[Bug tree-optimization/96272] Failure to optimize overflow check

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96272

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:fe78528c05fdd562f21e12675781473b0fbe892e

commit r11-5957-gfe78528c05fdd562f21e12675781473b0fbe892e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Dec 12 14:48:47 2020 +0100

    widening_mul: Recognize another form of ADD_OVERFLOW [PR96272]

    The following patch recognizes another form of hand written
    __builtin_add_overflow (this time _p), in particular when
    the code does unsigned
    if (x > ~0U - y)
    or
    if (x <= ~0U - y)
    it can be optimized (if the subtraction turned into ~y is single use)
    into
    if (__builtin_add_overflow_p (x, y, 0U))
    or
    if (!__builtin_add_overflow_p (x, y, 0U))
    and generate better code, e.g. for the first function in the testcase:
    -       movl    %esi, %eax
            addl    %edi, %esi
    -       notl    %eax
    -       cmpl    %edi, %eax
    -       movl    $-1, %eax
    -       cmovnb  %esi, %eax
    +       jc      .L3
    +       movl    %esi, %eax
    +       ret
    +.L3:
    +       orl     $-1, %eax
            ret
    on x86_64.  As for the jumps vs. conditional move case, that is some CE
    issue with complex branch patterns we should fix up no matter what, but
    in this case I'm actually not sure if branchy code isn't better, overflow
    is something that isn't that common.

    2020-12-12  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/96272
            * tree-ssa-math-opts.c (uaddsub_overflow_check_p): Add OTHER
argument.
            Handle BIT_NOT_EXPR.
            (match_uaddsub_overflow): Optimize unsigned a > ~b into
            __imag__ .ADD_OVERFLOW (a, b).
            (math_opts_dom_walker::after_dom_children): Call
match_uaddsub_overflow
            even for BIT_NOT_EXPR.

            * gcc.dg/tree-ssa/pr96272.c: New test.