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

[Aleksey Shipilev]

WIP.

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Commit messages:
 - Backport 09a047f00c88d14505c42a966dedbc87b9be5bdf

Changes: https://git.openjdk.org/jdk25u/pull/382/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=382&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/pull/382.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/382/head:pull/382

PR: https://git.openjdk.org/jdk25u/pull/382