[foreign-memaccess+abi] RFR: Split foreign vector load and store by null or not null base

[Radoslaw Smogura]

Split store / load operation by if checking if base is null
or not null.

When this happens base in Unsafe is not perceived with mixed
access by VM, and VM does not insert barriers.

Test results gives the expected values where the case of polluted access is 2x multiplication of normal access.

After

Benchmark                                    (size)  Mode  Cnt    Score     Error  Units
MemorySegmentVectorAccess.arrayCopy            1024  avgt   10    7.437 ±   0.195  ns/op
MemorySegmentVectorAccess.directSegments       1024  avgt   10   15.593 ±   0.371  ns/op
MemorySegmentVectorAccess.heapSegments         1024  avgt   10   16.997 ±   0.118  ns/op
MemorySegmentVectorAccess.pollutedSegments2    1024  avgt   10   58.673 ± 105.783  ns/op
MemorySegmentVectorAccess.pollutedSegments3    1024  avgt   10   67.216 ±  16.157  ns/op
MemorySegmentVectorAccess.pollutedSegments4    1024  avgt   10  122.567 ± 263.950  ns/op
MemorySegmentVectorAccess.pollutedSegments5    1024  avgt   10  114.725 ± 209.183  ns/op


Before

Benchmark                                    (size)  Mode  Cnt    Score   Error  Units
MemorySegmentVectorAccess.arrayCopy            1024  avgt   10    8.547 ± 0.115  ns/op
MemorySegmentVectorAccess.directSegments       1024  avgt   10   15.536 ± 0.082  ns/op
MemorySegmentVectorAccess.heapSegments         1024  avgt   10   15.818 ± 0.101  ns/op
MemorySegmentVectorAccess.pollutedSegments2    1024  avgt   10  146.380 ± 1.127  ns/op
MemorySegmentVectorAccess.pollutedSegments3    1024  avgt   10  290.784 ± 7.274  ns/op
MemorySegmentVectorAccess.pollutedSegments4    1024  avgt   10  297.187 ± 5.096  ns/op
MemorySegmentVectorAccess.pollutedSegments5    1024  avgt   10  310.166 ± 9.310  ns/op


Additonally with profiling `load` and `store` method arguments as
described in [1]

Benchmark                                    (size)  Mode  Cnt    Score   Error  Units
MemorySegmentVectorAccess.arrayCopy            1024  avgt   10    7.480 ± 0.169  ns/op
MemorySegmentVectorAccess.directSegments       1024  avgt   10   15.497 ± 0.062  ns/op
MemorySegmentVectorAccess.heapSegments         1024  avgt   10   16.829 ± 0.132  ns/op
MemorySegmentVectorAccess.pollutedSegments2    1024  avgt   10  145.436 ± 1.081  ns/op
MemorySegmentVectorAccess.pollutedSegments3    1024  avgt   10  291.081 ± 2.297  ns/op
MemorySegmentVectorAccess.pollutedSegments4    1024  avgt   10  305.388 ± 7.518  ns/op
MemorySegmentVectorAccess.pollutedSegments5    1024  avgt   10  303.931 ± 3.412  ns/op


[1] https://github.com/openjdk/panama-foreign/pull/700

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

Commit messages:
 - Split foreign vector load and store by null or not null base

Changes: https://git.openjdk.org/panama-foreign/pull/711/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=711&range=00
  Stats: 26 lines in 1 file changed: 15 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/711.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/711/head:pull/711

PR: https://git.openjdk.org/panama-foreign/pull/711