[clang] [Doc][HLSL] Add documentation for root signature. (PR #83933)
Chris B via cfe-commits
cfe-commits at lists.llvm.org
Mon Mar 4 19:43:38 PST 2024
================
@@ -0,0 +1,210 @@
+====================
+HLSL Root Signatures
+====================
+
+.. contents::
+ :local:
+
+Usage
+=====
+
+In HLSL, the `root signature
+<https://learn.microsoft.com/en-us/windows/win32/direct3d12/root-signatures>`_
+defines what types of resources are bound to the graphics pipeline.
+
+A root signature can be specified in HLSL as a `string
+<https://learn.microsoft.com/en-us/windows/win32/direct3d12/specifying-root-signatures-in-hlsl#an-example-hlsl-root-signature>`_.
+The string contains a collection of comma-separated clauses that describe root
+signature constituent components.
+
+There are two mechanisms to compile an HLSL root signature. First, it is
+possible to attach a root signature string to a particular shader via the
+RootSignature attribute (in the following example, using the MyRS1 entry
+point):
+
+.. code-block:: c++
+
+ [RootSignature(MyRS1)]
+ float4 main(float4 coord : COORD) : SV_Target
+ {
+ …
+ }
+
+The compiler will create and verify the root signature blob for the shader and
+embed it alongside the shader byte code into the shader blob.
+
+The other mechanism is to create a standalone root signature blob, perhaps to
+reuse it with a large set of shaders, saving space. The name of the define
+string is specified via the usual -E argument. For example:
+
+.. code-block:: c++
+ dxc.exe -T rootsig_1_1 MyRS1.hlsl -E MyRS1 -Fo MyRS1.fxo
+
+Note that the root signature string define can also be passed on the command
+line, e.g, -D MyRS1=”…”.
+
+Root Signature Grammar
+======================
+
+.. code-block:: c++
+
+ RootSignature : (RootElement(,RootElement)?)?
+
+ RootElement : RootFlags | RootConstants | RootCBV | RootSRV | RootUAV | DescriptorTable | StaticSampler
+
+ RootFlags : 'RootFlags' '(' (RootFlag(|RootFlag)?)? ')'
+
+ RootFlag : 'ALLOW_INPUT_ASSEMBLER_INPUT_LAYOUT' | 'DENY_VERTEX_SHADER_ROOT_ACCESS'
+
+ RootConstants : 'RootConstants' '(' 'num32BitConstants' '=' NUMBER ',' bReg (',' 'space' '=' NUMBER)? (',' 'visibility' '=' SHADER_VISIBILITY)? ')'
+
+ RootCBV : 'CBV' '(' bReg (',' 'space' '=' NUMBER)? (',' 'visibility' '=' SHADER_VISIBILITY)? (',' 'flags' '=' DATA_FLAGS)? ')'
+
+ RootSRV : 'SRV' '(' tReg (',' 'space' '=' NUMBER)? (',' 'visibility' '=' SHADER_VISIBILITY)? (',' 'flags' '=' DATA_FLAGS)? ')'
+
+ RootUAV : 'UAV' '(' uReg (',' 'space' '=' NUMBER)? (',' 'visibility' '=' SHADER_VISIBILITY)? (',' 'flags' '=' DATA_FLAGS)? ')'
+
+ DescriptorTable : 'DescriptorTable' '(' (DTClause(|DTClause)?)? (',' 'visibility' '=' SHADER_VISIBILITY)? ')'
+
+ DTClause : CBV | SRV | UAV | Sampler
+
+ CBV : 'CBV' '(' bReg (',' 'numDescriptors' '=' NUMBER)? (',' 'space' '=' NUMBER)? (',' 'offset' '=' DESCRIPTOR_RANGE_OFFSET)? (',' 'flags' '=' DATA_FLAGS)? ')'
+
+ SRV : 'SRV' '(' tReg (',' 'numDescriptors' '=' NUMBER)? (',' 'space' '=' NUMBER)? (',' 'offset' '=' DESCRIPTOR_RANGE_OFFSET)? (',' 'flags' '=' DATA_FLAGS)? ')'
+
+ UAV : 'UAV' '(' uReg (',' 'numDescriptors' '=' NUMBER)? (',' 'space' '=' NUMBER)? (',' 'offset' '=' DESCRIPTOR_RANGE_OFFSET)? (',' 'flags' '=' DATA_FLAGS)? ')'
+
