[GHC] #10148: Optimization causes repeated computation

[GHC]

#10148: Optimization causes repeated computation
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        Reporter:  akio              |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1-rc1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"9f0f99fd41ff82cc223d3b682703e508efb564d2/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="9f0f99fd41ff82cc223d3b682703e508efb564d2"
 Fix a long-standing bug in the demand analyser

 This patch fixes Trac #10148, an outright and egregious
 bug in the demand analyser.

 It is explained in Note [Demand on case-alternative binders]
 in Demand.hs.

 I did some other minor refactoring.

 To my astonishment I got some big compiler perf changes

 * perf/compiler/T5837: bytes allocated -76%
 * perf/compiler/T5030: bytes allocated -10%
 * perf/compiler/T3294: max bytes used  -25%

 Happy days
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10148#comment:10>
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