In bug #165282 I'm adding code which assumes that all WebAssembly.Instance have the same pinned registers. I'm doing this because wasm->wasm calls are generated at Module time, without knowing which import will be provided at Instance time. We could instead generate one stub per type of outcall: - wasm w/ fast memory -> wasm w/o memory - wasm w/ fast memory -> wasm w/ slow memory - wasm w/o memory -> wasm w/ fast memory - wasm w/o memory -> wasm w/ slow memory - wasm w/ slow memory -> wasm w/ fast memory - wasm w/ slow memory -> wasm w/o memory I'm not sure the complexity (and potential for bugs!) are worth it at this point in time.