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

[Dingli Zhang]

On Fri, 29 Aug 2025 00:02:42 GMT, Cesar Soares Lucas <cslucas at openjdk.org> wrote:

> 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%.

Thanks for this patch! I've made similar changes on RISC-V.
Could you please add those as well? https://github.com/DingliZhang/jdk/commit/495b07fe690ef7e3fe828fd2be27c4259c739c23
I've tested the `hotspot_gc_shenandoah` on the SG2042 with fastdebug and found no failures.
Specjbb testing on the SG2042 is ongoing. I'll update the results later.

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

PR Comment: https://git.openjdk.org/jdk/pull/26999#issuecomment-3235958508