Previously, these isel optimizations were disabled if the AND could
be selected as a ANDI instruction. This patch disables the optimizations
only if the immediate is valid for C.ANDI. If we can't use C.ANDI,
we might be able to compress the shift instructions instead.
I'm not checking the C extension since we have relatively poor test
coverage of the C extension. Without C extension the code size
should be equal. My only concern would be if the shift+andi had
better latency/throughput on a particular CPU.
I did have to add a peephole to match SRLIW if the input is zexti32
to prevent a regression in rv64zbp.ll.
Reviewed By: luismarques
Differential Revision: https://reviews.llvm.org/D122701
When shifting by a byte-multiple:
bswap (shl X, C) --> lshr (bswap X), C
bswap (lshr X, C) --> shl (bswap X), C
This is the backend version of D122010 and an alternative
suggested in D120648.
There's an extra check to make sure the shift amount is
valid that was not in the rough draft.
I'm not sure if there is a larger motivating case for RISCV (bug report?),
but the ARM diffs show a benefit from having a late version of the
transform (because we do not combine the loads in IR).
Differential Revision: https://reviews.llvm.org/D122655
