GHC compiled program slower with -O1 than -O0
simonpj at microsoft.com
Mon Mar 19 11:25:10 EDT 2007
| I've written a Haskell program which goes slower with -O1 (19 seconds)
| than -O0 (12 seconds). Is this considered to be a bug? How interested
| are you in tracking this down?
Yes, very interested. Should not happen.
One thing to check is heap usage and GC time. Does GC time, or residency (both reported by -Sstderr) go up a lot? It's possible that an optimisation is changing space behaviour for the worse.
Does it still happen if you use profiling? If so, the profile should narrow down the culprit a lot. That might avoid the need to reproduce it elsewhere.
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