[foreign-memaccess+abi] RFR: 8311594: Avoid GlobalSession liveness check [v2]

[Jorn Vernee]

> This patch overrides `checkValidStateRaw` in GlobalSession, to do nothing. The current `checkValidStateRaw` in MemorySessionImpl checks the owner thread, and liveness, which are both not needed for the global session.
> 
> Since the state field is mutable, I found that the JIT can not fold away the liveness check. This has a very marginal effect on performance, but since the fix is also very non-intrusive, I think it's okay to do.
> 
> I've added 2 new benchmarks that I've used to measure the difference. One measures the performance of MS::copy, and the other measures MS::get. Both use a special `ALL` segment which spans `0` to `Long.MAX_VALUE`, which means that the target address can be used as an offset when doing the accesses. This helps the bounds checks being eliminated, and makes the result of overriding `checkValidStateRaw` in GlobalSession easier to see.
> 
> Here are some of the interesting numbers:
> 
> Before:
> 
> 
> Benchmark                                  Mode  Cnt  Score   Error  Units
> MemorySegmentCopyALL.panama_ALL_to_ALL     avgt   30  7.788 ± 0.029  ns/op
> MemorySegmentCopyALL.unsafe_array_to_addr  avgt   30  7.543 ± 0.018  ns/op
> 
> Benchmark                               Mode  Cnt  Score   Error  Units
> MemorySegmentGet.segment_ALL_unaligned  avgt   30  0.486 ± 0.002  ns/op
> MemorySegmentGet.unsafe                 avgt   30  0.398 ± 0.003  ns/op
> 
> 
> After:
> 
> 
> Benchmark                                  Mode  Cnt  Score   Error  Units
> MemorySegmentCopyALL.panama_ALL_to_ALL     avgt   30  7.571 ± 0.017  ns/op
> MemorySegmentCopyALL.unsafe_array_to_addr  avgt   30  7.550 ± 0.019  ns/op
> 
> Benchmark                               Mode  Cnt  Score   Error  Units
> MemorySegmentGet.segment_ALL_unaligned  avgt   30  0.409 ± 0.002  ns/op
> MemorySegmentGet.unsafe                 avgt   30  0.397 ± 0.003  ns/op

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Add global session polluted benchmark

-------------

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/844/files
  - new: https://git.openjdk.org/panama-foreign/pull/844/files/7943fd33..f366dc34

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=844&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=844&range=00-01

  Stats: 6 lines in 1 file changed: 3 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/844.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/844/head:pull/844

PR: https://git.openjdk.org/panama-foreign/pull/844