id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
3059	3 different behaviours depending on profiling settings and on a used-only-once form being top-level	jkff		"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."	bug	closed	low	7.0.1	Compiler	6.10.1	invalid			Windows	x86	None/Unknown	Unknown