This patch adds handling of rotation patterns with constant shift amounts - the next bit will be how we want to support non-uniform constant vectors.
Differential Revision: https://reviews.llvm.org/D87452
Fold or(zext(bitreverse(x)),shl(zext(bitreverse(y)),bw/2) -> bitreverse(or(zext(x),shl(zext(y),bw/2))
Practically this is the same as the BSWAP pattern so we might as well handle it.
This adds a general combine that can be used to fold:
or(zext(OP(x)), shl(zext(OP(y)),bw/2))
-->
OP(or(zext(x), shl(zext(y),bw/2)))
Allowing us to widen 'concat-able' style or+zext patterns - I've just set this up for BSWAP but we could use this for other similar ops (BITREVERSE for instance).
We already do something similar for bitop(bswap(x),bswap(y)) --> bswap(bitop(x,y))
Fixes PR45715
Reviewed By: @lebedev.ri
Differential Revision: https://reviews.llvm.org/D79041
Simon Pilgrim