patch applied (ghc-6.8/ghc): Add iterative coalescing to graph coloring allocator

[Ben Lippmeier]

Fri Sep  7 10:23:15 PDT 2007  Ben.Lippmeier at anu.edu.au
  * Add iterative coalescing to graph coloring allocator
  
  Iterative coalescing interleaves conservative coalesing with the regular
  simplify/scan passes. This increases the chance that nodes will be coalesced
  as they will have a lower degree than at the beginning of simplify. The end
  result is that more register to register moves will be eliminated in the
  output code, though the iterative nature of the algorithm makes it slower
  compared to non-iterative coloring.
  
  Use -fregs-iterative  for graph coloring allocation with iterative coalescing
      -fregs-graph      for non-iterative coalescing.
  
  The plan is for iterative coalescing to be enabled with -O2 and have a 
  quicker, non-iterative algorithm otherwise. The time/benefit tradeoff
  between iterative and not is still being tuned - optimal graph coloring
  is NP-hard, afterall..

    M ./compiler/main/DynFlags.hs -1 +3
    M ./compiler/nativeGen/AsmCodeGen.lhs -18 +12
    M ./compiler/nativeGen/GraphBase.hs +3
    M ./compiler/nativeGen/GraphColor.hs -86 +103
    M ./compiler/nativeGen/GraphOps.hs -17 +125
    M ./compiler/nativeGen/RegAllocColor.hs -6 +19