[clang] [X86_32][C++] fix 0 sized struct case in vaarg. (PR #86388)

[Longsheng Mou via cfe-commits]

https://github.com/CoTinker updated https://github.com/llvm/llvm-project/pull/86388

>From 54f75d7068d0acf336d6d1e61bcf800ff52cc310 Mon Sep 17 00:00:00 2001
From: Longsheng Mou <moulongsheng at huawei.com>
Date: Sat, 23 Mar 2024 17:53:58 +0800
Subject: [PATCH] [X86_32] fix 0 sized struct case in vaarg.

struct SuperEmpty { struct{ int a[0];} b;};
Such 0 sized structs in c++ mode can not be ignored in i386 for
that c++ fields are never empty.But when EmitVAArg, its size is
0, so that va_list not increase.Maybe we can ignore this kind of
arguments.
---
 clang/lib/CodeGen/Targets/X86.cpp      |  4 ++++
 clang/test/CodeGenCXX/regparm.cpp      |  2 +-
 clang/test/CodeGenCXX/x86_32-vaarg.cpp | 22 ++++++++++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp
index 16d52bee3490b..26ff4e4ac0a3b 100644
--- a/clang/lib/CodeGen/Targets/X86.cpp
+++ b/clang/lib/CodeGen/Targets/X86.cpp
@@ -795,6 +795,10 @@ ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty, CCState &State,
     if (!IsWin32StructABI && isEmptyRecord(getContext(), Ty, true))
       return ABIArgInfo::getIgnore();
 
+    // Ignore 0 sized structs.
+    if (TI.Width == 0)
+      return ABIArgInfo::getIgnore();
+
     llvm::LLVMContext &LLVMContext = getVMContext();
     llvm::IntegerType *Int32 = llvm::Type::getInt32Ty(LLVMContext);
     bool NeedsPadding = false;
diff --git a/clang/test/CodeGenCXX/regparm.cpp b/clang/test/CodeGenCXX/regparm.cpp
index 1fd471c2d0727..b9735485db8de 100644
--- a/clang/test/CodeGenCXX/regparm.cpp
+++ b/clang/test/CodeGenCXX/regparm.cpp
@@ -32,7 +32,7 @@ struct S3 {
   } a;
 };
 __attribute((regparm(2))) void foo4(S3 a, int b);
-// CHECK: declare void @_Z4foo42S3i(ptr noundef byval(%struct.S3) align 4, i32 inreg noundef)
+// CHECK: declare void @_Z4foo42S3i(i32 inreg noundef)
 void bar3(S3 a, int b) {
   foo4(a, b);
 }
diff --git a/clang/test/CodeGenCXX/x86_32-vaarg.cpp b/clang/test/CodeGenCXX/x86_32-vaarg.cpp
index a3f2791484362..90665652a0286 100644
--- a/clang/test/CodeGenCXX/x86_32-vaarg.cpp
+++ b/clang/test/CodeGenCXX/x86_32-vaarg.cpp
@@ -18,3 +18,25 @@ empty empty_record_test(int z, ...) {
   __builtin_va_start(list, z);
   return __builtin_va_arg(list, empty);
 }
+
+typedef struct {
+  struct {
+    int a[0];
+  } b;
+} SortOfEmpty;
+
+// CHECK-LABEL: @_Z18test_sort_of_emptyiz(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[RESULT_PTR:%.*]] = alloca ptr, align 4
+// CHECK-NEXT:    [[Z_ADDR:%.*]] = alloca i32, align 4
+// CHECK-NEXT:    [[LIST:%.*]] = alloca ptr, align 4
+// CHECK-NEXT:    store ptr [[AGG_RESULT:%.*]], ptr [[RESULT_PTR]], align 4
+// CHECK-NEXT:    store i32 [[Z:%.*]], ptr [[Z_ADDR]], align 4
+// CHECK-NEXT:    call void @llvm.va_start.p0(ptr [[LIST]])
+// CHECK-NEXT:    ret void
+//
+SortOfEmpty test_sort_of_empty(int z, ...) {
+  __builtin_va_list list;
+  __builtin_va_start(list, z);
+  return __builtin_va_arg(list, SortOfEmpty);
+}