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Re: Question on updating ssa for virtual operands (PR tree-optimization/22543)
- From: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- To: Daniel Berlin <dberlin at dberlin dot org>
- Cc: Dorit Naishlos <DORIT at il dot ibm dot com>, gcc at gcc dot gnu dot org
- Date: Sat, 13 Aug 2005 18:33:47 +0200
- Subject: Re: Question on updating ssa for virtual operands (PR tree-optimization/22543)
- References: <1123858571.7425.43.camel@linux.site>
Hello,
> > The other thing we could try to do is put virtual variables in loop-closed-
> > form, at least just before the vectorizer, and at least just for some
> > loops. Does this sound reasonabale? (By the way, why don't we keep virtual
> > variables in loop-closed-form?)
>
> We used to, nobody could come up with a good reason to keep doing it, so
> we stopped.
there were couple of good reasons (consistency, faster updating
after loop unrolling and loop header copying). However, LCSSA for virtual
operands is memory expensive and this overweighted the advantages (in
particular, slower updating during loop manipulations is compensated
by everything else being faster).
Zdenek