[clang] [CIR] Copy byval records as bytes in CallConvLowering (PR #227170)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clangir

Author: Bruno Cardoso Lopes (bcardosolopes)

<details>
<summary>Changes</summary>

A byval record argument was copied with a whole-record cir.load/cir.store, both in the callee (into the parameter's slot) and at call sites (into the byval temporary). A record's LLVM type is built from one member for a union, so bytes that are padding in that member but data in another were dropped. A clang built with -fclangir miscompiled itself this way: TemplateArgument, passed by value, lost its integer bit width.

Use cir.copy instead when the value comes straight from memory.

With this fix, the `-fclangir`-built clang passes check-clang with zero failures, identical to the same clang built without -fclangir.

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Full diff: https://github.com/llvm/llvm-project/pull/227170.diff


10 Files Affected:

- (modified) clang/lib/CIR/Dialect/Transforms/TargetLowering/CIRABIRewriteContext.cpp (+41-2) 
- (added) clang/test/CIR/CodeGen/call-conv-lowering-x86_64-byval-union.c (+41) 
- (modified) clang/test/CIR/CodeGen/call-conv-lowering-x86_64-non-byval.cpp (+2-4) 
- (modified) clang/test/CIR/CodeGen/call-conv-lowering-x86_64-variadic.c (+16-16) 
- (modified) clang/test/CIR/CodeGen/call.c (+4-4) 
- (modified) clang/test/CIR/Transforms/abi-lowering/indirect-byval.cir (+3-4) 
- (modified) clang/test/CIR/Transforms/abi-lowering/indirect-call.cir (+3-2) 
- (modified) clang/test/CIR/Transforms/abi-lowering/indirect-non-byval-forward-param.cir (+11-18) 
- (modified) clang/test/CIR/Transforms/abi-lowering/x86_64-struct-indirect.cir (+2-4) 
- (modified) clang/test/CIR/Transforms/abi-lowering/x86_64-union.cir (+2-3) 


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</details>


https://github.com/llvm/llvm-project/pull/227170