[GHC] #9434: GHC.List.reverse does not fuse

[GHC]

#9434: GHC.List.reverse does not fuse
-------------------------------------+-------------------------------------
              Reporter:  dfeuer      |            Owner:
                  Type:  bug         |           Status:  patch
              Priority:  normal      |        Milestone:
             Component:              |          Version:  7.9
  libraries/base                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:  Runtime     |       Blocked By:
  performance bug                    |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by dfeuer):

 Replying to [comment:4 simonpj]:
 > That looks helpful.  But allocation probably should never go up.  Do you
 know why it does so in constraints?
 >
 > I use `-ticky` a lot to track down these kind of things.
 >
 > Simon

 I don't know how to use `-ticky` yet. How would I get nofib compiled with
 that? My best guess about constraints is that it's all about the evil
 spirit in the machine, by which I mean the inliner. One phenomenon I saw
 in some of my little tests was that inlining thresholds make things rather
 less compositional than one might like. That is, if `f x = ... g ...` and
 `g y = ... h ...`, then inlining `h` can make `g` "too big", so then `g`
 won't be inlined in `f` unless someone leans on the compiler to do so. My
 bet is that something that calls reverse is not being inlined as a result,
 and therefore some other optimization opportunity is missed.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9434#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler