RFR: 8350118: Simplify the layout access VarHandle [v2]

[Maurizio Cimadamore]

On Fri, 21 Feb 2025 22:19:08 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review remarks, dates, some more simplifications
>
> Benchmark results for the latest revision appears performance neutral. bytestacks same as last revision. 11 jobs left in tier 1-3, no failure so far. Also created CSR for this minor behavioral change.
> 
> Benchmark                                                (polluteProfile)  Mode  Cnt  Score   Error  Units
> LoopOverNonConstantHeap.BB_get                                      false  avgt   30  0.934 ± 0.027  ns/op
> LoopOverNonConstantHeap.BB_get                                       true  avgt   30  0.946 ± 0.028  ns/op
> LoopOverNonConstantHeap.BB_loop                                     false  avgt   30  0.208 ± 0.004  ms/op
> LoopOverNonConstantHeap.BB_loop                                      true  avgt   30  0.211 ± 0.003  ms/op
> LoopOverNonConstantHeap.segment_get                                 false  avgt   30  1.123 ± 0.040  ns/op
> LoopOverNonConstantHeap.segment_get                                  true  avgt   30  1.120 ± 0.040  ns/op
> LoopOverNonConstantHeap.segment_loop                                false  avgt   30  0.205 ± 0.004  ms/op
> LoopOverNonConstantHeap.segment_loop                                 true  avgt   30  0.202 ± 0.003  ms/op
> LoopOverNonConstantHeap.segment_loop_instance                       false  avgt   30  0.209 ± 0.005  ms/op
> LoopOverNonConstantHeap.segment_loop_instance                        true  avgt   30  0.202 ± 0.003  ms/op
> LoopOverNonConstantHeap.segment_loop_instance_unaligned             false  avgt   30  0.209 ± 0.004  ms/op
> LoopOverNonConstantHeap.segment_loop_instance_unaligned              true  avgt   30  0.210 ± 0.004  ms/op
> LoopOverNonConstantHeap.segment_loop_readonly                       false  avgt   30  0.206 ± 0.004  ms/op
> LoopOverNonConstantHeap.segment_loop_readonly                        true  avgt   30  0.206 ± 0.005  ms/op
> LoopOverNonConstantHeap.segment_loop_slice                          false  avgt   30  0.203 ± 0.002  ms/op
> LoopOverNonConstantHeap.segment_loop_slice                           true  avgt   30  0.207 ± 0.004  ms/op
> LoopOverNonConstantHeap.segment_loop_unaligned                      false  avgt   30  0.206 ± 0.004  ms/op
> LoopOverNonConstantHeap.segment_loop_unaligned                       true  avgt   30  0.209 ± 0.003  ms/op
> LoopOverNonConstantHeap.unsafe_get                                  false  avgt   30  0.386 ± 0.017  ns/op
> LoopOverNonConstantHeap.unsafe_get                                   true  avgt   30  0.381 ± 0.017  ns/op
> LoopOverNonConstantHeap.unsafe_loop                ...

Great work @liach -- I've bumped the number of reviewers as this whole area is rather tricky, and I think the PR can probably benefit from another independent pass.

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PR Comment: https://git.openjdk.org/jdk/pull/23720#issuecomment-2681378356