#3055: Int / Word / IntN / WordN are unequally optimized
-------------------------------------+--------------------------------------
Reporter: claus | Owner:
Type: run-time performance bug | Status: new
Priority: normal | Component: Compiler
Version: 6.11 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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A lot of thought has been put into optimizing usage of `Int`, but not all
of these tweaks have been copied for usage of `Word`, and the specific-
size versions of both have even fewer optimizations. The consequence is
that switching from signed to unsigned, or from unspecified to specified
size, can result in dramatic performance loss.
- builtin rules (`prelude/PrelRules`) cover `Int` and `Word`, but not
sized alternatives
- `SPECIALI[SZ]E` pragmas cover `Int`, but little of the others. Try
{{{
find libraries/ -name _darcs -prune -o -name *hs |
xargs grep SPECIAL | grep '\<Int\|\<Word'
}}}
- some instances have special cases for `Int`, but not for the others (for
instance, the `Enum` instance for `Int` uses specialised `enumFromTo`
code, the `Word` version uses generic code; `base/GHC/Enum.hs` and
`base/GHC/Word.hs`)
- some `RULES` help optimizing the special cases for `Int` further (again,
see the `Enum` instance for `Int` for an example)
See this thread [http://www.haskell.org/pipermail/glasgow-haskell-
users/2009-February/016705.html "Int vs Word performance?"] for more
discussion.
related tickets: #2270, #3051
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3055>
GHC <http://www.haskell.org/ghc/>
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