feature: [spv-front] Support for OpAtomicCompareExchange, fixes #6296

[schell]

Connections

• [naga spv-in] Support for OpAtomicCompareExchange #6296
• [spv-in] Atomics support #4489

Description
Adds support for parsing and executing OpAtomicCompareExchange in the SPIR-V frontend.
This concludes the work to support atomics in the SPIR-V frontend, excluding test clean-up.

Testing

RUST_LOG=trace cargo watch -x 'test -p naga --features spv-in,wgsl-in,wgsl-out -- --nocapture atomic_compare_exchange'

Checklist

• First, merge [naga spv-in] Let BlockContext hold a &mut Module. #6682.
• Run cargo fmt.
• Run taplo format.
• Run cargo clippy. If applicable, add:
  • --target wasm32-unknown-unknown
  • --target wasm32-unknown-emscripten
• Run cargo xtask test to run tests.
• Add change to CHANGELOG.md. See simple instructions inside file.

[jimblandy]

Okay, I got into reviewing this, but ended up filing other stuff I noticed in the process (#6670 and #6671). I'll pick it up again tomorrow.

[jimblandy]

The changes to type_gen.rs are not the way we should handle this. That file should remain unchanged by this PR.

Instead, BlockContext should borrow a shared reference to Module::special_types in addition to all the other bits and pieces it borrows, and then it should simply look up the appropriate crate::PredeclaredType::AtomicCompareExchangeWeakResult key in SpecialTypes::predeclared_types. It knows it will find the entry, because parse put them both there.

[jimblandy]

@schell Just a heads up, I pushed a tiny cleanup commit to this branch.

[jimblandy]

The way this PR causes the atomic result types to be included in all modules built from SPIR-V source is not great. But it's not straightforward to address unless we fix #6679.

[jimblandy]

Okay, I've put up #6682 to fix #6679, rebased this PR on top of that, and then made the atomic struct creation work the way it should. This PR now makes no changes to the snapshot output files.

[jimblandy]

This PR cannot be merged, in its current form, until #6682 is merged.

[jimblandy]

If I understand correctly, this is the final phase of your work on SPIR-V atomic input. If that's the case, then it's time to remove the tests in front/spv/mod.rs, and turn atomic_compare_exchange.spv into an ordinary snapshot test.

[schell]

Cleaning up the tests is still a part of my intended work. My grant project goes to the end of the year (and I've re-applied for 2025 as well).

Since I pushed a fix for some of my comments, for clarity I want to re-post the remaining items as a new review.

[jimblandy]

It's okay to address the tests in a subsequent PR. For now, here are the only remaining items to be addressed. Pretty minor, this looks good otherwise.

[schell]

Your last two comments have been addressed @jimblandy, I think we're g2g 👍 .

[jimblandy]

Looks great!

[jimblandy]

Note, this is still blocked on #6682.

[schell]

Thank you @jimblandy ! 🙇