get(vm, propertyName, attributes, hasInferredType);
> }
>     
> ALWAYS_INLINE PropertyOffset Structure::get(VM& vm, PropertyName propertyName, unsigned& attributes)
> {
>+    bool hasInferredType;
>+    return get(vm, propertyName, attributes, hasInferredType);
>+}
>+
>+ALWAYS_INLINE PropertyOffset Structure::get(VM& vm, PropertyName propertyName, unsigned& attributes, bool& hasInferredType)
>+{
>     ASSERT(!isCompilationThread());
>     ASSERT(structure()->classInfo() == info());
> 
>@@ -101,6 +101,7 @@ ALWAYS_INLINE PropertyOffset Structure::
>         return invalidOffset;
> 
>     attributes = entry->attributes;
>+    hasInferredType = entry->hasInferredType;
>     return entry->offset;
> }
> 
>Index: Source/JavaScriptCore/runtime/VM.cpp
>===================================================================
>--- Source/JavaScriptCore/runtime/VM.cpp	(revision 190059)
>+++ Source/JavaScriptCore/runtime/VM.cpp	(working copy)
>@@ -51,6 +51,7 @@
> #include "HostCallReturnValue.h"
> #include "Identifier.h"
> #include "IncrementalSweeper.h"
>+#include "InferredTypeTable.h"
> #include "Interpreter.h"
> #include "JITCode.h"
> #include "JSAPIValueWrapper.h"
>@@ -241,6 +242,8 @@ VM::VM(VMType vmType, HeapType heapType)
>     propertyTableStructure.set(*this, PropertyTable::createStructure(*this, 0, jsNull()));
>     weakMapDataStructure.set(*this, WeakMapData::createStructure(*this, 0, jsNull()));
>     inferredValueStructure.set(*this, InferredValue::createStructure(*this, 0, jsNull()));
>+    inferredTypeStructure.set(*this, InferredType::createStructure(*this, 0, jsNull()));
>+    inferredTypeTableStructure.set(*this, InferredTypeTable::createStructure(*this, 0, jsNull()));
>     functionRareDataStructure.set(*this, FunctionRareData::createStructure(*this, 0, jsNull()));
>     exceptionStructure.set(*this, Exception::createStructure(*this, 0, jsNull()));
>     promiseDeferredStructure.set(*this, JSPromiseDeferred::createStructure(*this, 0, jsNull()));
>Index: Source/JavaScriptCore/runtime/VM.h
>===================================================================
>--- Source/JavaScriptCore/runtime/VM.h	(revision 190059)
>+++ Source/JavaScriptCore/runtime/VM.h	(working copy)
>@@ -302,6 +302,8 @@ public:
>     Strong<Structure> propertyTableStructure;
>     Strong<Structure> weakMapDataStructure;
>     Strong<Structure> inferredValueStructure;
>+    Strong<Structure> inferredTypeStructure;
>+    Strong<Structure> inferredTypeTableStructure;
>     Strong<Structure> functionRareDataStructure;
>     Strong<Structure> exceptionStructure;
>     Strong<Structure> promiseDeferredStructure;
>Index: Source/JavaScriptCore/tests/stress/prop-type-boolean-then-string.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-boolean-then-string.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-boolean-then-string.js	(working copy)
>@@ -0,0 +1,29 @@
>+function foo(o) {
>+    return !!o.f;
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, true);
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== true)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, "hello");
>+var result = foo(o);
>+if (result !== true)
>+    throw "Error: bad result at end (true): " + result;
>+bar(o, "");
>+result = foo(o);
>+if (result !== false)
>+    throw "Error: bad result at end (false): " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-int32-then-string.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-int32-then-string.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-int32-then-string.js	(working copy)
>@@ -0,0 +1,25 @@
>+function foo(o) {
>+    return o.f + 1;
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, 42);
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== 43)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, "hello");
>+var result = foo(o);
>+if (result !== "hello1")
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-number-then-string.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-number-then-string.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-number-then-string.js	(working copy)
>@@ -0,0 +1,25 @@
>+function foo(o) {
>+    return o.f + 1;
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, 4.2);
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== 5.2)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, "hello");
>+var result = foo(o);
>+if (result !== "hello1")
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-object-or-other-then-string.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-object-or-other-then-string.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-object-or-other-then-string.js	(working copy)
>@@ -0,0 +1,33 @@
>+String.prototype.g = 44;
>+
>+function foo(o) {
>+    return o.f == {toString:function() { return "hello"; }};
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+var p = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, null);
>+for (var i = 0; i < 5; ++i)
>+    bar(p, {g:43});
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== false)
>+        throw "Error: bad result for o: " + result;
>+    result = foo(p);
>+    if (result !== false)
>+        throw "Error: bad result for p: " + result;
>+}
>+
>+bar(o, "hello");
>+var result = foo(o);
>+if (result !== true)
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-object-then-string.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-object-then-string.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-object-then-string.js	(working copy)
>@@ -0,0 +1,25 @@
>+function foo(o) {
>+    return o.f == {toString:function() { return "hello"; }};
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, {});
