[GHC] #11126: Entered absent arg in a Repa program

[GHC]

#11126: Entered absent arg in a Repa program
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        Reporter:  tuplanolla        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by jscholl):

 I could halfway reproduce this: The following program has an intermediate
 state where a value ({{{arr2}}}) is marked with {{{<L,A>}}} which is later
 used again (in the unfolding of {{{getIt}}}). This does however not
 completely trigger the bug as {{{arr2}}} gets marked too early, i.e.
 worker-wrapper is not yet running. Then the simplifier inlines {{{getIt}}}
 and {{{arr2}}} is referenced again, so when worker-wrapper runs everything
 has the correct strictness.

 However, if I somehow could convince the compiler to run the worker-
 wrapper transformation before phase 0 the program has a good chance to
 trigger the bug. Even if it does not, I think the usage of {{{arr2}}}
 should not be {{{<L,A>}}} as it could be still referenced if {{{getIt}}}
 is inlined.

 I used the following command to generate the core2core log (ghc 7.10.3):

 {{{ghc -c Unfold.hs -ddump-simpl -dsuppress-coercions -dsuppress-type-
 applications -dsuppress-uniques -dsuppress-module-prefixes -dverbose-
 core2core -O -fstrictness-before=0}}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11126#comment:6>
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