[Sema] Allow unmarked overloadable functions.

This patch extends the `overloadable` attribute to allow for one
function with a given name to not be marked with the `overloadable`
attribute. The overload without the `overloadable` attribute will not
have its name mangled.

So, the following code is now legal:

  void foo(void) __attribute__((overloadable));
  void foo(int);
  void foo(float) __attribute__((overloadable));

In addition, this patch fixes a bug where we'd accept code with
`__attribute__((overloadable))` inconsistently applied. In other words,
we used to accept:

  void foo(void);
  void foo(void) __attribute__((overloadable));

But we will do this no longer, since it defeats the original purpose of
requiring `__attribute__((overloadable))` on all redeclarations of a
function.

This breakage seems to not be an issue in practice, since the only code
I could find that had this pattern often looked like:

  void foo(void);
  void foo(void) __attribute__((overloadable)) __asm__("foo");
  void foo(int) __attribute__((overloadable));

...Which can now be simplified by simply removing the asm label and
overloadable attribute from the redeclaration of `void foo(void);`

Differential Revision: https://reviews.llvm.org/D32332

llvm-svn: 306467

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/mangle-ms.cpp b/clang/test/CodeGenCXX/mangle-ms.cpp
index ee0f50e5e2d..7e2f17f27a9 100644
--- a/clang/test/CodeGenCXX/mangle-ms.cpp
+++ b/clang/test/CodeGenCXX/mangle-ms.cpp
@@ -399,6 +399,13 @@ template void fn_tmpl<extern_c_func>();
 extern "C" void __attribute__((overloadable)) overloaded_fn() {}
 // CHECK-DAG: @"\01?overloaded_fn@@$$J0YAXXZ"
 
+extern "C" void overloaded_fn2() {}
+// CHECK-DAG: @overloaded_fn2
+//
+extern "C" void __attribute__((overloadable)) overloaded_fn3();
+extern "C" void overloaded_fn3() {}
+// CHECK-DAG: @overloaded_fn3
+
 namespace UnnamedType {
 struct S {
   typedef struct {} *T1[1];