[llvm] [RFC][CodeGen] Add generic target feature checks for intrinsics (PR #201470)

[Shilei Tian via llvm-commits]

shiltian wrote:

> > This would require a mutable cache, which is not ideal.
> 
> This is what mutable is for

Right, but I generally prefer not to use `mutable`, since it often indicates a layering violation or a design issue. In this particular case, `TargetSubtargetInfo` doesn't own any data members today, so I'd rather not introduce a mutable one unless there's a strong reason to do so.

https://github.com/llvm/llvm-project/pull/201470