[clang] [Cygwin] va_list must be treated like normal Windows (PR #143115)

[Tomohiro Kashiwada via cfe-commits]

https://github.com/kikairoya updated 
https://github.com/llvm/llvm-project/pull/143115

>From c64472a188825a1d814ea0523a6097d25949d6fb Mon Sep 17 00:00:00 2001
From: kikairoya <kikair...@gmail.com>
Date: Sun, 25 May 2025 14:07:29 +0900
Subject: [PATCH 1/2] [Cygwin] va_list must be treated like normal Windows

Handling of va_list on Cygwin environment must be matched to normal
Windows environment.
A new test file is added as existing test contains a unsupported
functionality.
---
 clang/lib/Basic/Targets/X86.h           |  3 ++
 clang/test/CodeGen/X86/cygwin-varargs.c | 37 +++++++++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 clang/test/CodeGen/X86/cygwin-varargs.c

diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
index 780385f9c9bc5..92aa9b5dc92cb 100644
--- a/clang/lib/Basic/Targets/X86.h
+++ b/clang/lib/Basic/Targets/X86.h
@@ -979,6 +979,9 @@ class LLVM_LIBRARY_VISIBILITY CygwinX86_64TargetInfo : 
public X86_64TargetInfo {
     if (Opts.CPlusPlus)
       Builder.defineMacro("_GNU_SOURCE");
   }
+  BuiltinVaListKind getBuiltinVaListKind() const override {
+    return TargetInfo::CharPtrBuiltinVaList;
+  }
 };
 
 class LLVM_LIBRARY_VISIBILITY DarwinX86_64TargetInfo
diff --git a/clang/test/CodeGen/X86/cygwin-varargs.c 
b/clang/test/CodeGen/X86/cygwin-varargs.c
new file mode 100644
index 0000000000000..1d2b9af8a0225
--- /dev/null
+++ b/clang/test/CodeGen/X86/cygwin-varargs.c
@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -triple x86_64-windows-gnu -emit-llvm < %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-cygwin -emit-llvm < %s | FileCheck %s
+
+// copy ms_abi block only from ../ms_abi.c
+
+struct foo {
+  int x;
+  float y;
+  char z;
+};
+// CHECK: %[[STRUCT_FOO:.*]] = type { i32, float, i8 }
+
+void f(int a, ...) {
+  // CHECK-LABEL: define dso_local void @f
+  __builtin_va_list ap;
+  __builtin_va_start(ap, a);
+  // CHECK: %[[AP:.*]] = alloca ptr
+  // CHECK: call void @llvm.va_start
+  int b = __builtin_va_arg(ap, int);
+  // CHECK: %[[AP_CUR:.*]] = load ptr, ptr %[[AP]]
+  // CHECK-NEXT: %[[AP_NEXT:.*]] = getelementptr inbounds i8, ptr %[[AP_CUR]], 
i64 8
+  // CHECK-NEXT: store ptr %[[AP_NEXT]], ptr %[[AP]]
+  double _Complex c = __builtin_va_arg(ap, double _Complex);
+  // CHECK: %[[AP_CUR2:.*]] = load ptr, ptr %[[AP]]
+  // CHECK-NEXT: %[[AP_NEXT2:.*]] = getelementptr inbounds i8, ptr 
%[[AP_CUR2]], i64 8
+  // CHECK-NEXT: store ptr %[[AP_NEXT2]], ptr %[[AP]]
+  // CHECK-NEXT: load ptr, ptr %[[AP_CUR2]]
+  struct foo d = __builtin_va_arg(ap, struct foo);
+  // CHECK: %[[AP_CUR3:.*]] = load ptr, ptr %[[AP]]
+  // CHECK-NEXT: %[[AP_NEXT3:.*]] = getelementptr inbounds i8, ptr 
%[[AP_CUR3]], i64 8
+  // CHECK-NEXT: store ptr %[[AP_NEXT3]], ptr %[[AP]]
+  __builtin_va_list ap2;
+  __builtin_va_copy(ap2, ap);
+  // CHECK: call void @llvm.va_copy
+  __builtin_va_end(ap);
+  // CHECK: call void @llvm.va_end
+}

>From ac40213cffd5f34d35ec737a82585623756af2a1 Mon Sep 17 00:00:00 2001
From: Tomohiro Kashiwada <kikair...@gmail.com>
Date: Sat, 7 Jun 2025 15:41:43 +0900
Subject: [PATCH 2/2] Update clang/lib/Basic/Targets/X86.h

Co-authored-by: jeremyd2019 <git...@jdrake.com>
---
 clang/lib/Basic/Targets/X86.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
index 92aa9b5dc92cb..92e8edfec0151 100644
--- a/clang/lib/Basic/Targets/X86.h
+++ b/clang/lib/Basic/Targets/X86.h
@@ -979,6 +979,7 @@ class LLVM_LIBRARY_VISIBILITY CygwinX86_64TargetInfo : 
public X86_64TargetInfo {
     if (Opts.CPlusPlus)
       Builder.defineMacro("_GNU_SOURCE");
   }
+
   BuiltinVaListKind getBuiltinVaListKind() const override {
     return TargetInfo::CharPtrBuiltinVaList;
   }

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