RFR: 8356949: AArch64: Tighten up template interpreter method entry code

[Chad Rakoczy]

On Mon, 19 May 2025 22:16:27 GMT, Chad Rakoczy <duke at openjdk.org> wrote:

> [JDK-8356949](https://bugs.openjdk.org/browse/JDK-8356949)
> 
> This change is the aarch64 version of [JDK-8352415](https://bugs.openjdk.org/browse/JDK-8352415). 
> 
> To improve interpreter performance, which is important for faster startup, the method entry code was refactored to reuse some memory accesses and also spread them out to allow more latency-hiding hardware mechanisms to kick in.
> 
> Additional testing:
> 
> - [x] Ad-hoc -Xint benchmarks
> - [x] Linux aarch64 server fastdebug, tier 1/2/3/4

A simple bench mark shows a slight performance improvement but not as much as was measured on x86_64 

Benchmark 1: ./build/linux-aarch64-server-release/images/jdk/bin/java -Xms1g -Xmx1g -XX:+UseSerialGC -Xint -jar JavacBenchApp.jar 1
  
# Before

  Time (mean ± σ):      1.361 s ±  0.003 s    [User: 1.328 s, System: 0.042 s]
  Range (min … max):    1.358 s …  1.365 s    10 runs

# After

  Time (mean ± σ):      1.358 s ±  0.002 s    [User: 1.312 s, System: 0.056 s]
  Range (min … max):    1.355 s …  1.362 s    10 runs

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PR Comment: https://git.openjdk.org/jdk/pull/25312#issuecomment-2895874191