+ Sampler : 'Sampler' '(' sReg (',' 'numDescriptors' '=' NUMBER)? (',' 'space' '=' NUMBER)? (',' 'offset' '=' DESCRIPTOR_RANGE_OFFSET)? (',' 'flags' '=' NUMBER)? ')'
+
+
+ SHADER_VISIBILITY : 'SHADER_VISIBILITY_ALL' | 'SHADER_VISIBILITY_VERTEX' | 'SHADER_VISIBILITY_HULL' | 'SHADER_VISIBILITY_DOMAIN' | 'SHADER_VISIBILITY_GEOMETRY' | 'SHADER_VISIBILITY_PIXEL' | 'SHADER_VISIBILITY_AMPLIFICATION' | 'SHADER_VISIBILITY_MESH'
+
+ DATA_FLAGS : 'DATA_STATIC_WHILE_SET_AT_EXECUTE' | 'DATA_VOLATILE'
+
+ DESCRIPTOR_RANGE_OFFSET : 'DESCRIPTOR_RANGE_OFFSET_APPEND' | NUMBER
+
+ StaticSampler : 'StaticSampler' '(' sReg (',' 'filter' '=' FILTER)? (',' 'addressU' '=' TEXTURE_ADDRESS)? (',' 'addressV' '=' TEXTURE_ADDRESS)? (',' 'addressW' '=' TEXTURE_ADDRESS)? (',' 'mipLODBias' '=' NUMBER)? (',' 'maxAnisotropy' '=' NUMBER)? (',' 'comparisonFunc' '=' COMPARISON_FUNC)? (',' 'borderColor' '=' STATIC_BORDER_COLOR)? (',' 'minLOD' '=' NUMBER)? (',' 'maxLOD' '=' NUMBER)? (',' 'space' '=' NUMBER)? (',' 'visibility' '=' SHADER_VISIBILITY)? ')'
+
+ bReg : 'b' NUMBER
+
+ tReg : 't' NUMBER
+
+ uReg : 'u' NUMBER
+
+ sReg : 's' NUMBER
+
+ FILTER : 'FILTER_MIN_MAG_MIP_POINT' | 'FILTER_MIN_MAG_POINT_MIP_LINEAR' | 'FILTER_MIN_POINT_MAG_LINEAR_MIP_POINT' | 'FILTER_MIN_POINT_MAG_MIP_LINEAR' | 'FILTER_MIN_LINEAR_MAG_MIP_POINT' | 'FILTER_MIN_LINEAR_MAG_POINT_MIP_LINEAR' | 'FILTER_MIN_MAG_LINEAR_MIP_POINT' | 'FILTER_MIN_MAG_MIP_LINEAR' | 'FILTER_ANISOTROPIC' | 'FILTER_COMPARISON_MIN_MAG_MIP_POINT' | 'FILTER_COMPARISON_MIN_MAG_POINT_MIP_LINEAR' | 'FILTER_COMPARISON_MIN_POINT_MAG_LINEAR_MIP_POINT' | 'FILTER_COMPARISON_MIN_POINT_MAG_MIP_LINEAR' | 'FILTER_COMPARISON_MIN_LINEAR_MAG_MIP_POINT' | 'FILTER_COMPARISON_MIN_LINEAR_MAG_POINT_MIP_LINEAR' | 'FILTER_COMPARISON_MIN_MAG_LINEAR_MIP_POINT' | 'FILTER_COMPARISON_MIN_MAG_MIP_LINEAR' | 'FILTER_COMPARISON_ANISOTROPIC' | 'FILTER_MINIMUM_MIN_MAG_MIP_POINT' | 'FILTER_MINIMUM_MIN_MAG_POINT_MIP_LINEAR' | 'FILTER_MINIMUM_MIN_POINT_MAG_LINEAR_MIP_POINT' | 'FILTER_MINIMUM_MIN_POINT_MAG_MIP_LINEAR' | 'FILTER_MINIMUM_MIN_LINEAR_MAG_MIP_POINT' | 'FILTER_MINIMUM_MIN_LINEAR_MAG_POINT_MIP_LINEAR' | 'FILTER_MINIMUM_MIN_MAG_LINEAR_MIP_POINT' | 'FILTER_MINIMUM_MIN_MAG_MIP_LINEAR' | 'FILTER_MINIMUM_ANISOTROPIC' | 'FILTER_MAXIMUM_MIN_MAG_MIP_POINT' | 'FILTER_MAXIMUM_MIN_MAG_POINT_MIP_LINEAR' | 'FILTER_MAXIMUM_MIN_POINT_MAG_LINEAR_MIP_POINT' | 'FILTER_MAXIMUM_MIN_POINT_MAG_MIP_LINEAR' | 'FILTER_MAXIMUM_MIN_LINEAR_MAG_MIP_POINT' | 'FILTER_MAXIMUM_MIN_LINEAR_MAG_POINT_MIP_LINEAR' | 'FILTER_MAXIMUM_MIN_MAG_LINEAR_MIP_POINT' | 'FILTER_MAXIMUM_MIN_MAG_MIP_LINEAR' | 'FILTER_MAXIMUM_ANISOTROPIC'
+
+ TEXTURE_ADDRESS : 'TEXTURE_ADDRESS_WRAP' | 'TEXTURE_ADDRESS_MIRROR' | 'TEXTURE_ADDRESS_CLAMP' | 'TEXTURE_ADDRESS_BORDER' | 'TEXTURE_ADDRESS_MIRROR_ONCE'
+
+ COMPARISON_FUNC : 'COMPARISON_NEVER' | 'COMPARISON_LESS' | 'COMPARISON_EQUAL' | 'COMPARISON_LESS_EQUAL' | 'COMPARISON_GREATER' | 'COMPARISON_NOT_EQUAL' | 'COMPARISON_GREATER_EQUAL' | 'COMPARISON_ALWAYS'
+
+ STATIC_BORDER_COLOR : 'STATIC_BORDER_COLOR_TRANSPARENT_BLACK' | 'STATIC_BORDER_COLOR_OPAQUE_BLACK' | 'STATIC_BORDER_COLOR_OPAQUE_WHITE'
+
+
+Serialized format
+======================
+The root signature string is parsed and serialized into a binary format. The
