SPIR-V: Emit RayTmaxKHR builtin for RayTCurrent IOP

[MarijnS95]

Fixes #3322

HitTKHR was removed from the spec as it merely shadows RayTmaxKHR. Emitting it results in invalid SPIR-V:

generated SPIR-V is invalid: Operand 3 of Decorate requires one of these capabilities: RayTracingNV
  OpDecorate %6 BuiltIn HitTNV

Replace the builtin by RayTmaxKHR if NV_ray_tracing is not enabled to resolve this.

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Is this valid in all of the cases outlined here? I assume - given that that commit says it shadows RayTmax anyway, likely also on NV - that the max is updated upon hit?

[AppVeyorBot]

✅ Build DirectXShaderCompiler 1.0.4019 completed (commit a7a340874d by @MarijnS95)

[ehsannas]

yeah I think it should cover everything

[ehsannas]

More context:
HitTKHR has been removed as it is an alias for RayTMaxKHR. See: KhronosGroup/SPIRV-Headers@bdd2aa3

[ehsannas]

@MarijnS95 would you be able to share a shader that reproduces the issue, so we can add it as a unit test? Or add a unit test to this PR? (adding a unit test is easy. See https://github.com/microsoft/DirectXShaderCompiler/pull/2512/files as an example). You can just have a // CHECK: for RayTmaxKHR

[MarijnS95]

More context:
HitTKHR has been removed as it is an alias for RayTMaxKHR. See: KhronosGroup/SPIRV-Headers@bdd2aa3

@ehsannas Already in the main PR description as well as the topmost commit, including the link to that SPIRV-Headers change :)

@MarijnS95 would you be able to share a shader that reproduces the issue, so we can add it as a unit test? Or add a unit test to this PR? (adding a unit test is easy. See https://github.com/microsoft/DirectXShaderCompiler/pull/2512/files as an example). You can just have a // CHECK: for RayTmaxKHR

Done, writing tests is the easy part but realising disassembly prints these as RayTmaxNV (small m, NV instead of KHR) takes most of the time.
I didn't add tests to all possible (nv) shaders though, and KHR only has a closesthit test shader.

[ehsannas]

Sounds good. Thanks

[ehsannas]

LGTM. I'll merge once the bots are green.

[AppVeyorBot]

✅ Build DirectXShaderCompiler 1.0.4023 completed (commit c44dbfb437 by @MarijnS95)