[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:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       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:  #7206             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"bb338f2eb706a3137bf6675e3ddbf96d4fe4f4aa/ghc" bb338f2/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="bb338f2eb706a3137bf6675e3ddbf96d4fe4f4aa"
 Algebraically simplify add/sub with carry/overflow

 Previously, the `{add,sub}{Int,Word}C#` PrimOps weren't handled
 in PrelRules (constant folding and algebraic simplification) at all.
 This implements the necessary logic, so that using these primitives
 isn't too punishing compared to their well-optimised, overflow-unaware
 counterparts.

 This is so that using these primitives in `enumFromThenTo @Int` can
 be optimized by constant folding, reducing closure sizes.

 Reviewers: bgamari, simonpj, hsyl20

 Reviewed By: bgamari, simonpj

 Subscribers: AndreasK, thomie, carter

 GHC Trac Issues: #8763

 Differential Revision: https://phabricator.haskell.org/D4605
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:65>
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