https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108803
--- 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 by 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
