[Haskell] GHC 64bit?

Simon Marlow simonmar at microsoft.com
Fri Feb 13 17:24:51 EST 2004

> Dell's poweredge server with the max 12gb RAM costs $15k.
> Moore's law says that
> 1. you only need an extra bit/year.
> 2. processing that extra bit will cost 50% less next year
> Though perhaps processing time is not linear with
> the number of bits for historical/architectural
> reasons....?
> I presume that, if we are conservative in the
> number of bits we use then we don't run into the
> ptr driven storage problem that Axel described.
> In particular, if we need only 2 or 4 times as
> much memory, we should only grow pointers by 1 or
> 2 bits...rather than growing immediately all the
> way to 64...
> Perhaps there could be a command line option to
> specify desired ptr size.  I assume it is
> impossible to adjust pointer size dynamically at
> runtime depending on memory consumption (I
> assume you would do it at garbage collection time
> if it were possible).

Using pointers of a size other than the machine's native word size
should be possible.  We experimented recently with adding tag bits to
pointers, and in the process discovered all the places where you would
need to convert between "abstract" pointers and real pointers, which are
the same places you would need to modify if you were to use some kind of
compressed representation for pointers.


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