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Subject: [Bug tree-optimization/97386] [8/9 Regression] wrong code with
 __builtin_bswap16() of rotated 64bit value
Date: Thu, 22 Apr 2021 16:48:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97386

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-8 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:615b19069a9afd9faf803d6888ac49d03065762d

commit r8-10860-g615b19069a9afd9faf803d6888ac49d03065762d
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Oct 13 19:13:26 2020 +0200

    combine: Fix up simplify_shift_const_1 for nested ROTATEs [PR97386]

    The following testcases are miscompiled (the first one since my
improvements
    to rotate discovery on GIMPLE, the other one for many years) because
    combiner optimizes nested ROTATEs with narrowing SUBREG in between (i.e.
    the outer rotate is performed in shorter precision than the inner one) =
to
    just one ROTATE of the rotated constant.  While that (under certain
    conditions) can work for shifts, it can't work for rotates where we can
only
    do that with rotates of the same precision.

    2020-10-13  Jakub Jelinek  <jakub@redhat.com>

            PR rtl-optimization/97386
            * combine.c (simplify_shift_const_1): Don't optimize nested ROT=
ATEs
if
            they have different modes.

            * gcc.c-torture/execute/pr97386-1.c: New test.
            * gcc.c-torture/execute/pr97386-2.c: New test.

    (cherry picked from commit 1a98b22b0468214ae8463d075dacaeea1d46df15)=