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The Vulkan/SPIR-V memory model was built on the foundation of the C++ memory model, but ended up diverging in a number of places.

A lot of how GPU programming models work across modern graphics APIs has evolved through years of development, reflecting the markets that those APIs have targeted. Naturally, the Vulkan/SPIR-V memory model has made several decisions that reflect this. We added several new facets to the model, including scopes, storage classes, and memory availability and visibility operations to name some of the more prominent ones.

However, It is not a strict superset either, and there are a few places where some features have been omitted for similar reasons. For example, sequential consistency is not supported, and forward progress guarantees are limited.

This post aims to give a high-level overview of the differences, explaining what the differences are, why they are different, and how (if at all) C++ concepts can map to the Vulkan/SPIR-V memory model. It is aimed primarily at people already familiar with the C++ memory model who either want to get some insight into what the differences are or those who are curious about why we took the direction we did.