[jdk21u-dev] RFR: 8328264: AArch64: remove UseNeon condition in CRC32 intrinsic

[Dmitry Chuyko]

This is a clean backport of a tiny enhancement in one of aarch64 crc32 implementations. Similar to JDK 23 -UseNeon makes no sense in update releases either https://github.com/openjdk/jdk/pull/18294#issuecomment-1997727704

Benchmarking results for jdk21u on Graviton 2, `-XX:-UseCRC32 -XX:-UseCryptoPmullForCRC32`:


Benchmark                  (count)   Mode  Cnt      Score    Error   Units
TestCRC32.testCRC32Update       64  thrpt    4  15263.125 ± 20.681  ops/ms
TestCRC32.testCRC32Update      128  thrpt    4   7746.327 ±  7.583  ops/ms
TestCRC32.testCRC32Update      256  thrpt    4   3904.416 ±  3.398  ops/ms
TestCRC32.testCRC32Update      512  thrpt    4   1959.262 ±  1.617  ops/ms
TestCRC32.testCRC32Update     2048  thrpt    4    489.607 ±  0.286  ops/ms
TestCRC32.testCRC32Update    16384  thrpt    4     61.355 ±  0.991  ops/ms
TestCRC32.testCRC32Update    65536  thrpt    4     15.318 ±  0.270  ops/ms
-->
TestCRC32.testCRC32Update       64  thrpt    4  18649.642 ± 40.169  ops/ms
TestCRC32.testCRC32Update      128  thrpt    4  11265.168 ± 13.246  ops/ms
TestCRC32.testCRC32Update      256  thrpt    4   6188.989 ±  4.609  ops/ms
TestCRC32.testCRC32Update      512  thrpt    4   3254.121 ±  3.669  ops/ms
TestCRC32.testCRC32Update     2048  thrpt    4    846.038 ±  0.861  ops/ms
TestCRC32.testCRC32Update    16384  thrpt    4    107.056 ±  0.116  ops/ms
TestCRC32.testCRC32Update    65536  thrpt    4     26.780 ±  0.041  ops/ms


JDK-8329749 is an optional follow-up for this backport.

Testing: tier1,2 on linux-aarch64.

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

Commit messages:
 - Backport 9ca4ae3d3b746f1d75036d189ff98f02b73b948f

Changes: https://git.openjdk.org/jdk21u-dev/pull/1462/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1462&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328264
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1462.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1462/head:pull/1462

PR: https://git.openjdk.org/jdk21u-dev/pull/1462