[jdk11u-dev] RFR: 8235870: C2 crashes in IdealLoopTree::est_loop_flow_merge_sz()

[Goetz Lindenmaier]

I backport this for parity with 11.0.17-oracle.

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Commit messages:
 - Backport 9549cd28779934f3f4846a82031f7afa17edde0d

Changes: https://git.openjdk.org/jdk11u-dev/pull/1256/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1256&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8235870
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1256.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1256/head:pull/1256

PR: https://git.openjdk.org/jdk11u-dev/pull/1256