Two changes, both very significant:
Two changes, both very significant:

* vreg <-> vreg joining now works, enable it unconditionally when joining
  is enabled (which is the default).
* Fix a serious pessimization of spill code where we were saying that a
  spilled DEF operand was live into the subsequent instruction.  This allows
  for substantially better code when spilling starts to happen.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@14993 91177308-0d34-0410-b5e6-96231b3b80d8

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