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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/108803] [10/11/12/13 Regression] wrong code for 128bit
 rotate on aarch64-unknown-linux-gnu with -Og
Date: Thu, 16 Feb 2023 18:14:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108803

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
On the other side, if we knew that the backend would use something like the
shifts with masking, we could then avoid the extra reverse unsigned shift b=
y 1
+ reverse unsigned shift by (63 - op1) & 63 plus two shifts by op1 & 63 and
could do instead a single shift by -op1 & 63 (plus as before two shifts by =
op1
& 63).
So replace the current problematic code for foo in #c2 with:
        subs    w5, w2, #64
        lsl     x6, x0, x5
-       lsr     x3, x0, 1
-       mov     w4, 63
-       sub     w4, w4, w2
-       lsr     x3, x3, x4
+       neg     w4, w2
+       lsr     x3, x0, x4
        lsl     x1, x1, x2
        orr     x1, x3, x1
        lsl     x0, x0, x2
        csel    x0, xzr, x0, pl
        csel    x1, x6, x1, pl
        ret=