[GHC] #11735: Optimize coercionKind

[GHC]

#11735: Optimize coercionKind
-------------------------------------+-------------------------------------
        Reporter:  goldfire          |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      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 tdammers):

 Replying to [comment:43 goldfire]:
 > OK. I've fixed a few testsuite failures. I think this is probably
 correct now. (CircleCI reports a bunch of errors in `profiling`, but I
 can't repro locally.)
 >
 > What happens when you benchmark?

 Curiously, the latest version clocks in at about 25 seconds for
 Grammar.hs, so almost as fast, but not quite, as the fastest we've seen so
 far (~21 seconds):

 {{{
         Mon Jan 29 09:43 2018 Time and Allocation Profiling Report
 (Final)

            ghc-stage2 +RTS -p -RTS -B/home/tobias/well-
 typed/devel/ghc/inplace/lib Grammar.hs -ddump-stg -ddump-simpl -ddump-to-
 file -fforce-recomp

         total time  =       25.95 secs   (25950 ticks @ 1000 us, 1
 processor)
         total alloc = 33,815,717,032 bytes  (excludes profiling overheads)

 COST CENTRE           MODULE     SRC
 %time %alloc

 simplCast             Simplify   compiler/simplCore/Simplify.hs:871:62-87
 26.0   21.8
 CoreTidy              HscMain    compiler/main/HscMain.hs:1253:27-67
 19.9   24.7
 Stg2Stg               HscMain    compiler/main/HscMain.hs:1489:12-44
 17.6   20.9
 addCoerce-pushCoTyArg Simplify
 compiler/simplCore/Simplify.hs:(1251,12)-(1254,36)   10.5    9.0
 tc_rn_src_decls       TcRnDriver
 compiler/typecheck/TcRnDriver.hs:(494,4)-(556,7)      7.3    6.0
 subst_ty              TyCoRep    compiler/types/TyCoRep.hs:2240:28-32
 3.5    4.4
 coercionKind          Coercion   compiler/types/Coercion.hs:1711:3-7
 2.1    4.6
 zonkTopDecls          TcRnDriver
 compiler/typecheck/TcRnDriver.hs:(445,16)-(446,43)    1.1    0.9
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:44>
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