[Cygwin] va_list must be treated like normal Windows

[kikairoya]

Handling of va_list on Cygwin environment must be matched to normal Windows environment.

The existing test test/CodeGen/ms_abi.c seems relevant, but it contains __attribute__((sysv_abi)), which is not supported on Cygwin. The new test is based on the __attribute__((ms_abi)) portion of that test.

[llvmbot]

@llvm/pr-subscribers-backend-x86

@llvm/pr-subscribers-clang

Author: Tomohiro Kashiwada (kikairoya)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/143115.diff

2 Files Affected:

• (modified) clang/lib/Basic/Targets/X86.h (+3)
• (added) clang/test/CodeGen/X86/cygwin-varargs.c (+37)

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
+}

[jeremyd2019]

LGTM

[mstorsjo]

LGTM, with one minor comment.

[mstorsjo]

Not sure how relevant the comment about where it is copied from is, when looking at the test file in the future. (It's perhaps more relevant as part of the commit message.)

[kikairoya]

Updated description.