[HLSL] Array by-value parameter passing #70123
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Some of the documentation for this is available here: The initial PR is: #79382 |
llvm-beanz
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HLSL constant sized array function parameters do not decay to pointers. Instead constant sized array types are preserved as unique types for overload resolution, template instantiation and name mangling. This implements the change by adding a new `ArrayParameterType` which represents a non-decaying `ConstantArrayType`. The new type behaves the same as `ConstantArrayType` except that it does not decay to a pointer. Values of `ConstantArrayType` in HLSL decay during overload resolution via a new `HLSLArrayRValue` cast to `ArrayParameterType`. `ArrayParamterType` values are passed indirectly by-value to functions in IR generation resulting in callee generated memcpy instructions. The behavior of HLSL function calls is documented in the [draft language specification](https://microsoft.github.io/hlsl-specs/specs/hlsl.pdf) under the Expr.Post.Call heading. Additionally the design of this implementation approach is documented in [Clang's documentation](https://clang.llvm.org/docs/HLSL/FunctionCalls.html) Resolves #70123
EugeneZelenko
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@llvm/issue-subscribers-clang-frontend Author: Chris B (llvm-beanz)
In HLSL arrays when passed as parameters to functions are passed by-value. This is implemented in DXIL by creating a temporary of the array then passing the pointer-decayed temporary in place of the parameter.
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-function-parameters AC:
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In HLSL arrays when passed as parameters to functions are passed by-value. This is implemented in DXIL by creating a temporary of the array then passing the pointer-decayed temporary in place of the parameter.
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-function-parameters
AC:
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