[llvm] [RFC][AMDGPU] Add vulkan:private/nonprivate MMRAs support (PR #78573)

[Sameer Sahasrabuddhe via llvm-commits]

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@@ -10,6 +10,20 @@
 /// Memory legalizer - implements memory model. More information can be
 /// found here:
 ///   http://llvm.org/docs/AMDGPUUsage.html#memory-model
+///
+/// Notes on the Vulkan Memory Model, which is controlled by the
+/// `amdgpu.vulkan.memory-model` module flag. When that flag
+/// is provided:
+/// - vulkan:private operations cannot be atomic, and as such
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ssahasra wrote:

"cannot be atomic" is way too imprecise. The exact spec is that "private operations are not synchronized in a running shader and hence they can always be cached".

https://github.com/llvm/llvm-project/pull/78573