#3059: 3 different behaviours depending on profiling settings and on a
used-only-
once form being top-level
--------------------+-------------------------------------------------------
Reporter: jkff | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.10.1 | Severity: normal
Keywords: | Testcase:
Os: Windows | Architecture: x86
--------------------+-------------------------------------------------------
Below are two versions of a program using regex-tdfa-1.0.
The versions differ in whether a form that is used exactly once in 'main'
is top-level or declared inside 'where' in main.
Both versions are compiled with/without profiling and the profiled version
is called with/without +RTS -p.
I obtain three drastically different performance results and, in the case
where the form is top-level and profiling is turned on, a compilation bug
is clearly seen.
{{{
module Main where
import Text.Regex.TDFA
import qualified Data.ByteString.Lazy.Char8 as L
import qualified Data.ByteString.Char8 as S
main = putStrLn . show . length . filter (pat . S.concat . L.toChunks) .
replicate 100000 $ L.pack "Hello world foo=123 whereas bar=456 Goodbye"
pat = (=~ ".*foo=([0-9]+).*bar=([0-9]+).*")
ghc -O2 --make regex-test.hs
./regex-test +RTS -s
0.00s
ghc -O2 --make -prof -auto-all regex-test.hs
./regex-test +RTS -s
265.31s
./regex-test +RTS -p
276.84s
'compile' is called 100000 times.
module Main where
import Text.Regex.TDFA
import qualified Data.ByteString.Lazy.Char8 as L
import qualified Data.ByteString.Char8 as S
main = putStrLn . show . length . filter (pat . S.concat . L.toChunks) .
replicate 100000 $ L.pack "Hello world foo=123 whereas bar=456 Goodbye"
where pat = (=~ ".*foo=([0-9]+).*bar=([0-9]+).*")
ghc -O2 --make regex-test.hs
./regex-test +RTS -s
8.86s
(I don't know how this result appeared: it is too small to result from
1mln regex compilations, but too big to be 'normal')
ghc -O2 --make -prof -auto-all regex-test.hs
./regex-test +RTS -s
0.00s
./regex-test +RTS -p
0.00s
'compile' is called 2 times.
}}}
Core for the first program with/without profiling differs in the aspect
that with profiling, the partial application (=~) does not get memoized.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3059>
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