[GHC] #4276: -O0 runs in constant space, -O1 and -O2 don't

[GHC]

#4276: -O0 runs in constant space, -O1 and -O2 don't
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    Reporter:  guest    |       Owner:                         
        Type:  bug      |      Status:  new                    
    Priority:  normal   |   Component:  Compiler               
     Version:  6.12.1   |    Keywords:  optimization space leak
    Testcase:           |   Blockedby:                         
          Os:  Windows  |    Blocking:                         
Architecture:  x86      |     Failure:  Runtime performance bug
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 Enabling optimization changes the space complexity of this small program,
 which seems like a bug.  Run the attached program with command line
 argument equal to 22 or greater.

 Description of the program: given a real valued function f, compute the
 sum f(x_i) over an increasingly finer and finer mesh of sample points.
 If the new mesh shares points with the old mesh this can be computed
 somewhat more efficiently by reusing the previous sum.

 Looking at the Time and Allocation report, it seems like the optimized
 versions of the program are actually computing the sum 2 ** n times
 instead of n times.  This is probably related to what is causing the space
 behavior.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4276>
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