RFR(S): 8199784: PhaseIdealLoop::place_near_use() might return wrong control with loop strip mining

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8199784/webrev.00/

When a Load is sunk out of a loop, if one of the uses is a Phi of a
strip mined CountedLoop, PhaseIdealLoop::place_near_use() should return
the entry control of the OuterStripMinedLoop.

I couldn't write a test case that would trigger this and I'm not even
sure it's even possible. We're seeing this with some graph patterns that
are specific to Shenandoah but I think it's better to have this fixed
anyway.

Roland.