[GHC] #13536: Program which terminates instantly in GHC 8.0.2 runs for minutes with 8.2.1

[GHC]

#13536: Program which terminates instantly in GHC 8.0.2 runs for minutes with 8.2.1
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      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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Changes (by simonpj):

 * cc: nomeata (added)


Comment:

 > The culprit is apparently the new STG CSE pass

 Ah yes!  We very carefully run a final demand-analysis just before tidy-
 core, precisely to ensure that the used-once info (which can get
 invalidated) is correct before code gen. But the STG CSE pass is undoing
 that goodness.  Total disaster.

 I'll think about how best to do this.  Copying Joachim who added CSE for
 STG>

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13536#comment:11>
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