RFR(XS): 8235870: C2 crashes in IdealLoopTree::est_loop_flow_merge_sz()

[Patric Hedlin]

Dear all,

I would like to ask for help to review the following change/update:

Issue:  https://bugs.openjdk.java.net/browse/JDK-8235870
Webrev: http://cr.openjdk.java.net/~phedlin/tr8235870/

8235870: C2 crashes in IdealLoopTree::est_loop_flow_merge_sz()

     Method missing necessary checks, made more robust.

Testing: hs-tier1-3, LuceneBench24H


Best regards,
Patric