Implement the `modf` HLSL Function

[farzonl]

• Implement modf clang builtin,
• Link modf clang builtin with hlsl_intrinsics.h
• Add sema checks for modf to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for modf to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/modf.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/modf-errors.hlsl
• Create the int_dx_modf intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_modf to 29 in DXIL.td
• Create the modf.ll and modf_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_modf intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the modf lowering and map it to int_spv_modf in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/modf.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
29	Round_z	6.0	()

SPIR-V

ModfStruct:

Description:

ModfStruct

Same semantics as in Modf, except that the entire result is in the
instruction’s result; there is not a pointer operand to write through.

Result Type must be an OpTypeStruct with two members. Member 0
holds the fractional part. Member 1 holds the whole number part. These
two members, and the Result Type must all have the same type. This
structure type must be explicitly declared by the module.

Number	Operand 1	Operand 2	Operand 3	Operand 4
36	<id> x

Test Case(s)

Example 1

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

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

HLSL:

Splits the value x into fractional and integer parts, each of which has the same sign as x.

ret modf(x, out ip)

Parameters

Item	Description
x	[in] The x input value.
ip	[out] The integer portion of x.

Return Value

The signed-fractional portion of x.

Type Description

Name	In/Out	Template Type	Component Type	Size
x	in	scalar, vector, or matrix	float, int	any
ip	out	same as input x	float, int	same dimension(s) as input x
ret	out	same as input x	float, int	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)	yes (vs_1_1 only)

Requirements

Requirement	Value
Header	Corecrt_math.h

See also

Intrinsic Functions (DirectX HLSL)

[pow2clk]

Expanded on DXIL. Op on SPIRV