[GHC] #13861: Take more advantage of STG representation invariance (follows up #9291)

[GHC]

#13861: Take more advantage of STG representation invariance (follows up #9291)
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        Reporter:  heisenbug         |                Owner:  heisenbug
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      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 heisenbug):

 Now that #14373 is up for review, it is time to revisit this one. It turns
 out that coercion between small and big families is not an issue any more
 (provided that wip/T14373 gets merged). From big family with ptr-tag 7 we
 anyway only can go to small family ptr-tag 7 if the tags in the info table
 match, so everything is okay. My conservative 1..6 assessment above is not
 needed. We can safely have 1..7.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13861#comment:12>
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