Implement the `reflect` HLSL Function

[farzonl]

• implement reflect in the hlsl_intrinsics.h
• Implement reflect spirv target builtin in clang/include/clang/Basic/BuiltinsSPIRV.td
• Add a spirv fast path in hlsl_detail.h in the form

#if (__has_builtin(__builtin_spirv_reflect))
  return __builtin_spirv_reflect(...);
#else
  return ...; // regular behavior
#endif

• Add codegen for spirv reflect builtin to EmitSPIRVBuiltinExpr in CGBuiltin.cpp
• Add HLSL codegen tests to clang/test/CodeGenHLSL/builtins/reflect.hlsl
• Add SPIRV builtin codegen tests to clang/test/CodeGenSPIRV/Builtins/reflect.c
• Add sema tests to clang/test/SemaHLSL/BuiltIns/reflect-errors.hlsl
• Add spirv sema tests to clang/test/CodeGenSPIRV/Builtins/reflect-errors.c
• Create the int_spv_reflect intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the reflect lowering and map it to int_spv_reflect in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/reflect.ll
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/opencl/reflect.ll

DirectX

There were no DXIL opcodes found for reflect. That should make it easy to do entirely in the frontend.
In DXC it was done via emitting llvmir. We do not want to do that in upstream.

SPIR-V

Reflect:

Description:

Reflect

For the incident vector I and surface orientation N, the result is
the reflection direction:

I - 2 * dot(N, I) * N

N must already be normalized in order to achieve the desired result.

The operands must all be a scalar or vector whose component type is
floating-point.

Result Type and the type of all operands must be the same type.

Number	Operand 1	Operand 2	Operand 3	Operand 4
71	<id> I	<id> N

Test Case(s)

Example 1

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

export float4 fn(float4 p1, float4 p2) {
    return reflect(p1, p2);
}

HLSL:

Returns a reflection vector using an incident ray and a surface normal.

ret reflect(i, n)

Parameters

Item	Description
i	[in] A floating-point, incident vector.
n	[in] A floating-point, normal vector.

Return Value

A floating-point, reflection vector.

Remarks

This function calculates the reflection vector using the following formula: v = i - 2 * n * dot(i n) .

Type Description

Name	Template Type	Component Type	Size
i	vector	float	any
n	vector	float	same dimension(s) as input i
ret	vector	float	same dimension(s) as input i

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 1 (DirectX HLSL) and higher shader models	yes

See also

Intrinsic Functions (DirectX HLSL)

[jerryyiransun]

Hello, is anyone currently working on this issue? If not, I’d like to take it on.

[farzonl]

@jerryyiransun we are redesigning how we are going to do some of these intrinsics to be header only implementations. I’m on vacation right now. Give me two weeks and i’ll rewrite this ticket to match our expectations.

[jerryyiransun]

@farzonl Thank you for the update, I'll wait for the updated ticket and proceed based on the revised expectations. Enjoy your vacation!