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Re: [patch, powerpc] increase array alignment for Altivec
- From: David Edelsohn <dje dot gcc at gmail dot com>
- To: Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>, Sandra Loosemore <sandra at codesourcery dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Thu, 23 May 2013 12:17:22 -0400
- Subject: Re: [patch, powerpc] increase array alignment for Altivec
- References: <CAGWvnynN5o0uiTS-ERo+oy9PRboe2u+=8UN4v-U5CmWV1GgDAw at mail dot gmail dot com> <519BEBD1 dot 3090109 at codesourcery dot com> <CAGWvnyma77XtxbTEasQbqXmLhGRZuOBFJsXLUyY7Wdd_Mw5JBg at mail dot gmail dot com> <519BFFAD dot 9000102 at codesourcery dot com> <CAGWvnykcxe=Lx7f98z++jzezDxC-wx_cqVQVexqvgoVs8Gbdcw at mail dot gmail dot com> <1369312180 dot 14043 dot 50 dot camel at gnopaine> <519E2DBA dot 3060204 at codesourcery dot com> <1369322318 dot 14043 dot 52 dot camel at gnopaine>
On Thu, May 23, 2013 at 11:18 AM, Bill Schmidt
<wschmidt@linux.vnet.ibm.com> wrote:
> On Thu, 2013-05-23 at 08:54 -0600, Sandra Loosemore wrote:
>> On 05/23/2013 06:29 AM, Bill Schmidt wrote:
>> >
>> > Sandra and David,
>> >
>> > The array-alignment patch is performance-neutral with respect to
>> > CPU2006. All variations were in the noise range.
>>
>> Well, that settles it; I don't see any reason to pursue the patch any
>> further if it's not a performance win after all. It probably helped on
>> some specific program or benchmark our original customer was interested
>> in but that was in an older version of GCC, etc.
>>
>> Bill, thanks very much for helping with this.
>
> I'm not sure that's the right message to take away here -- this was just
> verifying that we didn't see a benchmarking problem with the patch. It
> seems likely that the patch does have benefits; they just aren't exposed
> in the particular benchmarks in SPEC CPU2006.
>
> I think the patch is worth pursuing, since there aren't any negative
> consequences in reporting benchmarks.
Sandra,
I completely agree with Bill. The intention of the benchmark run was a
quick sniff test that the patch did not cause any significant
performance degradation, not that the limited set of benchmarks showed
improvement.
I want to have a version of the patch committed. The only question now
is how much of the patch can be committed without exposing potential
incompatibilities between different object files.
Thanks, David