[jdk13u-dev] RFR: 8247502: PhaseStringOpts crashes while optimising effectively dead code

[Olga Mikhaltsova]

I'd like to backport JDK-8247502 to jdk13u for parity with jdk11u.
The original patch applied cleanly.
Tested with tier1, tier2. No regression in tests.

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Commit messages:
 - Backport a14490dd161b9ac9b4f900489fd84e756ff6e740

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/189/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=189&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8247502
  Stats: 9 lines in 1 file changed: 9 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/189.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/189/head:pull/189

PR: https://git.openjdk.java.net/jdk13u-dev/pull/189