What happens on this testcase is with the out of bounds rotate we get:
Trying 13 -> 16:
13: r129:SI=r132:DI#0<-<0x20
REG_DEAD r132:DI
16: r123:DI=r129:SI<0
REG_DEAD r129:SI
Successfully matched this instruction:
(set (reg/v:DI 123 [ <retval> ])
(const_int 0 [0]))
during combine. So, perhaps we could also change simplify-rtx.c to punt
if it is out of bounds rather than trying to optimize anything.
Or, but probably GCC11 material, if we decide that ROTATE/ROTATERT doesn't
have out of bounds counts or introduce targetm.rotate_truncation_mask,
we should truncate the argument instead of punting.
Punting is better for backports though.
2020-01-30 Jakub Jelinek <jakub@redhat.com>
PR middle-end/93505
* combine.c (simplify_comparison) <case ROTATE>: Punt on out of range
rotate counts.
* gcc.c-torture/compile/pr93505.c: New test.
