[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, 1 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 3c916a30d17..d640a126989 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7274,6 +7274,15 @@ Sema::CheckSingleAssignmentConstraints(QualType LHSType, ExprResult &CallerRHS,
     // structures.
     // FIXME: We also fall through for atomics; not sure what should
     // happen there, though.
+  } else if (RHS.get()->getType() == Context.OverloadTy) {
+    // As a set of extensions to C, we support overloading on functions. These
+    // functions need to be resolved here.
+    DeclAccessPair DAP;
+    if (FunctionDecl *FD = ResolveAddressOfOverloadedFunction(
+            RHS.get(), LHSType, /*Complain=*/false, DAP))
+      RHS = FixOverloadedFunctionReference(RHS.get(), DAP, FD);
+    else
+      return Incompatible;
   }
 
   // C99 6.5.16.1p1: the left operand is a pointer and the right is
@@ -11986,7 +11995,7 @@ bool Sema::DiagnoseAssignmentResult(AssignConvertType ConvTy,
     
   if (SecondType == Context.OverloadTy)
     NoteAllOverloadCandidates(OverloadExpr::find(SrcExpr).Expression,
-                              FirstType);
+                              FirstType, /*TakingAddress=*/true);
 
   if (CheckInferredResultType)
     EmitRelatedResultTypeNote(SrcExpr);