Convert CSE phase to not rely too much on NodeIndex
https://bugs.webkit.org/show_bug.cgi?id=107616

Reviewed by Geoffrey Garen.
        
- Instead of looping over the graph (which assumes that you can simply loop over all
  nodes without considering blocks first) to reset node.replacement, do that in the
  loop that sets up relevantToOSR, just before running CSE on the block.
        
- Instead of having a relevantToOSR bitvector indexed by NodeIndex, made
  NodeRelevantToOSR be a NodeFlag. We had exactly one bit left in NodeFlags, so I did
  some reshuffling to fit it in.

* dfg/DFGCSEPhase.cpp:
(JSC::DFG::CSEPhase::CSEPhase):
(JSC::DFG::CSEPhase::eliminateIrrelevantPhantomChildren):
(JSC::DFG::CSEPhase::performNodeCSE):
(JSC::DFG::CSEPhase::performBlockCSE):
(CSEPhase):
* dfg/DFGNodeFlags.h:
(DFG):
* dfg/DFGNodeType.h:
(DFG):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140504 268f45cc-cd09-0410-ab3c-d52691b4dbfc