[Bug middle-end/105984] [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

cvs-commit at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Thu Jun 16 12:36:42 GMT 2022


--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:


commit r13-1133-g74e6a40335765077e235269f19d2d9905d0d9e44
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Jun 16 14:36:04 2022 +0200

    match.pd: Fix up __builtin_mul_overflow_p signed type optimization

    Earlier in the simplification pattern, we require that @0 has compatible
    type to the type of IMAGPART_EXPR, but for @1 which is a non-zero constant
    all we require is that it the constant fits into that type.
    Later the code checks if the constant is negative, because when min / max
    values are divided by negative divisor, lo will be higher than hi.
    In the following testcase, @1 has unsigned char type, while @0 has
    int type, so @1 which is 254 is wi::neg_p and we were swapping lo and hi,
    even when @1 cast to int isn't negative.

    We could use tree_int_cst_sgn (@1) < 0 as the check instead and it would
    work both for narrower types of @1 and even same or wider ones, but
    I've noticed we probably don't want to call fold_convert (TREE_TYPE (@0),
    twice and when we save that result in a temporary, we can just use
    on that temporary.

    2022-06-16  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/105984
            * match.pd (__builtin_mul_overflow_p (x, cst, (stype) 0) ->
            x > stype_max / cst || x < stype_min / cst): fold_convert @1
            to TREE_TYPE (@0) just once and test for negative divisor
            also on that folded constant instead of on @1.

            * gcc.c-torture/execute/pr105984.c: New test.

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