3 different behaviours depending on profiling settings and on a used-only-once form being top-level

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.

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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