cranelift: Always consider sret arguments used#8664
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jameysharp merged 2 commits intobytecodealliance:mainfrom May 20, 2024
Merged
cranelift: Always consider sret arguments used#8664jameysharp merged 2 commits intobytecodealliance:mainfrom
jameysharp merged 2 commits intobytecodealliance:mainfrom
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In bytecodealliance#8438 we stopped emitting register bindings for unused arguments, based on the use-counts from `compute_use_states`. However, that doesn't count the use of the struct-return argument that's automatically added after lowering when the `rets` instruction is generated in the epilogue. As a result, using a struct-return argument caused register allocation to panic due to the VReg not being defined anywhere. This commit adds a use to the struct-return argument so that it's always available in the epilogue. Fixes bytecodealliance#8659
cfallin
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May 20, 2024
| let mut value_ir_uses = SecondaryMap::with_default(ValueUseState::Unused); | ||
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| if let Some(sret_param) = sret_param { | ||
| value_ir_uses[sret_param] = ValueUseState::Once; |
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Could we add a comment here to note it starts at Once (for the one use that is the implicit return), but can still be updated below?
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Actually, should I just start it at Multiple in case there are multiple epilogues? The definition of the sret vreg can't participate in load-sinking or anything so I don't think the value really matters, but I guess it should be "correct" anyway?
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Oh, yes, that makes more sense actually, I agree. It's unlikely to matter as you say but might as well get the analysis right...
alexcrichton
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* cranelift: Always consider sret arguments used In bytecodealliance#8438 we stopped emitting register bindings for unused arguments, based on the use-counts from `compute_use_states`. However, that doesn't count the use of the struct-return argument that's automatically added after lowering when the `rets` instruction is generated in the epilogue. As a result, using a struct-return argument caused register allocation to panic due to the VReg not being defined anywhere. This commit adds a use to the struct-return argument so that it's always available in the epilogue. Fixes bytecodealliance#8659 * Review comments
alexcrichton
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* cranelift: Always consider sret arguments used In #8438 we stopped emitting register bindings for unused arguments, based on the use-counts from `compute_use_states`. However, that doesn't count the use of the struct-return argument that's automatically added after lowering when the `rets` instruction is generated in the epilogue. As a result, using a struct-return argument caused register allocation to panic due to the VReg not being defined anywhere. This commit adds a use to the struct-return argument so that it's always available in the epilogue. Fixes #8659 * Review comments Co-authored-by: Jamey Sharp <jsharp@fastly.com>
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In #8438 we stopped emitting register bindings for unused arguments, based on the use-counts from
compute_use_states. However, that doesn't count the use of the struct-return argument that's automatically added after lowering when theretsinstruction is generated in the epilogue. As a result, using a struct-return argument caused register allocation to panic due to the VReg not being defined anywhere.This commit adds a use to the struct-return argument so that it's always available in the epilogue.
Fixes #8659