[PATCH] D30123: [InstCombine] shrink truncated shuffle with constant operand

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D30123#680573, @efriedma wrote:

> "the mask doesn't change"
>
> That's technically true... but doesn't really match the spirit of the rule that we don't change shuffle masks.  Many targets have shuffles that only work at specific widths.


I knew I might be pushing the limits here by generalizing too much. :)
In the motivating example, we have a splat mask, so we could still do a limited form of this transform and catch that case. Can we assume that any splat shuffle is safe to transform in target-independent IR?


https://reviews.llvm.org/D30123