[spv-in] Atomics support

[schell]

Naga's SPIR-V frontend does not currently handle atomic operations. Using an atomic operation (in this case spirv_std::arch::atomic_i_increment in a rust-gpu shader) leads to a parse error:

UnsupportedInstruction(Function, AtomicIIncrement)

I'm treating this as the tracking issue for adding atomics to the spv frontend.

Milestone 1

Completion of milestone 1 will be a proof-of-strategy, after which that strategy can be re-applied to complete atomics support for all operations. First atomic operations support will be documented in the renderling devlog as a method / PoC to help in the completion of other operations.

• spv-in parsing Op::AtomicIIncrement #5702
• spv-in upgrading AtomicIIncrement type #5775

Milestone 2

Rinse and repeat, adding support for more atomic operations, until all have been exhausted.

• spv-in parse more atomic ops #5824

Milestone 3 & Follow up work

Cleaning up tests, bugfixes that might pop up, and generally making this feature more maintainable - tying up any loose ends.

• [naga spv-in] Atomic tests should use the standard snapshot machinery #6292
• [naga spv-in] Support for OpAtomicCompareExchange #6296
  • feature: [spv-front] Support for OpAtomicCompareExchange, fixes #6296 #6590

[schell]

I've submitted a proposal to NLNet to fund this issue. If they accept my proposal I'll likely pick this up after the holidays.

[tombh]

So AtomicIIncrement is working in v22.0? I'm just wondering if Bevy's upcoming v0.15 release (the current release is still on naga v0.20.0) will support some SPIRV atomics. Though I understand we'll have to wait for #5824 to get more functions, like say AtomicIDecrement. Also, I wonder if that will be a patch bump so that we can use Cargo's [patch.crates-io] to get more atomics?

[cwfitzgerald]

This is just parsing, not fully translating them, as far as im aware. @schell is that a correct assessment?

[schell]

@tombh AtomicIIncrement should indeed be working in 0.22! Please let me know if naga does not accept your shader that uses this op!

@cwfitzgerald #5702 was the parsing portion of support for AtomicIIncrement and #5775 is actually the bulk of atomics support (it's the whole type-upgrade thing). #5824 add support for parsing more ops and after it lands naga will support all atomic ops except for AtomicCompareExchange, which is going to take just a bit more infrastructure to support.

[cwfitzgerald]

Oh snap, how did I miss that! That's awesome

[tombh]

Great news @schell! I atomically increment your awesomeness 😆

[schell]

Great news @schell! I atomically increment your awesomeness 😆

OMG that's a good one 🤣 ! 🙇