On 29 March 2014 12:43, Kai Zhang
Hi cafe,
Inline sometimes can cause problems, at least in following case:
import qualified Data.Vector as V import Data.List
f ∷ String → (String → Int → Char) → [Int] → String f str g idx = map (g str) idx
h ∷ String → Int → Char {-# INLINE h #-} h s i = (V.fromList $ sort s) V.! i
slow ∷ String → [Int] → String slow str = f str h
fast ∷ String → [Int] → String fast str = map ((V.fromList $ sort str) V.!)
main = do let testString = replicate 100000 'a' iterations = replicate 1000 100 putStrLn $ fast testString iterations putStrLn $ slow testString iterations
Without inline (remove the inline pragma), "slow" would be much faster. I suspect this is because ghc can build a "persistent structure" for the partial applied function. After inline, each call of "g" will try to build a new vector. How can I tell ghc not to inline some specific functions? Or are there other ways to resolve this issue?
There's the NOINLINE and INLINEABLE pragmas. Though I'm going through some of my own code where I waved the INLINE-hammer around rather heavily only to find that whilst it doesn't make much of a difference on my main x86_64 machine, on the x86 laptop I tested it on it made the code much slower. So I'm also interested in finding better ways of determining where and when INLINE is helpful (rather than blindly removing some INLINEs and re-profiling to see what difference it makes, as in many cases it *does* require the INLINE for performance).
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