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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/108583] [13 Regression] wrong code with vector division
 by uint16 at -O2
Date: Sun, 12 Mar 2023 18:44:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108583

--- Comment #29 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tamar Christina <tnfchris@gcc.gnu.org=
>:

https://gcc.gnu.org/g:81fd62d1378b7ddc1fa0967cbddcdcdcdd2d8d8c

commit r13-6619-g81fd62d1378b7ddc1fa0967cbddcdcdcdd2d8d8c
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Sun Mar 12 18:42:04 2023 +0000

    middle-end: Implement preferred_div_as_shifts_over_mult [PR108583]

    This now implements a hook
    preferred_div_as_shifts_over_mult that indicates whether a target prefe=
rs
that
    the vectorizer decomposes division as shifts rather than multiplication
when
    possible.

    In order to be able to use this we need to check whether the current
precision
    has enough bits to do the operation without any of the additions
overflowing.

    We use range information to determine this and only do the operation if
we're
    sure am overflow won't occur. This now uses ranger to do this range che=
ck.

    This seems to work better than vect_get_range_info which uses range_que=
ry,
but I
    have not switched the interface of vect_get_range_info over in this PR =
fix.

    As Andy said before initializing a ranger instance is cheap but not fre=
e,
and if
    the intention is to call it often during a pass it should be instantiat=
ed
at
    pass startup and passed along to the places that need it.  This is a big
    refactoring and doesn't seem right to do in this PR.  But we should in =
GCC
14.

    Currently we only instantiate it after a long series of much cheaper
checks.

    gcc/ChangeLog:

            PR target/108583
            * target.def (preferred_div_as_shifts_over_mult): New.
            * doc/tm.texi.in: Document it.
            * doc/tm.texi: Regenerate.
            * targhooks.cc (default_preferred_div_as_shifts_over_mult): New.
            * targhooks.h (default_preferred_div_as_shifts_over_mult): New.
            * tree-vect-patterns.cc (vect_recog_divmod_pattern): Use it.

    gcc/testsuite/ChangeLog:

            PR target/108583
            * gcc.dg/vect/vect-div-bitmask-4.c: New test.
            * gcc.dg/vect/vect-div-bitmask-5.c: New test.=