RFA: patch for register migration

[Vladimir Makarov]

Richard Kenner wrote:

>    The reason for local register allocator is historical.  It makes all
>    allocator faster (how fast computers were in 1980).  We can easyly rid
>    off the local register allocator (just leave updating equivalent
>    register optimization from local) and do all work in global.c.  
>
>I don't follow.  global.c is quadratic.  How would uit be practical to
>use it to allocate all registers?
>  
>
  I don't plan to rid off it.  I think it will not improve code but make 
compiler slower.  I wrote about this because Dan mentioned that one weak 
point of the original register allocator is division on local and global 
allocator.  Actually I am not agree with this.  Bob Morgan (who has 
particular interest in register allocation) proposed even more passes in 
his book.  Combining compiler passes (combined register allocator, insn 
scheduling and register allocator, insn scheduiling and code selection 
and register allocator) is an interesting approach especially when they 
are looking for optimal solutions.  But IMHO it is in field of 
researches not in compiler engineering field.

   In any case on my opinion global.c without local-alloc.c still will 
be faster for real programs than the new ra.

Vlad