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Subject: [Bug tree-optimization/104420] [12 Regression] Inconsistent checks
 for X * 0.0 optimization
Date: Wed, 09 Feb 2022 14:24:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104420

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:

https://gcc.gnu.org/g:2d3c477599b02b06e338acd5f5098ee7a3fe6176

commit r12-7130-g2d3c477599b02b06e338acd5f5098ee7a3fe6176
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Wed Feb 9 14:21:08 2022 +0000

    [PATCH] PR tree-optimization/104420: Fix checks for constant folding X*=
0.0

    This patch resolves PR tree-optimization/104420, which is a P1 regressi=
on
    where, as observed by Jakub Jelinek, the conditions for constant folding
    x*0.0 are incorrect (following my patch for PR tree-optimization/96392).
    The multiplication x*0.0 may yield a negative zero result, -0.0, if X is
    negative (not just if x may be negative zero).  Hence (without -ffast-m=
ath)
    (int)x*0.0 can't be optimized to 0.0, but (unsigned)x*0.0 can be consta=
nt
    folded.  This adds a bunch of test cases to confirm the desired behavio=
ur,
    and removes an incorrect test from gcc.dg/pr96392.c which checked for t=
he
    wrong behaviour.

    2022-02-09  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            PR tree-optimization/104420
            * match.pd (mult @0 real_zerop): Tweak conditions for constant
            folding X*0.0 (or X*-0.0) to HONOR_SIGNED_ZEROS when appropriat=
e.

    gcc/testsuite/ChangeLog
            PR tree-optimization/104420
            * gcc.dg/pr104420-1.c: New test case.
            * gcc.dg/pr104420-2.c: New test case.
            * gcc.dg/pr104420-3.c: New test case.
            * gcc.dg/pr104420-4.c: New test case.
            * gcc.dg/pr96392.c: Remove incorrect test.=