Bug? flow_find_cross_jump deletes USE insns ...

[Ulrich Weigand]

Richard Henderson wrote:
>On Tue, Jan 15, 2002 at 09:41:04PM +0100, Ulrich Weigand wrote:
> So CSE can never make the optimization you describe above.
>
>Ok, sounds like you're safe.

Great, thanks.  I'll check in the variant that uses
CALL_INSN_FUNCTION_USAGE.

>> (I don't think there would be much benefit of trying to add this
>> optimization on our platform, given that the two call sequences
>> are basically equivalent - one load from memory, one indirect call ...)
>
>Yes, but one uses lazy binding and the other doesn't.  So ideally
>you'd attempt to do this.  Whether it ocurrs often enough to make
>it worth your while is another story.

Well, the PLT stubs themselves are quite inefficient currently,
because they incur a large penalty due to address generation
interlocks (they are so short there is no way to alleviate that
by instruction scheduling).

Therefore I have even been thinking of doing it the other way
around and prefering indirect calls over PLT stub calls.  However,
you're right about lazy binding ...

In any case, I won't be attempting any such optimization in the 3.1
time frame; maybe at some later point.


Mit freundlichen Gruessen / Best Regards

Ulrich Weigand

--
  Dr. Ulrich Weigand
  Linux for S/390 Design & Development
  IBM Deutschland Entwicklung GmbH, Schoenaicher Str. 220, 71032 Boeblingen
  Phone: +49-7031/16-3727   ---   Email: Ulrich.Weigand@de.ibm.com