RFR(S): 8212673: jtreg/applications/runthese/RunThese30M.java fails in C2 with "assert(!had_error) failed: bad dominance"

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8212673/webrev.00/

In PhiNode::Ideal(): 

  Node* uin = unique_input(phase, false); 
  if (uin == NULL && can_reshape) { 
    uncasted = true; 
    uin = unique_input(phase, true); 
  } 

can find a unique input by looking trough cast. But code below: 

      if ((is_loop && !uin->eqv_uncast(in(LoopNode::EntryControl))) || 
          (!is_loop && is_unsafe_data_reference(uin))) { 

eqv_uncast can fail because it looks through casts and load barriers if
the unique input is a load barrier. This then causes a valid input to a
Phi to be set to top.

I propose to backout JDK-8212603 and add calls to step_over_gc_barrier()
to locking optimization code only instead (which was the motivation for
JDK-8212603).

Roland.