[PATCH] D89050: Add support for !noundef metatdata on loads

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

In D89050#2320052 <https://reviews.llvm.org/D89050#2320052>, @nikic wrote:

> In D89050#2320036 <https://reviews.llvm.org/D89050#2320036>, @jdoerfert wrote:
>
>>> For some frontends (that model safe languages) it might be that *all* loads are noundef.
>>
>> I would consider a function/module attribute for this.
>
> Only loads emitted by the frontend would be noundef, optimization may introduce or move loads in a way that they are no longer noundef. I think such an attribute would violate LLVMs usual attribute design, as optimizations would now have to worry about dropping function attributes when performing speculation etc (is there any precedent for something like this?) We'd also lose the noundef property for all loads in a function at once, if a single one of them is speculated.

Yeah, good point ;). Bundling `noundef` in a single assume still works though ;)


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