Extreme performance degradation on minor code change

The attached code runs two similar calculations (call them a and b) 1000 times. If I calculate a and then b and then do the same 1000 times again the code runs in:

time ./tests/BadPerform 

real    0m40.429s
user    0m40.360s
sys     0m0.054s

If I run a 1000 times, then b 1000 times, the code runs in:

time ./tests/GoodPerform 

real    0m0.083s
user    0m0.081s
sys     0m0.001s

These are the times for ghc 6.6.1. For ghc 6.8.2, the first time reduces to 34s and the second time is identical.

Reproducing this bug is a bit involved: My program links to glpk which in turn uses gmp. Thus, you would have to:

• install GLPK somewhere

• extract the attached sparsePolyhedra-0.1.0 cabal package

• create a local copy of libgmp and libglpk in which all symbols containing gmp are renamed to mygmp

  * cd to sparsePolyhedra-0.1.0

  * in genLibs.sh change the paths containing /users/absint/simona/local/lib to where you installed GMP and GLPK

  * run genLibs.sh which will create local copies of

• in sparsePolyhedra.cabal change the path /users/absint/simona/current/source/sparseDomain to the current directory

• build and register the cabal package

• compile the attached BadPerform.hs and GoodPerform.hs

I guess this is quite complicated. I could send you the IM Core of these two files instead, if that helps.

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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