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

Xiang Li via cfe-commits cfe-commits at lists.llvm.org
Thu Mar 21 07:17:27 PDT 2024


================
@@ -0,0 +1,258 @@
+====================
+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.)
+
+TODO: replace the following link with actual serialized format. 
+    DXC implementation of the serialization could be find `here
+    <https://github.com/microsoft/DirectXShaderCompiler/blob/main/lib/DxilRootSignature/DxilRootSignatureSerializer.cpp#L41>`_
+
+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. 
+
+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 a constant 
+initializer to save things like space and NumDescriptors in LLVM IR. 
+
+CGHLSLRuntime will generate metadata to link the global variable as root 
+signature for given entry function. 
+
+In LLVM DirectX backend, the global variable will be serialized and saved as 
+another global variable with section 'RTS0' with the serialized root signature 
+as initializer in DXContainerGlobals pass. 
----------------
python3kgae wrote:

Added.

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


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