PR19039 causes regression of 3.9% in SPEC int

[Giovanni Bajo]

Steven Bosscher <stevenb@suse.de> wrote:

>> Would you mind posting your RTL-based loop header copying patch to
>> gcc-patches?  Not only might it be catching more optimizations than
>> out-of-ssa is causing, but as a solution it might be more suitable
>> for gcc 4.0 (depending upon compile-time performance impact,
>> ugliness, intrusivenss, corrections to Andrew's "quick fix", etc...).
>
> I'm unimpressed by either RTL loop header copying, or Andrew's fix,
> both just paper over the underlying problem.  The real problem is
> that apparently we are creating a situation where copy propagation
> makes coalescing impossible.  Fix that and you don't get the extra
> basic block - bug fixed, done.


Yes, but as you said, we ought to fix this one way or another in 4.0. Mostafa's
patch is at least written and tested, and it shows a big improvement. Andrew,
as the original author of the out-of-ssa pass, do you believe that this bug
(http://gcc.gnu.org/PR19038) can be properly fixed in time for 4.0?

Giovanni Bajo