[Bug tree-optimization/26939] PRE confuses loop number of iterations analysis

[dberlin at dberlin dot org]

------- Comment #6 from dberlin at gcc dot gnu dot org  2006-03-30 14:43 -------
Subject: Re:  PRE confuses loop number of
        iterations analysis

On Thu, 2006-03-30 at 14:37 +0000, rguenth at gcc dot gnu dot org wrote:
> 
> ------- Comment #5 from rguenth at gcc dot gnu dot org  2006-03-30 14:37 -------
> Loop header copying for the inner loop is required for # of iterations analysis
> - though we should move that header copy out of the outer loop, too, if
> possible.

Again, you should spend your time improving SCEV, or improving the # of
iterations analysis.  Really.   You are saying "we want to copy loop
headers, but don't want PRE to take advantage of the copied loop
headers".

If we can copy the loop header and prove that we iterate at least once
(or whatever condition this proves for # of iterations analysis), you
should be able to do it without copying the loop header as well.

Though, it's probably just better to teach SCEV to deal with the code
that PRE has made, since improving SCEV improves a lot of things.


> 
> 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26939