HLSL Working Group

2025-07-17 - HLSL Working Group Minutes

  • Discussion topics
    • Shader semantics implementation: https://github.com/llvm/wg-hlsl/pull/296
      • @tex3d and @Keenuts discussed the documentation of HLSL semantic annotations.
        • @tex3d mentioned the need to document DXC’s behavior including how system values are organized.
        • Action Item to @Keenuts to expand documentation on DXC’s behavior
      • @tex3d mentioned that the current implementation needs to be revised to handle additional use cases and complexity.
      • @Keenuts has a branch supporting input, output and user semantics in progress.
    • Root Signature driver options in clang: https://github.com/llvm/wg-hlsl/pull/320
      • @inbelic walked through his proposal for bringing over driver options from DXC to Clang-DXC.
      • Some of the options are very straightforward, like -force-rootsig-ver. Others are more complicated.
      • There was a discussion of how and when root signature validation occurs in Clang and DXC.
        • @bogner: I think being consistent with whatever we do for that makes sense.
        • @bogner: …in DXC, all of this stuff happens late. I think in Clang, we have to be a little bit more deliberate about some of these things because the things that are done in like the AST and Sema.
      • Qstrip_rootsignature fairly common and widely used, and we will need to support it
      • setrootsignature is also used when attaching separately compiled root signatures
        • @tex3d suggested container manipulation in a separate tool similar to dxa in DXC.
        • @llvm-beanz suggested adding support in objcopy which would align with idomatic practices in LLVM and Clang
        • Driver options could be implemented in terms of an external tool for compatability and made more efficient later if performance is a problem.
      • @tex3d noted that the verifyrootsignature validates the shader bindings against the root signature. This option is essential for ensuring the validity of the root signature and shader combination
      • The Frs option was also discussed.
        • @bogner suggested adding this as a driver action to post-process the output file
      • Action Item to @inbelic: Create a scenario for objcopy support to handle container manipulation support.
    • Scalarizer pass generating invalid DXIL: https://github.com/llvm/llvm-project/issues/149345
      • Agreement seems to be that this is a bug in the scalarizer pass which needs investigation.
    • Lowering of structs to DXIL: https://github.com/llvm/llvm-project/issues/147109
      • Did not get to this topic, will be carried over to next week.

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