[clang] [X86_64] fix empty structure vaarg in c++ (PR #77907)
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Fri Jan 12 03:07:02 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-x86
Author: None (hstk30-hw)
<details>
<summary>Changes</summary>
SizeInBytes of empty structure is 0 in C, while 1 in C++. And empty structure argument of the function is ignored in X86_64 backend.As a result, the value of variable arguments in C++ is incorrect. fix #<!-- -->77036
---
Full diff: https://github.com/llvm/llvm-project/pull/77907.diff
2 Files Affected:
- (modified) clang/lib/CodeGen/Targets/X86.cpp (+5)
- (added) clang/test/CodeGen/X86/x86_64-vaarg.c (+15)
``````````diff
diff --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp
index d053f41ab168f5..c2c11280838b12 100644
--- a/clang/lib/CodeGen/Targets/X86.cpp
+++ b/clang/lib/CodeGen/Targets/X86.cpp
@@ -2989,6 +2989,11 @@ static Address EmitX86_64VAArgFromMemory(CodeGenFunction &CGF,
// an 8 byte boundary.
uint64_t SizeInBytes = (CGF.getContext().getTypeSize(Ty) + 7) / 8;
+
+ if (isEmptyRecord(CGF.getContext(), Ty, true)) {
+ SizeInBytes = 0;
+ }
+
llvm::Value *Offset =
llvm::ConstantInt::get(CGF.Int32Ty, (SizeInBytes + 7) & ~7);
overflow_arg_area = CGF.Builder.CreateGEP(CGF.Int8Ty, overflow_arg_area,
diff --git a/clang/test/CodeGen/X86/x86_64-vaarg.c b/clang/test/CodeGen/X86/x86_64-vaarg.c
new file mode 100644
index 00000000000000..ae201a2d3f3017
--- /dev/null
+++ b/clang/test/CodeGen/X86/x86_64-vaarg.c
@@ -0,0 +1,15 @@
+// RUN: %clang -xc++ -target x86_64-linux-gnu -emit-llvm -S -o - %s | FileCheck %s
+
+struct Empty {};
+
+struct Empty emptyvar;
+
+void take_args(int a, ...) {
+ // CHECK: %overflow_arg_area = load ptr, ptr %overflow_arg_area_p, align 8
+ // CHECK-NEXT: %overflow_arg_area.next = getelementptr i8, ptr %overflow_arg_area, i32 0
+ // CHECK-NEXT: store ptr %overflow_arg_area.next, ptr %overflow_arg_area_p, align 8
+ __builtin_va_list l;
+ __builtin_va_start(l, a);
+ emptyvar = __builtin_va_arg(l, struct Empty);
+ __builtin_va_end(l);
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/77907
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