RFR: 8370822: Improve performance for MemorySegment::fill

[Per Minborg]

On Fri, 31 Oct 2025 14:17:29 GMT, Igor Rudenko <duke at openjdk.org> wrote:

> Hello Per-Ake,
> 
> I explored the corresponding code using JITWatch. My analysis shows that the patch reduces the number of instructions (in both bytecode and JIT-compiled assembly). However, as your benchmarks demonstrate, this does not lead to measurable overall performance improvement, the differences fall within normal noise.
> 
> So, the idea for the patch may be clarity and maintainability, as it simplifies and shortens the code.
> 
> Thanks.

Interesting observation. I think reducing bytecode is also important. Are you able to share some JIT-compiled assembly before/after?

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PR Comment: https://git.openjdk.org/jdk/pull/28031#issuecomment-3473498832