我想问一下Haskell和C++编译器是否可以以同样的方式优化函数调用。
请看下面的代码。在下面的示例中,Haskell 明显比 C++ 快。
我听说 Haskell 可以编译为 LLVM,并且可以通过 LLVM 通道进行优化。此外,我听说 Haskell 在幕后有一些重要的优化。
但以下示例应该能够以相同的性能工作。
我想问一下:
- 为什么我的 C++ 示例基准比 Haskell 慢?
- 代码可以进一步优化吗?
(我正在使用 LLVM-3.2 和 GHC-7.6)。
C++代码:
#include <cstdio>
#include <cstdlib>
int b(const int x){
return x+5;
}
int c(const int x){
return b(x)+1;
}
int d(const int x){
return b(x)-1;
}
int a(const int x){
return c(x) + d(x);
}
int main(int argc, char* argv[]){
printf("Starting...\n");
long int iternum = atol(argv[1]);
long long int out = 0;
for(long int i=1; i<=iternum;i++){
out += a(iternum-i);
}
printf("%lld\n",out);
printf("Done.\n");
}
编译为clang++ -O3 main.cpp
哈斯克尔代码:
module Main where
import qualified Data.Vector as V
import System.Environment
b :: Int -> Int
b x = x + 5
c x = b x + 1
d x = b x - 1
a x = c x + d x
main = do
putStrLn "Starting..."
args <- getArgs
let iternum = read (head args) :: Int in do
putStrLn $ show $ V.foldl' (+) 0 $ V.map (\i -> a (iternum-i))
$ V.enumFromTo 1 iternum
putStrLn "Done."
编译为ghc -O3 --make -fforce-recomp -fllvm ghc-test.hs
速度结果:
Running testcase for program 'cpp/a.out'
-------------------
cpp/a.out 100000000 0.0% avg time: 105.05 ms
cpp/a.out 200000000 11.11% avg time: 207.49 ms
cpp/a.out 300000000 22.22% avg time: 309.22 ms
cpp/a.out 400000000 33.33% avg time: 411.7 ms
cpp/a.out 500000000 44.44% avg time: 514.07 ms
cpp/a.out 600000000 55.56% avg time: 616.7 ms
cpp/a.out 700000000 66.67% avg time: 718.69 ms
cpp/a.out 800000000 77.78% avg time: 821.32 ms
cpp/a.out 900000000 88.89% avg time: 923.18 ms
cpp/a.out 1000000000 100.0% avg time: 1025.43 ms
Running testcase for program 'hs/main'
-------------------
hs/main 100000000 0.0% avg time: 70.97 ms (diff: 34.08)
hs/main 200000000 11.11% avg time: 138.95 ms (diff: 68.54)
hs/main 300000000 22.22% avg time: 206.3 ms (diff: 102.92)
hs/main 400000000 33.33% avg time: 274.31 ms (diff: 137.39)
hs/main 500000000 44.44% avg time: 342.34 ms (diff: 171.73)
hs/main 600000000 55.56% avg time: 410.65 ms (diff: 206.05)
hs/main 700000000 66.67% avg time: 478.25 ms (diff: 240.44)
hs/main 800000000 77.78% avg time: 546.39 ms (diff: 274.93)
hs/main 900000000 88.89% avg time: 614.12 ms (diff: 309.06)
hs/main 1000000000 100.0% avg time: 682.32 ms (diff: 343.11)
EDIT当然我们不能比较语言的速度,而是比较实现的速度。
但我很好奇 Ghc 和 C++ 编译器是否可以以同样的方式优化函数调用
我根据您的帮助使用新的基准和代码编辑了问题:)