RFR: 8334247: [PPC64] Consider trap based nmethod entry barriers [v4]

[Martin Doerr]

On Fri, 22 Aug 2025 09:08:21 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> We can shrink nmethod entry barriers to 4 instructions (from 8) using conditional trap instructions. Some benchmarks seem to show very small improvements. At least the code size reduction is an advantage.
>
> Martin Doerr has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'origin' into 8334247_PPC64_trap_based_nmethod_entry_barrier
>  - Move nmethod entry barrier code up in the signal handler.
>  - Merge remote-tracking branch 'origin' into 8334247_PPC64_trap_based_nmethod_entry_barrier
>  - Merge remote-tracking branch 'origin' into 8334247_PPC64_trap_based_nmethod_entry_barrier
>  - 8334247: [PPC64] Consider trap based nmethod entry barriers

Waiting for https://github.com/openjdk/jdk/pull/26399. Will need to resolve.

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PR Comment: https://git.openjdk.org/jdk/pull/24135#issuecomment-3213809994