[GHC] #10014: Data.Array.Base.elems needlessly calls bounds.

22 Jan 2015

      #10014: Data.Array.Base.elems needlessly calls bounds.
-------------------------------------+-------------------------------------
              Reporter:  ekmett      |             Owner:  ekmett
                  Type:  feature     |            Status:  new
  request                            |         Milestone:
              Priority:  normal      |           Version:  7.8.4
             Component:  Core        |  Operating System:  Unknown/Multiple
  Libraries                          |   Type of failure:  Runtime
              Keywords:              |  performance bug
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 {{{
 elems arr = case bounds arr of
     (_l, _u) -> [unsafeAt arr i | i <- [0 .. numElements arr - 1]]
 }}}

 It never uses the result.

 I'd propose simplifying it to

 {{{
 elems arr = [unsafeAt arr i | i <- [0 .. numElements arr - 1]]
 }}}

 It appears at some point someone optimized it to use the `unsafeAt`, but
 never removed the bounds check.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10014
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