commit 356232b687b98328aa28c64889b429a7649c0db1
author George Steed <george.steed@arm.com> Thu Mar 14 05:12:21 2024
committer Frank Barchard <fbarchard@chromium.org> Thu Apr 25 21:23:55 2024
tree 7a799cb2669aa1300f88b65ba2bfd54df8812dd5
parent 4f52235a6719eba097ccac60d84bd2c23bad89ed

[AArch64] Replace UQXTN{,2} with UZP2 in Convert16To8Row_NEON

The existing code makes use of a pair of shifts to put the bits we want
in the low part of each vector lane and then a pair of UQXTN and UQXTN2
instructions to perform a saturating cast down from 16-bit elements to
8-bit elements. We can instead achieve the same thing by adding eight to
the first shift amount so that the bits we want appear in the high half
of the lane, doing the saturation at the same time, and then simply use
UZP2 to pull out the high halves of each lane in a single instruction.

Reduction in runtime for Convert16To8Row_NEON:

  Cortex-A55: -19.7%
 Cortex-A510: -23.5%
  Cortex-A76: -35.4%
   Cortex-X2: -34.1%

Bug: libyuv:976
Change-Id: I9a80c0f4f2c6b5203f23e422c0970d3167052f91
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/5463950
Reviewed-by: Frank Barchard <fbarchard@chromium.org>