#1179: 20x slow down with -O or -O2
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Reporter: dons | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.6
Severity: normal | Keywords: slow
Difficulty: Unknown | Testcase:
Architecture: Multiple | Os: Linux
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This program:
{{{
http://www.cse.unsw.edu.au/~dons/code/nobench/spectral/calendar/
}}}
Suffers a misoptimisation when compiled with -O or -O2.
When compiled with -Onot:
{{{
serenity$ ghc -Onot --make -o calendar calendar.hs -no-recomp
[1 of 1] Compiling Main ( calendar.hs, calendar.o )
Linking calendar ...
serenity$ time ./calendar 1993 10000 > /dev/null
./calendar 1993 10000 > /dev/null 0.02s user 0.00s system 99% cpu 0.021
total
}}}
When compiled with -O:
{{{
serenity$ ghc -O --make -o calendar calendar.hs -no-recomp
[1 of 1] Compiling Main ( calendar.hs, calendar.o )
Linking calendar ...
serenity$ time ./calendar 1993 10000 > /dev/null
./calendar 1993 10000 > /dev/null 5.00s user 0.01s system 99% cpu 5.011
total
}}}
And with -O2:
{{{
serenity$ time ./calendar 1993 10000 > /dev/null
./calendar 1993 10000 > /dev/null 4.95s user 0.01s system 100% cpu 4.953
total
}}}
Reproduced in amd64 and x86 linux.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1179>
GHC <http://www.haskell.org/ghc/>
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