decompression: optimize ExtractOffset for Arm #136
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Inspired by kExtractMasksCombined, this patch uses shift to replace table lookup. On Arm the codegen is 2 shift ops (lsl+lsr). Comparing to previous ldr which requires 4 cycles latency, the lsl+lsr only need 2 cycles. Slight (~0.3%) uplift observed on N1, and ~3% on A72. Signed-off-by: Jun He <jun.he@arm.com> Change-Id: I5b53632d22d9e5cf1a49d0c5cdd16265a15de23b
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@pwnall This looks good to me too. |
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@JunHe77 Thank you for this contribution! I started the process of getting this PR merged through our internal repository. When the process completes, this PR will be merged. |
pwnall
approved these changes
Aug 12, 2021
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Inspired by kExtractMasksCombined, this patch uses shift
to replace table lookup. On Arm the codegen is 2 shift ops
(lsl+lsr). Comparing to the previous ldr which requires 4 cycles
latency, the lsl+lsr only needs 2 cycles.
Slight (~0.3%) uplift was observed on N1, and ~3% on A72.
Signed-off-by: Jun He jun.he@arm.com
Change-Id: I5b53632d22d9e5cf1a49d0c5cdd16265a15de23b