[jdk11u-dev] RFR: 8251358: Clean up Access configuration after Shenandoah barrier change

[Aleksey Shipilev]

This is third (and final) patch in the series to cleanup/revert the GC BarrierSets to most current state.

The primitive accesses APIs were added for Shenandoah GC, in the incarnation that exposed both from- and to-copies to the runtime system (see JDK-8199781). Since then, Shenandoah greatly simplified this by switching to a strong to-space invariant, which obviates the need for this API. Therefore, it was removed in JDK 14. This patch reverts JDK 11 parts to that shape as well, which should simplify 11u maintenance.

This patch effectively reverts additions of:
  8199735: Mark word updates need to use Access API
  8251358: Clean up Access configuration after Shenandoah barrier change

Note that it leaves HeapAccess barriers over mark words, which means the GC code would potentially experience (nop, empty) GC barriers when accessing mark word. While awkward, this is the way current post-JDK-8251358 behaves. This should probably be cleaned up upstream first, see JDK-8272654.

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Commit messages:
 - Backport e63b90cc17d3ad08361f0a959f919ae79dd768bf

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/251/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=251&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251358
  Stats: 238 lines in 43 files changed: 1 ins; 91 del; 146 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/251.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/251/head:pull/251

PR: https://git.openjdk.java.net/jdk11u-dev/pull/251