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microsoft / DirectXShaderCompiler

This repo hosts the source for the DirectX Shader Compiler which is based on LLVM/Clang.
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[SPIR-V] vk::ext_capability doesn't propagate correctly #6576

Closed nipunG314 closed 1 month ago

nipunG314 commented 5 months ago

Description

The [[vk::ext_capability(...)]] tag doesn't propagate if it isn't attached to a [[vk::ext_instruction(...)]] tag. It should either work on every method/function or give errors/warnings on the ones its not supposed to work on/will be ignored. Right now, we're forced to create a specialized version of the same templated function if we want to support a capability only on certain types (e.g. PhysicalStorageBufferAddresses for pointers, but not for builtin types like uint32_t)

Steps to Reproduce

https://godbolt.org/z/PjY3TTq1K

The [[vk::ext_capability(/*PhysicalStorageBufferAddresses */ 5347 )]] at line 17 isn't being propagated correctly. If you uncomment line 13, it compiles correctly.

Actual Behavior

fatal error: generated SPIR-V is invalid: Operand 2 of TypePointer requires one of these capabilities: PhysicalStorageBufferAddresses 
  %spirvIntrinsicType = OpTypePointer PhysicalStorageBuffer %uint

note: please file a bug report on https://github.com/Microsoft/DirectXShaderCompiler/issues with source code if possible

Compiler returned: 5

Environment

sudonatalie commented 4 months ago

Thanks for reporting @nipunG314 !

These are the rules for where vk::ext_capability can be used, but agreed that error messaging should be improved.

  • [[vk::ext_capability(uint _capability_)]]
    • An attribute to specify OpCapability instruction.
    • It can be an attribute of vk::ext_execution_mode(...), vk::ext_execution_mode_id(...), a function declared with vk::ext_instruction(...), or a function declared with [[vk::ext_type_def(...)]]. We can use multiple [[vk::ext_extension(string extension_name)]] for a single function.
    • uint capability must be a constant expression.

https://github.com/microsoft/DirectXShaderCompiler/wiki/GL_EXT_spirv_intrinsics-for-SPIR-V-code-gen

s-perron commented 1 month ago

In general, we do not want these attributes to propagate. We want it close to the feature that actually requires the extension or capability.

For your case, I would recommend addin it to the typedef:

https://github.com/microsoft/DirectXShaderCompiler/blob/9c6b2c1275e41cc385b2034aa2716ec2303a62d6/tools/clang/test/CodeGenSPIRV/spv.inline.capability.hlsl#L9-L10