[GHC] #16039: 'GHC.Magic.noinline <var>' should not float out

[GHC]

#16039: 'GHC.Magic.noinline <var>' should not float out
-------------------------------------+-------------------------------------
        Reporter:  heisenbug         |                Owner:  heisenbug
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.10.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  FloatOut
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15155            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 > a bunch of expressions (e.g noinline @ (Role -> Type -> MCoercionN ->
 Coercion) mkGReflCo) that are destined for class dictionaries got floated
 out for no reason.

 Interesting.  Which pass did this?

 I suspect that we should have invariants like
 {{{
 exprIsTrivial e   implies   notWorthFloating e
 exprIsTrivial e   implies   exprIsCheapX e
 }}}
 I wonder if these are true right now?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16039#comment:12>
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