================
@@ -411,7 +412,48 @@ static void emitAtomicCmpXchg(CodeGenFunction &CGF,
AtomicExpr *E, bool IsWeak,
CGF.Builder.SetInsertPoint(StoreExpectedBB);
// Update the memory at Expected with Old's value.
- CGF.Builder.CreateStore(Old, Val1);
+llvm::Type *ExpectedType = ExpectedResult.getElementType();
+const llvm::DataLayout &DL = CGF.CGM.getDataLayout();
+uint64_t ExpectedSizeInBytes = DL.getTypeStoreSize(ExpectedType);
+
+if (ExpectedSizeInBytes == Size) {
+ // Sizes match: store directly
+ CGF.Builder.CreateStore(Old, ExpectedResult);
+
+} else {
+ // store only the first ExpectedSizeInBytes bytes of Old
+ llvm::Type *OldType = Old->getType();
+
+ llvm::Align SrcAlignLLVM = DL.getABITypeAlign(OldType);
+ llvm::Align DstAlignLLVM = DL.getABITypeAlign(ExpectedType);
+
+ clang::CharUnits SrcAlign =
clang::CharUnits::fromQuantity(SrcAlignLLVM.value());
+ clang::CharUnits DstAlign =
clang::CharUnits::fromQuantity(DstAlignLLVM.value());
+
+ // Allocate temporary storage for Old value
+ llvm::AllocaInst *Alloca = CGF.CreateTempAlloca(OldType, "old.tmp");
----------------
efriedma-quic wrote:
I think there's a variant of CreateTempAlloca that returns an Address?
https://github.com/llvm/llvm-project/pull/78707
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