[MS] Treat ignored explicit calling conventions as an explicit __cdecl

The CCCR_Ignore action is only used for Microsoft calling conventions,
mainly because MSVC does not warn when a calling convention would be
ignored by the current target. This behavior is actually somewhat
important, since windows.h uses WINAPI (which expands to __stdcall)
widely. This distinction didn't matter much before the introduction of
__vectorcall to x64 and the ability to make that the default calling
convention with /Gv. Now, we can't just ignore __stdcall for x64, we
have to treat it as an explicit __cdecl annotation.

Fixes PR42531

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@365579 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index e4e6a19dba48ce5bda0e0e2172dff839907b3e27..802ca52371a58b3e5d29b9cd2de0e9b9f1071d1c 100644 (file)
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -4655,10 +4655,22 @@ bool Sema::CheckCallingConvAttr(const ParsedAttr &Attrs, CallingConv &CC,
   } else {
     A = TI.checkCallingConvention(CC);
   }
-  if (A != TargetInfo::CCCR_OK) {
-    if (A == TargetInfo::CCCR_Warning)
-      Diag(Attrs.getLoc(), diag::warn_cconv_ignored)
-          << Attrs << (int)CallingConventionIgnoredReason::ForThisTarget;
+
+  switch (A) {
+  case TargetInfo::CCCR_OK:
+    break;
+
+  case TargetInfo::CCCR_Ignore:
+    // Treat an ignored convention as if it was an explicit C calling convention
+    // attribute. For example, __stdcall on Win x64 functions as __cdecl, so
+    // that command line flags that change the default convention to
+    // __vectorcall don't affect declarations marked __stdcall.
+    CC = CC_C;
+    break;
+
+  case TargetInfo::CCCR_Warning: {
+    Diag(Attrs.getLoc(), diag::warn_cconv_ignored)
+        << Attrs << (int)CallingConventionIgnoredReason::ForThisTarget;
 
     // This convention is not valid for the target. Use the default function or
     // method calling convention.
@@ -4668,6 +4680,8 @@ bool Sema::CheckCallingConvAttr(const ParsedAttr &Attrs, CallingConv &CC,
       IsVariadic = FD->isVariadic();
     }
     CC = Context.getDefaultCallingConvention(IsVariadic, IsCXXMethod);
+    break;
+  }
   }
 
   Attrs.setProcessingCache((unsigned) CC);

diff --git a/test/CodeGen/calling-conv-ignored.c b/test/CodeGen/calling-conv-ignored.c
new file mode 100644 (file)
index 0000000..e49d4c4
--- /dev/null
+++ b/test/CodeGen/calling-conv-ignored.c
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -triple i686-windows-msvc   -emit-llvm -o - %s | FileCheck %s --check-prefix=X86
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm -o - %s | FileCheck %s --check-prefix=X64
+// RUN: %clang_cc1 -triple i686-windows-msvc   -emit-llvm -o - %s -fdefault-calling-conv=vectorcall | FileCheck %s --check-prefix=X86-VEC
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm -o - %s -fdefault-calling-conv=vectorcall | FileCheck %s --check-prefix=X64-VEC
+
+void foo_default(const char *lpString1, const char *lpString2);
+void __stdcall foo_std(const char *lpString1, const char *lpString2);
+void __fastcall foo_fast(const char *lpString1, const char *lpString2);
+void __vectorcall foo_vector(const char *lpString1, const char *lpString2);
+
+void __cdecl bar() {
+  foo_default(0, 0);
+  foo_std(0, 0);
+  foo_fast(0, 0);
+  foo_vector(0, 0);
+}
+
+// X86-LABEL: define dso_local void @bar()
+// X86:   call void @foo_default(i8* null, i8* null)
+// X86:   call x86_stdcallcc void @"\01_foo_std@8"(i8* null, i8* null)
+// X86:   call x86_fastcallcc void @"\01@foo_fast@8"(i8* inreg null, i8* inreg null)
+// X86:   call x86_vectorcallcc void @"\01foo_vector@@8"(i8* inreg null, i8* inreg null)
+// X86:   ret void
+
+// X64-LABEL: define dso_local void @bar()
+// X64:   call void @foo_default(i8* null, i8* null)
+// X64:   call void @foo_std(i8* null, i8* null)
+// X64:   call void @foo_fast(i8* null, i8* null)
+// X64:   call x86_vectorcallcc void @"\01foo_vector@@16"(i8* null, i8* null)
+// X64:   ret void
+
+// X86-VEC-LABEL: define dso_local void @bar()
+// X86-VEC:   call x86_vectorcallcc void @"\01foo_default@@8"(i8* inreg null, i8* inreg null)
+// X86-VEC:   call x86_stdcallcc void @"\01_foo_std@8"(i8* null, i8* null)
+// X86-VEC:   call x86_fastcallcc void @"\01@foo_fast@8"(i8* inreg null, i8* inreg null)
+// X86-VEC:   call x86_vectorcallcc void @"\01foo_vector@@8"(i8* inreg null, i8* inreg null)
+// X86-VEC:   ret void
+
+// X64-VEC-LABEL: define dso_local void @bar()
+// X64-VEC:   call x86_vectorcallcc void @"\01foo_default@@16"(i8* null, i8* null)
+// X64-VEC:   call void @foo_std(i8* null, i8* null)
+// X64-VEC:   call void @foo_fast(i8* null, i8* null)
+// X64-VEC:   call x86_vectorcallcc void @"\01foo_vector@@16"(i8* null, i8* null)
+// X64-VEC:   ret void
+