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Date: Thu, 18 Mar 2004 12:38:00 -0000
From: Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz>
To: Steven Bosscher <stevenb@suse.de>
Cc: gcc@gcc.gnu.org
Subject: Re: [tree-ssa] Dce & infinite loops
Message-ID: <20040318123444.GA26804@atrey.karlin.mff.cuni.cz>
References: <20040318122130.GA24448@atrey.karlin.mff.cuni.cz> <200403181331.57192.stevenb@suse.de>
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Hello,

> > I may be wrong, but IIRC it is incorrect to remove infinite loops, as
> > happens currently for example for the following code:
> >
> > int main(void)
> > {
> >   unsigned i;
> >
> >   for (i = 1; i != 0; i+=2);
> >
> >   return 0;
> > }
> 
> Removing an infinte loop is indeed wrong.  Hence this comment
> in tree-ssa-dce.c:
> 
>   /* Some blocks don't have an immediate post dominator.  This can happen
>      for example with infinite loops.  Removing an infinite loop is an
>      inappropriate transformation anyway...  */
> 
> If we remove that infinite loop, you found a bug.

the problem is that the loop in the example above has an exit (that is
never taken); therefore the code in tree-ssa-dce.c you cite does not
handle it.

Zdenek