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Re: Unnecessary PRE optimization

From: Paolo Bonzini <bonzini at gnu dot org>
To: Steven Bosscher <stevenb dot gcc at gmail dot com>
Cc: Bingfeng Mei <bmei at broadcom dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, "dberlin at dberlin dot org" <dberlin at dberlin dot org>
Date: Wed, 23 Dec 2009 14:28:06 +0100
Subject: Re: Unnecessary PRE optimization
References: <7FB04A5C213E9943A72EE127DB74F0AD93D8DE261E@SJEXCHCCR02.corp.ad.broadcom.com> <571f6b510912230401p59e79a74gb4fe6dfc13c0617d@mail.gmail.com>

On 12/23/2009 01:01 PM, Steven Bosscher wrote:

On Wed, Dec 23, 2009 at 12:49 PM, Bingfeng Mei<bmei@broadcom.com> wrote:
Hello,
I encounter an issue with PRE optimization, which created worse
Is this at -O2 or -O3?

I think this could be fixed if fwprop propagated addresses into loops; it doesn't because it made performance worse on x86. The real reason is "address_cost on x86 sucks and nobody knows how to fix it exactly", but the performance hit was bad enough that we (Steven Bosscher and I) decided to put that hack into fwprop.

Paolo

Follow-Ups:
- Re: Unnecessary PRE optimization
  - From: Joern Rennecke
- RE: Unnecessary PRE optimization
  - From: Bingfeng Mei

References:
- Unnecessary PRE optimization
  - From: Bingfeng Mei
- Re: Unnecessary PRE optimization
  - From: Steven Bosscher

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