[PATCH] D14664: [ARM] Match VABDL from log2 shuffles.

[Tim Northover via llvm-commits]

On 16 November 2015 at 10:36, Renato Golin via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> It seems that this pattern is only valid if the original types were unsigned to begin with, which is a fair assumption, but Is there any guarantee that the zero-extend is exclusively used in unsigned values, or are there some legalization patterns that could zero extend for other reasons?

I don't follow this. The incoming IR takes some bit-patterns and
produces (hopefully well-defined) output bit-patterns. Whether the
types involved were originally signed or unsigned in the source
language is intentionally irrelevant. If you can produce the same
black-box function starting from signed types, good on you and we'll
optimise it anyway.

Cheers.

Tim.