[PATCH] D32737: [Constants][SVE] Represent the runtime length of a scalable vector

[Chris Lattner via Phabricator via llvm-commits]

lattner added a comment.

In https://reviews.llvm.org/D32737#760276, @chandlerc wrote:

> In https://reviews.llvm.org/D32737#759325, @rengolin wrote:
>
> > @echristo @chandlerc @lattner @majnemer Ping.
> >
> > This is a trivial change, discussed in the past, and I'm inclined to approve.
>
>
> Uh, where was it discussed? It's entirely possible I missed it, but I can't find any consensus on any of the threads that we actually want to support runtime vector width in LLVM's IR.


...

> For the record, I remain unconvinced that LLVM's IR should support non-constant vector widths

I agree with Chandler on this.  Making something a first class type in LLVM has wide reaching effects, including requiring the ability to load/store/phi the value, pass it by argument, etc.  Vikram had a research project many many years ago to do the exact same sort of thing.  It failed because of these and other reasons.

What are the semantics of select when the two vectors have different width?  Does store do a memory allocation?

-Chris


https://reviews.llvm.org/D32737