[GHC] #13025: Type family reduction irregularity (change from 7.10.3 to 8.0.1)

[GHC]

#13025: Type family reduction irregularity (change from 7.10.3 to 8.0.1)
-------------------------------------+-------------------------------------
        Reporter:  acowley           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeFamilies
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:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 There does appear to be a difference in the `bench-builder-all` benchmark
 suite. The full results are available at
 https://gist.github.com/RyanGlScott/386da12bc71fd2fadae2362b257c41bc. The
 most noticeable differences come in the `vinyl` and `vinyl-plus`
 benchmarks. On GHC HEAD, I get:

 {{{
 benchmarking vinyl
 time                 106.9 µs   (106.7 µs .. 107.0 µs)
                      1.000 R²   (1.000 R² .. 1.000 R²)
 mean                 106.7 µs   (106.5 µs .. 106.9 µs)
 std dev              653.4 ns   (506.9 ns .. 847.7 ns)

 benchmarking vinyl-lens
 time                 83.98 µs   (83.97 µs .. 84.00 µs)
                      1.000 R²   (1.000 R² .. 1.000 R²)
 mean                 83.97 µs   (83.96 µs .. 83.98 µs)
 std dev              40.09 ns   (33.48 ns .. 47.87 ns)
 }}}

 After reverting 1722fa106e10e63160bb2322e2ccb830fd5b9ab3, you get:

 {{{
 benchmarking vinyl
 time                 62.27 µs   (62.25 µs .. 62.28 µs)
                      1.000 R²   (1.000 R² .. 1.000 R²)
 mean                 62.28 µs   (62.26 µs .. 62.30 µs)
 std dev              58.65 ns   (47.95 ns .. 71.78 ns)

 benchmarking vinyl-lens
 time                 62.07 µs   (62.01 µs .. 62.13 µs)
                      1.000 R²   (1.000 R² .. 1.000 R²)
 mean                 62.02 µs   (61.98 µs .. 62.05 µs)
 std dev              122.0 ns   (106.2 ns .. 144.8 ns)
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13025#comment:8>
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