Commits on Nov 30, 2023

1. [Clang] Introduce scoped variants of GNU atomic functions …

   Summary:
   The standard GNU atomic operations are a very common way to target
   hardware atomics on the device. With more hetergenous devices being
   introduced, the concept of memory scopes has been in the LLVM language
   for awhile via the `syncscope` modifier. For targets, such as the GPU,
   this can change code generation depending on whether or not we only need
   to be consistent with the memory ordering with the entire system, the
   single GPU device, or lower.
   
   Previously these scopes were only exported via the `opencl` and `hip`
   variants of these functions. However, this made it difficult to use
   outside of those languages and the semantics were different from the
   standard GNU versions. This patch introduces a `__scoped_atomic` variant
   for the common functions. There was some discussion over whether or not
   these should be overloads of the existing ones, or simply new variants.
   I leant towards new variants to be less disruptive.
   
   The scope here can be one of the following
   
   ```
   __MEMORY_SCOPE_SYSTEM // All devices and systems
   __MEMORY_SCOPE_DEVICE // Just this device
   __MEMORY_SCOPE_WRKGRP // A 'work-group' AKA CUDA block
   __MEMORY_SCOPE_WVFRNT // A 'wavefront' AKA CUDA warp
   __MEMORY_SCOPE_SINGLE // A single thread.
   ```
   Naming consistency was attempted, but it is difficult to cpature to full
   spectrum with no many names. Suggestions appreciated.

   

   jhuber6 committed Nov 30, 2023
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