[8u] RFR 8253353: Crash in C2: guarantee(n != NULL) failed: No Node

[Zhengyu Gu]

I would like to backport this patch to openjdk8u for parity with Oracle 
8u331. The patch fixes a fatal crash initially reported for openjdk8u, 
so it should be backported.

Bug: https://bugs.openjdk.java.net/browse/JDK-8253353

The backport is based on jdk11u backport, which is closer to 8u.
Patch: https://hg.openjdk.java.net/jdk-updates/jdk11u/rev/04682d78ae28

The patch still does not apply cleanly.
- 8u does not have PhaseIdealLoop::create_outer_strip_mined_loop() 
method, stripped corresponding change in the method.
- Slight context different in IdealLoopTree declaration.


8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8253353-8u/webrev.00/

Test:
   passed compiler/loopopts/TestNestedIrreducibleLoopsMain.java test

Thanks,

-Zhengyu