QingShan Zhang 4bd186c0ff [PowerPC] Exploit the rldicl + rldicl when and with mask ...

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

2020-04-17 05:24:00 +00:00

5.5 KiB

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