RFR: 8335390: C2 MergeStores: wrong result with Unsafe [v2]

[Emanuel Peter]

> In JDK23, I introduced `MergeStores` [JDK-8318446](https://bugs.openjdk.org/browse/JDK-8318446) https://github.com/openjdk/jdk/pull/16245.
> 
> I now realized that the pointer-parsing has some issues with `Unsafe` stores. Thus, I disable the optimization for those for now.
> 
> **Future Work**
> In [JDK-8335392](https://bugs.openjdk.org/browse/JDK-8335392), I plan to redesign the pointer-parsing, and enable more features, including `Unsafe` stores.

Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:

  run test only on 64-bit

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19964/files
  - new: https://git.openjdk.org/jdk/pull/19964/files/d327e186..c9477f89

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19964&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19964&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19964.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19964/head:pull/19964

PR: https://git.openjdk.org/jdk/pull/19964