[GHC] #10980: Deriving Read instance from datatype with N fields leads to N^2 code size growth

[GHC]

#10980: Deriving Read instance from datatype with N fields leads to N^2 code size
growth
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        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by slyfox):

 Replying to [comment:5 simonpj]:
 > Slyfox, can you give a small example of what the code looks like before
 and after your change?  I can see that turning 4 lines into 1 (by creating
 a new function definition) is good, but at best that makes it 4 times
 smaller, which is not the difference between linear and quadratic.

 I've rechecked the measurement and you are correct! Quadratic behaviour
 stil presents
 in manually converted sources. Seems I was looking at the wrong binary
 files when tweaking things.

 Apologies for the confusion :(

 (for completness) attaching source file before and after transformation
 for 200-entries file:
 {{{
 $ ghc -c -fforce-recomp -c -O1 M_200_auto.hs
 $ ghc -c -fforce-recomp -c -O1 M_200_manual.hs
 $ size M_200_auto.o M_200_manual.o

    text    data     bss     dec     hex filename
 3268679   41520       0 3310199  328277 M_200_auto.o
  674695   16424       0  691119   a8baf M_200_manual.o
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10980#comment:6>
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