[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
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #16005
Differential Rev(s):                 |         Wiki Page:
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 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:

 - +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>
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