[jdk17u-dev] RFR: 8268276: Base64 Decoding optimization for x86 using AVX-512 [v3]

[Scott Gibbons]

> This is a backport of JDK-8268276: Base64 Decoding optimization for x86 using AVX-512.
> 
> We have had numerous customer requests for this functionality to be backported due to the ~19x performance improvement.
>  
> Original patch does not apply cleanly to 17u, because of a bug that was identified in the original commit, but not fixed until the later Base64 Encode acceleration enhancement was complete.  The fix is on line 6039 of src/hotspot/cpu/x86/stubGenerator_x86_64.cpp and has been included in this PR.  All four "translatedX" registers needed to be checked for illegal characters in the input stream.
> 
> Risk: I view the risk of this backport to be minimal.  This code has been in use for many months with no bugs reported.
>  
> Testing: x86_64 build, affected tests, tier1, tier2
>  
> Thanks,
> --Scott

Scott Gibbons has updated the pull request incrementally with two additional commits since the last revision:

 - Merge branch 'Decode-backport' of https://github.com/asgibbons/jdk17u-dev into Decode-backport
 - Hand-merging bugfix 9a1bbaf8db0e869ab76be8ab1bd0ddeb23693e7e

-------------

Changes:
  - all: https://git.openjdk.org/jdk17u-dev/pull/840/files
  - new: https://git.openjdk.org/jdk17u-dev/pull/840/files/2fc2c571..dbf7ed14

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=840&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=840&range=01-02

  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/840.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/840/head:pull/840

PR: https://git.openjdk.org/jdk17u-dev/pull/840