[jdk15u-dev] RFR: 8270886: Crash in PhaseIdealLoop::verify_strip_mined_scheduling

[Yuri Nesterenko]

I'd like to backport this fix to 15u for attempted parity with major releases. Clean backport.

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Commit messages:
 - Backport 6afcf5f5a243be10e2ec61229819c298ccce3267

Changes: https://git.openjdk.java.net/jdk15u-dev/pull/214/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=214&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270886
  Stats: 175 lines in 2 files changed: 171 ins; 4 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk15u-dev/pull/214.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk15u-dev pull/214/head:pull/214

PR: https://git.openjdk.java.net/jdk15u-dev/pull/214