Draft: nir: Make scoped barriers first-class
For background, Mali only has one type of barrier, so I want control + memory combined. But that requires scoped barriers, and for historical reasons, we have two completely different kind of barriers in NIR:
- Scoped barriers, used in SPIR-V for some drivers only.
- GLSL-style barriers
This MR adds a pass to lower GLSL style barriers to scoped barriers, from which combining can use a variant of the existing pass. In the near future I'd like to fix up the tree to use scoped barriers exclusively, since they are a strict superset of functionality.