[GHC] #11710: Fusion of a simple listArray call is very fragile

[GHC]

#11710: Fusion of a simple listArray call is very fragile
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.3
      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):  Phab:D2023
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"0db05941668814094c2b18b3d35e1deaed36c210/ghc"
 0db05941/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="0db05941668814094c2b18b3d35e1deaed36c210"
 DsExpr: Rip out static/dynamic check in list desugaring

 Previously we would try to break explicit lists into a dynamic prefix
 and static tail and desugar the former into a `build` expression.
 Unfortunately, this heuristic resulted in surprising behavior
 (see #11710) and wasn't pulling its weight. Here we drop it (along with
 the `-fsimple-list-literals` flag), leaving only the list length
 heuristic to determine whether `build` or cons list desugaring should be
 used.

 Test Plan: Validate

 Reviewers: simonpj, austin

 Reviewed By: simonpj

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2023

 GHC Trac Issues: #11710
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11710#comment:7>
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