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Re: [Patch, i386] Turn on -fschedule-insns and -fsched-pressure by default for x86-64

From: Paolo Bonzini <bonzini at gnu dot org>
To: "Fang, Changpeng" <Changpeng dot Fang at amd dot com>
Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, "sebpop at gmail dot com" <sebpop at gmail dot com>, "hjl dot tools at gmail dot com" <hjl dot tools at gmail dot com>, "Yazdani, Reza" <Reza dot Yazdani at amd dot com>
Date: Tue, 07 Dec 2010 20:23:22 +0100
Subject: Re: [Patch, i386] Turn on -fschedule-insns and -fsched-pressure by default for x86-64
Newsgroups: gmane.comp.gcc.patches
References: <D4C76825A6780047854A11E93CDE84D004C17683E8@SAUSEXMBP01.amd.com>

On 12/06/2010 09:04 PM, Fang, Changpeng wrote:

Hi,

Attached is the patch that proposes to turn on -fschedule-insns and -fsched-pressure by default at
-O2 or higher (for speed-runs only) for x86-64 systems.  Enablement of these two flags could improve
the performance of floating point programs (For CFP2006, 2.29% under -O2, and  1.34% under -O3).
There is no apparent performance  impact on integer programs (as expected).

We have investigated this optimization since 4.5, and it is the time to turn on these two flags to enjoy
the performance gains.

I think enabling rename registers whenever schedule_insns2 is enabled would achieve almost the same freedom without risking bugs like 46829. There are just too many singleton register classes in i386 for schedule-insns to work. :(

Paolo

Follow-Ups:
- Re: [Patch, i386] Turn on -fschedule-insns and -fsched-pressure by default for x86-64
  - From: Jack Howarth
- Re: [Patch, i386] Turn on -fschedule-insns and -fsched-pressure by default for x86-64
  - From: Jack Howarth

References:
- [Patch, i386] Turn on -fschedule-insns and -fsched-pressure by default for x86-64
  - From: Fang, Changpeng

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