Subgroup Operations

[Lichtso]

This continues the work of #2523, which looks like it was abandoned.

Voter operations (booleans):

• subgroupBallot() -> vec4<u32>
• subgroupBallot(vote: bool) -> vec4<u32>
• subgroupAll(vote: bool) -> bool
• subgroupAny(vote: bool) -> bool

Gather operations (scalars and vectors of f32, i32, u32):

• subgroupBroadcastFirst(value) -> value
• subgroupBroadcast(value, index) -> value
• subgroupShuffle(value, index) -> value
• subgroupShuffleDown(value, index_offset) -> value
• subgroupShuffleUp(value, index_offset) -> value
• subgroupShuffleXor(value, index_mask) -> value

Reduce operations (scalars and vectors of i32, u32):

• subgroupAnd(value) -> value
• subgroupOr(value) -> value
• subgroupXor(value) -> value

Reduce operations (scalars and vectors of f32, i32, u32):

• subgroupAdd(value) -> value
• subgroupMul(value) -> value
• subgroupMin(value) -> value
• subgroupMax(value) -> value

Scan operations (scalars and vectors of f32, i32, u32):

• subgroupPrefixExclusiveAdd(value) -> value
• subgroupPrefixExclusiveMul(value) -> value
• subgroupPrefixInclusiveAdd(value) -> value
• subgroupPrefixInclusiveMul(value) -> value

Built-ins values added to the compute stage only:

• num_subgroups: u32
• subgroup_id: u32

Built-ins values added to the compute stage and fragment stage:

• subgroup_size: u32
• subgroup_invocation_id: u32

---

• Implement wgsl-in
• Implement wgsl-out
• Implement spv-in
• Implement spv-out
• Implement glsl-out
• Implement hlsl-out
• Implement msl-out
• Implement dot-out
• Snapshots / tests
• FRAGMENT quad group operations
• Decide what kinds of subgroupBarrier() make sense
• Compaction
• Analyzer
• Validation

[exrook]

I've added some more changes on top of your branch to my branch:
diff: https://github.com/Lichtso/naga/compare/subgroup_operations...exrook:naga:wgsl_minimal_subgroup

I think at this point we probably have all the features we'd want for the first iteration of this, modulo any review changes.

[cwfitzgerald]

Hello, thank you for your PR against Naga!

As part of gfx-rs/wgpu#4231, we have moved development of Naga into the wgpu repository in the Naga subfolder. We have transferred all issues, but we are unable to automatically transfer PRs.

As such, please recreate your PR against the wgpu repository. We apologize for the inconvenience this causes, but will make contributing to both projects more streamlined going forward.

We are leaving PRs open, but once they are transferred, please close the original Naga PR.