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I'm not sure if this is a bug, but using ghc -prof -auto-all and manual SCC annotations for non-toplevel functions produces very different results from moving the same function to toplevel:

fib n = nfib' n
  where
    nfib' n = {-# SCC "nfib'" #-} nfib n -- %time: 0 (both individual and inherited)
      where
        nfib n = if n < 2 then 1 else nfib (n-1) + nfib (n-2)

fib n = nfib' n
nfib' n = nfib n -- %time: 100 (both individual and inherited)
  where
    nfib n = if n < 2 then 1 else nfib (n-1) + nfib (n-2)

This happens with both -O0 and -O2, even when these functions are not exported. Adding a NOINLINE for nfib' doesn't change anything.

Computing the correct inherited time for the SCC would be useful to pinpoint the cost centres inside a more complex function. Currently one needs to move them to toplevel to get the same effect. Given that the toplevel route works, it's also counterintuitive that manual SCC annotations don't.

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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