RFR(S): 8194993: Loop Strip Mining has some leftover debugging code

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8194993/webrev.00/

I noticed I left some debugging code in the logic that finalized the
outer loop of strip mined loops. If the strip mined loop has stores that
were sunk out of the loop and stores on the back edge then a
ShouldNotReachHere() is hit. I never managed to write a test case that
triggers both conditions and they've never been caught by testing so
far. Anyway, we don't want a crash if that ever happens in the wild and
we probably don't want to ship untested code. What I propose instead is
that if that ever happens, we simply drop the outer loop and leave the
inner loop as it is (no strip mining). I left an assert so if that does
happen we have a chance to fix that corner case.

Roland.