[jdk11u-dev] RFR: 8271340: Crash PhaseIdealLoop::clone_outer_loop

[Martin Doerr]

Clean Backport of JDK-8271340.

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Commit messages:
 - Backport 2abf3b3b2743947282300ee8416611559e49fca0

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/485/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=485&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271340
  Stats: 183 lines in 4 files changed: 140 ins; 41 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/485.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/485/head:pull/485

PR: https://git.openjdk.java.net/jdk11u-dev/pull/485