Implement the lit HLSL Function

[farzonl]

• Write implementation in hlsl_intrinsics.h
• Add sema checks for lit to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/lit.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/lit-errors.hlsl
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/lit.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
23	Log	6.0	()

SPIR-V

FMax:

Description:

FMax

Result is y if x < y; otherwise result is x. Which operand is
the result is undefined if one of the operands is a NaN.

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.
Results are computed per component.

Number	Operand 1	Operand 2	Operand 3	Operand 4
40	<id> x	<id> y

Test Case(s)

Example 1

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

export float4 fn(float p1, float p2, float p3) {
    return lit(p1, p2, p3);
}

HLSL:

Returns a lighting coefficient vector.

ret lit(n_dot_l, n_dot_h, m)

This function returns a lighting coefficient vector (ambient, diffuse, specular, 1) where:

• ambient = 1
• diffuse = n · l < 0 ? 0 : n · l
• specular = n · l < 0 || n · h < 0 ? 0 : (n · h) ^ m

Where the vector n is the normal vector, l is the direction to light and h is the half vector.

Parameters

Item	Description
n_dot_l	[in] The dot product of the normalized surface normal and the light vector.
n_dot_h	[in] The dot product of the half-angle vector and the surface normal.
m	[in] A specular exponent.

Return Value

The lighting coefficient vector.

Type Description

Name	Template Type	Component Type	Size
n_dot_l	scalar	float	1
n_dot_h	scalar	float	1
m	scalar	float	1
ret	vector	float	4

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 2 (DirectX HLSL) and higher shader models	yes
Shader Model 1 (DirectX HLSL)	yes (vs_1_1 only)

See also

Intrinsic Functions (DirectX HLSL)

[farzonl]

Do this one all in the header. @farzonl clean the body up