The flow graph has been simplified to remove the special branch, join,
and exit nodes.  All nodes are now basic blocks (possibly empty to
preserve edge-split form) with a distinguished entry and exit block.

Most trivial expressions are not added to the flow graph as
instructions.  The assigned variable analyzer has been changed to
sometimes work right-to-left so that right subexpressions can be
marked as trivial.

The reaching definitions analysis has been temporarily removed, and
the analyses that depended on it (primitivity analysis, dead code
marking) as well.

Review URL: http://codereview.chromium.org/1530003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4307 ce2b1a6d-e550-0410-aec6-3dcde31c8c00