[SPIRV][DX] Share one test between backends

[Keenuts]

One big issue with DirectXShaderCompiler was test coverage: DXIL and SPIR-V backends had their own tests. When a bug was found in one, the other wasn't always checked. This lead to unequal support of HLSL for both backends. We'd like to avoid those issues here, hence the test-sharing.

By default, all the tests in this folder are marked as requiring DirectX. But as SPIR-V support grows, each test drop this requirement, and check the SPIR-V behavior.

I would have preferred to mark new tests as XFAIL for SPIR-V by default, so we could differentiate real unsupported tests (as SPIR-V has no equivalent), from newly added tests. But the way LIT is built, I don't think this is possible.

[Keenuts]

The buildkite failure seems to be related to the quoting of the - *_result.json. Seems unrelated to this change.

[llvm-beanz]

I don't think this is the right approach for test sharing. These tests all specifically test code in the DirectX backend, they aren't the kinds of tests that should be shared with the SPIR-V backend.

[bogner]

Would it make the most sense to have a place like test/Frontend/HLSL/ (to match lib/Frontend/HLSL - though there isn't such a directory yet)? This would provide a common place for HLSL specific constructs like numthreads and resources at least.

[Keenuts]

Would it make the most sense to have a place like test/Frontend/HLSL/ (to match lib/Frontend/HLSL - though there isn't such a directory yet)? This would provide a common place for HLSL specific constructs like numthreads and resources at least.

Yes, this makes sense. I don't know what the broader community will think of having frontend-specific tests here, but I do agree it would make sense.
Reverted the initial changes, and moved the shared test to the new folder.

[bogner]

This looks good to me. @llvm-beanz are you happy with this approach?

[llvm-beanz]

LGTM. At some point we'll want to expand the list of supported targets, but we can think about that later.

[Keenuts]

Thanks!
Added @michalpaszkowski on the SPIR-V side.

[michalpaszkowski]

Thanks @Keenuts for working on this! LGTM!

[Keenuts]

rebased on main for merge

[Keenuts]

One failure on presubmit: python formatting. From the logs it's a bad argument, infra related (https://github.com/llvm/llvm-project/actions/runs/6259826929/job/16996615363?pr=65975).
Unrelated.