[11u] RFR 8231550: C2: ShouldNotReachHere() in verify_strip_mined_scheduling

[Roland Westrelin]

Original bug:
  https://bugs.openjdk.java.net/browse/JDK-8231550
  https://hg.openjdk.java.net/jdk/jdk/rev/bada0782842a

Original patch does not apply cleanly to 11u because:

- in file loopnode.cpp, the implementation of
  PhaseIdealLoop::get_late_ctrl() is slightly different. Applied change
  is otherwise identical to original patch.

- the patch includes a shenandoah change that doesn't apply for 11u

- I add to provide an implementation for LoadBarrierNode::adr_type() for
  ZGC

11u webrev:
  http://cr.openjdk.java.net/~roland/8231550.11u/webrev.00/

Testing: x86_64 build, verified new test fails without the patch and
runs fine with it, tier2

Roland.