[Bug tree-optimization/97832] AoSoA complex caxpy-like loops: AVX2+FMA -Ofast 7 times slower than -O3

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97832

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

https://gcc.gnu.org/g:ce670e4faafb296d1f1a7828d20f8c8ba4686797

commit r12-1329-gce670e4faafb296d1f1a7828d20f8c8ba4686797
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Nov 18 14:17:34 2020 +0100

    tree-optimization/97832 - handle associatable chains in SLP discovery

    This makes SLP discovery handle associatable (including mixed
    plus/minus) chains better by swapping operands across the whole
    chain.  To work this adds caching of the 'matches' lanes for
    failed SLP discovery attempts, thereby fixing a failed SLP
    discovery for the slp-pr98855.cc testcase which results in
    building an operand from scalars as expected.  Unfortunately
    this makes us trip over the cost threshold so I'm XFAILing the
    testcase for now.

    For BB vectorization all this doesn't work because we have no way
    to distinguish good from bad associations as we eventually build
    operands from scalars and thus not fail in the classical sense.

    2021-05-31  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/97832
            * tree-vectorizer.h (_slp_tree::failed): New.
            * tree-vect-slp.c (_slp_tree::_slp_tree): Initialize
            failed member.
            (_slp_tree::~_slp_tree): Free failed.
            (vect_build_slp_tree): Retain failed nodes and record
            matches in them, copying that back out when running
            into a cached fail.  Dump start and end of discovery.
            (dt_sort_cmp): New.
            (vect_build_slp_tree_2): Handle associatable chains
            together doing more aggressive operand swapping.

            * gcc.dg/vect/pr97832-1.c: New testcase.
            * gcc.dg/vect/pr97832-2.c: Likewise.
            * gcc.dg/vect/pr97832-3.c: Likewise.
            * g++.dg/vect/slp-pr98855.cc: XFAIL.