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Re: define_split

From: Joern Rennecke <amylaar at spamcop dot net>
To: Paolo Bonzini <bonzini at gnu dot org>
Cc: roy rosen <roy dot 1rosen at gmail dot com>, Michael Meissner <meissner at linux dot vnet dot ibm dot com>, gcc at gcc dot gnu dot org
Date: Tue, 09 Nov 2010 13:38:17 -0500
Subject: Re: define_split
References: <AANLkTinXSp9FefVHXWMm1FL-A040r+1wzoi1juyUuBL+@mail.gmail.com> <20101108201655.GA14062@hungry-tiger.westford.ibm.com> <AANLkTi=Wa2tNAHJNzo0sWt7=3099vJSHMLs6ag8y3Gxj@mail.gmail.com> <20101109042209.8ud7scl0ckksko4w-nzlynne@webmail.spamcop.net> <4CD96EAC.3070602@gnu.org> <20101109113804.0oamo2x3c4gos8kc-nzlynne@webmail.spamcop.net> <4CD97D6D.1060707@gnu.org>

Quoting Paolo Bonzini <bonzini@gnu.org>:

On 11/09/2010 05:38 PM, Joern Rennecke wrote:

A define_insn will be recognized in all contexts.
Having an insn pattern for an insn that does not actually exist can cause
all kinds of unintended consequences as the optimizers try to generate
and recognize 'optimized' patterns, or when reload does its stuff.


Before reload that is not a problem at all, I think, actually it can be
an advantage.


No, it is a code quality problem.  And yes, I have seen actual
SH patterns being recognized that were not wanted, and lead to worse
code overall.

Follow-Ups:
- Re: define_split
  - From: Michael Meissner

References:
- Re: define_split
  - From: Michael Meissner
- Re: define_split
  - From: roy rosen
- Re: define_split
  - From: Joern Rennecke
- Re: define_split
  - From: Paolo Bonzini
- Re: define_split
  - From: Joern Rennecke
- Re: define_split
  - From: Paolo Bonzini

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