[PATCH] D134648: [LangRef] Update text for vscale to be more flexible but maintain original intent.

[Paul Walker via Phabricator via llvm-commits]

paulwalker-arm added a comment.

In D134648#3817518 <https://reviews.llvm.org/D134648#3817518>, @aemerson wrote:

> In D134648#3815329 <https://reviews.llvm.org/D134648#3815329>, @nikic wrote:
>
>> I don't think we can allow this as long as vscale constant expressions are supported (these are currently represented via gep of scalable type). I am rather strongly opposed to having constants that are not in fact constant, so this change should only happen after a migration towards `llvm.vscale` intrinsics.
>
> I haven't been following the scalable types story in a lot of detail, but doesn't disallowing GEP of scalable types imply that pointer calculations need to be done via decomposed integer arithmetic? Does this break for non-integral pointer types?

I believe the ask here relates only to GEP based ConstantExpr expressions and is presumably part of the wider effort to limit how ConstantExprs are used.  I don't object to the proposal as I've never liked this representation of vscale as to my mind it doesn't consider how DataLayout could mean the result isn't quite what you'd expect.


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