Various dx fixes to make it preserve locals and debug info.

Various dx fixes to make it preserve locals and debug info.

The SCCP pass checks if a register has associated local info before
attepting to prune branches or replace values with constants. Also, the
register allocator reserves a register for each local in a method. This
could be later improved by only reserving registers for the lengths of
their lifetimes as specified by the local info table.

Change-Id: I654ac014a9aac530f1db0db7d5cdef7535ff49bf