[MSVC Compatibility] Permit static_cast from void-ptr to function-ptr

The MSVC 2013 and 2015 implementation of std::atomic is specialized for
pointer types.  The member functions are implemented using a static_cast
from void-ptr to function-ptr which is not allowed in the standard.
Permit this conversion if -fms-compatibility is present.

This fixes PR23733.

llvm-svn: 238877

3 files changed, 14 insertions, 0 deletions

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 9ccd5adf21a..d79aeb2e8f1 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5390,6 +5390,10 @@ def err_bad_const_cast_dest : Error<
   "which is not a reference, pointer-to-object, or pointer-to-data-member">;
 def ext_cast_fn_obj : Extension<
   "cast between pointer-to-function and pointer-to-object is an extension">;
+def ext_ms_cast_fn_obj : ExtWarn<
+  "static_cast between pointer-to-function and pointer-to-object is a "
+  "Microsoft extension">,
+  InGroup<Microsoft>;
 def warn_cxx98_compat_cast_fn_obj : Warning<
   "cast between pointer-to-function and pointer-to-object is incompatible with C++98">,
   InGroup<CXX98CompatPedantic>, DefaultIgnore;
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 091e77936c1..8683d03007d 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -1081,6 +1081,14 @@ static TryCastResult TryStaticCast(Sema &Self, ExprResult &SrcExpr,
           Kind = CK_BitCast;
           return TC_Success;
         }
+
+        // Microsoft permits static_cast from 'pointer-to-void' to
+        // 'pointer-to-function'.
+        if (Self.getLangOpts().MSVCCompat && DestPointee->isFunctionType()) {
+          Self.Diag(OpRange.getBegin(), diag::ext_ms_cast_fn_obj) << OpRange;
+          Kind = CK_BitCast;
+          return TC_Success;
+        }
       }
       else if (DestType->isObjCObjectPointerType()) {
         // allow both c-style cast and static_cast of objective-c pointers as 
diff --git a/clang/test/SemaCXX/MicrosoftCompatibility-cxx98.cpp b/clang/test/SemaCXX/MicrosoftCompatibility-cxx98.cpp
index 0c7d354c306..e72878e3024 100644
--- a/clang/test/SemaCXX/MicrosoftCompatibility-cxx98.cpp
+++ b/clang/test/SemaCXX/MicrosoftCompatibility-cxx98.cpp
@@ -6,3 +6,5 @@ enum ENUM; // expected-warning {{forward references to 'enum' types are a Micros
 ENUM *var = 0;     
 ENUM var2 = (ENUM)3;
 enum ENUM1* var3 = 0;// expected-warning {{forward references to 'enum' types are a Microsoft extension}}
+
+void (*PR23733)() = static_cast<void (*)()>((void *)0); // expected-warning {{static_cast between pointer-to-function and pointer-to-object is a Microsoft extension}}