Disallow reinterpret_cast from pointer to bool on Windows

This became allowed by accident in r131201, but triggers an assert.
That patch added an exception to allow conversion from pointers to
narrow integral types for MSVC compatibility. However, a pointer can
already be converted to bool in a civilized manner; allowing conversion
via reinterpret_cast is a bad idea.

Fixes PR16222.

llvm-svn: 183394

clang/lib/Sema/SemaCast.cpp

@@ -1813,10 +1813,12 @@ static TryCastResult TryReinterpretCast(Sema &Self, ExprResult &SrcExpr,
     assert(srcIsPtr && "One type must be a pointer");
     // C++ 5.2.10p4: A pointer can be explicitly converted to any integral
     //   type large enough to hold it; except in Microsoft mode, where the
-    //   integral type size doesn't matter.
+    //   integral type size doesn't matter (except we don't allow bool).
+    bool MicrosoftException = Self.getLangOpts().MicrosoftExt &&
+                              !DestType->isBooleanType();
     if ((Self.Context.getTypeSize(SrcType) >
          Self.Context.getTypeSize(DestType)) &&
-         !Self.getLangOpts().MicrosoftExt) {
+         !MicrosoftException) {
       msg = diag::err_bad_reinterpret_cast_small_int;
       return TC_Failed;
     }

clang/test/Sema/MicrosoftExtensions.c

@@ -76,6 +76,9 @@ void pointer_to_integral_type_conv(char* ptr) {
    short sh = (short)ptr;
    ch = (char)ptr;
    sh = (short)ptr;
+
+   // This is valid ISO C.
+   _Bool b = (_Bool)ptr;
 }
 
 

clang/test/SemaCXX/MicrosoftExtensions.cpp

@@ -167,8 +167,14 @@ void pointer_to_integral_type_conv(char* ptr) {
    short sh = (short)ptr;
    ch = (char)ptr;
    sh = (short)ptr;
-} 
 
+   // These are valid C++.
+   bool b = (bool)ptr;
+   b = static_cast<bool>(ptr);
+
+   // This is bad.
+   b = reinterpret_cast<bool>(ptr); // expected-error {{cast from pointer to smaller type 'bool' loses information}}
+}
 
 namespace friend_as_a_forward_decl {