#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.
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4276>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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