[clang] 631248d - [X86_64] fix empty structure vaarg in c++ (#77907)

[via cfe-commits]

Author: hstk30-hw
Date: 2024-03-21T09:25:24+08:00
New Revision: 631248dcd26fdec772cedb569be94ff8f12d0901

URL: https://github.com/llvm/llvm-project/commit/631248dcd26fdec772cedb569be94ff8f12d0901
DIFF: https://github.com/llvm/llvm-project/commit/631248dcd26fdec772cedb569be94ff8f12d0901.diff

LOG: [X86_64] fix empty structure vaarg in c++ (#77907)

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

Co-authored-by: Longsheng Mou <moulongsheng at huawei.com>

Added: 
    clang/test/CodeGenCXX/x86_64-vaarg.cpp

Modified: 
    clang/lib/CodeGen/Targets/X86.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp
index 2291c991fb1107..1ec0f159ebcb8a 100644
--- a/clang/lib/CodeGen/Targets/X86.cpp
+++ b/clang/lib/CodeGen/Targets/X86.cpp
@@ -3019,6 +3019,10 @@ Address X86_64ABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
   ABIArgInfo AI = classifyArgumentType(Ty, 0, neededInt, neededSSE,
                                        /*isNamedArg*/false);
 
+  // Empty records are ignored for parameter passing purposes.
+  if (AI.isIgnore())
+    return CGF.CreateMemTemp(Ty);
+
   // AMD64-ABI 3.5.7p5: Step 1. Determine whether type may be passed
   // in the registers. If not go to step 7.
   if (!neededInt && !neededSSE)

diff  --git a/clang/test/CodeGenCXX/x86_64-vaarg.cpp b/clang/test/CodeGenCXX/x86_64-vaarg.cpp
new file mode 100644
index 00000000000000..f0177906a09a81
--- /dev/null
+++ b/clang/test/CodeGenCXX/x86_64-vaarg.cpp
@@ -0,0 +1,23 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -x c -o - %s | FileCheck %s
+
+typedef struct { struct {} a; } empty;
+
+// CHECK-LABEL: @{{.*}}empty_record_test
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[RETVAL:%.*]] = alloca [[STRUCT_EMPTY:%.*]], align 1
+// CHECK-NEXT:    [[Z_ADDR:%.*]] = alloca i32, align 4
+// CHECK-NEXT:    [[LIST:%.*]] = alloca [1 x %struct.__va_list_tag], align 16
+// CHECK-NEXT:    [[TMP:%.*]] = alloca [[STRUCT_EMPTY]], align 1
+// CHECK-NEXT:    store i32 [[Z:%.*]], ptr [[Z_ADDR]], align 4
+// CHECK-NEXT:    [[ARRAYDECAY:%.*]] = getelementptr inbounds [1 x %struct.__va_list_tag], ptr [[LIST]], i64 0, i64 0
+// CHECK-NEXT:    call void @llvm.va_start(ptr [[ARRAYDECAY]])
+// CHECK-NEXT:    [[ARRAYDECAY1:%.*]] = getelementptr inbounds [1 x %struct.__va_list_tag], ptr [[LIST]], i64 0, i64 0
+// CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr align 1 [[RETVAL]], ptr align 1 [[TMP]], i64 {{.*}}, i1 false)
+// CHECK-NEXT:    ret void
+empty empty_record_test(int z, ...) {
+  __builtin_va_list list;
+  __builtin_va_start(list, z);
+  return __builtin_va_arg(list, empty);
+}