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Being able to use SVE2 functionality for these kernels has a number of performance wins compared to the existing Neon code: * For the Y component calculation we are able to use UMULH, versus the existing UMULL x2 + UZP2 sequence in Neon. * For the RGBTORGBA8 calculation we are able to take advantage of interleaving narrowing instructions, allowing us to use ST2 rather than ST4 for the store. This is a big performance win on some micro-architectures where ST4 is costly. * The use of predication means we do not need to add "any" kernels, we can simply rerun the calculation with a not-full predicate for the final iteration. To avoid the overhead of generating a predicate register on every iteration we duplicate the loop body and only generate a predicate on the final iteration of the loop. This costs a small amount on the final iteration but should still be significantly quicker than the overhead of a function call needed by the "any" cases. Duplicating the loop body to reduce the use of the WHILELT instruction improves little core performance by ~12% by itself but has negligable impact on other micro-architectures. Reduction in runtime for the new SVE2 implementation compared to the existing Neon implementation on selected micro-architectures: Cortex-A510: -36.5% Cortex-A720: -17.3% Cortex-X2: -11.3% Bug: libyuv:973 Change-Id: I2a485f0dfa077a56f96b80a667ad38bbea47b4b4 Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/5424739 Reviewed-by: Frank Barchard <fbarchard@chromium.org> |
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