[PATCH] D94444: [RFC][Scalable] Add scalable shuffle intrinsic to extract evens from a pair of vectors

Tue Jan 19 13:21:59 PST 2021

cameron.mcinally added a subscriber: ctetreau.
cameron.mcinally added a comment.

> Having said that, I wonder if we should revisit the idea of allowing shuffle vectors to accept step vector masks?

At today's sync-up meeting, this met strong resistance. @ctetreau argued that we don't want to allow a stepvector constant as the shuffle vector mask operand, since that could lead to slippery slope of constant initializer strings. Chris, correct my paraphrase if you'd like...

In D94444#2497697 <https://reviews.llvm.org/D94444#2497697>, @paulwalker-arm wrote:

> <A x Elt> llvm.experimental.vector.extract.elements(<B x Elt> %invec, i32 index, i32 stride)
>
> Where index and stride are required to be constant immediate values with "stride > 0" and "0 <= index < stride".

Thinking about this some more, this wouldn't be too bad to implement. I'm okay going this route, unless anyone feels strongly against it...

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