[Bug 1720832] Re: Optimized memcmp for arm64

[Launchpad Bug Tracker]

This bug was fixed in the package glibc - 2.26-0ubuntu2

---------------
glibc (2.26-0ubuntu2) artful; urgency=medium

  * Cherry-pick some changes from Debian git for a few pending Ubuntu bugfixes:
    - Update to master and drop redundant submitted-tst-tlsopt-powerpc.diff.
    - debian/patches/any/local-cudacc-float128.diff: Local patch to prevent
      defining __HAVE_FLOAT128 on NVIDIA's CUDA compilers (LP: #1717257)
    - debian/patches/arm/git-arm64-memcmp.diff: Backport optimized memcmp
      for AArch64, improving performance from 25% to 500% (LP: #1720832)
    - debian/patches/amd64/git-x86_64-search.diff: Backport upstream commit
      to put x86_64 back in the search path, like in 2.25 (LP: #1718928)
    - debian/rules.d/debhelper.mk: Filter python hooks in stage1 (LP: #1715366)

 -- Adam Conrad <adconrad at ubuntu.com>  Wed, 11 Oct 2017 14:21:40 -0600

** Changed in: glibc (Ubuntu)
       Status: Confirmed => Fix Released

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https://bugs.launchpad.net/bugs/1720832

Title:
  Optimized memcmp for arm64

Status in glibc package in Ubuntu:
  Fix Released

Bug description:
  A patch has recently landed upstream to optimize memcmp for AArch64:

  commit 922369032c604b4dcfd535e1bcddd4687e7126a5
  Author: Wilco Dijkstra <wdijkstr at arm.com>
  Date:   Thu Aug 10 17:00:38 2017 +0100

      [AArch64] Optimized memcmp.
      
      This is an optimized memcmp for AArch64.  This is a complete rewrite
      using a different algorithm.  The previous version split into cases
      where both inputs were aligned, the inputs were mutually aligned and
      unaligned using a byte loop.  The new version combines all these cases,
      while small inputs of less than 8 bytes are handled separately.
      
      This allows the main code to be sped up using unaligned loads since
      there are now at least 8 bytes to be compared.  After the first 8 bytes,
      align the first input.  This ensures each iteration does at most one
      unaligned access and mutually aligned inputs behave as aligned.
      After the main loop, process the last 8 bytes using unaligned accesses.
      
      This improves performance of (mutually) aligned cases by 25% and
      unaligned by >500% (yes >6 times faster) on large inputs.
      
              * sysdeps/aarch64/memcmp.S (memcmp):
              Rewrite of optimized memcmp.

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