[jdk21u] RFR: 8316679: C2 SuperWord: wrong result, load should not be moved before store if not comparable

[Aleksey Shipilev]

Unclean backport to fix the vectorization bug. The patch is unclean because JDK 21u does not have [JDK-8312332](https://bugs.openjdk.org/browse/JDK-8312332) refactoring, that I do not want to backport. I have reapplied the patch by renaming `SWPointer` again.

Note @eme64, @TobiHartmann.

Additional testing:
 - [x] MacOS AArch64 Server fastdebug, new regression test fails without the patch, passes with it
 - [x] MacOS AArch64 Server fastdebug, `compiler/loopopts`
 - [ ] Linux x86_64 server fastdebug, `tier1 tier2 tier3 tier4`

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

Commit messages:
 - Backport 48f1a925e528cc9f8cd6c727129918e0e49b3429

Changes: https://git.openjdk.org/jdk21u/pull/327/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=327&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316679
  Stats: 110 lines in 2 files changed: 103 ins; 4 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u/pull/327.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/327/head:pull/327

PR: https://git.openjdk.org/jdk21u/pull/327