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Date: Thu, 29 Apr 2010 21:34:06 +0300
Message-ID: <p2o320e992a1004291134i502cec2ap3a6d5c013aa84853@mail.gmail.com>
Subject: min function, why is it so slow?
From: Eray Ozkural <examachine@gmail.com>
To: caml-list@inria.fr
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X-Spam: no; 0.00; eray:01 ozkural:01 inlining:01 ocamlopt:01 -inline:01 inlined:01 util:01 inlining:01 eray:01 ozkural:01 bilkent:01 inline:01 define:02 defined:02 groups:02 

Hello there,

Although I turn on inlining in ocamlopt (-inline 10), I think that the
min function is not quite inlined. Indeed, it's faster if I just
inline it myself (if a<b a then a else b). It's almost twice as fast
this way. Which makes me thinking. I suppose a procedure call cost is
incurred. This doesn't change when I define min for two parameters
myself in another module. What do you think I am doing wrong?


In  the following, the first loop is (more than) twice as slow, where
min is defined as

let min a b = if a <= b then a else b


                      for i=1 to  10000000 do
                        x1 := !x1 + (Util.min a1.(i-1) a1.(i));
                      done

                      for i=1 to  10000000 do
                        x1 := !x1 + (if a1.(i-1) <= a1.(i) then a1.(i-1)
                                      else a1.(i))

Time elapsed: 0.189798 (first loop)
Time elapsed: 0.079624 (second loop)

Can someone please explain to me what's going on here? Perhaps there
is inlining, but after inlining, some optimization passes aren't
performed?

Best,

-- 
Eray Ozkural, PhD candidate.  Comp. Sci. Dept., Bilkent University, Ankara
http://groups.yahoo.com/group/ai-philosophy
http://myspace.com/arizanesil http://myspace.com/malfunct