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
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