PR33113

[Jack Howarth <howarth at bromo dot med dot uc dot edu>]

Ira and Dorit,
   Is there any chance that PR33113 will be addressed for
gcc 4.5? If I recall correctly, it was one of the last
major issues with vectorization in gfortran that wasn't
addressed yet. Dorit made the following comment back in
Aug 2008...

>From: Dorit Nuzman <DORIT@il.ibm.com>
>Date: Tue, 12 Aug 2008 14:48:07 +0300
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>Jack Howarth <howarth@bromo.msbb.uc.edu> wrote on 10/08/2008 19:00:08:
>
>> Dorit,
>>     I believe the attached email has the most detailed discussion of the
>> issue that I recall seeing. Perhaps Tobias can expand on these previous
>> conversations.
>>               Jack
>> ps I was hoping that the graphite code generation would be enabled by
>>default
>> at -O3 in gcc 4.4 and that the vectorization code could be modified to
>utilize
>> its presence to do some optimizations on gfortran flat arrays which will
>now
>> have stride information via graphite.
>
>Hi Jack,
>
>There is currently no connection between the Graphite pass and any passes
>that follow it. We will be looking into how to incorporate vectorization
>with Graphite, but that will not happen during the 4.4 timeframe. However,
>I think that this is not a prerequisite for vectorizing flat arrays; AFAIU,
>Graphite itself is based on the scev analysis, so whichever stride
>information Graphite gets out of scev, the vectorizer can already get it
>too. Following our discussion below I had opened PR33113, where it turned
>out that scev can easily be made to return symbolic stride information
>instead of failing, and the problem is only inside the vectorizer which
>needs to be enhanced to handle symbolic strides. I would actually be
>interested in enabling that - I will try to look into it in the coming
>weeks.
>
>dorit

I ask because we seem to only get marginal improvements in the Polyhedron
2005 benchmarks between recent releases and these missed vectorization
opportunities might provide a significant performance increase for those
benchmarks. Thanks in advance for any clarifications.
               Jack