[lworld] RFR: 8250951: [lworld] Escape analysis fails due to oop access to flat array

[Tobias Hartmann]

When storing null, C2 should only mark array as not-flat after the null-check.

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Commit messages:
 - 8250951: [lworld] Escape analysis fails due to oop access to flat array

Changes: https://git.openjdk.java.net/valhalla/pull/130/files
 Webrev: https://webrevs.openjdk.java.net/valhalla/130/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8250951
  Stats: 13 lines in 1 file changed: 4 ins; 2 del; 7 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/130.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/130/head:pull/130

PR: https://git.openjdk.java.net/valhalla/pull/130