From: Max Bolingbroke

On 4 February 2011 02:35, Steve Severance wrote:

...

Wholly support moving OSX to x64. x86 should be supported only on a best effort basis for legacy.

Moving from x86 to x64 has advantages and disadvantages from my POV. Advantages: * Able to address more memory * More registers for code generation * Haskell dependencies wouldn't need to be built for x86 on Snow Leopard (though if we swapped to x64 on Leopard as well, the Leopard users would start having to build 64-bit libraries specially)

Disadvantages: * Pointers become wider, and Haskell data structures mostly consist of pointers. This will bloat memory use of Haskell programs. * Generated binaries won't work on older Macs that don't have a 64-bit OS/CPU. This is important if you are distributing compiled Haskell binaries, which is not something I personally do but which is probably important to support

Did I miss anything?

I'm moderately in favor of making the primary supported platform x86_64, except for the distribution issue. If i386 were maintained but not necessarily targeted for improvement that would be fine by me.

I don't know if anyone using a 64-bits GHC on e.g. Linux has reported experience of whether moving to 64-bits is a net win or not from a performance perspective. My guess is that it is a win for certain classes of programs (numerically intensive, "high performance Haskell"), and a loss for programs making extensive use of laziness, boxed data structures etc.

For my code, x86_64 (OS X) is a net win. It's sometimes significantly faster, and hasn't ever been noticeably slower. The biggest gains seems to be I/O, although I haven't really investigated this. Cheers, John