================
@@ -0,0 +1,562 @@
+====================
+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 main entry
+point):
+
+.. code-block::
+
+ #define RS "RootFlags( ALLOW_INPUT_ASSEMBLER_INPUT_LAYOUT | " \
+ "DENY_VERTEX_SHADER_ROOT_ACCESS), " \
+ "CBV(b0, space = 1, flags = DATA_STATIC), " \
+ "SRV(t0), " \
+ "UAV(u0), " \
+ "DescriptorTable( CBV(b1), " \
+ " SRV(t1, numDescriptors = 8, " \
+ " flags = DESCRIPTORS_VOLATILE), " \
+ " UAV(u1, numDescriptors = unbounded, " \
+ " flags = DESCRIPTORS_VOLATILE)), " \
+ "DescriptorTable(Sampler(s0, space=1, numDescriptors = 4)), " \
+ "RootConstants(num32BitConstants=3, b10), " \
+ "StaticSampler(s1)," \
+ "StaticSampler(s2, " \
+ " addressU = TEXTURE_ADDRESS_CLAMP, " \
+ " filter = FILTER_MIN_MAG_MIP_LINEAR )"
+
+ [RootSignature(MyRS)]
+ 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:: sh
+
+ 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 could also used in form of StateObject like this:
+
+.. code-block::
+
+ GlobalRootSignature MyGlobalRootSignature =
+ {
+ "DescriptorTable(UAV(u0))," // Output texture
+ "SRV(t0)," // Acceleration structure
+ "CBV(b0)," // Scene constants
+ "DescriptorTable(SRV(t1, numDescriptors = 2))" // Static index and
vertex buffers.
+ };
+
+ LocalRootSignature MyLocalRootSignature =
+ {
+ "RootConstants(num32BitConstants = 4, b1)" // Cube constants
+ };
+
+
+Root Signature Grammar
+======================
+
+.. code-block:: peg
+
+ 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. (With the pointers translated to offsets.)
+
+It will be look like this:
+
+.. code-block:: c++
+
+ namespace dxbc {
+ namespace SerializedRootSignature {
+ namespace v_1_0 {
+
+ struct DxilContainerDescriptorRange {
+ uint32_t RangeType;
+ uint32_t NumDescriptors;
+ uint32_t BaseShaderRegister;
+ uint32_t RegisterSpace;
+ uint32_t OffsetInDescriptorsFromTableStart;
+ };
+
+ struct ContainerRootDescriptor {
+ uint32_t ShaderRegister;
+ uint32_t RegisterSpace;
+ };
+ }
+ namespace v_1_1 {
+
+ struct ContainerDescriptorRange {
+ uint32_t RangeType;
+ uint32_t NumDescriptors;
+ uint32_t BaseShaderRegister;
+ uint32_t RegisterSpace;
+ uint32_t Flags;
+ uint32_t OffsetInDescriptorsFromTableStart;
+ };
+
+ struct ContainerRootDescriptor {
+ uint32_t ShaderRegister;
+ uint32_t RegisterSpace;
+ uint32_t Flags;
+ };
+ }
+
+ struct ContainerRootDescriptorTable {
+ uint32_t NumDescriptorRanges;
+ uint32_t DescriptorRangesOffset;
+ };
+
+ struct RootConstants {
+ uint32_t ShaderRegister;
+ uint32_t RegisterSpace = 0;
+ uint32_t Num32BitValues;
+ };
+
+ struct ContainerRootParameter {
+ uint32_t ParameterType;
+ uint32_t ShaderVisibility;
+ uint32_t PayloadOffset;
+ };
+
+ 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 ContainerRootSignatureDesc {
+ uint32_t Version;
+ uint32_t NumParameters;
+ uint32_t RootParametersOffset;
+ uint32_t NumStaticSamplers;
+ uint32_t StaticSamplersOffset;
+ uint32_t Flags;
+ };
+ }
+ }
+
+
+The binary representation begins with a **DxilContainerRootSignatureDesc**
+object.
