[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:                    |
-------------------------------------+-------------------------------------

Comment (by tdammers):

 Replying to [comment:55 simonpj]:
 > Do you have allocation numbers for these runs?
 >
 > The mysterious thing is that `NthCo` caching makes things slightly
 worse.   Of course the `NthCo` constructors have an extra field, but I'm
 still quite surprised that's a visible worsening.   So I think it might be
 worth a little more digging into the worsening in `8ac966971e`, really
 just to discover if we have accidentally left money on the table.

 Yes, of course.

 This is `8ac966971e`:

 {{{
         Tue Jan 30 11:25 2018 Time and Allocation Profiling Report
 (Final)

            ghc-stage2 +RTS -p -RTS -B/home/tobias/well-
 typed/devel/ghc/inplace/lib ./cases/Grammar.hs -o ./a -fforce-recomp

         total time  =       12.87 secs   (12865 ticks @ 1000 us, 1
 processor)
         total alloc = 14,385,409,080 bytes  (excludes profiling overheads)

 COST CENTRE             MODULE     SRC
 %time %alloc

 simplCast               Simplify
 compiler/simplCore/Simplify.hs:871:62-87             33.7   32.4
 addCoerce-pushCoTyArg   Simplify
 compiler/simplCore/Simplify.hs:(1236,12)-(1237,72)   13.1   13.1
 tc_rn_src_decls         TcRnDriver
 compiler/typecheck/TcRnDriver.hs:(494,4)-(556,7)     12.3   14.0
 subst_ty                TyCoRep    compiler/types/TyCoRep.hs:2237:28-32
 6.7   10.4
 CoreTidy                HscMain    compiler/main/HscMain.hs:1253:27-67
 4.4    3.9
 coercionKind            Coercion   compiler/types/Coercion.hs:1725:3-7
 2.6    6.0
 zonkTopDecls            TcRnDriver
 compiler/typecheck/TcRnDriver.hs:(445,16)-(446,43)    2.0    2.2
 load'.checkHowMuch      GhcMake
 compiler/main/GhcMake.hs:(270,9)-(272,27)             2.0    0.0
 simplCast-simplCoercion Simplify
 compiler/simplCore/Simplify.hs:1224:57-77             1.6    1.5
 simplExprF1-Lam         Simplify   compiler/simplCore/Simplify.hs:896:5-39
 1.6    2.2
 deSugar                 HscMain    compiler/main/HscMain.hs:511:7-44
 1.5    1.3
 simplCast-addCoerce     Simplify
 compiler/simplCore/Simplify.hs:1225:53-71             1.4    1.3
 tcRnImports             TcRnDriver
 compiler/typecheck/TcRnDriver.hs:240:20-50            1.0    0.1
 Parser                  HscMain
 compiler/main/HscMain.hs:(316,5)-(384,20)             0.9    1.6
 }}}

 Which isn't actually significantly worse than `4eb140f564`:

 {{{
         Tue Jan 30 11:45 2018 Time and Allocation Profiling Report
 (Final)

            ghc-stage2 +RTS -p -RTS -B/home/tobias/well-
 typed/devel/ghc/inplace/lib ./cases/Grammar.hs -o ./a -fforce-recomp

         total time  =       12.38 secs   (12380 ticks @ 1000 us, 1
 processor)
         total alloc = 14,385,403,880 bytes  (excludes profiling overheads)

 COST CENTRE             MODULE     SRC
 %time %alloc

 simplCast               Simplify
 compiler/simplCore/Simplify.hs:871:62-87             34.3   32.4
 addCoerce-pushCoTyArg   Simplify
 compiler/simplCore/Simplify.hs:(1236,12)-(1237,72)   13.3   13.1
 tc_rn_src_decls         TcRnDriver
 compiler/typecheck/TcRnDriver.hs:(494,4)-(556,7)     12.7   14.0
 subst_ty                TyCoRep    compiler/types/TyCoRep.hs:2225:28-32
 7.0   10.4
 CoreTidy                HscMain    compiler/main/HscMain.hs:1253:27-67
 4.5    3.9
 coercionKind            Coercion   compiler/types/Coercion.hs:1707:3-7
 2.9    6.0
 zonkTopDecls            TcRnDriver
 compiler/typecheck/TcRnDriver.hs:(445,16)-(446,43)    2.0    2.2
 simplExprF1-Lam         Simplify   compiler/simplCore/Simplify.hs:896:5-39
 1.8    2.2
 simplCast-simplCoercion Simplify
 compiler/simplCore/Simplify.hs:1224:57-77             1.7    1.5
 deSugar                 HscMain    compiler/main/HscMain.hs:511:7-44
 1.6    1.3
 simplCast-addCoerce     Simplify
 compiler/simplCore/Simplify.hs:1225:53-71             1.4    1.3
 simplIdF                Simplify
 compiler/simplCore/Simplify.hs:868:61-79              1.0    0.5
 Parser                  HscMain
 compiler/main/HscMain.hs:(316,5)-(384,20)             1.0    1.6
 }}}

 This is only about 4% more execution time, and 0.000035% more allocations.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:57>
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