[Bug middle-end/100810] [12 Regression] wrong code at -O1 and above on x86_64-linux-gnu since r12-397-gda9e6e63d1ae22e530ec7baf59f6ed028bf05776

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100810

--- Comment #16 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Alexandre Oliva <aoliva@gcc.gnu.org>:

https://gcc.gnu.org/g:be2861fe8c527a5952257462ceca899bb43b1452

commit r13-972-gbe2861fe8c527a5952257462ceca899bb43b1452
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Fri Jun 3 03:59:03 2022 -0300

    [PR105665] ivopts: check defs of names in base for undefs

    The patch for PR 100810 tested for undefined SSA_NAMEs appearing
    directly in the base expression of the potential IV candidate, but
    that's not enough.  The testcase for PR105665 shows an undefined
    SSA_NAME has the same ill effect if it's referenced as an PHI_NODE arg
    in the referenced SSA_NAME.  The variant of that test shows it can be
    further removed from the referenced SSA_NAME.

    To avoid deep recursion, precompute maybe-undefined SSA_NAMEs: start
    from known-undefined nonvirtual default defs, and propagate them to
    any PHI nodes reached by a maybe-undefined arg, as long as there
    aren't intervening non-PHI uses, that would imply the maybe-undefined
    name must be defined at that point, otherwise it would invoke
    undefined behavior.  Also test for intervening non-PHI uses of DEFs in
    the base expr.

    The test for intervening uses implemented herein relies on dominance;
    this could be further extended, regarding conditional uses in every
    path leading to a point as an unconditional use dominating that point,
    but I haven't implemented that.


    for  gcc/ChangeLog

            PR tree-optimization/105665
            PR tree-optimization/100810
            * tree-ssa-loop-ivopts.cc
            (ssa_name_maybe_undef_p, ssa_name_set_maybe_undef): New.
            (ssa_name_any_use_dominates_bb_p, mark_ssa_maybe_undefs): New.
            (find_ssa_undef): Check precomputed flag and intervening uses.
            (tree_ssa_iv_optimize): Call mark_ssa_maybe_undefs.

    for  gcc/testsuite/ChangeLog

            PR tree-optimization/105665
            PR tree-optimization/100810
            * gcc.dg/torture/pr105665.c: New.