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Subject: [Bug tree-optimization/102906] [12 regression]
 gcc.target/arm/ivopts-4.c fails since r12-4526
Date: Wed, 10 Nov 2021 22:13:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102906

--- Comment #20 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Aldy Hernandez <aldyh@gcc.gnu.org>:

https://gcc.gnu.org/g:e82c382971664d6fd138cc36020db4b1a91885c6

commit r12-5138-ge82c382971664d6fd138cc36020db4b1a91885c6
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Wed Nov 10 13:21:59 2021 +0100

    Allow loop header copying when first iteration condition is known.

    As discussed in the PR, the loop header copying pass avoids doing so
    when optimizing for size.  However, sometimes we can determine the
    loop entry conditional statically for the first iteration of the loop.

    This patch uses the path solver to determine the outgoing edge
    out of preheader->header->xx.  If so, it allows header copying.  Doing
    this in the loop optimizer saves us from doing gymnastics in the
    threader which doesn't have the context to determine if a loop
    transformation is profitable.

    I am only returning true in entry_loop_condition_is_static for
    a true conditional.  Technically a false conditional is also
    provably static, but allowing any boolean value causes a regression
    in gfortran.dg/vector_subscript_1.f90.

    I would have preferred not passing around the query object, but the
    layout of pass_ch and should_duplicate_loop_header_p make it a bit
    awkward to get it right without an outright refactor to the
    pass.

    Tested on x86-64 Linux.

    gcc/ChangeLog:

            PR tree-optimization/102906
            * tree-ssa-loop-ch.c (entry_loop_condition_is_static): New.
            (should_duplicate_loop_header_p): Call
entry_loop_condition_is_static.
            (class ch_base): Add m_ranger and m_query.
            (ch_base::copy_headers): Pass m_query to
            entry_loop_condition_is_static.
            (pass_ch::execute): Allocate and deallocate m_ranger and
            m_query.
            (pass_ch_vect::execute): Same.

    gcc/testsuite/ChangeLog:

            * gcc.dg/tree-ssa/pr102906.c: New test.=