Very poor constant folding

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.

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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Very poor constant folding