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Subject: [Bug tree-optimization/105198] [9/10 Regression] Wrong code for C
 loop (GCC 12 -O2, GCC 11 -O3)
Date: Fri, 06 May 2022 12:47:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105198

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:29e8fe04e707910b1bcf15cbc2b582ee0e0e93d6

commit r10-10595-g29e8fe04e707910b1bcf15cbc2b582ee0e0e93d6
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Apr 8 13:13:29 2022 +0200

    tree-optimization/105198 - wrong code with predictive commoning

    When predictive commoning looks for a looparound PHI it tries
    to match the entry value definition (a load) up with the appropriate
    member of the chain.  But it fails to consider stmts clobbering
    the very same memory location inbetween the load and loop entry.

    In theory we could be more clever on must aliases that would be
    also picked up from a load (so not exactly stmt_kills_ref_p) and
    use the stored value from that if it is an exact match.  But we
    currently have no way to propagate this information inside predcom.

    2022-04-08  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/105198
            * tree-predcom.c (find_looparound_phi): Check whether
            the found memory location of the entry value is clobbered
            inbetween the value we want to use and loop entry.

            * gcc.dg/torture/pr105198.c: New testcase.

    (cherry picked from commit e5453bcc217ea4ac53a4ac277661d6ef0ccd425b)=