It's part of #3440, the compiler optimization metabug: "function-valued argument inlining"
https://github.com/JuliaLang/julia/issues/3440 On Thursday, April 23, 2015 at 9:34:48 AM UTC-5, Mauro wrote: > > Thanks! In that case, I'll file an issue then to get this noted. Also, > I think there is no (general) issue on the bad performance of higher > order functions. Should I file that too? > > On Thu, 2015-04-23 at 15:52, Jameson Nash <vtjn...@gmail.com> wrote: > > The short answer is that there is a certain set of optimizations that > have > > been implemented in Julia, but still a considerable set that has not > been > > implemented. This falls into the category of optimizations that have not > > been implemented. Pull requests are always welcome (although I do not > > recommend this one as a good beginner / "up-for-grabs" issue). > > > > On Thu, Apr 23, 2015 at 9:18 AM Mauro <mauro...@runbox.com> wrote: > > > >> It is well know that Julia struggles with type inference in higher > order > >> functions. This usually leads to slow code and memory allocations. > >> There are a few hacks to work around this. Anyway, the question I have > >> is: Why can't Julia do better with in-place functions? > >> > >> In short, a higher-order function like this: > >> > >> function f(fn!,ar) > >> for i=1:n > >> fn!(ar, i) # fn! updates ar[i] somehow, returns nothing > >> nothing # to make sure output of f is discarded > >> end > >> end > >> > >> has almost as bad a performance (runtime and allocation-wise) as > >> > >> function g(fn,ar) > >> for i=1:n > >> ar[i] = fn(ar[i]) > >> end > >> end > >> > >> A in-depth, ready to run example is here: > >> https://gist.github.com/mauro3/f17da10247b0bad96f1a > >> Including output of @code_warntype. > >> > >> So, why is Julia allocating memory when running f? Nothing of f gets > >> assigned to anything. > >> > >> Would this be something which is fixable more easily than the whole of > >> the higher-order performance issues? If so, is there an issue for > this? > >> > >> Having good in-place higher order functions would go a long way with > >> numerical computations. Thanks! > >> > >
