patch applied (ghc): Improve optimisation of cost centres

[Simon Peyton Jones]

Fri Sep 11 04:56:30 PDT 2009  simonpj at microsoft.com
  * Improve optimisation of cost centres
  Ignore-this: 9964cfe9d39b12eb10724cd1f3fee6b5
  
  This patch fixes test failures for the profiling way for drv001.
  The problem was that the arity of a function was decreasing during
  "optimisation" because of interaction with SCC annotations.
  In particular
        f = /\a. scc "f" (h x)    -- where h had arity 2
  and h gets inlined, led to
        f = /\a. scc "f" let v = scc "f" x in \y. <blah>
  
  Two main changes:
  
  1.  exprIsTrivial now says True for (scc "f" x)
      See Note [SCCs are trivial] in CoreUtils
  
  2.  The simplifier eliminates nested pushing of the same cost centre:
    	scc "f" (...(scc "f" e)...) 
    	==>  scc "f" (...e...)
  
  
  

    M ./compiler/coreSyn/CoreUtils.lhs -7 +12
    M ./compiler/profiling/CostCentre.lhs -1 +8
    M ./compiler/simplCore/Simplify.lhs -1 +4

View patch online:
http://darcs.haskell.org/ghc/_darcs/patches/20090911115630-1287e-df6fb875ff122027b48d9c9cd3e0dab3d9fd85a5.gz