If we are and the constant like 0xFFFFFFC00000, for now, we are using several
instructions to generate this 48bit constant and final an "and". However, we
could exploit it with two rotate instructions.
MB ME MB+63-ME
+----------------------+ +----------------------+
|0000001111111111111000| -> |0000000001111111111111|
+----------------------+ +----------------------+
0 63 0 63
Rotate left ME + 1 bit first, and then, mask it with (MB + 63 - ME, 63),
finally, rotate back. Notice that, we need to round it with 64 bit for the
wrapping case.
Reviewed by: ChenZheng, Nemanjai
Differential Revision: https://reviews.llvm.org/D71831
For now, PowerPC will using several instructions to get the constant and "and" it with the following case:
define i32 @test1(i32 %a) {
%and = and i32 %a, -2
ret i32 %and
}
However, we could exploit it with the rotate mask instructions.
MB ME
+----------------------+
|xxxxxxxxxxx00011111000|
+----------------------+
0 32 64
Notice that, we can only do it if the MB is larger than 32 and MB <= ME as
RLWINM will replace the content of [0 - 32) with [32 - 64) even we didn't rotate it.
Differential Revision: https://reviews.llvm.org/D71829
QingShan Zhang