IRGen: fix async typed throws miscompiles on Wasm - #89715
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Thanks, this looks good. My only remaining comment is that you keep talking about ind_error in the comments when this AFAIK doesn't actually refer to anything specific; probably best to just talk about the indirect error slot normally in prose.
# Conflicts: # test/Interpreter/async_typed_throws_wasm.swift # Conflicts: # test/stdlib/Result+asyncInit.swift
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Cherry-pick of #89715, merged as 4c99082 **Explanation**: On wasm32 the WebAssembly backend pads the `swiftself` and `swifterror` parameters, which left the indirect typed-error pointer and the `swiftself`/context slot at different LLVM-IR positions for Thin versus Thick async callers; caller and callee then disagreed on which trailing pointer held the typed-error slot and miscompiled async typed-throws calls (#89155: `Result.init(catching:) async` trapped in a value-witness copy on Wasm). With this change `SignatureExpansion::expandAsyncEntryType` now emits `addIndirectThrowingResult` before the `swiftself`/context slot, so the trailing pair is always `[ind_error, swiftself]` and Thin and Thick agree on the position regardless of parameter padding. The result-shape decision moves behind one gate, `hasTrailingAsyncErrorContextPair` (`GenCall.h`), consumed by the three sites that read these slots positionally: `AsyncCallEmission::setFromCallee`, `AsyncPartialApplicationForwarderEmission`, and `AsyncNativeCCEntryPointArgumentEmission::mapAsyncParameters` (the last also pre-extracts the witness-method Self/witness-table that trail the pair). **Scope**: IRGen async typed-throws lowering only; while resulting LLVM IR has different ordering of parameters, non-Wasm native codegen is unchanged. **Risk**: Low. Non-Wasm codegen is unchanged (the reorder only moves IR operands; `swiftself`/`swifterror` stay register-pinned by attribute). The only calling-convention change is on Wasm, which was already miscompiling. **Testing**: New execution test reproduces #89155 on Wasm; IRGen tests updated to pin the new parameter order. **Issue**: #89320, rdar://177615931 **Reviewed by**: @drexin @kateinoigakukun @rjmccall
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Follow up to currently-reverted #89416.
On wasm32 the WebAssembly backend pads the
swiftselfandswifterrorparameters, which left the indirect typed-error pointer and theswiftself/context slot at different LLVM-IR positions for Thin versus Thick async callers; caller and callee then disagreed on which trailing pointer held the typed-error slot and miscompiled async typed-throws calls (#89155:Result.init(catching:) asynctrapped in a value-witness copy on Wasm).With this change
SignatureExpansion::expandAsyncEntryTypenow emitsaddIndirectThrowingResultbefore theswiftself/context slot, so the trailing pair is always[ind_error, swiftself]and Thin and Thick agree on the position regardless of parameter padding. The result-shape decision moves behind one gate,hasTrailingAsyncErrorContextPair(GenCall.h), consumed by the three sites that read these slots positionally:AsyncCallEmission::setFromCallee,AsyncPartialApplicationForwarderEmission, andAsyncNativeCCEntryPointArgumentEmission::mapAsyncParameters(the last also pre-extracts the witness-method Self/witness-table that trail the pair).Each consumer carries an assertion that fires if the gate ever diverges from the slots actually filled.
Fixes #89320.