#12743: Profiling wrongly attributes allocations to a function with Int# result -------------------------------------+------------------------------------- Reporter: | Owner: MikolajKonarski | Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Profiling can't decide whether the given function allocates or not at all. The code snippet says it all: {{{ {-# LANGUAGE MagicHash #-} import GHC.Exts -- ghc -prof --make bork.hs -fprof-auto -O1 -- ./bork +RTS -s -P -RTS main = do let f :: Int -> Int# -- {-# NOINLINE f #-} f x = case x `div` 17 of I# i -> i -- {-# NOINLINE g #-} g h = sum $ map (\y -> I# (h y)) [0..1000000] g f `seq` return () -- COST CENTRE MODULE %time %alloc ticks bytes -- main.g Main 73.6 93.3 159 224000328 -- main.f Main 24.1 6.7 52 16000016 -- main.g.\ Main 2.3 0.0 5 0 -- When either of the NOINLINE is enabled, the profile becomes: -- COST CENTRE MODULE %time %alloc ticks bytes -- main.g Main 72.9 93.3 161 224000328 -- main.f Main 16.7 0.0 37 0 -- main.g.\ Main 10.4 6.7 23 16000016 -- So, does f actually allocate or not? -- Profiling is quite a bit less useful if it can't answer that reliably, -- because in larger code snippets it's hard to decide from source -- or from Core/STG. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12743 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler