[Bug tree-optimization/18694] [4.0 regression] loop miscompilation at -O1 (-ftree-ch)

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From law at redhat dot com  2004-12-09 16:47 -------
Subject: Re:  [4.0 regression] loop
	miscompilation at -O1 (-ftree-ch)

On Thu, 2004-12-09 at 14:19 +0000, schwab at suse dot de wrote:
> ------- Additional Comments From schwab at suse dot de  2004-12-09 14:19 -------
> The patch does no good on ia64, it causes the stage2 compiler to be  
> miscompiled. 
Any chance you could do a little analysis on this?  All Kazu's change
does is cause us to ignore certain (bogus) equivalences.  If that's
causing stage2 to be mis-compiled, then, well we've clearly got deeper
problems.

Having at least a rough idea of the root cause of the ia64 failure 
would be good as I can keep that issue in mind as a rethink how the
jump thread selection code ought to work when dealing with loops.

You might be able to at least get some idea of the failure mode by
looking at what jumps are threaded by DOM before/after Kazu's patch.
That may be faster than actually sitting down with the debugger to
figure out what's being mis-compiled.

Jeff



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18694