[GHC] #11196: TypeInType performance regressions

[GHC]

#11196: TypeInType performance regressions
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.2
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by thomie):

 * failure:  None/Unknown => Compile-time performance bug


@@ -12,1 +12,1 @@
-   * T9872d, '''down''' by 91.8%  (see below)
+   * T9872d, '''down''' by 22%  (see below)

New description:

 This ticket is to track the handful of performance regressions seen with
 the addition of `TypeInType`. It is quite possibly a good idea to break
 these out into separate tickets, but until we investigate, they're all
 bundled here.

 The regressions are (all in bytes allocated, unless otherwise noted):
   * T3064, up by 14.9%
   * T5030, up by 61.8%
   * T5837, up by 13%
   * T5321Fun, up by 11%
   * T5631, up by 39%
   * T9872d, '''down''' by 22%  (see below)
   * T9872a, up by 33.6%
   * T9872c, up by 59.4%
   * T9872b, up by 49.4%
   * T9675, up by 29.7%, and peak megabytes allocated up by 28.4%
   * haddock.base, up by 12.4%
   * haddock.Cabal, up by 9.5%

 I did add an optimization around type family reduction (the function
 `zonk_eq_types` in !TcCanonical) that could cause such a drastic
 reduction.

--

Comment:

 For the record: T9872d went down by 22% (the description first claimed
 92%, which probably resulted from a typo), from 726679784 to 566134504
 bytes allocated. Since then it has dropped another 8% to 506691240
 (64-bit).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11196#comment:16>
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