+
+The object will be followed by an array of
+**DxilContainerRootParameter/Parameter1** objects located at
+**DxilContainerRootSignatureDesc::RootParametersOffset**, which corresponds to
+the size of **DxilContainerRootSignatureDesc**.
+
+Then it will be an array of
+**DxilStaticSamplerDesc** at
+**DxilContainerRootSignatureDesc::StaticSamplersOffset**.
+
+Subsequently, there will be detailed object (**DxilRootConstants**,
+**DxilContainerRootDescriptorTable**, or
+**DxilRootDescriptor/DxilContainerRootDescriptor1**, depending on the
parameter
+type) for each **DxilContainerRootParameter** in the array. With
+**DxilContainerRootParameter.PayloadOffset** pointing to the detailed object.
+
+In cases where the detailed object is a **DxilContainerRootDescriptorTable**,
+it is succeeded by an array of
+**DxilContainerDescriptorRange/DxilContainerDescriptorRange1** at
+**DxilContainerRootDescriptorTable.DescriptorRangesOffset**.
+
+The layout could be look like this for the MyRS in above example:
+.. code-block:: c++
+
+ struct SerializedRS {
+ ContainerRootSignatureDesc RSDesc;
+ ContainerRootParameter rootParameters[6];
+ StaticSamplerDesc samplers[2];
+
+ // Extra part for each RootParameter in rootParameters.
+
+ // RootConstants/RootDescriptorTable/RootDescriptor dependent on
ParameterType.
+ // For RootDescriptorTable, the extra part will be like
+
+ // struct {
+
+ // RootDescriptorTable table;
+
+ // ContainerDescriptorRange ranges[NumDescriptorRangesForTheTable];
+
+ // };
+
+ struct {
+
+ RootConstants b0;
+
+ ContainerRootDescriptor t1;
+
+ ContainerRootDescriptor u1;
+
+ struct {
+
+ ContainerRootDescriptor tab0;
+
+ ContainerDescriptorRange tab0Ranges[2];
+
+ } table0;
+
+ struct {
+
+ ContainerRootDescriptor tab1;
+
+ ContainerDescriptorRange tab1Ranges[1];
+
+ } table1;
+
+ RootConstants b10;
+
+ };
+
+ };
+
+
+Life of a Root Signature
+========================
+
+The root signature in a compiler begins with a string in the root signature
+attribute and ends with a serialized root signature in the DXContainer.
+
+To report errors as early as possible, root signature string parsing should
+occur in Sema.
+
+To ensure that a used resource has a binding in the root signature, this
+information should be accessible in the backend to make sure legal dxil is
+generated.
+
+
+Implementation Details
+======================
+
+The root signature string will be parsed in Clang.
+The parsing
+will happened when build HLSLRootSignatureAttr, standalone root signature blob
+or local/global root signature.
+
+A new AST node HLSLRootSignatureDecl will be added to represent the root
+signature in the AST.
+
+Assuming the cost to parse root signature string is cheap,
+HLSLRootSignatureDecl will follow common Clang approach which only save the
+string in the AST.
+A root signature will be parsed twice, once in Sema for diagnostic and once in
+clang code generation for generating the serialized root signature.
+The first parsing will check register overlap and run on all root signatures
+in the translation unit.
+The second parsing will calculate the offset for serialized root signature and
+only run on the root signature for the entry function or local/global root
+signature which used in SubobjectToExportsAssociation.
+
+HLSLRootSignatureDecl will have method to parse the string for diagnostic and
+generate the SerializedRS mentioned above.
+
+A HLSLRootSignatureAttr will be created when meet RootSignature attribute in
+HLSL.
+It will defined as below.
+
+.. code-block::
+
+ def HLSLEntryRootSignature: InheriableAttr {
----------------
damyanp wrote:
Typo?
```suggestion
def HLSLEntryRootSignature: InheritableAttr {
```
https://github.com/llvm/llvm-project/pull/83933
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