[GHC] #13001: EnumFromThenTo is is not a good producer

[GHC]

#13001: EnumFromThenTo is is not a good producer
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        Reporter:  George            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  MacOS X           |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by akio):

 > since GHC doesn't know c is strict, it'll allocate a thunk for the
 second argument.

 This is true. I was actually referring to another source of allocation:
 since the call to `c` is under-saturated, evaluating this call involves
 allocating a closure for the partial-application of `c`. This is also the
 case when the final consumer is `foldl'` instead of `length`.

 I think this is a general argument for marking *all* `FB` functions
 `INLINE [0]`. If `p = build pFB` is advertised as a good producer, a user
 would expect `foldl' f z p` to allocate no intermediate data structure.
 However, if `pFB` is not inlined, this expression will necessarily
 allocate a few closures for each eliminated cons cell.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13001#comment:7>
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