[11] RFR(XS): 8197563: assert(is_Loop()) crash in PhaseIdealLoop::try_move_store_before_loop()

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8197563/webrev.00/

The method being compiled has an infinite loop and the head of the loop
is not converted to a LoopNode. A store is moved out of the infinite
loop. Some code I added with 8186027 (C2: loop strip mining) assumes the
head is a loop and we hit the assert failure. The fix I propose is not
never try to move a store out of loop if the head is not a LoopNode.

Roland.