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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/57994] New: Constant folding of infinity
Date: Fri, 26 Jul 2013 15:13:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57994

            Bug ID: 57994
           Summary: Constant folding of infinity
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org

double f(){
  return __builtin_exp(-__builtin_huge_val());
}

As noticed in PR57974, we fail to fold this to a constant. Indeed, in
do_mpfr_arg1, the relevant code is protected by if (real_isfinite (ra) ...

mpfr handles infinite values, so it should be doable, at least with -ffast-math
(there might be some errno issues with default options).