space profiling

[Stephen Weeks]

> You could just use 64-bit bins, but then the space requirements double again
> (8 bytes of bin for every byte of object code) and now the generated code at
> each allocation point is a 32-bit add to a 64-bit counter.  That seems to push
> harder for calling a procedure which can do it and do the linking to save
> space.

The largest program we know of is MLton, whose text segment is currently just
under 6M.  I can live with 48M (since it's not in the MLton heap), although I
agree that's pushing it.

Another possibility would be to coalesce the bins.  How bad would it be to
cut the number of bins in half?