Re: Inner-loop optimization regression from 3.3 to 3.4

["Zack Weinberg" <zack at codesourcery dot com>]

Jan Hubicka <jh@suse.cz> writes:

> Overall I do believe that such things are very target specific and
> require knowledge of branch probabilities and costs to be done properly,
> so it belongs to backend.  I wrote ifcvt imporvement to deal with such a
> testcases at:
> http://gcc.gnu.org/ml/gcc-patches/2002-06/msg00026.html
> It is able to combine || and && style tests (sequence of branches
> targetting the same destination)
>
> It is used on hammer branch for a while and does not appear to cause any
> problems now when RTL sharing issues are sorted out.  It causes small
> but measurable SPEC imrovement (about 2points if I recall correctly).
> I can update the patch easilly for current tree if it would be
> considered for mainline.  There is small conflict with related IA-64
> specific work for multiway branches.  ALso I was told that for IA-64 we
> may extend the patch to deal with sequence of multiple branches, not
> only combining two at a time.

This looks like a worthwhile thing to have, and since it addresses a
regression I would say it could go in early in stage 3, if you were
willing to update it and resolve the conflict with the IA-64.

zw