[GHC] #13220: Performance regressions in testsuite from join points

[GHC]

#13220: Performance regressions in testsuite from join points
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        Reporter:  lukemaurer        |                Owner:  lukemaurer
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 I now believe the culprit is this added line in originally `lintCoreVar`,
 now `lintVarOcc`:
 {{{#!diff
 +        ; ensureEqTys ty ty' $ mkBndrOccTypeMismatchMsg var' var ty' ty
 }}}
 Reasoning: `perf` showed that when running with `-dcore-lint`, the single
 function that takes the most time after the garbage collector is
 `nonDetCmpTypeX_go`. Before the join points patch, it took 6.5% of the
 total time. After, it took 9.1% of the total time. And there seems to be
 nothing that corresponds to this `ensureEqTys` call before the join points
 patch.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13220#comment:25>
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