RFR: 8281811: assert(_base == Tuple) failed: Not a Tuple after JDK-8280799 [v2]

[Roland Westrelin]

> The crash occurs because a Shenandoah barrier is expanded between the
> Start node and its control projection. One of the test cases I added
> also shows the same failure with a barrier expansion between a MemBar
> and its control projection. The barrier is expanded at the control
> that PhaseIdealLoop assigns to it.
> 
> This code:
> https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/loopnode.cpp#L5756
> I added back with JDK-8280799 is what's causing the incorrect
> placement of the barrier.
> 
> The fix I propose is to skip that logic if the loop opts pass is for
> barrier expansion as there's no range check elimination then.

Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into JDK-8281811
 - test
 - fix

-------------

Changes: https://git.openjdk.java.net/jdk/pull/7494/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7494&range=01
  Stats: 90 lines in 3 files changed: 74 ins; 0 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7494.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7494/head:pull/7494

PR: https://git.openjdk.java.net/jdk/pull/7494