Profiling wrongly attributes allocations to a function with Int# result

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.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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