[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

2 files changed, 13 insertions, 0 deletions

diff --git a/test/CodeGen/mangle-ms.c b/test/CodeGen/mangle-ms.c
index 0ad43d5e06..042c72e6d7 100644
--- a/test/CodeGen/mangle-ms.c
+++ b/test/CodeGen/mangle-ms.c
@@ -2,3 +2,12 @@
 
 // CHECK: define void @"\01?f@@$$J0YAXP6AX@Z@Z"
 __attribute__((overloadable)) void f(void (*x)()) {}
+
+// CHECK: define void @f
+void f(void (*x)(int)) {}
+
+// CHECK: define void @g
+void g(void (*x)(int)) {}
+
+// CHECK: define void @"\01?g@@$$J0YAXP6AX@Z@Z"
+__attribute__((overloadable)) void g(void (*x)()) {}
diff --git a/test/CodeGen/mangle.c b/test/CodeGen/mangle.c
index 46ef512f69..f94139bc5e 100644
--- a/test/CodeGen/mangle.c
+++ b/test/CodeGen/mangle.c
@@ -9,6 +9,10 @@ void __attribute__((__overloadable__)) f0(int a) {}
 // CHECK: @_Z2f0l
 void __attribute__((__overloadable__)) f0(long b) {}
 
+// Unless it's unmarked.
+// CHECK: @f0
+void f0(float b) {}
+
 // CHECK: @bar
 
 // These should get merged.