[lworld] RFR: 8271330: [lworld] SIGSEGV in MemNode::find_previous_store

[Tobias Hartmann]

Another bug that showed up now because it requires AVX-512 VLBW capable machines (and we added them to our test infra only recently). The problem is that default value store elimination to inline type arrays introduced by [JDK-8189802](https://bugs.openjdk.java.net/browse/JDK-8189802) invokes `MemNode::find_previous_store` on non-zero stores which confused `ClearArrayNode::step_through`.

This patch disables the code for now. I've filed [JDK-8271339](https://bugs.openjdk.java.net/browse/JDK-8271339) to re-enable it.

Best regards,
Tobias

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Commit messages:
 - 8271330: [lworld] SIGSEGV in MemNode::find_previous_store

Changes: https://git.openjdk.java.net/valhalla/pull/502/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=502&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271330
  Stats: 10 lines in 1 file changed: 0 ins; 8 del; 2 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/502.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/502/head:pull/502

PR: https://git.openjdk.java.net/valhalla/pull/502