[m-dev.] An optimization worth doing.

[Fergus Henderson]

Thomas Charles CONWAY, you wrote:
> 
> Now, because in both cases we want the first field (irrespective
> of the tag), it would be cheaper to simply mask off the tag at
> runtime (use an expression equivalent to (ptr & (!0x07))[0]) to
> avoid the branch.

This optimization would also be a very useful for red-black trees.

-- 
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