I think gcc 4.x have much better optimizations than 3.x since SSA added.I
donot know if there are very good IR for functional language optimization. Is
it hard for STG language to analysis this kind of code?> go !x !y !i
> | i == 1000000000 = printf "%f\n" (x+y)
> | otherwise = go (x*y/3) (x*9) (i+1)
btw: I always hope to see a C/C++ language compiler writen by haskell.I think
it might be much easier to add a new optimization :)
在2007-02-11，Rafael Almeida <[EMAIL PROTECTED]> 写道：
On 2/10/07, Donald Bruce Stewart <[EMAIL PROTECTED]> wrote: > The following C
program was described on #haskell > > #include <stdio.h> > > int main() > { >
double x = 1.0/3.0; > double y = 3.0; > int i = 1; > for (; i<=1000000000; i++)
{ > x = x*y/3.0; > y = x*9.0; > } > printf("%f\n", x+y); > } > > > Which was
translated to the following Haskell: > > {-# OPTIONS -fexcess-precision #-} > >
import Text.Printf > > main = go (1/3) 3 1 > > go :: Double -> Double -> Int ->
IO () > go !x !y !i > | i == 1000000000 = printf "%f\n" (x+y) > | otherwise =
go (x*y/3) (x*9) (i+1) I've compiled the exactly same programs, passing the
same parameters to the compiler as you did, but I've got a very different
result: $ ghc -O -fexcess-precision -fbang-patterns -optc-O3 -optc-ffast-math\
-optc-mfpmath=sse -optc-msse2 loop.hs -o haskell_loop $ time ./haskell_loop
3.3333333333333335 real 0m14.092s user 0m14.057s sys 0m0.036s $ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.6 While the haskell
program took so long, the C program went really faster than the haskell
version: $ gcc -O3 -ffast-math -mfpmath=sse -msse2 -std=c99 loop.c -o c_loop $
time ./c_loop 3.333333 real 0m0.001s user 0m0.000s sys 0m0.000s $ gcc --version
gcc (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21) I'm using debian etch
(linux), my processor is a pentium 4 3.0ghz, which has sse and sse2 (or at
least /proc/cpuinfo says so). As for memory, it probably doesn't matter much in
this test, but I have 512mB of ram. In a similar thread that was posted at
comp.lang.functional (it was actually regarding ocaml vs C++, you can find it
on google groups at http://tinyurl.com/292ps6 ) the same kind of discrepancy
occurred. Showing that this kind of benchmarking is usually not very accurate
or, at least, that my processor is not well suited for functional languages :P.
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