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Re: Transformations to increase parallelism
- From: <tm_gccmail at mail dot kloo dot net>
- To: Ayal Zaks <ZAKS at il dot ibm dot com>
- Cc: Jan Hoogerbrugge <hoogerbrugge at hotmail dot com>,Dorit Naishlos <DORIT at il dot ibm dot com>, gcc at gcc dot gnu dot org
- Date: Thu, 24 Jul 2003 13:01:22 -0700 (PDT)
- Subject: Re: Transformations to increase parallelism
On Wed, 23 Jul 2003, Ayal Zaks wrote:
> In response to: http://gcc.gnu.org/ml/gcc/2003-07/msg01606.html
> >
> >Toshi
>
> Yes, and possibly yes again.
> In general, instead of generating a series of pairwise dependent insns:
>
> load_inc r2,4(r1)
> ...
> load_inc r3,4(r1)
> ...
> load_inc r4,4(r1)
>
> we prefer to generate:
>
> load r2,4(r1)
> ...
> load r3,8(r1)
> ...
> load_inc r4,12(r1)
>
> because on power4 (1) load_inc is more expensive than load in terms of
> resource utilization, and (2) removing data-dependencies allows faster
> time to start (out-of-order) execution.
> I think we ran across such redundant pre-increment modes compiling
> gap/integer.c.
>
> Ayal.
This is almost the exact same problem I mentioned in:
http://gcc.gnu.org/ml/gcc/2003-07/msg00646.html
So, it is not Power4-specific.
Toshi