PowerPC register and memory cost model

[David Edelsohn]

	Okay, well this is interesting.  I guess this gives us something
more that we need to explore for PowerPC performance, but I do not know
which version to commit in the interim.

	I tried the memory_move_cost function I posted yesterday with both
four (4) times the word size (equivalent to GCC default) and six (6) times
the word size (equivalent to current PowerPC port).  The interesting
differences are:

			   COST = 4		   COST = 6

ParseVid (INT)           196.0  usecs		 *166.3  usecs
MPEG (INT)              *125.9  usecs		  136.7  usecs
PixBlend (INT)           261.4  usecs		 *254.6  usecs
Rijndael (INT)          *120.3  usecs		  121.2  usecs
VolInt (FP)             *134.3  usecs		  140.7  usecs

	Comments, recommendations, and suggestions are welcome.

David