RFR: 8327647: Occasional SIGSEGV in markWord::displaced_mark_helper() for SPECjvm2008 sunflow

[Matias Saavedra Silva]

A misplaced memory barrier causes a very intermittent crash on on some aarch64 systems. This patch adds an appropriate LoadLoad barrier after a constant pool cache field entry is loaded.

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Commit messages:
 - Corrected comments
 - Merge branch 'master' into membar_8327647
 - Removed unneeded push/pop
 - Merge branch 'master' into membar_8327647
 - Replace use of r0 with noreg
 - Added membars after load_field_entry() calls
 - 8327647: Occasional SIGSEGV in markWord::displaced_mark_helper() for SPECjvm2008 sunflow

Changes: https://git.openjdk.org/jdk/pull/18477/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18477&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327647
  Stats: 23 lines in 3 files changed: 14 ins; 5 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/18477.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18477/head:pull/18477

PR: https://git.openjdk.org/jdk/pull/18477