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

[Aleksey Shipilev]

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%.

I see `virtual NMethodPatchingType nmethod_patching_type() { return NMethodPatchingType::conc_data_patch; }` in Shenandoah PPC64 and RISC-V barrier sets as well. Those should likely go away as well?

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

PR Comment: https://git.openjdk.org/jdk/pull/26999#issuecomment-3235890936