[GHC] #14826: Flatten data types extending other data types in STG

[GHC]

#14826: Flatten data types extending other data types in STG
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        Reporter:  nomeata           |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.5
      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 nomeata):

 One might be able to state this in terms of unboxed sums, yes.

 >  That way, we can drop the 'only once' requirement. Well, I guess this
 still involves non-id coercions...

 You mean the requirement that only one `Foo` can be flattened into a
 `Result`? Yes, if you do this with multiple ones you either get non-id
 coercions (which party defeat the purpose). Or, of all types are defined
 in the same module, you can maybe to a smart constructor tag allocation
 scheme where `Foo` gets tags 1…3, `Bar` gets tags 4…6, and `data FooBar =
 Foo !Foo | Bar !Bar` can now be flattened simply to a pointer to a `Foo`
 or a `Bar` value.

 But let’s focus on the simple case first that does not require a global
 constructor pointer allocation pass :-)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14826#comment:3>
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