reinterpret_cast to reference of a bit-field is not allowed.

Fixes rdar://9202628 & http://llvm.org/PR9564.

llvm-svn: 130024

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -2879,6 +2879,8 @@ def err_bad_cxx_cast_member_pointer_size : Error<
   "cannot %select{||reinterpret_cast||C-style cast|}0 from member pointer "
   "type %1 to member pointer type %2 of different size">;
 def err_bad_static_cast_incomplete : Error<"%0 is an incomplete type">;
+def err_bad_reinterpret_cast_bitfield : Error<
+  "reinterpret_cast of a bit-field to %2 needs its address which is not allowed">;
 
 // These messages don't adhere to the pattern.
 // FIXME: Display the path somehow better.

clang/lib/Sema/SemaCXXCast.cpp

@@ -1326,6 +1326,13 @@ static TryCastResult TryReinterpretCast(Sema &Self, ExprResult &SrcExpr,
     // C++ 5.2.10p10: [...] a reference cast reinterpret_cast<T&>(x) has the
     //   same effect as the conversion *reinterpret_cast<T*>(&x) with the
     //   built-in & and * operators.
+
+    // Cannot get address of a bitfield.
+    if (SrcExpr.get()->getObjectKind() == OK_BitField) {
+      msg = diag::err_bad_reinterpret_cast_bitfield;
+      return TC_NotApplicable;
+    }
+
     // This code does this transformation for the checked types.
     DestType = Self.Context.getPointerType(DestTypeTmp->getPointeeType());
     SrcType = Self.Context.getPointerType(SrcType);

clang/test/SemaCXX/reinterpret-cast.cpp

@@ -108,3 +108,8 @@ void const_arrays() {
   (void)reinterpret_cast<char *>(s); // expected-error {{reinterpret_cast from 'const STRING *' (aka 'char const (*)[10]') to 'char *' casts away qualifiers}}
   (void)reinterpret_cast<const STRING *>(c);
 }
+
+namespace PR9564 {
+  struct a { int a : 10; }; a x;
+  int *y = &reinterpret_cast<int&>(x.a); // expected-error {{reinterpret_cast of a bit-field to 'int &' needs its address which is not allowed}}
+}