[GHC] #9291: Don't reconstruct sum types if the type subtly changes

[GHC]

#9291: Don't reconstruct sum types if the type subtly changes
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        Reporter:  schyler           |                Owner:  nomeata
            Type:  feature request   |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.8.2
      Resolution:  fixed             |             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:D2871
       Wiki Page:                    |
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Comment (by heisenbug):

 Replying to [comment:42 Joachim Breitner <mail@…>]:
 > In [changeset:"19d5c7312bf0ad9ae764168132aecf3696d5410b/ghc"
 19d5c73/ghc]:
 > {{{
 > #!CommitTicketReference repository="ghc"
 revision="19d5c7312bf0ad9ae764168132aecf3696d5410b"
 > Add a CSE pass to Stg (#9291)
 >
 > ...
 >
 > Introduces the flag -fstg-cse, enabled by default with -O for now. It
 > might also be a good candidate for -O2.

 Will you revisit the `-O2` inclusion sometime later? /me was always under
 the impression that all performance-increasing optimisations from `-O`
 would be included in `-O2`.

 >
 > Differential Revision: https://phabricator.haskell.org/D2871
 > }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9291#comment:44>
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