RFR: backport of 8191887

[Aleksey Shipilev]

On 01/31/2018 04:31 PM, Roland Westrelin wrote:
> I hit 8191887 when running specjvm with Shenandoah. This was fixed
> upstream so I propose we cherry pick it. The fix doesn't apply
> cleanly so here it is on top of the current shenandoah repo:
> 
> http://cr.openjdk.java.net/~roland/shenandoah/8191887/webrev.00/

Yes please, anything that helps resolves conflicts during the merges is cool.

Please push it as:
 "Cherry-pick 8191887: assert(b->is_Bool()) in PhaseIdealLoop::clone_iff() due to Opaque4 node"

-Aleksey