RFR(XS): 8227384: C2 compilation fails with "graph should be schedulable" when running with -XX:-EliminateLocks

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8227384/webrev.00/

The mark word load for unlocking is created after the release lock
membar with both control and memory set to projections of the
membar. Because the allocation is non escaping, when the load is later
processed, its memory is changed to be above the membar while the
control is unchanged. A precedence edge is added by anti dependence
checking to force the load above the membar while its control is
below. As a result, the graph is not schedulable.

The fix I propose is to not set control on the mark work loads. I
suppose control was set to guarantee the loads don't float above a null
check but now that C2 doesn't eliminate CastPPs early that should not
happen.

Roland.