microsoft / microsoft/DirectXShaderCompiler
[SPIR-V] NoContraction from precise does not propagate to functions
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- C++
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Description
Description
When I mark vs output position as precise, I expect to get precise semantics for all computations that contribute to it's value. However, when I put computations in a separate function, the NoContraction decorators are not applied to the computations inside the function, even though it is inlined in the final SpirV.
Steps to Reproduce
Here the NoContraction decorations are missing https://godbolt.org/z/xoj5hbh5T
And here (using macro instead of function) they are present https://godbolt.org/z/eGfbh5z6E
Actual Behavior
Missing NoContraction has led to artifacts on vulkan where it was fine on dx12 when using same shader codebase for SpirV and DXIL generation.
Environment
- DXC version 1.9.2602, also reproduced with 1.8.2505.1
- Host Operating System Windows 10 Pro 22H2 (also reproduced on other machines)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the two Godbolt reproductions and compare the generated SPIR-V for the separate-function and macro cases. Trace how precise on the vertex-position output is propagated during compilation and inlining. Done means computations inside the separate function receive the expected NoContraction decorations, matching the macro case.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- compilers, computer-graphics
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100