[Bug rtl-optimization/114902] [14 Regression] wrong code at -O3 with "-fno-tree-vrp -fno-expensive-optimizations -fno-tree-dominator-opts" on x86_64-linux-gnu

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114902

--- Comment #18 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:840bc6741680a9c4b58fa1005f19a5d2e7d4be1f

commit r12-10530-g840bc6741680a9c4b58fa1005f19a5d2e7d4be1f
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed May 15 18:37:17 2024 +0200

    combine: Fix up simplify_compare_const [PR115092]

    The following testcases are miscompiled (with tons of GIMPLE
    optimization disabled) because combine sees GE comparison of
    1-bit sign_extract (i.e. something with [-1, 0] value range)
    with (const_int -1) (which is always true) and optimizes it into
    NE comparison of 1-bit zero_extract ([0, 1] value range) against
    (const_int 0).
    The reason is that simplify_compare_const first (correctly)
    simplifies the comparison to
    GE (ashift:SI something (const_int 31)) (const_int -2147483648)
    and then an optimization for when the second operand is power of 2
    triggers.  That optimization is fine for power of 2s which aren't
    the signed minimum of the mode, or if it is NE, EQ, GEU or LTU
    against the signed minimum of the mode, but for GE or LT optimizing
    it into NE (or EQ) against const0_rtx is wrong, those cases
    are always true or always false (but the function doesn't have
    a standardized way to tell callers the comparison is now unconditional).

    The following patch just disables the optimization in that case.

    2024-05-15  Jakub Jelinek  <jakub@redhat.com>

            PR rtl-optimization/114902
            PR rtl-optimization/115092
            * combine.cc (simplify_compare_const): Don't optimize
            GE op0 SIGNED_MIN or LT op0 SIGNED_MIN into NE op0 const0_rtx or
            EQ op0 const0_rtx.

            * gcc.dg/pr114902.c: New test.
            * gcc.dg/pr115092.c: New test.

    (cherry picked from commit 0b93a0ae153ef70a82ff63e67926a01fdab9956b)