Implement the `D3DCOLORtoUBYTE4` HLSL Function

[farzonl]

• implement D3DCOLORtoUBYTE4 in thehlsl_intrinsics.h header
• Add codegen tests to clang/test/CodeGenHLSL/builtins/D3DCOLORtoUBYTE4.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/D3DCOLORtoUBYTE4-errors.hlsl

DirectX

There were no DXIL opcodes found for D3DCOLORtoUBYTE4. 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.

SPIRV

There is no SPIRV opcode, but SPIRV has a custom implementation. We should try to consolidate behavior between backends. If you need to pick between implementations treat the implementation targeting the DirectX backend as the working spec.

Test Case(s)

Example 1

//dxc D3DCOLORtoUBYTE4_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export int4 fn(float4 p1) {
    return D3DCOLORtoUBYTE4(p1);
}

HLSL:

Converts a floating-point, 4D vector set by a D3DCOLOR to a UBYTE4.

ret D3DCOLORtoUBYTE4(x)

This function swizzles and scales components of the x parameter. Use this function to compensate for the lack of UBYTE4 support in some hardware.

Parameters

Item	Description
x	[in] The floating-point vector4 to convert.

Return Value

The UBYTE4 representation of the x parameter.

Type Description

Name	Template Type	Component Type	Size
x	vector	float	4
ret	vector	integer	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)	vs_1_1

See also

Intrinsic Functions (DirectX HLSL)

[davidcook-msft]

@farzonl to review and update the item

[Icohedron]

I am currently working on this issue.