+binary format is a sequence of bytes that can be used to create a root signature
+object in the Direct3D 12 API. The binary format is defined by the
+`D3D12_ROOT_SIGNATURE_DESC (for rootsig_1_0)
+<https://learn.microsoft.com/en-us/windows/win32/api/d3d12/ns-d3d12-d3d12_root_signature_desc>`_
+or `D3D12_ROOT_SIGNATURE_DESC1 (for rootsig_1_1)
+<https://learn.microsoft.com/en-us/windows/win32/api/d3d12/ns-d3d12-d3d12_root_signature_desc1>`_
+structure in the Direct3D 12 API.
+
+
+
+Implementation Details
+======================
+
+The root signature string will be parsed in the HLSL frontend.
+The parsing
+will happened when build HLSLRootSignatureAttr or when build standalone root
+signature blob.
+
+The root signature parsing will generate a VersionedRootSignatureDesc object
+that represents the root signature string.
+VersionedRootSignatureDesc is a struct that contains a RootSignatureVersion
+and a RootSignatureDesc.
+
+.. code-block:: c++
+ struct DescriptorRange {
+ DescriptorRangeType RangeType;
+ uint32_t NumDescriptors = 1;
+ uint32_t BaseShaderRegister;
+ uint32_t RegisterSpace = 0;
+ DescriptorRangeFlags Flags = DescriptorRangeFlags::None;
+ uint32_t OffsetInDescriptorsFromTableStart = DescriptorRangeOffsetAppend;
+ };
+
+ struct RootDescriptorTable {
+ std::vector<DescriptorRange> DescriptorRanges;
+ };
+ struct RootConstants {
+ uint32_t ShaderRegister;
+ uint32_t RegisterSpace = 0;
+ uint32_t Num32BitValues;
+ };
+
+ struct RootDescriptor {
+ uint32_t ShaderRegister;
+ uint32_t RegisterSpace = 0;
+ RootDescriptorFlags Flags = RootDescriptorFlags::None;
+ };
+ struct RootParameter {
+ RootParameterType ParameterType;
+ std::variant<RootDescriptorTable, RootConstants, RootDescriptor>
+ Parameter;
+ ShaderVisibility ShaderVisibility = ShaderVisibility::All;
+ };
+
+ struct StaticSamplerDesc {
+ Filter Filter = Filter::ANISOTROPIC;
+ TextureAddressMode AddressU = TextureAddressMode::Wrap;
+ TextureAddressMode AddressV = TextureAddressMode::Wrap;
+ TextureAddressMode AddressW = TextureAddressMode::Wrap;
+ float MipLODBias = 0.f;
+ uint32_t MaxAnisotropy = 16;
+ ComparisonFunc ComparisonFunc = ComparisonFunc::LessEqual;
+ StaticBorderColor BorderColor = StaticBorderColor::OpaqueWhite;
+ float MinLOD = 0.f;
+ float MaxLOD = MaxLOD;
+ uint32_t ShaderRegister;
+ uint32_t RegisterSpace = 0;
+ ShaderVisibility ShaderVisibility = ShaderVisibility::All;
+ };
+
+ struct RootSignatureDesc {
+ std::vector<RootParameter> Parameters;
+ std::vector<StaticSamplerDesc> StaticSamplers;
+ RootSignatureFlags Flags;
+ };
+
+ struct VersionedRootSignatureDesc {
+ RootSignatureVersion Version;
+ RootSignatureDesc Desc;
+ };
+
+Things like DescriptorRangeType and RootDescriptorFlags will be enums.
+
+After parsing, the VersionedRootSignatureDesc will be translated into a
+constant global variable in the clang AST and save to the
+HLSLRootSignatureAttr.
----------------
llvm-beanz wrote:
We don't need a new AST node other than the AST node being added for the attribute. We can add additional data members to that AST node and allow it to store the root signature information in a representation that is convenient for generating diagnostics and later serializing.
https://github.com/llvm/llvm-project/pull/83933
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