[GHC] #13027: Core lint errors compiling containers HEAD with GHC HEAD

[GHC]

#13027: Core lint errors compiling containers HEAD with GHC HEAD
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        Reporter:  erikd             |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Building GHC      |            Test Case:
  failed                             |  simplCore/should_compile/T13027
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 Is there a reason ''not'' to make `exprOkForSpeculation` more lenient for
 `reallyUnsafePtrEquality#`? Having it otherwise seems inconsistent, but
 it's also possible that it doesn't enable useful floating or that it's too
 much trouble to make it happen. I dug around just a bit, and the only
 other lazy primitives I could find that might be safe for speculation were
 `unpackClosure#` and (under certain circumstances, maybe) `seq`.

 I'm somewhat concerned about the fact that the problem tracking
 evaluatedness was only revealed "by chance", because
 `exprOkForSpeculation` is (seemingly) too conservative about
 `reallyUnsafePtrEquality#`. Is there some way to make this tracking more
 robust? I understand that you and Max Bolingbroke worked on some possibly-
 related ideas in "Types are Calling Conventions". What's your intuition
 about whether the type system can help here without making life horrible?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13027#comment:22>
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