[Bug tree-optimization/65206] vectorized version of loop is removed, dependence analysis fails for *&a[i] vs a[j]

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65206

--- 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:f92901a508305f291fcf2acae0825379477724de

commit r12-3677-gf92901a508305f291fcf2acae0825379477724de
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Sep 8 14:42:31 2021 +0200

    tree-optimization/65206 - dependence analysis on mixed pointer/array

    This adds the capability to analyze the dependence of mixed
    pointer/array accesses.  The example is from where using a masked
    load/store creates the pointer-based access when an otherwise
    unconditional access is array based.  Other examples would include
    accesses to an array mixed with accesses from inlined helpers
    that work on pointers.

    The idea is quite simple and old - analyze the data-ref indices
    as if the reference was pointer-based.  The following change does
    this by changing dr_analyze_indices to work on the indices
    sub-structure and storing an alternate indices substructure in
    each data reference.  That alternate set of indices is analyzed
    lazily by initialize_data_dependence_relation when it fails to
    match-up the main set of indices of two data references.
    initialize_data_dependence_relation is refactored into a head
    and a tail worker and changed to work on one of the indices
    structures and thus away from using DR_* access macros which
    continue to reference the main indices substructure.

    There are quite some vectorization and loop distribution opportunities
    unleashed in SPEC CPU 2017, notably 520.omnetpp_r, 548.exchange2_r,
    510.parest_r, 511.povray_r, 521.wrf_r, 526.blender_r, 527.cam4_r and
    544.nab_r see amendments in what they report with -fopt-info-loop while
    the rest of the specrate set sees no changes there.  Measuring runtime
    for the set where changes were reported reveals nothing off-noise
    besides 511.povray_r which seems to regress slightly for me
    (on a Zen2 machine with -Ofast -march=native).

    2021-09-08  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/65206
            * tree-data-ref.h (struct data_reference): Add alt_indices,
            order it last.
            * tree-data-ref.c (free_data_ref): Release alt_indices.
            (dr_analyze_indices): Work on struct indices and get DR_REF as
tree.
            (create_data_ref): Adjust.
            (initialize_data_dependence_relation): Split into head
            and tail.  When the base objects fail to match up try
            again with pointer-based analysis of indices.
            * tree-vectorizer.c (vec_info_shared::check_datarefs): Do
            not compare the lazily computed alternate set of indices.

            * gcc.dg/torture/20210916.c: New testcase.
            * gcc.dg/vect/pr65206.c: Likewise.