Re: [GHC] #683: RULES for recursive functions don't work properly

#683: RULES for recursive functions don't work properly
-----------------------+----------------------------------------------------
  Reporter:  simonpj   |          Owner:  simonpj
      Type:  bug       |         Status:  new    
  Priority:  low       |      Milestone:         
 Component:  Compiler  |        Version:  6.4.1  
  Severity:  normal    |     Resolution:         
  Keywords:            |             Os:  Unknown
Difficulty:  Unknown   |   Architecture:  Unknown
-----------------------+----------------------------------------------------
Comment (by simonpj):

 Before I forget, here's the beginning of a modification to address the
 original problem.  It's not implemented, but I thought I'd leave the notes
 here in case it pops up as an issue again.
 {{{
 hunk ./compiler/basicTypes/BasicTypes.lhs 329
 +
 +Note [RulesOnly]
 +~~~~~~~~~~~~~~~~
 +The RulesOnly boolean is True if the only reason the Id is a
 +loop-breaker only because of recursion through a RULE. In that case,
 +we can ignore the loop-breaker-ness for inlining purposes.  Example
 +(from GHC.Enum):
 +
 +  eftInt :: Int# -> Int# -> [Int]
 +  eftInt x y = ...(non-recursive)...
 +
 +  {-# INLINE [0] eftIntFB #-}
 +  eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
 +  eftIntFB c n x y = ...(non-recursive)...
 +
 +  {-# RULES
 +  "eftInt"  [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x
 y)
 +  "eftIntList"  [1] eftIntFB  (:) [] = eftInt
 +   #-}
 +
 +The two look mutually recursive only because of their RULES;
 +we don't want that to inhibit inlining!
 +
 hunk ./compiler/basicTypes/BasicTypes.lhs 364
 -                       -- in a group of recursive definitions
 +       !RulesOnly      --   in a group of recursive definitions
 +[_^I_][_^I_][_^I_][_$_]
 +
 +type RulesOnly = Bool  -- See Note [RulesOnly]
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/683>
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