[GHC] #8763: forM_ [1..N] does not get fused (10 times slower than go function)

[GHC]

#8763: forM_ [1..N] does not get fused (10 times slower than go function)
-------------------------------------+-------------------------------------
        Reporter:  nh2               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.6.3
      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:                    |
-------------------------------------+-------------------------------------

Comment (by akio):

 Here is a test case that does not require criterion. With `ghc-8.0.1 -O2
 -ddump-simpl`, you can see that `foo` is compiled into code that uses a
 top-level CAF containing `GHC.Enum.eftInt 0# 799#`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:27>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler