Win64: Silently ignore __stdcall, __fastcall, and __thiscall

MSVC doesn't warn on this. Users are expected to apply the WINAPI macro
to functions passed by pointer to the Win32 API, and this macro expands
to __stdcall. This means we end up with a lot of useless noisy warnings
about ignored calling conventions when compiling code with clang for
Win64.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@230668 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/TargetInfo.h

@@ -842,7 +842,8 @@ public:
 
   enum CallingConvCheckResult {
     CCCR_OK,
-    CCCR_Warning
+    CCCR_Warning,
+    CCCR_Ignore,
   };
 
   /// \brief Determines whether a given calling convention is valid for the

lib/Basic/Targets.cpp

@@ -3626,19 +3626,31 @@ public:
     IntPtrType = SignedLongLong;
     this->UserLabelPrefix = "";
   }
+
   void getTargetDefines(const LangOptions &Opts,
                                 MacroBuilder &Builder) const override {
     WindowsTargetInfo<X86_64TargetInfo>::getTargetDefines(Opts, Builder);
     Builder.defineMacro("_WIN64");
   }
+
   BuiltinVaListKind getBuiltinVaListKind() const override {
     return TargetInfo::CharPtrBuiltinVaList;
   }
+
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
-    return (CC == CC_C ||
-            CC == CC_X86VectorCall ||
-            CC == CC_IntelOclBicc ||
-            CC == CC_X86_64SysV) ? CCCR_OK : CCCR_Warning;
+    switch (CC) {
+    case CC_X86StdCall:
+    case CC_X86ThisCall:
+    case CC_X86FastCall:
+      return CCCR_Ignore;
+    case CC_C:
+    case CC_X86VectorCall:
+    case CC_IntelOclBicc:
+    case CC_X86_64SysV:
+      return CCCR_OK;
+    default:
+      return CCCR_Warning;
+    }
   }
 };
 } // end anonymous namespace

lib/Sema/SemaDeclAttr.cpp

@@ -3393,9 +3393,12 @@ bool Sema::CheckCallingConvAttr(const AttributeList &attr, CallingConv &CC,
 
   const TargetInfo &TI = Context.getTargetInfo();
   TargetInfo::CallingConvCheckResult A = TI.checkCallingConvention(CC);
-  if (A == TargetInfo::CCCR_Warning) {
-    Diag(attr.getLoc(), diag::warn_cconv_ignored) << attr.getName();
+  if (A != TargetInfo::CCCR_OK) {
+    if (A == TargetInfo::CCCR_Warning)
+      Diag(attr.getLoc(), diag::warn_cconv_ignored) << attr.getName();
 
+    // This convention is not valid for the target. Use the default function or
+    // method calling convention.
     TargetInfo::CallingConvMethodType MT = TargetInfo::CCMT_Unknown;
     if (FD)
       MT = FD->isCXXInstanceMember() ? TargetInfo::CCMT_Member : 

test/Sema/MicrosoftCompatibility-x64.c

@@ -1,8 +1,13 @@
-// RUN: %clang_cc1 %s -fsyntax-only -Wno-unused-value -Wmicrosoft -verify -fms-compatibility -triple x86_64-pc-win32
-int __stdcall f(void); /* expected-warning {{calling convention '__stdcall' ignored for this target}} */
+// RUN: %clang_cc1 %s -Wmicrosoft -verify -fms-compatibility -triple x86_64-pc-win32
 
-/* This should compile without warning because __stdcall is treated
-as __cdecl in MS compatibility mode for x64 compiles*/
+// None of these should warn. stdcall is treated as equivalent to cdecl on
+// x64.
+// expected-no-diagnostics
+
+int __stdcall f(void);
 int __cdecl f(void) {
   return 0;
 }
+int __stdcall func_std(void);
+int __thiscall func_this(void);
+int __fastcall func_fast(void);