define_split

[Michael Meissner]

On Tue, Nov 09, 2010 at 01:38:17PM -0500, Joern Rennecke wrote:
> 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.

Generally you need to tighten the pattern conditions to make sure it doesn't
match.

-- 
Michael Meissner, IBM
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