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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/115454] std::experimental::find_last_set is buggy on
 x86-64-v4
Date: Fri, 21 Jun 2024 16:25:58 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115454

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Matthias Kretz
<mkretz@gcc.gnu.org>:

https://gcc.gnu.org/g:fbd088a069b172cae4e268abe2d38e567ef97990

commit r13-8861-gfbd088a069b172cae4e268abe2d38e567ef97990
Author: Matthias Kretz <m.kretz@gsi.de>
Date:   Fri Jun 14 15:11:25 2024 +0200

    libstdc++: Fix find_last_set(simd_mask) to ignore padding bits

    With the change to the AVX512 find_last_set implementation, the change
    to AVX512 operator!=3D is unnecessary. However, the latter was not
    producing optimal code and unnecessarily set the padding bits. In
    theory, the compiler could determine that with the new !=3D
    implementation, the bit operation for clearing the padding bits is a
    no-op and can be elided.

    Signed-off-by: Matthias Kretz <m.kretz@gsi.de>

    libstdc++-v3/ChangeLog:

            PR libstdc++/115454
            * include/experimental/bits/simd_x86.h (_S_not_equal_to): Use
            neq comparison instead of bitwise negation after eq.
            (_S_find_last_set): Clear unused high bits before computing
            bit_width.
            * testsuite/experimental/simd/pr115454_find_last_set.cc: New
            test.

    (cherry picked from commit 1340ddea0158de3f49aeb75b4013e5fc313ff6f4)=