[GHC] #7585: Core lint failure when optimizing coercions in branched axioms

[GHC]

#7585: Core lint failure when optimizing coercions in branched axioms
-------------------------------+--------------------------------------------
Reporter:  goldfire            |          Owner:  goldfire        
    Type:  bug                 |         Status:  new             
Priority:  normal              |      Component:  Compiler        
 Version:  7.7                 |       Keywords:  TypeFamilies    
      Os:  Unknown/Multiple    |   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |      Blockedby:                  
Blocking:                      |        Related:                  
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Comment(by eir@…):

 commit a6ab0a40ac750914640613c77148e948fabf35d5
 {{{
 Author: Richard Eisenberg <eir at cis.upenn.edu>
 Date:   Tue Jan 15 17:19:37 2013 -0500

     Fix Trac #7585.

     The coercion optimizer was optimizing coercions inside of branched
     axiom applications, sometimes invalidating the branch choice within
     the axiom application. Now, we check to make sure we are not
     invalidating this invariant before proceeding with the optimization.

  compiler/coreSyn/CoreLint.lhs  |   41 +------------------
  compiler/types/OptCoercion.lhs |   88
 +++++++++++++++++++++++++++++++++++-----
  2 files changed, 79 insertions(+), 50 deletions(-)
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7585#comment:1>
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