Instead of spilling and then immediately restoring eax to resolve
memory to memory moves, the gap move resolver now tracks registers
that are known to be free and uses one if available.  If not it spills
but restores lazily when the spilled value is needed or at the end of
the algorithm.

Instead of using esi for resolving cycles and assuming it is free to
overwrite because it can be rematerialized, the gap move resolver now
resolves cycles using swaps, possibly using a free register as above.

The algorithm is also changed to be simpler: a recursive depth-first
traversal of the move dependence graph.  It uses a list of moves to be
performed (because it mutates the moves themselves), but does not use
any auxiliary structure other than the control stack.  It does not
build up a separate list of scheduled moves to be interpreted by the
code generate, but emits code on the fly.

Review URL: http://codereview.chromium.org/6263005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6344 ce2b1a6d-e550-0410-aec6-3dcde31c8c00