[PATCH] D108741: [GlobalDCE] Handle non-vfunc entries in vtables during VFE

Sun Sep 26 12:09:26 PDT 2021

fhahn added a comment.

In D108741#3021933 <https://reviews.llvm.org/D108741#3021933>, @pcc wrote:

> In D108741#3021793 <https://reviews.llvm.org/D108741#3021793>, @kubamracek wrote:
>
>> @pcc, could I ask for some details about your last comment? I'm specifically wondering whether you're against proceeding with the change from this review.
>
> Sorry, but I think I'm against it because the mechanism that you've chosen seems like an abuse of the !type metadata, since the metadata is meant to be used as a reference point for accesses relative to it, and not as a way of marking up specific fields by itself. As a more practical concern, it has no way of representing the situation where the pointer at the address point is not eligible for VFE.
>
> Here's one alternative proposal: can we make it so that any vtable slots that are eligible for VFE are represented using a new type of Constant (similar to dso_local_equivalent)? This also has the advantage that frontends could also use it for global variables as well as functions.

A potentially more lightweight solution may be providing a way to opt-in to the stricter interpretation. That way, we ensure no existing users are disturbed while not having to add more invasive changes. Do you think the additional complexity a new type of Constant carries its weight if it is only used to support the swift VFE case?

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  https://reviews.llvm.org/D108741/new/

https://reviews.llvm.org/D108741