[jdk26] RFR: 8373502: C2 SuperWord: speculative check uses VPointer variable was pinned after speculative check, leading to bad graph

[Emanuel Peter]

Clean backport of https://github.com/openjdk/jdk/pull/28783 to JDK26.

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Commit messages:
 - Backport 00050f84d44f3ec23e9c6da52bffd68770010749

Changes: https://git.openjdk.org/jdk/pull/28929/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28929&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373502
  Stats: 112 lines in 3 files changed: 112 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28929.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28929/head:pull/28929

PR: https://git.openjdk.org/jdk/pull/28929