[llvm] [IR][Attributes] Take "best" from Callbase/Call Function when getting attributes (PR #112985)

[via llvm-commits]

goldsteinn wrote:

> Can you please check the compile-time impact?
> 
> Our general convention is to let the CB attribute take precedence over the Callee attribute, as long as it exists. I don't think doing an actual intersection (thus requiring to always look up _both_ attributes) is going to be practically useful, as we shouldn't place worse call-site attributes in the first place.

I guess it all seems flimsy to me.
With no real mechanism protecting "only better attrs on callsite" it seems liable to be violated (although granted I don't think much consequence).
Either way, there doesn't seem to be much if any compile time consequence due to this change:
https://llvm-compile-time-tracker.com/compare.php?from=170dab9972df3f6e905502db1846bb05fb444ec4&to=3ebc28d018e0f8716d78fbf23c34a3e7d00a41d4&stat=instructions:u


https://github.com/llvm/llvm-project/pull/112985