FFM performance tweaks

[Brian S O'Neill]

I've already been running some tests against build 24 to see what affect 
pull 21810 has. Tests using the transformed VarHandle technique didn't 
show much improvement. I just started running tests which access the 
(effectively) unbounded MemorySegment and will report back in about an hour.

On 2024-11-19 06:42 AM, Maurizio Cimadamore wrote:
> Hi,
> some performance tweaks have landed in the JDK 24 early access build 
> (build 24):
> 
> https://jdk.java.net/24/
> 
> They are:
> 
> https://git.openjdk.org/jdk/pull/21764
> https://git.openjdk.org/jdk/pull/21810
> 
> The former contains some optimizations for `MemorySegment
> 
> ` which should improve scalarization - see [1]. The second contains an 
> improvement to the way we perform the liveness check, which should make 
> such check provably redundant for segments backed by the global arena. 
> This should improve the performance of workarounds using an “everything” 
> segment to access off-heap memory with minimal impact from bound checks [2].
> 
> As JDK 24 is moving closer to rampdown phase [3], it would be great to 
> give such changes a try and report back.
> 
> Cheers
> Maurizio
> 
> [1] - https://mail.openjdk.org/pipermail/panama-dev/2024-October/020702.html
> [2] - https://mail.openjdk.org/pipermail/panama-dev/2024-October/020736.html
> [3] - https://openjdk.org/projects/jdk/24/
> 
> ​
> 
> ​