[SPIR-V] Add proposal for vk::push_constant #360
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Adds proposal to implement VK push constant support in Clang.
| - There can only be one ``[[vk::push_constant]]`` attribute in the shader. | ||
| - There can be no VLA in the struct type (or a nested struct type). | ||
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| DXC allows any storage class to be attached to a push constant. I believe |
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Good call. Please list which storage classes are currently accepted by DXC, that will not be supported in Clang.
We should update DXC to match 202X?
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Keywords DXC accepts are:
- extern
- static
- groupshared
- shared
- uniform
Seems like [const] [extern] uniform is the good class, but [const] auto/none should be allowed as the attributes implies const extern uniform already.
| This being a Vulkan specific feature, the attribute is ignored when targeting | ||
| DXIL. This means the push constant global becomes part of the cbuffer when | ||
| building for DXIL. | ||
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| The attribute being ignored, the variable belong to the cbuffer, meaning no | ||
| additional handling is required. |
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I still don't fully understand all of the requirements for HLSL attributes in SEMA. For the resource work @hekota mentioned that for the clang based tools like the rewriter, the attributes will have to be in the AST.
Can you be more explicit about where and how it will be ignored?
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The AST will have the HLSLVkPushConstant attribute since parsing will see it. But in Sema, this attribute will be ignored, meaning we won't change the current behavior which is to put a global in the global cbuffer.
| Codegen will be left almost as-is as we simply load a variable in a different | ||
| address space. |
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Can you be more explicit about what the layout of the struct should be? I believe it is the same as a RWStructuredBuffer.
The DXC SPIR-V documentation does not mention it.
The rules in the Vulkan documentation give the same layout rules for push constant as storage buffers.
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Adds proposal to implement VK push constant support in Clang.
E2E implementation draft: llvm/llvm-project#166793