[GHC] #11374: `-Woverlapping-patterns` induced memory-blowup

[GHC]

#11374: `-Woverlapping-patterns` induced memory-blowup
-------------------------------------+-------------------------------------
           Reporter:  hvr            |             Owner:  gkaracha
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:  8.0.1
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I'm afraid I've found yet another case that still let's the pattern
 checker go crazy (courtesy of hackage:cryptol-2.2.5):

 {{{#!hs
 {-# LANGUAGE Haskell2010 #-}

 {-# OPTIONS_GHC -Woverlapping-patterns #-}
 module Bug where

 data Type   = TCon TCon [Type]
             | TUser String [Type] Type
             | TRec [(String,Type)]
             deriving (Show,Eq,Ord)

 data TCon   = TC TC
             | TF TFun
             deriving (Show,Eq,Ord)

 data TC     = TCNum Integer
             | TCInf
             | TCBit
             | TCSeq
             | TCFun
             | TCTuple Int
             deriving (Show,Eq,Ord)

 data TFun   = TCAdd
             | TCSub
             | TCMul
             | TCDiv
             | TCMod
             | TCLg2
             | TCExp
             | TCWidth
             | TCMin
             | TCMax
             | TCLenFromThen
             | TCLenFromThenTo
             deriving (Show, Eq, Ord, Bounded, Enum)

 simpFinTy :: Type -> Maybe [Type]
 simpFinTy ty = case ty of
     TCon (TC (TCNum _)) _ -> Just []

     TCon (TF tf) [t1]
       | TCLg2    <- tf -> Just [t1]
       | TCWidth  <- tf -> Just [t1]

     TCon (TF tf) [t1,t2]
       | TCAdd <- tf -> Just [t1, t2]
       | TCSub <- tf -> Just [t1]
       | TCMul <- tf -> Just [t1, t2]
       | TCDiv <- tf -> Just [t1]
       | TCMod <- tf -> Just []
       | TCExp <- tf -> Just [t1, t2]
       | TCMin <- tf -> Nothing
       | TCMax <- tf -> Just [t1, t2]

     TCon (TF tf) [_,_,_]
       | TCLenFromThen   <- tf -> Just []
       | TCLenFromThenTo <- tf -> Just []

     _ -> Nothing
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11374>
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