[Haskell-cafe] Building Haskell Platform natively for 64bit Windows

[Nicu Ionita]

Am 09.06.2011 19:44, schrieb Andrew Coppin:
> On 09/06/2011 06:54 AM, Scott Lawrence wrote:
>> On 06/09/2011 01:47 AM, Jason Dagit wrote:
>>> Have you checked this by looking at the generated assembly?  I
>>> generated some assembly from GHC on windows.  Here is what it looks
>>> ilke:
>>> http://hpaste.org/47610
>>>
>>> My assembly-fu is not strong enough to tell if it's using 64bit 
>>> instructions.
>>>
>> It would appear to be 32-bit. (pushl instead of pushq&  no instances of
>> aligning to 8-byte boundaries)
>
> The general register naming scheme on x86 is:
>
>   AL, AH: 8 bits
>   AX: 16 bits
>   EAX: 32 bits
>   RAX: 64 bits
>
> There's a lot of code there, but from what I can see, it's all 
> operating on 32-bit registers. So I'd say this is 32-bit code.
>
> On the other hand, I still think it would be worth actually 
> benchmarking this stuff to see how much difference it makes. Wouldn't 
> surprise me if the CPU designers did some clever trickery with 
> pipelining and superscalar execution to make two adjacent 32-bit 
> instructions execute the same way as a single 64-bit instruction would...
>
> (I've seen various sources claim that running software in 64-bit mode 
> only gives you a 2% speedup. Then again, they presumably aren't 
> testing with chess software which heavily utilises explicit 64-bit 
> operations.)
>
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For a chess engine this is for sure not true. I guess that this is one 
of very few domains where it really matters! The most (basic) operations 
with bitboards are anding, oring, xoring, shifting and (for magic 
bitboards) multiplying 64 bits values. When using 32 bits you need for 
some of these more then double time to achieve the same.

I was wondering if there is a possibility to support 64 bit native codes 
without other stuff (calling conventions, win64 specific system calls 
etc). This could be perhaps a first step to full 64 bit support. But 
from the code of ghc I could not understand what this would mean.

Nicu