[llvm] [AMDGPU][InsertWaitCnts] Make HWEvent a BitMask (PR #203864)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

> Why not use `BitmaskEnum` to generate the bitwise ops? That file already creates a familiar interface for all bitmask enums. For example, `BitmaskEnum` already has a `^=` operator which can be used to unset individual bits. That seems cleaner than the bespoke `remove()`.

I addressed the other comments, but the simple reason is that having some additional operators is valuable. If we just have a raw enum class + BitMaskEnum it creates friction in some places. Examples:

- No default initialization
- Lots of operations need separate functions, so no dot operator.

I initially started this as an enum class exactly like that but after I wasted time tracking down a bug due to an uninitialized mask + seeings thins like `contains(A, B)` which weren't self-documenting, I preferred to do this instead and I am much happier with it


https://github.com/llvm/llvm-project/pull/203864