[Bug ipa/110753] [14 Regression] ICE in meet_with_1, at ipa-cp.cc:1057

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110753

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Aldy Hernandez <aldyh@gcc.gnu.org>:

https://gcc.gnu.org/g:53fcd3bdbc9104a8acdc79134d8d272d7eead0fd

commit r14-3326-g53fcd3bdbc9104a8acdc79134d8d272d7eead0fd
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Fri Aug 18 12:41:46 2023 +0200

    [irange] Return FALSE if updated bitmask is unchanged [PR110753]

    The mask/value pair we track in the irange is a bit fickle in that it
    can sometimes contradict the bitmask inherent in the range.  This can
    happen when a series of calculations yield a combination such as:

            [3, 1000] MASK 0xfffffffe VALUE 0x0

    The mask/value above implies that the lowest bit is a known 0, which
    would exclude the 3 in the range.  At one time we tried keeping mask
    and ranges 100% consistent, but the performance penalty was too high
    (5% in VRP).  Also, it's unclear whether the intersection of two
    incompatible known bits should make the whole range undefined, or
    just the contradicting bits.  This is all documented in
    irange::get_bitmask().  We could revisit both of these assumptions
    in the future.

    In this testcase IPA ends up with a range where the lower 2 bits are
    expected to be 0, but the range is [1,1].

            [irange] long int [1, 1] MASK 0xfffffffffffffffc VALUE 0x0

    This causes irange::union_bitmask() to think an update occurred, when
    no semantic change happened, thus triggering an assert in IPA-cp.  We
    could get rid of the assert, but it's cleaner to make
    irange::{union,intersect}_bitmask always tell the truth.  Beside, the
    ranger's cache also depends on union being truthful.

            PR ipa/110753

    gcc/ChangeLog:

            * value-range.cc (irange::union_bitmask): Return FALSE if updated
            bitmask is semantically equivalent to the original mask.
            (irange::intersect_bitmask): Same.
            (irange::get_bitmask): Add comment.

    gcc/testsuite/ChangeLog:

            * gcc.dg/tree-ssa/pr110753.c: New test.