Module naga::front::atomic_upgrade
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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:
- The GLSL front end could use this transformation as well.