On Wed, Oct 31, 2007 at 03:37:12PM +0000, Neil Mitchell wrote: > Hi > > I've been working on optimising Haskell for a little while > (http://www-users.cs.york.ac.uk/~ndm/supero/), so here are my thoughts > on this. The Clean and Haskell languages both reduce to pretty much > the same Core language, with pretty much the same type system, once > you get down to it - so I don't think the difference between the > performance is a language thing, but it is a compiler thing. The > uniqueness type stuff may give Clean a slight benefit, but I'm not > sure how much they use that in their analyses. > > Both Clean and GHC do strictness analysis - I don't know which one > does better, but both do quite well. I think Clean has some > generalised fusion framework, while GHC relies on rules and short-cut > deforestation. GHC goes through C-- to C or ASM, while Clean has been > generating native code for a lot longer. GHC is based on the STG > machine, while Clean is based on the ABC machine - not sure which is > better, but there are differences there. > > My guess is that the native code generator in Clean beats GHC, which > wouldn't be too surprising as GHC is currently rewriting its CPS and > Register Allocator to produce better native code.
I don't think the register allocater is being rewritten so much as it is
being written:
[EMAIL PROTECTED]:/tmp$ cat X.hs
module X where
import Foreign
import Data.Int
memset :: Ptr Int32 -> Int32 -> Int -> IO ()
memset p v i = p `seq` v `seq` case i of
0 -> return ()
_ -> poke p v >> memset (p `plusPtr` sizeOf v) v (i - 1)
[EMAIL PROTECTED]:/tmp$ ghc -fbang-patterns -O2 -c -fforce-recomp -ddump-asm
X.hs
...
X_zdwa_info:
movl 8(%ebp),%eax
testl %eax,%eax
jne .LcH6
movl $base_GHCziBase_Z0T_closure+1,%esi
addl $12,%ebp
jmp *(%ebp)
.LcH6:
movl 4(%ebp),%ecx
movl (%ebp),%edx
movl %ecx,(%edx)
movl (%ebp),%ecx
addl $4,%ecx
decl %eax
movl %eax,8(%ebp)
movl %ecx,(%ebp)
jmp X_zdwa_info
...
Admittedly that's better than it used to be (I recall 13 memory
references last time I tested it), but still... the reason for your
performance woes should be quite obvious in that snippet.
Stefan
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