[GHC] #11222: Teach strictness analysis about `catch`-like operations

[GHC]

#11222: Teach strictness analysis about `catch`-like operations
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        Reporter:  bgamari           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       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):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"9915b6564403a6d17651e9969e9ea5d7d7e78e7f/ghc"
 9915b656/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="9915b6564403a6d17651e9969e9ea5d7d7e78e7f"
 Make demand analysis understand catch

 As Trac #11222, and #10712 note, the strictness analyser
 needs to be rather careful about exceptions.  Previously
 it treated them as identical to divergence, but that
 won't quite do.

 See Note [Exceptions and strictness] in Demand, which
 explains the deal.

 Getting more strictness in 'catch' and friends is a
 very good thing.  Here is the nofib summary, keeping
 only the big ones.

 --------------------------------------------------------------------------------
         Program           Size    Allocs   Runtime   Elapsed  TotalMem
 --------------------------------------------------------------------------------
           fasta          -0.1%     -6.9%     -3.0%     -3.0%     +0.0%
             hpg          -0.1%     -2.0%     -6.2%     -6.2%     +0.0%
        maillist          -0.1%     -0.3%      0.08      0.09     +1.2%
 reverse-complem          -0.1%    -10.9%     -6.0%     -5.9%     +0.0%
          sphere          -0.1%     -4.3%      0.08      0.08     +0.0%
            x2n1          -0.1%     -0.0%      0.00      0.00     +0.0%
 --------------------------------------------------------------------------------
             Min          -0.2%    -10.9%    -17.4%    -17.3%     +0.0%
             Max          -0.0%     +0.0%     +4.3%     +4.4%     +1.2%
  Geometric Mean          -0.1%     -0.3%     -2.9%     -3.0%     +0.0%

 On the way I did quite a bit of refactoring in Demand.hs
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11222#comment:3>
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