On Mon, Dec 19, 2011 at 12:26 AM, Antoine Latter <aslat...@gmail.com> wrote: > On Sun, Dec 18, 2011 at 2:57 PM, Alexey Khudyakov > <alexey.sklad...@gmail.com> wrote: >> Hello! >> >> >> I've found a puzzling performance problem with code which uses vector >> library and relies heavily on GHC to perform inlining and >> specialization. In some cases compiler refuses to specialize function >> and just copies there generic version which is slow. >> >> Here is smallest test case I've manages to make: >> > > This is a guess, but based on what I've read the GHC inliner only > fires when the function is fully saturated as declared - so if you > declare a function with one argument to the left of the '=' symbol, > the inliner only then inlines when it is applied to one value. > > This means that the un-inlined function is passed to criterion in the > first case, but not the second. > Yes. That's the case. I've checked the core and indeed in the first case function wasn't inlined.
> Does adding a SPECIALIZE pragma help? > Yes. Since GHC have a optimized version it chooses it. So it looks like that functions which must be inlined (e.g. to eliminate dictionaries) should be written with no parameters > variance = \vec -> G.sum vec This variant gets inlined. Otherwise SPECIALIZE pragma could help. Although it's annoying to write so many pragmas _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
