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

[Hal Finkel via Phabricator via llvm-commits]

hfinkel added a comment.

In https://reviews.llvm.org/D32737#760375, @rengolin wrote:

> In https://reviews.llvm.org/D32737#760310, @sanjoy wrote:
>
> > I've only lightly read the spec, but it looks like the vector length can be controlled by writing to the `ZCR_ELn` registers (so, e.g. user code could make a syscall to change the vector length)?
>
>
> As I explained to Hal on his comment, that is correct but doesn't have the effect you're expecting.


Which comment? FWIW, I didn't see a particular response.

In https://reviews.llvm.org/D32737#760310, @sanjoy wrote:

> I've only lightly read the spec, but it looks like the vector length can be controlled by writing to the `ZCR_ELn` registers (so, e.g. user code could make a syscall to change the vector length)?  If that's accurate, I think a constant `vscale` is not sufficient.


I'm also under the impression that this won't work because it would interfere with any ongoing vector calculations, spill code, etc. The point being that it is fixed for a particular process once the process begins (at least in practice).


https://reviews.llvm.org/D32737