[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)
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        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:                    |
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Comment (by nh2):

 Replying to [comment:30 simonpj]:
 > Real programs usually depend on input data.  So this probem may be less
 of a probem in practice than in benchmarks.

 Just wanted to chime in that I found this problem in a real-world program,
 where I looped over all 32-bit integers. Similarly, these known-at-
 compile-time iteration lists may appear in inner loops of algorithms or
 data structures (like B-trees with fixed B, or image convolution kernels
 with fixed size, e.g. 3x3 image templates).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:31>
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