[PATCH] Fix unfortunate interaction between foldSelectICmpAnd and urem

[David Majnemer]

We fail to convert a urem to an and if we have a select between two powers
of two.
The reason why is because it gets turned into (add (and (lshr V, C1), C2),
C2) and we can not tell that it is a power of two any more.

The most natural thing seems to be to teach isKnownToBeAPowerOfTwo that (X
& Y) + Y is a power of two or zero if Y is a power of two.

A patch is attached with a test case.

-- 
David Majnemer
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