Implement the `asfloat` HLSL Function

[llvm-beanz]

• Link asfloat clang builtin (__builtin_bit_cast) with `hlsl_intrinsics.h``
• Add codegen tests to clang/test/CodeGenHLSL/builtins/asfloat.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/asfloat-errors.hlsl

DirectX

There were no DXIL opcodes found for asfloat.

SPIR-V

Description:

Test Case(s)

Example 1

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

export float4 fn(float p1) {
    return asfloat(p1);
}

Example 2

//dxc asfloat_1_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export float4 fn(uint p1) {
    return asfloat(p1);
}

Example 3

//dxc asfloat_2_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export float4 fn(int p1) {
    return asfloat(p1);
}

HLSL:

Interprets the bit pattern of x as a floating-point number.

ret asfloat(x)

Parameters

Item	Description
x	[in] The input value.

Return Value

The input interpreted as a floating-point number.

Type Description

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

Function Overloads

`float<x> asfloat(float<x> value);` `float<x> asfloat(int<x> value);` `float<x> asfloat(uint<x> value);`

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 4 and higher shader models	yes
Shader Model 3 (DirectX HLSL)	no
Shader Model 2 (DirectX HLSL)	no
Shader Model 1 (DirectX HLSL)	no

Remarks

Older compilers incorrectly allowed asfloat(bool), but note that bool inputs are not supported.

See also

Intrinsic Functions (DirectX HLSL)

[farzonl]

@damyanp This one is already refined, but we should prioritize getting it assigned out. This is used in DirectML shader PixelPacking_Velocity.hlsli:28 and PixelPacking_Velocity.hlsli:41

[joaosaffran]

I can work on this

[joaosaffran]

This is currently awaiting changes on #107292 to be merged, such is introducing bit_cast implementation for HLSL, which is required for this changes.