#9349: excessive inlining with -fpre-inlining -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: Runtime | Blocked By: performance bug | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by klao): Here's a simplified example for this bug: {{{ import Control.Monad import Control.Concurrent.MVar expensive :: Int -> Int -> Int expensive n0 a = go n0 a where go 0 x = x go n x = go (n-1) ((x * 37 + 1973) `rem` 177) main :: IO () main = do mv <- newMVar (10 :: Int) let ex = expensive 100000 3 replicateM_ 30000 $ do x <- readMVar mv print $ x + ex }}} You could probably simplify it further. The important thing is that `ex` is the result of some expensive computation that incorrectly gets evaluated over and over again. And you have to put some "real" IO into the `replicateM_` for the bug to kick in (in the original example it was reading from the stdin, here I just read an MVar). Unlike the original example, here marking `ex` as `NOINLINE` does make the issue disappear. (Otherwise it's the same as the original example: nearly instantaneous with `-O0` or `-O -fno-pre-inlining`, but takes a looong time with `-O`.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9349#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler