[GHC] #12354: Word foldl' isn't optimized as well as Int foldl'

[GHC]

#12354: Word foldl' isn't optimized as well as Int foldl'
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        Reporter:  kjslag            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 >  it turns out that Word’s enumFromTo is never inlined, so this setup has
 no chance of fusing here

 So the short term solution is to add an INLINE for Word's `enumFromTo`?

 > Where does it stop?

 Well you might hope that you could write `eftInt`, `eftIntFB` once, at
 type `a` and SPECIALISE them.  That would save copying them manually.

 Writing rewrite rules that also specialise is something I have not thought
 much about though.  I suppose that, conceivably, all the fusion could
 happen generically (i.e. on the class-overloaded functions), before we
 specialise to the particular type.  To achieve that, we'd have to delay
 the class-op selection e.g.  `eunmFrom dEnumInt` --> `enumFrom_Int`.  But
 that ought to be possible.

 A good project here.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12354#comment:2>
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