[llvm] [FunctionAttrs] Treat byval calls as only reading ptrs (PR #122618)

[Nikita Popov via llvm-commits]

nikic wrote:

> @nikic do you think it makes sense to update `CallBase::onlyReadsMemory` with a similar check, or should I keep things as is?

I'm a bit less sure on that one. `byval readonly` on a function definition does mean something, which is that the byval copy is not read by the function. But from an external perspective, when analyzing a call-site, this distinction is not relevant. So overall I think it would make sense to change `CallBase::onlyReadsMemory` as well. But maybe as a followup PR?

https://github.com/llvm/llvm-project/pull/122618