[GHC] #7392: "the impossible happened" when compiling Types.Substitutions

[GHC]

#7392: "the impossible happened" when compiling Types.Substitutions
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    Reporter:  martindemello     |       Owner:                    
        Type:  bug               |      Status:  new               
    Priority:  normal            |   Milestone:                    
   Component:  Compiler          |     Version:  7.6.1             
    Keywords:                    |          Os:  Linux             
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash
  Difficulty:  Unknown           |    Testcase:                    
   Blockedby:                    |    Blocking:                    
     Related:                    |  
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Comment(by guest):

 I reduced the test case.

 {{{
 module M where

 import Data.List (foldl')

 data Type = ADT [Type]
 rnf (ADT ts) = foldl' (\acc x -> rnf x `seq` acc) () ts
 }}}

 This module is a stripped version of Types.Substitutions and crashes on
 `ghc-7.6.1 -O M.hs`. The optimization flag is important.

 GHC-7.7.20121024 compiles it fine. Therefore I think this ticket can be
 closed as fixed; perhaps you can a regression test to be safe.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7392#comment:2>
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