[llvm] r317292 - Avoid PLT for external calls when attribute nonlazybind is used.

[Rafael Avila de Espindola via llvm-commits]

Sriraman Tallam <tmsriram at google.com> writes:

>> The check for plt versus got should at the very least be after the
>> shouldAssumeDSOLocal call.
>>
>
> I tried doing this after shouldAssumeDSOLocal and this does not work well
> non-PIC binaries.  The external call will be considered local and generated
> without the @PLT but the linker will convert the call to PLT. This is the
> reason why I did it before "shouldAssumeDSOLocal". Let me take another look
> and see what I can do here.

Ah, that is why!

Yes, the linker hack of creating a dummy plt entry is really annoying.

I would say that what needs changing is shouldAssumeDSOLocal. It looks
like

-------------------------------------------------------------
  // If the IR producer requested that this GV be treated as dso local, obey.
  if (GV && GV->isDSOLocal())
    return true;

  // According to the llvm language reference, we should be able to just return
  // false in here if we have a GV, as we know it is dso_preemptable.
  // At this point in time, the various IR producers have not been transitioned
  // to always produce a dso_local when it is possible to do so. As a result we
  // still have some pre-dso_local logic in here to improve the quality of the
  // generated code:
....
-------------------------------------------------------------

So any addition that returns false in more cases is going on the right
direction. In particular, I think you a hitting the case inside

  if (IsExecutable) {
  ...
  }

And it should return false for NonLazyBind (with a comment why).

Cheers,
Rafael