Am Mittwoch 03 Februar 2010 16:44:31 schrieb Serge D. Mechveliani:
Dear GHC team,
It looks like ghc-6.12.1 reports erroneous time profiling -- when the Main module of the project is made under -O.
This is for ghc-6.12.1 made from source for Debian Linux and i386-like.
Main.main calls for Complete.complete, `complete' calls for eLoop inside its source. eLoop must take almost all the time. My whole user library is made under -O -prof, and --enable-library-profiling. Main is compiled by ghc $dmCpOpt -prof --make Main and run by ./Main +RTS -M400m -pT -RTS For this key, the profiling report Main.prof looks natural and shows eLoop -- 97%.
But for ghc $dmCpOpt -O -prof --make Make,
it shows a different thing: zero for eLoop and 99% for `main'.
Could be that eLoop is inlined with -O. Try ghc $dmCpOpt -O -prof -auto-all --make That should show eLoop (if that's a top-level declaration, otherwise you'd have to insert a pragma {-# SCC "eLoop" #-} manually).
How could this additional -O mislead the compiler? Also, as I recall, -O is still by default -- ?
No, default is "comile as fast as possible", no optimisations (-O0).
Could you explain, please?
Regards,
----------------- Serge Mechveliani mechvel@botik.ru