[GHC] #14672: Make likelyhood of branches/conditions available throughout the compiler.

[GHC]

#14672: Make likelyhood of branches/conditions available throughout the compiler.
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        Reporter:  AndreasK          |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4316
       Wiki Page:                    |  Phab:D4324 Phab:D4327
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Comment (by AndreasK):

 [https://phabricator.haskell.org/D4327 D4327] will add likeliness
 Information at the STG stage.

 Some of the next tasks to improve on this:

 * Take more advantage of this in the backend.
   - Allow the cmm parser to process likely information in switch
 statements.
   - Build switches in a manner that the most likely path is the fastest
 one.
   - Use this information for code layout optimization.
   - Add hints to more cmm code used within GHC.
   - Investigate other use cases.
 * Find a good way for users to provide this information.
   - Bikeshedding: Syntax, Semantics etc. for HsSyn
   - How to represent und use this in the core Pipeline
     - Simon M recommended using ticks for this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14672#comment:7>
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