[GHC] #14222: Simple text fusion example results in rather duplicative code

12 Sep 2017

      #14222: Simple text fusion example results in rather duplicative code
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           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           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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 Consider this program,
 {{{#!hs
 module T14221 where

 import Data.Text as T

 isNumeric :: Text -> Bool
 isNumeric t =
     T.all isNumeric' t && T.any isNumber t
   where
     isNumber c = '0' <= c && c <= '9'
     isNumeric' c = isNumber c
                 || c == 'e'
                 || c == 'E'
                 || c == '.'
                 || c == '-'
                 || c == '+'
 }}}

 Compiling with `-O` results in over 1 kilobyte of assembler. After looking
 at the simplified Core the issue becomes apparent: the case analysis of
 `isNumeric'` is duplicated six times,
 {{{#!hs
 case ww4_X2zB of {
   __DEFAULT -> GHC.Types.False;
   '+'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#);
   '-'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#);
   '.'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#);
   'E'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#);
   'e'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#)
 };
 }}}

 It seems to me that we would ideally try to share this bit. Of course,
 this may be quite tricky to do in practice.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14222
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