[jdk17u-dev] RFR: 8269404: Base64 Encoding optimization enhancements for x86 using AVX-512

[Scott Gibbons]

This is a backport of JDK-8269404: Base64 Encoding optimization enhancements for x86 using AVX-512. Backport is clean.

We have had numerous customer requests for this functionality to be backported due to the performance improvement.

There will be one additional PR for which this is a dependency. This dependency is dependent on PR #860.

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

Thanks,
--Scott

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Depends on: https://git.openjdk.org/jdk17u-dev/pull/860

Commit messages:
 - Backport 9cac94d581f240c10fe8fff2f803109a1ae30637

Changes: https://git.openjdk.org/jdk17u-dev/pull/861/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=861&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8269404
  Stats: 710 lines in 5 files changed: 349 ins; 235 del; 126 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/861.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/861/head:pull/861

PR: https://git.openjdk.org/jdk17u-dev/pull/861