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== false)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, "hello");
>+var result = foo(o);
>+if (result !== true)
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-other-then-string.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-other-then-string.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-other-then-string.js	(working copy)
>@@ -0,0 +1,25 @@
>+function foo(o) {
>+    return o.f == "hello";
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, null);
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== false)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, "hello");
>+var result = foo(o);
>+if (result !== true)
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-string-then-object.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-string-then-object.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-string-then-object.js	(working copy)
>@@ -0,0 +1,25 @@
>+function foo(o) {
>+    return o.f + " world";
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, "hello");
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result != "hello world")
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, {toString: function() { return "hello"; }});
>+var result = foo(o);
>+if (result != "hello world")
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-struct-or-other-then-string.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-struct-or-other-then-string.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-struct-or-other-then-string.js	(working copy)
>@@ -0,0 +1,36 @@
>+String.prototype.g = 44;
>+
>+function foo(o) {
>+    var tmp = o.f;
>+    if (tmp)
>+        return tmp.g;
>+    return 42;
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+var p = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, null);
>+for (var i = 0; i < 5; ++i)
>+    bar(p, {g:43});
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== 42)
>+        throw "Error: bad result for o: " + result;
>+    result = foo(p);
>+    if (result !== 43)
>+        throw "Error: bad result for p: " + result;
>+}
>+
>+bar(o, "hello");
>+var result = foo(o);
>+if (result !== 44)
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt-fold.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt-fold.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt-fold.js	(working copy)
>@@ -0,0 +1,34 @@
>+// This is like prop-type-struct-then-object.js, but it checks that the optimizing JITs emit the right type
>+// check above a hot put_by_id that starts polymorphic but is folded by AI.
>+
>+function foo(o) {
>+    return o.f.g;
>+}
>+
>+function bar(o, p, v) {
>+    if (isFinalTier() || o == p) {
>+        var tmp = p.f;
>+        o = p;
>+    }
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {f:{g:42}};
>+for (var i = 0; i < 10000; ++i) {
>+    bar(o, o, {g:42});
>+    bar({a:1, b:2}, o, {g:42});
>+}
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== 42)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, o, Object.create({g:43}));
>+var result = foo(o);
>+if (result !== 43)
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt-multi.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt-multi.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt-multi.js	(working copy)
>@@ -0,0 +1,30 @@
>+// This is like prop-type-struct-then-object.js, but it checks that the optimizing JITs emit the right type
>+// check above a hot polymorphic put_by_id that ends up being compiled as a MultiPutByOffset.
>+
>+function foo(o) {
>+    return o.f.g;
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {f:{g:42}};
>+for (var i = 0; i < 10000; ++i) {
>+    bar(o, {g:42});
>+    bar({a:1, b:2}, 42);
>+}
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== 42)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, Object.create({g:43}));
>+var result = foo(o);
>+if (result !== 43)
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-struct-then-object-opt.js	(working copy)
>@@ -0,0 +1,28 @@
>+// This is like prop-type-struct-then-object.js, but it checks that the optimizing JITs emit the right type
>+// check above a hot put_by_id.
>+
>+function foo(o) {
>+    return o.f.g;
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {f:{g:42}};
>+for (var i = 0; i < 10000; ++i)
>+    bar(o, {g:42});
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== 42)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, Object.create({g:43}));
>+var result = foo(o);
>+if (result !== 43)
>+    throw "Error: bad result at end: " + result;
>Index: Source/JavaScriptCore/tests/stress/prop-type-struct-then-object.js
>===================================================================
>--- Source/JavaScriptCore/tests/stress/prop-type-struct-then-object.js	(revision 0)
>+++ Source/JavaScriptCore/tests/stress/prop-type-struct-then-object.js	(working copy)
>@@ -0,0 +1,25 @@
>+function foo(o) {
>+    return o.f.g;
>+}
>+
>+function bar(o, v) {
>+    o.f = v;
>+}
>+
>+noInline(foo);
>+noInline(bar);
>+
>+var o = {};
>+for (var i = 0; i < 5; ++i)
>+    bar(o, {g:42});
>+
>+for (var i = 0; i < 10000; ++i) {
>+    var result = foo(o);
>+    if (result !== 42)
>+        throw "Error: bad result: " + result;
>+}
>+
>+bar(o, Object.create({g:43}));
>+var result = foo(o);
>+if (result !== 43)
>+    throw "Error: bad result at end: " + result;
>Index: Source/WTF/ChangeLog
>===================================================================
>--- Source/WTF/ChangeLog	(revision 190059)
>+++ Source/WTF/ChangeLog	(working copy)
>@@ -1,3 +1,15 @@
>+2015-09-17  Filip Pizlo  <fpizlo@apple.com>
>+
>+        JSC should infer property types
>+        https://bugs.webkit.org/show_bug.cgi?id=148610
>+
>+        Reviewed by Geoffrey Garen.
