[clang] [Doc][HLSL] Add documentation for root signature (PR #88781)
Damyan Pepper via cfe-commits
cfe-commits at lists.llvm.org
Mon Apr 15 14:00:13 PDT 2024
================
@@ -0,0 +1,291 @@
+====================
+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'
+
+GlobalRootSignature
+===================
+
+A GlobalRootSignature corresponds to a D3D12_GLOBAL_ROOT_SIGNATURE structure.
+
+The fields consist of some number of strings describing the parts of the root signature.
+The string should follow Root Signature Grammar.
+
+.. 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
+==================
+
+A LocalRootSignature corresponds to a D3D12_LOCAL_ROOT_SIGNATURE structure.
+
+Just like the global root signature subobject, the fields consist of some
+number of strings describing the parts of the root signature.
+The string should follow Root Signature Grammar.
+
+.. code-block::
+
+ LocalRootSignature MyLocalRootSignature =
+ {
+ "RootConstants(num32BitConstants = 4, b1)" // Cube constants
+ };
+
+
+SubobjectToExportsAssociation
+=============================
+
+By default, a subobject merely declared in the same library as an export is
+able to apply to that export.
+However, applications have the ability to override that and get specific about
+what subobject goes with which export. In HLSL, this "explicit association" is
+done using SubobjectToExportsAssociation.
+
+A SubobjectToExportsAssociation corresponds to a
+D3D12_DXIL_SUBOBJECT_TO_EXPORTS_ASSOCIATION structure.
----------------
damyanp wrote:
Why would a developer specify one of these? Say, below, there's `MyLocalRootSIgnatureAssociation`. What is done with that? Does the compiler look at it?
https://github.com/llvm/llvm-project/pull/88781
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