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

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

This basically looks right, but I think at least for doesNotCapture we'd be better off changing the API to automatically check byval. I looked at some of the other callers and many of them don't handle byval either, but should. (You can see in the test that FunctionAttrs infers readonly after your change, but still misses nocapture. That's because CaptureTracking doesn't check for byval.)

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