[GHC] #15646: ghci takes super long time to find the type of large fractional number

[GHC]

#15646: ghci takes super long time to find the type of large fractional number
-------------------------------------+-------------------------------------
        Reporter:  Johannkokos       |                Owner:
                                     |  JulianLeviston
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  GHCi              |              Version:  8.4.3
      Resolution:                    |             Keywords:  newcomer
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 JulianLeviston):

 Thanks for the direction. Apologies for taking so long to get back; I've
 had the flu.

 `-v3` output is fascinating (thanks, I wasn't aware of it), because
 nothing is marked as slow. I'll look into building a profiled compiler.

 The pause happens immediately before `1e100000000 :: Fractional p => p` is
 output. Here's the output for anyone following along's interest:

 {{{
 Expanse:ghc julian$ ./inplace/bin/ghc-stage2 -v3 -Rghc-timing -e ':t
 1e100000000'
 Glasgow Haskell Compiler, Version 8.7.20181012, stage 2 booted by GHC
 version 8.4.3
 Using binary package database:
 /Users/julian/code/haskell/ghc/inplace/lib/package.conf.d/package.cache
 package flags []
 loading package database
 /Users/julian/code/haskell/ghc/inplace/lib/package.conf.d
 wired-in package ghc-prim mapped to ghc-prim-0.5.3
 wired-in package integer-wired-in mapped to integer-gmp-1.0.2.0
 wired-in package base mapped to base-4.12.0.0
 wired-in package rts mapped to rts
 wired-in package template-haskell mapped to template-haskell-2.14.0.0
 wired-in package ghc mapped to ghc-8.7
 *** Parser [source]:
 !!! Parser [source]: finished in 0.83 milliseconds, allocated 0.489
 megabytes
 *** Desugar:
 *** Simplify [expr]:
 !!! Simplify [expr]: finished in 0.64 milliseconds, allocated 0.367
 megabytes
 *** CorePrep [expr]:
 !!! CorePrep [expr]: finished in 5.45 milliseconds, allocated 5.770
 megabytes
 *** ByteCodeGen [Ghci1]:
 !!! ByteCodeGen [Ghci1]: finished in 0.52 milliseconds, allocated 0.488
 megabytes
 Loading package ghc-prim-0.5.3 ... linking ... done.
 Loading package integer-gmp-1.0.2.0 ... linking ... done.
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name libiconv.dylib
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name liblibiconv.dylib
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name iconv.lib
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name libiconv.lib
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name libiconv.dll.a
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name iconv.dll.a
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name libiconv.a
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name iconv.a
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name libiconv
 *** gcc:
 gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE
 -B/Users/julian/code/haskell/ghc/libraries/base/dist-install/build
 --print-file-name iconv
 Loading package base-4.12.0.0 ... linking ... done.
 Search directories (user):
 Search directories (gcc):
 *** Parser [source]:
 !!! Parser [source]: finished in 0.15 milliseconds, allocated 0.153
 megabytes
 *** Desugar:
 *** Simplify [expr]:
 !!! Simplify [expr]: finished in 0.32 milliseconds, allocated 0.203
 megabytes
 *** CorePrep [expr]:
 !!! CorePrep [expr]: finished in 0.16 milliseconds, allocated 0.112
 megabytes
 *** ByteCodeGen [Ghci1]:
 !!! ByteCodeGen [Ghci1]: finished in 0.31 milliseconds, allocated 0.299
 megabytes
 *** Parser [source]:
 !!! Parser [source]: finished in 0.20 milliseconds, allocated 0.215
 megabytes
 *** Desugar:
 *** Simplify [expr]:
 !!! Simplify [expr]: finished in 0.35 milliseconds, allocated 0.224
 megabytes
 *** CorePrep [expr]:
 !!! CorePrep [expr]: finished in 0.15 milliseconds, allocated 0.089
 megabytes
 *** ByteCodeGen [Ghci1]:
 !!! ByteCodeGen [Ghci1]: finished in 0.36 milliseconds, allocated 0.351
 megabytes
 *** Parser [source]:
 !!! Parser [source]: finished in 0.09 milliseconds, allocated 0.043
 megabytes
 1e100000000 :: Fractional p => p
 Leaving GHCi.
 *** Deleting temp files:
 Deleting:
 *** Deleting temp dirs:
 Deleting:
 <<ghc: 223511272 bytes, 80 GCs, 12572972/49798120 avg/max bytes residency
 (9 samples), 154M in use, 0.000 INIT (0.003 elapsed), 4.102 MUT (4.434
 elapsed), 0.172 GC (0.187 elapsed) :ghc>>
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15646#comment:48>
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