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Re: -funsafe-loop-optimizations
- From: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- To: Olivier Galibert <galibert at pobox dot com>
- Cc: Richard Henderson <rth at redhat dot com>,David Edelsohn <dje at watson dot ibm dot com>,Daniel Berlin <dberlin at dberlin dot org>, gcc at gcc dot gnu dot org
- Date: Sat, 1 Jan 2005 17:53:47 +0100
- Subject: Re: -funsafe-loop-optimizations
- References: <20041231211409.GA22814@atrey.karlin.mff.cuni.cz> <Pine.LNX.4.60.0412311649170.6844@dberlin.org> <20041231232501.GA16663@redhat.com> <200501010543.j015h3D33264@makai.watson.ibm.com> <20050101101152.GA17037@redhat.com> <20050101155247.GA26830@dspnet.fr.eu.org>
Hello,
> > > While we discuss whether this should be the default or enabled at
> > > any optimization level, can we agree that users should be able to assert
> > > with a commandline option that they want less strict induction variable
> > > semantics?
> >
> > And/or a -W option that warns for these sorts of loops so that
> > (a) we can see how often this happens, really, (b) so that users
> > can fix the presumed mistake.
>
> If you could detect them and warn for them, you could not optimize
> them in the first place (and that's what happens when the boundaries
> are constants). They're detectable only at runtime and even en not
> necessarily easily.
I think Richard means issuing warning in case where
-funsafe-loop-optimizations causes us to ignore some conditions
for optimizations we were not able to prove. Which definitely is
a good idea.
Zdenek