[PATCH] D109555: [APInt] Enable APInt to support zero bit integers.

[Jay Foad via Phabricator via llvm-commits]

foad added a comment.

> It doesn't make sense for a zero-width `APInt` to return true for isZero() but not produce a n-bit zero value for `sext(n)`.

You could just as well say: it doesn't make sense for a zero-width `APInt` to return true for isAllOnes() but not produce a n-bit all-ones value for `sext(n)`.

Zero-width ints satisfy both isZero() and (I assert) isAllOnes(), so something has to give. I think the solution is to say that `sext` is not defined on zero-width ints because...

> `sext` is a function defined based on the high bit of the existing value.

... a zero-width int doesn't //have// a high bit.


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  https://reviews.llvm.org/D109555/new/

https://reviews.llvm.org/D109555