[11u] RFR (XS) 8253353: Crash in C2: guarantee(n != NULL) failed: No Node

[Aleksey Shipilev]

Original bugfix:
   https://bugs.openjdk.java.net/browse/JDK-8253353
   https://git.openjdk.java.net/jdk16/commit/1926765f

This fixes the regression introduced by:
   https://bugs.openjdk.java.net/browse/JDK-8240576

...which was already backported to 11.0.8.

The patch is simple, but it fails to apply cleanly, because one of the asserts in loopnode.cpp 
cannot be placed automatically. I placed near "loop->_nest++" in 11u code.

11u variant:
   https://cr.openjdk.java.net/~shade/8253353/webrev.11u.01

Testing: tier{1,2,3}; new test fails without the patch, passes with it

-- 
Thanks,
-Aleksey