Implement the DispatchMesh HLSL Function

[farzonl]

• Implement DispatchMesh clang builtin,
• Link DispatchMesh clang builtin with hlsl_intrinsics.h
• Add sema checks for DispatchMesh to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for DispatchMesh to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/DispatchMesh.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/DispatchMesh-errors.hlsl
• Create the int_dx_DispatchMesh intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_DispatchMesh to 173 in DXIL.td
• Create the DispatchMesh.ll and DispatchMesh_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_DispatchMesh intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the DispatchMesh lowering and map it to int_spv_DispatchMesh in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/DispatchMesh.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
173	DispatchMesh	6.5	('amplification',)

SPIR-V

OpEmitMeshTasksEXT:

Description:

Reserved.

Capability:
MeshShadingEXT

Reserved.

Word Count	Opcode	Results	Operands
4 + variable	5294	<id> Group Count X	<id> Group Count Y	<id> Group Count Z	Optional <id> Payload

Test Case(s)

Example 1

//dxc DispatchMesh_test.hlsl -T lib_6_8 -enable-16bit-types -O0

[numthreads(1, 1, 1)]
[shader("amplification")]
export void fn(uint gtid : SV_GroupIndex) {

struct RayPayload
{
	float4 color;
	float distance;
};
uint p1;
uint p2;
uint p3;
RayPayload p4;

DispatchMesh(p1, p2, p3, p4);
}

SPIRV Example(s):

Example 2

//dxc DispatchMesh_spirv_test.hlsl -T lib_6_8 -E fn -enable-16bit-types -spirv -fspv-target-env=universal1.5 -fcgl -O0

struct RayPayload
{
	float4 color;
	float distance;
};

groupshared RayPayload p4;

[numthreads(1, 1, 1)]
[shader("amplification")]
void fn(uint gtid : SV_GroupIndex) {

uint p1;
uint p2;
uint p3;

DispatchMesh(p1, p2, p3, p4);
}

HLSL:

Syntax

void DispatchMesh(uint threadGroupCountX, uint threadGroupCountY, uint threadGroupCountZ, udt meshPayload);

Type Description

Name	Template Type	Component Type	Size
ret	void	void	0
threadGroupCountX	scalar	uint	1
threadGroupCountY	scalar	uint	1
threadGroupCountZ	scalar	uint	1
meshPayload	RayPayload Struct	RayPayload	1

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 6.5 and higher shader models	yes

Shader Stages

• Amplification Shader

See also

• Intrinsic Functions (DirectX HLSL)
• See DispatchMesh - intrinsic