[Bug tree-optimization/94899] Failure to optimize out add before compare with INT_MIN

cvs-commit at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Tue Jun 21 10:22:15 GMT 2022


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94899

--- Comment #5 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:ab981aab92cbc71918fbaadcf6fa64bdb2b69be7

commit r13-1187-gab981aab92cbc71918fbaadcf6fa64bdb2b69be7
Author: Arjun Shankar <arjun@redhat.com>
Date:   Tue Jun 21 12:12:11 2022 +0200

    match.pd: Remove "+ 0x80000000" in int comparisons [PR94899]

    Expressions of the form "X + CST < Y + CST" where:

    * CST is an unsigned integer constant with only the MSB set, and
    * X and Y's types have integer conversion ranks <= CST's

    can be simplified to "(signed) X < (signed) Y".

    This is because, assuming a 32-bit signed numbers,
    (unsigned) INT_MIN + 0x80000000 is 0, and
    (unsigned) INT_MAX + 0x80000000 is UINT_MAX.

    i.e. the result increases monotonically with signed input.

    This means:
    ((signed) X < (signed) Y) iff (X + 0x80000000 < Y + 0x80000000)

    gcc/
            PR tree-optimization/94899
            * match.pd (X + C < Y + C -> (signed) X < (signed) Y, if C is
            0x80000000): New simplification.
    gcc/testsuite/
            * gcc.dg/pr94899.c: New test.


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