[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


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306467 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/Lex/PPMacroExpansion.cpp b/lib/Lex/PPMacroExpansion.cpp
index a6bfc32e22..8af9a50cc2 100644
--- a/lib/Lex/PPMacroExpansion.cpp
+++ b/lib/Lex/PPMacroExpansion.cpp
@@ -1315,6 +1315,8 @@ static bool HasExtension(const Preprocessor &PP, StringRef Extension) {
            .Case("cxx_binary_literals", true)
            .Case("cxx_init_captures", LangOpts.CPlusPlus11)
            .Case("cxx_variable_templates", LangOpts.CPlusPlus)
+           // Miscellaneous language extensions
+           .Case("overloadable_unmarked", true)
            .Default(false);
 }