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Date: Sat, 28 Aug 2010 10:08:00 -0000
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Subject: Re: Better performance on older version of GCC
From: Xinliang David Li <davidxl@google.com>
To: Andrew Pinski <pinskia@gmail.com>
Cc: Corey Kasten <corey@materialintelligencellc.com>,        Richard Guenther <richard.guenther@gmail.com>,        Nathan Froyd <froydnj@codesourcery.com>, gcc@gcc.gnu.org
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Right -- I missed Richard's previous email regarding the options.

Thanks,

David

On Fri, Aug 27, 2010 at 5:21 PM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Fri, Aug 27, 2010 at 5:12 PM, Xinliang David Li <davidxl@google.com> w=
rote:
>> Briefly looked at it -- the trunk gcc also regresses a lot compared to
>> the binary you attached. (To match your binary, also added
>> -mfpmath=3D387 -m32 options)
>>
>> Two problems:
>>
>> 1) more register spills in the trunk version -- the old compiler seems
>> more effective in using fp stack registers;
>> 2) the complex multiplication -- the old version emits inline sequence
>> while the trunk version emits call to _muld3c intrinsinc.
>
> Neither of these seems like real bug reportable ones. =A0The first one
> is that due to -fexcess-precision=3Dstandard being default in 4.5 and
> above (see PR 323). =A0The second one is due to -fcx-limited-range not
> being default any more (I cannot remember the bug number which changed
> that though).
>
> Thanks,
> Andrew Pinski
>