Implement the `InstanceIndex` HLSL Function

[farzonl]

• Implement InstanceIndex clang builtin,
• Link InstanceIndex clang builtin with hlsl_intrinsics.h
• Add sema checks for InstanceIndex to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for InstanceIndex to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/InstanceIndex.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/InstanceIndex-errors.hlsl
• Create the int_dx_InstanceIndex intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_InstanceIndex to 142 in DXIL.td
• Create the InstanceIndex.ll and InstanceIndex_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_InstanceIndex intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the InstanceIndex lowering and map it to int_spv_InstanceIndex in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/InstanceIndex.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
142	InstanceIndex	6.3	('library', 'intersection', 'anyhit', 'closesthit')

SPIR-V

InstanceId

Short Description

InstanceId - Id associated with an intersected instance

Description

InstanceId
Decorating a variable in an intersection, any-hit, or closest hit shader
with the InstanceId decoration will make that variable contain the
index of the instance that intersects the current ray.

Valid Usage

• 
  VUID-InstanceId-InstanceId-04254
  The InstanceId decoration must be used only within the
  IntersectionKHR , AnyHitKHR , or ClosestHitKHR
Execution Model

• 
  VUID-InstanceId-InstanceId-04255
  The variable decorated with InstanceId must be declared using
  the Input Storage Class

• 
  VUID-InstanceId-InstanceId-04256
  The variable decorated with InstanceId must be declared as a
  scalar 32-bit integer value

Test Case(s)

Example 1

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

export uint fn() {
    return InstanceIndex();
}

SPIRV Example(s):

Example 2

//dxc InstanceIndex_spirv_test.hlsl -T ps_6_8 -E fn -enable-16bit-types -spirv -fspv-target-env=universal1.5 -fcgl -O0


uint fn( ) : SV_Target {

	return InstanceIndex();
}

HLSL:

The autogenerated index of the current instance in the top-level raytracing acceleration structure.

Syntax

uint InstanceIndex();

Remarks

This function can be called from the following raytracing shader types:

• Any Hit Shader
• Closest Hit Shader
• Intersection Shader

See also

Direct3D 12 Raytracing HLSL Reference