Turn (and (shl x, c2), c1) -> (slli (srli x, c3-c2), c3) if c1 is a
shifted mask with no leading zeros and c3 trailing zeros where c3
is greater than c2.
These tests have C1 as a shifted mask having no leading zeros and
C3 trailing zeros. If C3 is more than C2, we can select this as
(slli (srli x, C3-C2), C3).
Turn (and (shr x, c2), c1) -> (slli (srli x, c2+c3), c3) if c1 is a
shifted mask with c2 leading zeros and c3 trailing zeros.
When the leading zeros is C2+32 we can use SRLIW in place of SRLI.
These tests have C1 as a shifted mask having C2 leading zeros and some
number of trailing zeros, C3. We can select this as
(slli (srli x, C2+C3), C3) or (slli (srliw x, C2+C3), C3).
Craig Topper