[Sema] Make `&function_with_enable_if_attrs` an error

This fixes a bug where one can take the address of a conditionally
enabled function to drop its enable_if guards. For example:

  int foo(int a) __attribute__((enable_if(a > 0, "")));
  int (*p)(int) = &foo;
  int result = p(-1); // compilation succeeds; calls foo(-1)

Overloading logic has been updated to reflect this change, as well.

Functions with enable_if attributes that are always true are still
allowed to have their address taken.

Differential Revision: http://reviews.llvm.org/D13607

llvm-svn: 250090

1 files changed, 10 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index d87be3b..5099867 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -2236,6 +2236,16 @@ void CastOperation::CheckCStyleCast() {
     return;
   }
 
+  // Overloads are allowed with C extensions, so we need to support them.
+  if (SrcExpr.get()->getType() == Self.Context.OverloadTy) {
+    DeclAccessPair DAP;
+    if (FunctionDecl *FD = Self.ResolveAddressOfOverloadedFunction(
+            SrcExpr.get(), DestType, /*Complain=*/true, DAP))
+      SrcExpr = Self.FixOverloadedFunctionReference(SrcExpr.get(), DAP, FD);
+    else
+      return;
+    assert(SrcExpr.isUsable());
+  }
   SrcExpr = Self.DefaultFunctionArrayLvalueConversion(SrcExpr.get());
   if (SrcExpr.isInvalid())
     return;