[GHC] #16007: Implement `-Os`

[GHC]

#16007: Implement `-Os`
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        Reporter:  sgraf             |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #16005, #12915,   |  Differential Rev(s):
  #14226                             |
       Wiki Page:                    |
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Description changed by sgraf:

Old description:

> Popular C compilers like GCC or clang allow to optimise for binary size.
>
> Since there are multiple ways in which GHC trades code size for faster
> programs, it might make sense to follow suit. This ticket is for tracking
> which optimisations/hacks in the compiler might be affected, as well as
>
> Feel free to add items to the following list:
>
> - potentially huge impact due to specialisation, liberate case and
> inlining
> - +0.1% increase in code size due to known calls instead of re-using
> generic apply thunks in #16005
> - -0.1% due to `-fstg-lift-lams` #9476

New description:

 Popular C compilers like GCC or clang allow to optimise for binary size.

 Since there are multiple ways in which GHC trades code size for faster
 programs, it might make sense to follow suit. This ticket is for tracking
 which optimisations/hacks in the compiler might be affected, as well as

 Feel free to add items to the following list:

 - potentially huge impact due to specialisation, liberate case and
 inlining
 - potential of -0.9% due to a second run of common block elimination
 (#14226)
 - +0.1% increase in code size due to known calls instead of re-using
 generic apply thunks in #16005
 - -0.1% due to `-fstg-lift-lams` #9476

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16007#comment:4>
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