[GHC] #7206: Implement cheap build

[GHC]

#7206: Implement cheap build
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              Reporter:  simonpj     |            Owner:  simonpj
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  ⊥
             Component:  Compiler    |          Version:  7.4.2
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Another thought.  Regardless of what we do here, it seems likely that GHC
 will sometimes make the wrong choice.  So we should give the programmer a
 way to make the "right" choice.

 Example.  Suppose `[1..10000]` is floated out and shared.  Then we should
 provide `duplicableEnumFromTo 1 10000` which means "please don't try to
 share me; instead fuse me with my consumers, even if that loses sharing".
 OK so you lose the nice notation, but you get to say what you want.

 (And if we switch so that `[1..1000]` is by-default not-shared, then we
 should provide a way force it to be shared: `nonDuplicableEnumFromTo 1
 1000`.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7206#comment:9>
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