[GHC] #11344: Rule "and/build" not firing

3 Jan 2016

      #11344: Rule "and/build" not firing
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           Reporter:  j.waldmann     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           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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 For this function
 {{{
 isprime_1 :: Int -> Bool
 isprime_1 n = n >= 2 &&
   ( and $ map (\t -> 0 < mod n t) $
        [2 .. truncate $ sqrt $ fromIntegral n] )
 }}}
 rule "and/build" is not firing with ghc-7.10.3.

 ghc-7.8.4 does fire the rule and produces much better (that is, non-
 allocating) code.

 I can get good code with 7.10 if I replace "and" by

 {{{
 import GHC.Base (build)

 {-# RULES
 "und/build"  forall (g::forall b.(Bool->b->b)->b->b) .
                 und (build g) = g (&&) True
  #-}

 {-# NOINLINE und #-}
 und :: [Bool] -> Bool
 und = foldr (&&) True
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11344
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