Implement the `atan2` HLSL Function

[llvm-beanz]

Note atan2 has been identified as a potential generic llvm intrinsic:
Investigation: #87367
RFC: https://discourse.llvm.org/t/rfc-all-the-math-intrinsics/78294

• Implement atan2 clang builtin,
• Link atan2 clang builtin with hlsl_intrinsics.h
• Add sema checks for atan2 to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for atan2 to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/atan2.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/atan2-errors.hlsl
• Create the int_atan2 intrinsic in Intrinsics.td
• Create the int_dx_atan2 intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_atan2 to 17 in DXIL.td
• Create the atan2.ll and atan2_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_atan2 intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the atan2 lowering and map it to int_spv_atan2 in SPIRVInstructionSelector::selectIntrinsic.
• In SPIRVInstructionSelector.cpp: SPIRVInstructionSelector::spvSelect Add

  case TargetOpcode::G_FATAN2:
    return selectExtInst(ResVReg, ResType, I, CL::atan2, GL::Atan2);

• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/atan2.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
17	Atan	6.0	()

SPIR-V

Atan2:

Description:

Atan2

Arc tangent. Result is an angle, in radians, whose tangent is y / x.
The signs of x and y are used to determine what quadrant the angle
is in. The range of result values is [-π, π] . Result is undefined if
x and y are both 0.

The operand x and y must be a scalar or vector whose component type
is 16-bit or 32-bit 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
25	<id> y	<id> x

Test Case(s)

Example 1

//dxc atan2_test.hlsl -T lib_6_8  -enable-16bit-types -spirv -fspv-target-env=universal1.5 -fcgl -O0

export float4 fn(float4 p1, float4 p2) {
    return atan2(p1, p2);
}

HLSL:

Returns the arctangent of two values (x,y).

ret atan2(y, x)

Parameters

Item	Description
y	[in] The y value.
x	[in] The x value.

Return Value

The arctangent of (y,x).

Remarks

The signs of the x and y parameters are used to determine the quadrant of the return values within the range of -π to π. The atan2 HLSL intrinsic function is well-defined for every point other than the origin, even if y equals 0 and x does not equal 0.

Type Description

Name	Template Type	Component Type	Size
y	same as input x	float	same dimension(s) as input x
x	scalar, vector, or matrix	float	any
ret	same as input x	float	same dimension(s) as input x

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

Requirements

Requirement	Value
Header	Corecrt_math.h

See also

Intrinsic Functions (DirectX HLSL)

[tex3d]

I can take this one.