[llvm] [IR] Make dead_on_return attribute sized (PR #171712)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Can you share how the DSE changes will look like?

It looks like we currently fail to use dead_on_return inside isNotVisibleOnUnwind(), but that would also have to check the range with this approach. Possibly dead_on_unwind also needs the argument?

One thing I'm wondering is whether it makes sense to make the argument optional, to avoid the need to prove that the access is within specific bounds in the cases where it's not relevant (e.g. the original motivation for dead_on_return, which is byval-like arguments).

https://github.com/llvm/llvm-project/pull/171712