[Bug middle-end/111151] [12/13/14 Regression] Wrong code at -O0 on x86_64-pc-linux-gnu

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111151

--- Comment #15 from GCC 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:c4f2c84e8fa369856aee76679590eb613724bfb0

commit r14-9668-gc4f2c84e8fa369856aee76679590eb613724bfb0
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 26 11:21:38 2024 +0100

    fold-const: Punt on MULT_EXPR in extract_muldiv MIN/MAX_EXPR case
[PR111151]

    As I've tried to explain in the comments, the extract_muldiv_1
    MIN/MAX_EXPR optimization is wrong for code == MULT_EXPR.
    If the multiplication is done in unsigned type or in signed
    type with -fwrapv, it is fairly obvious that max (a, b) * c
    in many cases isn't equivalent to max (a * c, b * c) (or min if c is
    negative) due to overflows, but even for signed with undefined overflow,
    the optimization could turn something without UB in it (where
    say a * c invokes UB, but max (or min) picks the other operand where
    b * c doesn't).
    As for division/modulo, I think it is in most cases safe, except if
    the problematic INT_MIN / -1 case could be triggered, but we can
    just punt for MAX_EXPR because for MIN_EXPR if one operand is INT_MIN,
    we'd pick that operand already.  It is just for completeness, match.pd
    already has an optimization which turns x / -1 into -x, so the division
    by zero is mostly theoretical.  That is also why in the testcase the
    i case isn't actually miscompiled without the patch, while the c and f
    cases are.

    2024-03-26  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/111151
            * fold-const.cc (extract_muldiv_1) <case MAX_EXPR>: Punt for
            MULT_EXPR altogether, or for MAX_EXPR if c is -1.

            * gcc.c-torture/execute/pr111151.c: New test.