[GHC] #6121: Very poor constant folding

[GHC]

#6121: Very poor constant folding
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 Reporter:  augustss                 |          Owner:                  
     Type:  bug                      |         Status:  new             
 Priority:  normal                   |      Component:  Compiler        
  Version:  7.4.1                    |       Keywords:                  
       Os:  Unknown/Multiple         |   Architecture:  Unknown/Multiple
  Failure:  Runtime performance bug  |       Testcase:                  
Blockedby:                           |       Blocking:                  
  Related:                           |  
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 GHC seems to lack constant folding for encodeFloat/decodeFloat.
 For many examples, compile the numeric-limits package on hackage, or just
 this snippet:
 {{{
 epsilon :: Double
 epsilon = r
   where r = 1 - encodeFloat (m-1) e
         (m, e) = decodeFloat (1 `asTypeOf` r)
 }}}
 This has a very simple value, but GHC refuses to compute it at compile
 time.  This in turn inhibits other constant folding that should be going
 on.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6121>
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