Implement the GetAttributeAtVertex HLSL Function

[farzonl]

• Implement GetAttributeAtVertex clang builtin,
• Link GetAttributeAtVertex clang builtin with hlsl_intrinsics.h
• Add sema checks for GetAttributeAtVertex to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for GetAttributeAtVertex to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/GetAttributeAtVertex.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/GetAttributeAtVertex-errors.hlsl
• Create the int_dx_GetAttributeAtVertex intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_GetAttributeAtVertex to 137 in DXIL.td
• Create the GetAttributeAtVertex.ll and GetAttributeAtVertex_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_GetAttributeAtVertex intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the GetAttributeAtVertex lowering and map it to int_spv_GetAttributeAtVertex in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/GetAttributeAtVertex.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
137	AttributeAtVertex	6.1	('pixel',)

SPIR-V

OpAccessChain:

Description:

Create a pointer into a composite object.

Result Type must be an OpTypePointer. Its Type
operand must be the type reached by walking the Base’s type hierarchy
down to the last provided index in Indexes, and its Storage Class
operand must be the same as the Storage Class of Base.

Base must be a pointer, pointing to the base of a composite object.

Indexes walk the type hierarchy to the desired depth, potentially down
to scalar granularity. The first index in Indexes selects the
top-level member/element/component/element of the base composite. All
composite constituents use zero-based numbering, as described by their
OpType…​ instruction. The second index applies similarly to that
result, and so on. Once any non-composite type is reached, there must be
no remaining (unused) indexes.

Each index in Indexes

• must have a scalar integer type
• is treated as signed
• if indexing into a structure, must be an OpConstant
  whose value is in bounds for selecting a member
• if indexing into a vector, array, or matrix, with the result type
  being a logical pointer type, causes undefined
  behavior if not in bounds.

Word Count	Opcode	Results	Operands
4 + variable	65	<id> Result Type	Result <id>	<id> Base	<id>, <id>, …​ Indexes

Test Case(s)

Example 1

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

[numthreads(1, 1, 1)]
[shader("pixel")]
float4 fn(nointerpolation float4 p1 : COLOR ) : SV_Target {
	uint p2 = 1;
	return GetAttributeAtVertex(p1, p2);
}

Example 2

//dxc GetAttributeAtVertex_1_test.hlsl -T lib_6_8 -enable-16bit-types -O0

[numthreads(1, 1, 1)]
[shader("pixel")]
uint4 fn(nointerpolation float4 p1 : COLOR ) : SV_Target {
	uint p2 = 1;
	return GetAttributeAtVertex(p1, p2);
}

Example 3

//dxc GetAttributeAtVertex_2_test.hlsl -T lib_6_8 -enable-16bit-types -O0

[numthreads(1, 1, 1)]
[shader("pixel")]
int4 fn(nointerpolation float4 p1 : COLOR ) : SV_Target {
	uint p2 = 1;
	return GetAttributeAtVertex(p1, p2);
}

HLSL:

Syntax

numeric<> GetAttributeAtVertex(numeric<> value, uint VertexID);

Type Description

Name	Template Type	Component Type	Size
ret	scalar, vector, or matrix	float or int	any
value	scalar, vector, or matrix	float or int	any
VertexID	scalar	uint	1

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 6.1 and higher shader models	yes

Shader Stages

• Pixel Shader

See also

• Intrinsic Functions (DirectX HLSL)
• See GetAttributeAtVertex MeshShader Usage.