Module naga::front::atomic_upgrade

Upgrade the types of scalars observed to be accessed as atomics to Atomic types.

In SPIR-V, atomic operations can be applied to any scalar value, but in Naga IR atomic operations can only be applied to values of type Atomic. Naga IR’s restriction matches Metal Shading Language and WGSL, so we don’t want to relax that. Instead, when the SPIR-V front end observes a value being accessed using atomic instructions, it promotes the value’s type from Scalar to Atomic. This module implements Module::upgrade_atomics, the function that makes that change.

Atomics can only appear in global variables in the Storage and Workgroup address spaces. These variables can either have Atomic types themselves, or be Arrays of such, or be Structs containing such. So we only need to change the types of globals and struct fields.

Naga IR Load expressions and Store statements can operate directly on Atomic values, retrieving and depositing ordinary Scalar values, so changing the types doesn’t have much effect on the code that operates on those values.

Future work:

• Atomics in structs are not implemented yet.

• The GLSL front end could use this transformation as well.

Enums

• Error