RFR: 8310159: Bulk copy with Unsafe::arrayCopy is slower compared to memcpy [v6]

[Steve Dohrmann]

> Update: the XorTest::xor results shown in this message used test code from PR commit 7cc272e862791 which was based on Maurizio Cimadamore's commit a788f066af17.  The XorTest has since been updated and XorTest::copy is no longer needed and has been removed from this pull request.  See comment [here](https://github.com/openjdk/jdk/pull/16575#issuecomment-1820006548) for updated performance data. 
> 
> Below is baseline data collected using a modified version of the java.lang.foreign.xor micro benchmark referenced by @mcimadamore  in the bug report.  I collected data on an Ubuntu 22.04 laptop with a Tigerlake i7-1185G7, which does support AVX512. 
> 
> Baseline data
> Benchmark     (arrayKind)  (sizeKind)  Mode  Cnt           Score          Error  Units
> --------------------------------------------------------------------------------------
> XorTest.copy     ELEMENTS       SMALL  avgt   30   584737355.767 ± 60414308.540  ns/op
> XorTest.copy     ELEMENTS      MEDIUM  avgt   30   272248995.683 ±  2924954.498  ns/op
> XorTest.copy     ELEMENTS       LARGE  avgt   30  1019200210.900 ± 28334453.652  ns/op
> XorTest.copy       REGION       SMALL  avgt   30     7399944.164 ±   216821.819  ns/op
> XorTest.copy       REGION      MEDIUM  avgt   30    20591454.558 ±   147398.572  ns/op
> XorTest.copy       REGION       LARGE  avgt   30    21649266.051 ±   179263.875  ns/op
> XorTest.copy     CRITICAL       SMALL  avgt   30       51079.357 ±      542.482  ns/op
> XorTest.copy     CRITICAL      MEDIUM  avgt   30        2496.961 ±       11.375  ns/op
> XorTest.copy     CRITICAL       LARGE  avgt   30         515.454 ±        5.831  ns/op
> XorTest.copy      FOREIGN       SMALL  avgt   30     7558432.075 ±    79489.276  ns/op
> XorTest.copy      FOREIGN      MEDIUM  avgt   30    19730666.341 ±   500505.099  ns/op
> XorTest.copy      FOREIGN       LARGE  avgt   30    34616758.085 ±   340300.726  ns/op
> XorTest.xor      ELEMENTS       SMALL  avgt   30   219832692.489 ±  2329417.319  ns/op
> XorTest.xor      ELEMENTS      MEDIUM  avgt   30   505138197.167 ±  3818334.424  ns/op
> XorTest.xor      ELEMENTS       LARGE  avgt   30  1189608474.667 ±  5877981.900  ns/op
> XorTest.xor        REGION       SMALL  avgt   30    64093872.804 ±   599704.491  ns/op
> XorTest.xor        REGION      MEDIUM  avgt   30    81544576.454 ±  1406342.118  ns/op
> XorTest.xor        REGION       LARGE  avgt   30    90091424.883 ±   775577.613  ns/op
> XorTest.xor      CRITICAL       SMALL  avgt   30    57231375.744 ±   438223.342  ns/op
> XorTest.x...

Steve Dohrmann has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:

 - Merge branch 'master' into memcpy
 - Updates based on reviewer (sviswa7) comments including
   - use asserts instead of conditionals in two logically unreachable blocks
   - remove unused function parmeters
   - use 64-byte vector path in pre-loop masked write
 - Merge branch 'master' into memcpy
 - Update full name
   Previous commit (fcbbc0d7880) added org.openjdk.bench.java.lang.ArrayCopyAlignedLarge benchmark
 - - remerge upstream master
   - remove ::copy test from XorTest
 - Merge branch 'master' into memcpy
 - - fix whitespace error
 - Merge branch 'master' of https://git.openjdk.org/jdk into memcpy
 - - bug fix: only generate / use large copy code if MaxVectorSize == 64
 - - fix whitespace issues
   - fix xor test foreign impl constructor signature
 - ... and 1 more: https://git.openjdk.org/jdk/compare/e47cf611...02ad27fa

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

Changes: https://git.openjdk.org/jdk/pull/16575/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16575&range=05
  Stats: 259 lines in 5 files changed: 259 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16575.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16575/head:pull/16575

PR: https://git.openjdk.org/jdk/pull/16575