[GHC] #14052: Significant GHCi speed regression with :module and `let` in GHC 8.2.1

[GHC]

#14052: Significant GHCi speed regression with :module and `let` in GHC 8.2.1
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        Reporter:  RyanGlScott       |                Owner:  osa1
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.2
       Component:  GHCi              |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11547            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 > I think regardless of the performance problems, #11547 (​Phab:D2447)
 should just be reverted.

 Reviewing this, I agree with you.  I see that in my original review of
 Phab:D2447 I wrote "I don't think I fully understand all the consequences,
 but I don't want to stand in the way".  This ticket shows some bad
 consequences.  And I don't think anyone is actively arguing for access to
 previously in-scope versions of `x`.

 It'd be polite to tell the original author of the patch
 ([https://phabricator.haskell.org/p/mniip/ mniip] I believe), in case he
 has reasons for wanting (some revised version of) his patch.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14052#comment:17>
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