[llvm] r189954 - Revert "Add r159136 back now that pr13124 has been fixed."

[Rafael Espíndola]

>> Say we have a "linkonce_odr unnamed_addr" in two translation units:
>> * In TU 1 this optimization kicks in and makes it hidden.
>> * In TU 2 it gets const merged with a constant that is *not* unnamed_addr,
>>    resulting in a non unnamed_addr constant with default visibility.
>
>
> That shouldn't happen. A hidden symbol doesn't get merged with anything
> outside its TU, right? I think you can just rename it.

hidden, not internal, so it does get merged.

But yes, one way to handle this without LTO is to make the
linkonce_odr symbol internal instead of hidden. This introduces a bit
of code duplication, but can be profitable if the function is really
small.

Wit gcc 4.8 when compiling

------------------------------
void f();
struct foo {
  typedef void (foo::*mptr)();
  virtual mptr zed();
  void bar() {
  }
  __attribute__((noinline)) void baz() {
    f();
  }
  virtual void bah() {
  };
};
foo::mptr foo::zed() {
  baz();
  return &foo::bar;
}
-------------------------------------

I get an internal _ZN3foo3bazEv.isra.0 function which effective
implements this optimization.


> Nick
>

Cheers,
Rafael