[GHC] #14663: Deriving Typeable for enumerations seems expensive

11 Jan 2018

      #14663: Deriving Typeable for enumerations seems expensive
-------------------------------------+-------------------------------------
           Reporter:  niteria        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I have a module `A10000` that looks like this:
 {{{
 module A10000 where

 data A = A
   | A00001
   | A00002
 ...
   | A10000
 }}}

 Currently compiling it with `./inplace/bin/ghc-stage2 A10000.hs +RTS -s`
 produces:
 {{{
 [1 of 1] Compiling A10000           ( A10000.hs, A10000.o )
    4,133,470,392 bytes allocated in the heap
    1,194,866,080 bytes copied during GC
      141,604,816 bytes maximum residency (14 sample(s))
          813,104 bytes maximum slop
              341 MB total memory in use (0 MB lost due to fragmentation)

                                      Tot time (elapsed)  Avg pause  Max
 pause
   Gen  0       329 colls,     0 par    0.551s   0.551s     0.0017s
 0.0246s
   Gen  1        14 colls,     0 par    0.453s   0.453s     0.0323s
 0.1031s

   TASKS: 4 (1 bound, 3 peak workers (3 total), using -N1)

   SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

   INIT    time    0.000s  (  0.000s elapsed)
   MUT     time    1.498s  (  1.730s elapsed)
   GC      time    1.004s  (  1.004s elapsed)
   EXIT    time    0.000s  (  0.006s elapsed)
   Total   time    2.502s  (  2.740s elapsed)

   Alloc rate    2,759,911,143 bytes per MUT second

   Productivity  59.9% of total user, 63.4% of total elapsed
 }}}

 I've noticed a lot of code getting generated (>500k lines of ASM),
 particularly interesting was code that supported `TyCon`s.

 I've tried again disabling the generation of `TyCon`s by modifying:
 {{{
 mkTypeRepTodoBinds :: [TypeRepTodo] -> TcM TcGblEnv
 mkTypeRepTodoBinds _ = getGblEnv
 }}}

 This is the result:
 {{{
 [1 of 1] Compiling A10000           ( A10000.hs, A10000.o )
    1,731,693,280 bytes allocated in the heap
      280,362,376 bytes copied during GC
       41,423,608 bytes maximum residency (10 sample(s))
          746,272 bytes maximum slop
              102 MB total memory in use (0 MB lost due to fragmentation)

                                      Tot time (elapsed)  Avg pause  Max
 pause
   Gen  0       401 colls,     0 par    0.111s   0.111s     0.0003s
 0.0065s
   Gen  1        10 colls,     0 par    0.124s   0.124s     0.0124s
 0.0298s

   TASKS: 4 (1 bound, 3 peak workers (3 total), using -N1)

   SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

   INIT    time    0.000s  (  0.000s elapsed)
   MUT     time    0.773s  (  0.889s elapsed)
   GC      time    0.235s  (  0.235s elapsed)
   EXIT    time    0.000s  (  0.007s elapsed)
   Total   time    1.008s  (  1.130s elapsed)

   Alloc rate    2,241,052,377 bytes per MUT second

   Productivity  76.7% of total user, 79.2% of total elapsed
 }}}

 It appears that by default I pay >50% of compile time for a feature that I
 probably won't use.

 I'm sorry if this is a duplicate, I've looked at
 https://ghc.haskell.org/trac/ghc/wiki/Typeable, but nothing seemed
 relevant.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14663
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