[clang] [Doc][HLSL] Add documentation for root signature. (PR #83933)

Xiang Li via cfe-commits cfe-commits at lists.llvm.org
Wed Mar 27 12:45:11 PDT 2024


================
@@ -0,0 +1,426 @@
+====================
+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++
+
+    #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(RS)]
+    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. (With the pointers translated to offsets.) 
+
+It will be look like this:
+
+.. code-block:: c++
+
+  struct DxilContainerRootDescriptor1 {
+    uint32_t ShaderRegister;
+    uint32_t RegisterSpace;
+    uint32_t Flags;
+  };
+
+  struct DxilContainerDescriptorRange {
+    uint32_t RangeType;
+    uint32_t NumDescriptors;
+    uint32_t BaseShaderRegister;
+    uint32_t RegisterSpace;
+    uint32_t OffsetInDescriptorsFromTableStart;
+  };
+
+  struct DxilContainerDescriptorRange1 {
+    uint32_t RangeType;
+    uint32_t NumDescriptors;
+    uint32_t BaseShaderRegister;
+    uint32_t RegisterSpace;
+    uint32_t Flags;
+    uint32_t OffsetInDescriptorsFromTableStart;
+  };
+
+  struct DxilContainerRootDescriptorTable {
+    uint32_t NumDescriptorRanges;
+    uint32_t DescriptorRangesOffset;
+  };
+
+  struct DxilContainerRootParameter {
+    uint32_t ParameterType;
+    uint32_t ShaderVisibility;
+    uint32_t PayloadOffset;
+  };
+
+  struct DxilContainerRootSignatureDesc {
+    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**.
+
+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 binary representation is finalized with an array of 
+**DxilStaticSamplerDesc** at 
+**DxilContainerRootSignatureDesc::StaticSamplersOffset**.
+
+Implementation Details
+======================
+
+The root signature string will be parsed in Clang. 
+The parsing 
+will happened when build HLSLRootSignatureAttr or when build standalone root 
+signature blob. 
+
+The root signature parsing will generate a HLSLRootSignatureAttr with member 
+represents the root signature string and the parsed information for each 
+resource in the root signature. It will bind to the entry function in the AST. 
+HLSLRootSignatureAttr will be something like this:
+Note, VersionedRootSignatureDesc is not D3D12_ROOT_SIGNATURE_DESC, it is just 
+a simple struct to collect all the information in the root signature string.
+
+.. 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;
+    };
+
+    class HLSLRootSignatureAttr : public InheritableAttr {
+    protected:
+      std::string RootSignatureStr;
+      VersionedRootSignatureDesc RootSignature;
+    };
+
+
+.. code-block:: c++
+
+    def HLSLEntryRootSignature: HLSLRootSignatureAttr {
+      let Spellings = [GNU<"RootSignature">];
+      let Subjects = Subjects<[HLSLEntry]>;
+      let LangOpts = [HLSL];
+      let Args = [StringArgument<"InputString">];
+    }
+
+For case compile to a standalone root signature blob, the 
+HLSLRootSignatureAttr will be bind to a fake empty entry.
+
+In clang code generation, the HLSLRootSignatureAttr in AST will be translated 
+into a global variable with struct type to express the layout and metadata to 
+save things like static sampler, root flags, space and NumDescriptors in LLVM IR. 
+The struct type will be look like this:
+
+.. code-block:: c++
+
+  %struct.TABLE0 = type { target("dx.rs.desc"),
+                          target("dx.rs.sampler")}
+
+  %struct.RS = type { target("dx.rs.rootconstant", 4), 
+                      %struct.TABLE0,
+                      target("dx.rs.rootdescriptor") }
+
+The metadata will be look like this:
+
+.. code-block:: c++
----------------
python3kgae wrote:

Changed to blank.

https://github.com/llvm/llvm-project/pull/83933


More information about the cfe-commits mailing list