Feat: start work on atomics, add atomic intrinsics

Author: RDambrosio016

crates/cuda_std/src/atomic.rs

@@ -0,0 +1,21 @@
+//! Atomic Types for modification of numbers in multiple threads in a sound way.
+//!
+//! # Core Interop
+//!
+//! Every type in this module works on the CPU (targets outside of nvptx). However, [`core::sync::atomic`] types
+//! do **NOT** work on the GPU currently. This is because CUDA atomics have some fundamental differences
+//! that make representing them fully with existing core types impossible:
+//!
+//! - CUDA has block-scoped, device-scoped, and system-scoped atomics, core does not make such a distinction (obviously).
+//! - CUDA trivially supports relaxed/acquire/release orderings on most architectures, but SeqCst and other orderings use
+//! specialized instructions on compute capabilities 7.x+, but can be emulated with fences/membars on 7.x >. This makes it difficult
+//! to hide away such details in the codegen.
+//! - CUDA has hardware atomic floats, core does not.
+//! - CUDA makes the distinction between "fetch, do operation, read" (`atom`) and "do operation" (`red`).
+//! - Core thinks CUDA supports 8 and 16 bit atomics, this is a bug in the nvptx target but it is nevertheless an annoying detail
+//! to silently trap on.
+//!
+//! Therefore we chose to go with the approach of implementing all atomics inside cuda_std. In the future, we may support
+//! a subset of core atomics, but for now, you will have to use cuda_std atomics.
+
+pub mod intrinsics;