[erlang-questions] dialyzer orelse filter slowness

Nick Conrad <>
Thu Mar 26 09:07:51 CET 2009


Hello,

I've got a module that dialyzer takes more than 15 minutes to analyze,  
and I've narrowed down the cause to a fairly long orelse expression  
that is being used as a filter in a list comprehension.  If I replace  
the orelse expression with a function call and make each individual  
test it's own function, dialyzer is much happier and completes within  
seconds.  Does anyone have an explanation for why dialyzer might take  
so long on the orelse's when used as a filter?

Here's a bit of code that demonstrates the issue, which I've seen  
using both R11B and R12B.

--
-module (test).
-export ([ foo/1 ]).

-ifdef (USE_ORELSE).
-define (bar (F),
         ((F) =:= a orelse
          (F) =:= b orelse
          (F) =:= c orelse
          (F) =:= d orelse
          (F) =:= e orelse
          (F) =:= f orelse
          (F) =:= g orelse
          (F) =:= h orelse
          (F) =:= i orelse
          (F) =:= j orelse
          (F) =:= k)).
-else.
-define (bar, bar_f).
          bar_f (a) -> true;
          bar_f (b) -> true;
          bar_f (c) -> true;
          bar_f (d) -> true;
          bar_f (e) -> true;
          bar_f (f) -> true;
          bar_f (g) -> true;
          bar_f (h) -> true;
          bar_f (i) -> true;
          bar_f (j) -> true;
          bar_f (k) -> true;
          bar_f (_) -> false.
-endif.

foo (List) ->
  [ F || F <- List, ?bar (F)].
--


% dialyzer --no_check_plt --src -c .
  Proceeding with analysis... done in 0m0.23s
done (passed successfully)

% dialyzer -DUSE_ORELSE=1 --no_check_plt --src -c .
  Proceeding with analysis... done in 0m32.24s
done (passed successfully)

Thanks!
- n



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