[GHC] #15703: Significant compilation time blowup when refactoring singletons-heavy code

[GHC]

#15703: Significant compilation time blowup when refactoring singletons-heavy code
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:
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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Comment (by RyanGlScott):

 I attached the results of compiling `Lib.hs` with `-dshow-passes` enabled.
 Of particular note is:

 {{{
 Result size of Float out(FOS {Lam = Just 0,
                               Consts = True,
                               OverSatApps = False})
   = {terms: 950, types: 14,499, coercions: 83,275, joins: 0/12}
 !!! Float out(FOS {Lam = Just 0,
                    Consts = True,
                    OverSatApps = False}) [Lib]: finished in 28.01
 milliseconds, allocated 19.390 megabytes
 *** Simplifier [Lib]:
 Result size of Simplifier iteration=1
   = {terms: 924, types: 12,141, coercions: 235,672, joins: 0/46}
 Result size of Simplifier iteration=2
   = {terms: 755, types: 5,948, coercions: 312,927, joins: 0/17}
 Result size of Simplifier iteration=3
   = {terms: 715, types: 3,828, coercions: 403,226, joins: 0/2}
 Result size of Simplifier
   = {terms: 703, types: 3,759, coercions: 228,342, joins: 0/2}
 !!! Simplifier [Lib]: finished in 208488.74 milliseconds, allocated
 373891.763 megabytes
 *** Simplifier [Lib]:
 Result size of Simplifier
   = {terms: 703, types: 3,759, coercions: 228,342, joins: 0/2}
 }}}

 The number of coercions appears to jump between float-out and the first
 simplifier pass. However, it's a later simplifier pass that takes up the
 bulk of the time (208488.74 milliseconds of it).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15703#comment:3>
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