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

[GHC]

#15703: Significant compilation time blowup when refactoring singletons-heavy code
-------------------------------------+-------------------------------------
        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 built this code using a profiled GHC 8.6.1. Here are the highlights:

 {{{
         Wed Oct  3 22:18 2018 Time and Allocation Profiling Report
 (Final)

            ghc-stage2 +RTS -p -RTS -B/u/rgscott/Software/ghc4/inplace/lib
 -O1 -fforce-recomp Lib.hs

         total time  =      276.05 secs   (276053 ticks @ 1000 us, 1
 processor)
         total alloc = 403,405,509,720 bytes  (excludes profiling
 overheads)

 COST CENTRE             MODULE   SRC
 %time %alloc

 simplCast-simplCoercion Simplify compiler/simplCore/Simplify.hs:1248:57-77
 75.8   76.8
 substTyWith             TyCoRep
 compiler/types/TyCoRep.hs:(2213,23)-(2214,50)   23.8   23.0
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15703#comment:2>
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