Re: [PATCH] Atom: Enabling unroll at O2 optimization level

[Igor Zamyatin <izamyatin at gmail dot com>]

On Wed, Apr 11, 2012 at 12:39 PM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Tue, Apr 10, 2012 at 8:43 PM, Igor Zamyatin <izamyatin@gmail.com> wrote:
>> Hi All!
>>
>> Here is a patch that enables unroll at O2 for Atom.
>>
>> This gives good performance boost on EEMBC 2.0 (~+8% in Geomean for 32
>> bits) with quite moderate code size increase (~5% for EEMBC2.0, 32
>> bits).
>
> 5% is not moderate. ?Your patch does enable unrolling at -O2 but not -O3,
> why? Why do you disable register renaming? ?check_imull requires a function
> comment.

Sure, enabling unroll for O3 could be the next step.
We can't avoid code size increase with unroll - what number do you
think will be appropriate?
Register renaming was the reason of several degradations during tuning process
Comment for check_imull was added

>
> This completely looks like a hack for EEMBC2.0, so it's definitely not ok.

Why? EEMBC was measured and result provided here just because this
benchmark considers to be very relevant for Atom

>
> -O2 is not supposed to give best benchmark results.

O2 is wide-used so performance improvement could be important for users.

>
> Thanks,
> Richard.
>
>>
>> Tested for i386 and x86-64, ok for trunk?

Updated patch attached

>>
>> Thanks,
>> Igor
>>
>> ChangeLog:
>>
>> 2012-04-10 ?Yakovlev Vladimir ?<vladimir.b.yakovlev@intel.com>
>>
>> ? ? ? ?* gcc/config/i386/i386.c (check_imul): New routine.
>> ? ? ? ?(ix86_loop_unroll_adjust): New target hook.
>> ? ? ? ?(ix86_option_override_internal): Enable unrolling on Atom at -O2.
>> ? ? ? ?(TARGET_LOOP_UNROLL_ADJUST): New define.

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