[Haskell-cafe] Switch optimization
tom at pledger.gen.nz
Sun Jun 10 21:39:52 EDT 2007
Stefan O'Rear wrote:
| On Mon, Jun 11, 2007 at 09:43:17AM +1000, Thomas Conway wrote:
| > codeLen 127 = 0
| > codeLen 128 = 1
| > ...
| > codeLen 255 = 8
| > Now, compiling with ghc 6.6.1 and -O3, I see that it generates a long
| > chain of conditional branches.
That's deeply tied in with Num being a subclass of Eq, isn't it?
Pattern matching for /non-numeric/ data constructors should be more
direct, at any optimisation level, thanks to the taglessness of the
| I'd suggest learning how to hack on GHC, I get a chain of branches even
| at the maximum optimization setting. Hackers are always appreciated!
Such a GHC hack may have to be limited to some known, standard numeric
types. User-defined numeric types may not provide anything that you
can use to look up a jump table.
How would an array go, as a user-level optimisation?
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