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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/53805] combine_comparisons changes trapping behavior
Date: Fri, 29 Jun 2012 12:19:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53805

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> 2012-06-29 12:19:07 UTC ---
(In reply to comment #1)
> We do not try to preserve traps instead we only try to not produce new ones.

That would make a lot of sense, and assuming it is the official policy I am
happy to learn that, but then why don't we optimize this testcase:

int f(double a,double b){
  if(a>=b) if(a<=b) return 1;
  return 0;
}

to
  if(a==b) return 1;
?

The test in combine_comparisons seems to deliberately check for any change of
the trapping condition, not just false->true.

I am happy to relabel this bug (or file a new one if you prefer) as a missed
optimization.