[GHC] #10260: last uses too much space with optimizations disabled

[GHC]

#10260: last uses too much space with optimizations disabled
-------------------------------------+-------------------------------------
        Reporter:  rwbarton          |                   Owner:  nomeata
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:
       Component:  Core Libraries    |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D844
-------------------------------------+-------------------------------------

Comment (by nomeata):

 `INLINEABLE` does not work; probably because the unfolding looks too
 large. But `INLINE` seems to work. So with this patch
 {{{
 -last = foldl (\_ x -> x) (errorEmptyList "last")
 +last xs = foldl (\_ x -> x) lastError xs
 +{-# INLINE last #-}
 +lastError = errorEmptyList "last"
 }}}
 we have
  * that `GHC.List.last` is used without `-O`, with the desired memory
 behaviour,
  * with `-O`, `last` gets inlined and fusion can happen.

 (`lastError` pulled out to not copy that wherever `last` is used).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10260#comment:7>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler