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Re: [patch] for PR 18687


Hello,

> David Edelsohn wrote:
> >	This patch has a good effect if -funroll-loops also is enabled,
> >but a very bad effect without.  For instance, on our tests, swim loses
> >nearly 20% performance with the patch when using options
> >
> >-O2 -mcpu=power4
> >
> >versus
> >
> >-O2 -mcpu=power4 -funroll-lops -fpeel-loops
> 
> That's disturbing.
> 
> Unless we were just getting incredibly lucky before, I'm concerned about 
> this issue, as using "-O2 -mcpu=power4" is the optimization setting more 
> likely to be used by most people.
> 
> Zdenek, from your original posting it sounded like the two improvements 
> that you made should not affect the generated code.  You describe (a) 
> memoizing the result of a frequently called function, and (b) speeding 
> up a check that gates whether or not it is possible to perform the 
> optimization.
> 
> Did you expect your change to have other side-effects?

no, this should have been purely compile time improvement.  I should
have time to check what's going on during this week.

Zdenek


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