[jdk25u-dev] RFR: 8370405: C2: mismatched store from MergeStores wrongly scalarized in allocation elimination

[Aleksey Shipilev]

Fixes JDK 21 -> JDK 25 regression in C2 that can lead to miscompilation. There is a regression test that captures the failure.

Additional testing:
 - [x] Linux x86_64 server fastdebug, new regression test fails without the fix, passes with it
 - [ ] Linux x86_64 server fastdebug, `all`

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Depends on: https://git.openjdk.org/jdk25u-dev/pull/9

Commit messages:
 - Backport 09a047f00c88d14505c42a966dedbc87b9be5bdf

Changes: https://git.openjdk.org/jdk25u-dev/pull/10/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u-dev&pr=10&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370405
  Stats: 375 lines in 5 files changed: 375 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk25u-dev/pull/10.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u-dev.git pull/10/head:pull/10

PR: https://git.openjdk.org/jdk25u-dev/pull/10