Fix #10092: empty ray payload struct generates invalid CUDA code

[szihs]

Add non-template optixTrace/optixTraverse overloads for the empty payload case. When Slang's type legalization eliminates an empty payload struct, the generated CUDA code omits the payload argument, which failed to match any existing prelude wrapper.

[coderabbitai]

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📝 Walkthrough

Walkthrough

Added non-template overloads for OptiX tracing, traversal, and invoke functions in the CUDA prelude header to support empty payload scenarios. These wrappers enable code generated when payloads are eliminated by type legalization to compile without providing payload arguments.

Changes

Cohort / File(s)	Summary
OptiX Empty Payload Overloads prelude/slang-cuda-prelude.h	Added four non-template function overloads: two variants of optixTrace, one optixTraverse, and one optixInvoke, each handling cases where payloads are absent by forwarding calls to existing functions with appropriate parameter omissions.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 Empty payloads, they said, won't compile,
So we crafted some wrappers with OptiX style,
No data to pass? No problem at all!
Our overloads answer the payload-less call! 🌟

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing CUDA code generation for empty ray payload structs by adding non-template overloads.
Description check	✅ Passed	The description is directly related to the changeset, explaining the problem (empty payload elimination) and the solution (non-template overloads for matching generated calls).

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✨ Finishing Touches

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• Post copyable unit tests in a comment

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[Copilot]

Pull request overview

Fixes CUDA/OptiX codegen for the case where Slang’s legalization removes an empty ray payload struct, causing generated CUDA to call optixTrace / optixTraverse without a payload argument that previously didn’t match any Slang-provided wrapper overload.

Changes:

• Added a non-template optixTrace(...) overload that accepts no payload argument and forwards to the native OptiX intrinsic.
• Added a non-template optixTraverse(...) overload that accepts no payload argument (but keeps the hitObj parameter for signature compatibility) and forwards to the native OptiX intrinsic.

[Copilot]

Please add a regression test that exercises the empty ray payload case on the CUDA target (e.g., a [raypayload] struct with no fields used with TraceRay/HitObject::TraceRay) and filecheck that the generated CUDA calls the new no-payload optixTrace/optixTraverse overload(s). This change fixes a codegen mismatch, but without a test it’s easy for future prelude/codegen changes to reintroduce the invalid CUDA call signature from #10092.