Implement the `f16tof32` HLSL Function

[farzonl]

• Implement f16tof32 clang builtin,
• Link f16tof32 clang builtin with hlsl_intrinsics.h
• Add sema checks for f16tof32 to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for f16tof32 to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/f16tof32.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/f16tof32-errors.hlsl
• Create the int_dx_f16tof32 intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_f16tof32 to 131 in DXIL.td
• Create the f16tof32.ll and f16tof32_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_f16tof32 intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the f16tof32 lowering and map it to int_spv_f16tof32 in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/f16tof32.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
131	LegacyF16ToF32	6.0	()

SPIR-V

UnpackHalf2x16:

Description:

UnpackHalf2x16

Result is the two-component floating-point vector with components
obtained by unpacking a 32-bit unsigned integer into a pair of 16-bit
values, interpreting those values as 16-bit floating-point numbers
according to the OpenGL Specification, and converting them to 32-bit
floating-point values. Subnormal numbers are either preserved or flushed
to zero, consistently within an implemenation.

The first component of the vector is obtained from the 16
least-significant bits of v; the second component is obtained from the
16 most-significant bits of v.

The v operand must be a scalar with 32-bit integer type.

Result Type must be a vector of 2 components whose type is 32-bit
floating point.

Number	Operand 1	Operand 2	Operand 3	Operand 4
62	<id> v

Test Case(s)

Example 1

//dxc f16tof32_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export float4 fn(uint4 p1) {
    return f16tof32(p1);
}

HLSL:

Converts the float16 stored in the low-half of the uint to a float.

Syntax

float f16tof32(
  in uint value
);

Parameters

value [in]

Type: uint

The input value.

Return value

Type: float

The converted value.

Remarks

The following overloaded versions are also available:

float2 f16tof32(uint2 value);
float3 f16tof32(uint3 value);
float4 f16tof32(uint4 value);

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 4 and higher shader models	yes

 

Although this function is available in Shader Model 4 and higher shader models, because it is emulated in 4.0 and 4.1, it is less perfomant on these shader models than it is on Shader Model 5.

This function is supported in the following types of shaders:

Vertex	Hull	Domain	Geometry	Pixel	Compute
x	x	x	x	x	x

 

See also

Intrinsic Functions

Shader Model 5