[GHC] #2552: SCC annotation behavior differs between toplevel and non-toplevel

[GHC]

#2552: SCC annotation behavior differs between toplevel and non-toplevel
------------------------------+---------------------------------------------
    Reporter:  Rauli          |       Owner:          
        Type:  bug            |      Status:  new     
    Priority:  normal         |   Component:  Compiler
     Version:  6.8.2          |    Severity:  normal  
    Keywords:  scc profiling  |    Testcase:          
Architecture:  x86            |          Os:  Linux   
------------------------------+---------------------------------------------
 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.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2552>
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