Changpeng Fang ca1154d1d4 AMDGPU: Disable pattern matching "x<<32-y>>32-y" to "bfe x, 0, y" (#114279) ...

It is not correct to lower "x<<32-y>>32-y" to "bfe x, 0, y". When y
equals to 32, the left-hand side is still x (unchanged), however, the
right-hand side will be evaluated to 0. So it is not always correct to
do such transformation.

We may be able to keep the pattern for immediate y while y is within [0,
31]. However, the immediate operands of the sub (32 - y) are easily
folded, and "(x << imm) >> imm" will be lowered to "and x,
(2^(32-imm))-1" anyway. So no bfe matching is needed.

2024-10-30 11:07:15 -07:00

6.6 KiB

Raw Blame History

View Raw