Graph coloring register allocator.
TODO: The colors in graphviz graphs for x86_64 and ppc could be nicer.
|:: (Outputable instr, Instruction instr)|
|-> UniqFM (UniqSet RealReg)|
the registers we can use for allocation
|-> UniqSet Int|
the set of available spill slots.
|-> [LiveCmmTop instr]|
code annotated with liveness information.
|-> UniqSM ([NatCmmTop instr], [RegAllocStats instr])|
code with registers allocated and stats for each stage of allocation
The top level of the graph coloring register allocator.