RFR: 8288302: Shenandoah: SIGSEGV in vm maybe related to jit compiling xerces

[Roland Westrelin]

During igvn, at a heap stable test, a dominating heap stable test is
found that can be used to optimize out the current one. But this area
of the graph is actually dying and the current test has lost one of
its projection already, something the logic doesn't expect and which
causes the crash. The fix I propose is to simply detect that the heap
stable test is dying and skip the transformation.

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jdk/pull/10491/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10491&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288302
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10491.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10491/head:pull/10491

PR: https://git.openjdk.org/jdk/pull/10491