RFR: 8364936: Shenandoah: Switch nmethod entry barriers to conc_instruction_and_data_patch

Fri Aug 29 00:08:16 UTC 2025

Please, review this patch to make nmethod entry barriers use `conc-instruction-and-data-patch` fence mechanics when ShenandoahGC is being used on AArch64. The patch also removes (including from JVMCI interface) the old constant that was being used only by Shenandoah on AArch64.

The patch has been tested with functional and performance benchmarks on AArch64. Improvements in DaCapo and Renaissance benchmarks can be as high as 30%. Maximum critical Jops in SPEC improved by ~10%.

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

Commit messages:
 - Change shenandoah nmethod entry barrier fence.

Changes: https://git.openjdk.org/jdk/pull/26999/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26999&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364936
  Stats: 16 lines in 6 files changed: 0 ins; 11 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/26999.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26999/head:pull/26999

PR: https://git.openjdk.org/jdk/pull/26999