>+
>+        * wtf/HashTable.h:
>+        (WTF::HashTableAddResult::HashTableAddResult): Make it possible to say "HashMap::AddResult result" without assigning anything to it yet.
>+        * wtf/PrintStream.h:
>+        (WTF::printInternal): Beef up printing of some common WTF types, in particular RefPtr<UniquedStringImpl>.
>+
> 2015-09-20  Youenn Fablet  <youenn.fablet@crf.canon.fr>
> 
>         Remove XHR_TIMEOUT compilation guard
>Index: Source/WTF/wtf/HashTable.h
>===================================================================
>--- Source/WTF/wtf/HashTable.h	(revision 190059)
>+++ Source/WTF/wtf/HashTable.h	(working copy)
>@@ -286,6 +286,7 @@ namespace WTF {
>     };
> 
>     template<typename IteratorType> struct HashTableAddResult {
>+        HashTableAddResult() : isNewEntry(false) { }
>         HashTableAddResult(IteratorType iter, bool isNewEntry) : iterator(iter), isNewEntry(isNewEntry) { }
>         IteratorType iterator;
>         bool isNewEntry;
>Index: Source/WTF/wtf/PrintStream.h
>===================================================================
>--- Source/WTF/wtf/PrintStream.h	(revision 190059)
>+++ Source/WTF/wtf/PrintStream.h	(working copy)
>@@ -31,6 +31,7 @@
> #include <wtf/FastMalloc.h>
> #include <wtf/Noncopyable.h>
> #include <wtf/RawPointer.h>
>+#include <wtf/RefPtr.h>
> #include <wtf/StdLibExtras.h>
> 
> namespace WTF {
>@@ -74,12 +75,14 @@ WTF_EXPORT_PRIVATE void printInternal(Pr
> WTF_EXPORT_PRIVATE void printInternal(PrintStream&, const StringImpl*);
> inline void printInternal(PrintStream& out, const AtomicStringImpl* value) { printInternal(out, bitwise_cast<const StringImpl*>(value)); }
> inline void printInternal(PrintStream& out, const UniquedStringImpl* value) { printInternal(out, bitwise_cast<const StringImpl*>(value)); }
>+inline void printInternal(PrintStream& out, const UniquedStringImpl& value) { printInternal(out, &value); }
> inline void printInternal(PrintStream& out, char* value) { printInternal(out, static_cast<const char*>(value)); }
> inline void printInternal(PrintStream& out, CString& value) { printInternal(out, static_cast<const CString&>(value)); }
> inline void printInternal(PrintStream& out, String& value) { printInternal(out, static_cast<const String&>(value)); }
> inline void printInternal(PrintStream& out, StringImpl* value) { printInternal(out, static_cast<const StringImpl*>(value)); }
> inline void printInternal(PrintStream& out, AtomicStringImpl* value) { printInternal(out, static_cast<const AtomicStringImpl*>(value)); }
> inline void printInternal(PrintStream& out, UniquedStringImpl* value) { printInternal(out, static_cast<const UniquedStringImpl*>(value)); }
>+inline void printInternal(PrintStream& out, UniquedStringImpl& value) { printInternal(out, &value); }
> WTF_EXPORT_PRIVATE void printInternal(PrintStream&, bool);
> WTF_EXPORT_PRIVATE void printInternal(PrintStream&, signed char); // NOTE: this prints as a number, not as a character; use CharacterDump if you want the character
> WTF_EXPORT_PRIVATE void printInternal(PrintStream&, unsigned char); // NOTE: see above.
>@@ -169,6 +172,12 @@ void printInternal(PrintStream& out, con
>     out.print(pointerDump(value.get()));
> }
> 
>+template<typename T>
>+void printInternal(PrintStream& out, const RefPtr<T>& value)
>+{
>+    out.print(pointerDump(value.get()));
>+}
>+
> template<typename T, typename U>
> class ValueInContext {
> public:
>Index: Tools/Scripts/run-jsc-stress-tests
>===================================================================
>--- Tools/Scripts/run-jsc-stress-tests	(revision 190059)
>+++ Tools/Scripts/run-jsc-stress-tests	(working copy)
>@@ -699,6 +699,10 @@ def runWithRAMSize(size)
>     run("ram-size-#{size}", "--forceRAMSize=#{size}")
> end
> 
>+def runNoJIT
>+    run("no-jit", "--useJIT=false")
>+end
>+
> def runNoLLInt
>     if $jitTests
>         run("no-llint", "--useLLInt=false")

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Attachments on bug 148610: 260294 | 260305 | 260312 | 260323 | 260376 | 260936 | 260955 | 260958 | 261049 | 261074 | 261136 | 261159 | 261216 | 261223 | 261240 | 261243 | 261256 | 261275 | 261284 | 261290 | 261295 | 261334 | 261417 | 261429 | 261483 | 261488 | 261675