<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/99136>99136</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Implement the `modf` HLSL Function
</td>
</tr>
<tr>
<th>Labels</th>
<td>
metabug,
backend:DirectX,
HLSL,
backend:SPIR-V,
bot:HLSL
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
farzonl
</td>
</tr>
</table>
<pre>
- [ ] 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.
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<th>Number</th>
<th>Operand 1</th>
<th>Operand 2</th>
<th>Operand 3</th>
<th>Operand 4</th>
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<td class="tableblock halign-left valign-top"><p>36</p></td>
<td
class="tableblock halign-left valign-top"><p><em><id></em><br />
<em>x</em></p></td>
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## Test Case(s)
### Example 1
```hlsl
//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 |
|-----------------------------------------------------------|------------------------------------------------|
| <span id="x"></span><span id="X"></span>*x*<br/> | \[in\] The x input value.<br/> |
| <span id="ip"></span><span id="IP"></span>*ip*<br/> | \[out\] The integer portion of *x*.<br/> |
## Return Value
The signed-fractional portion of x.
## Type Description
| Name | In/Out | [**Template Type**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md) | [**Component Type**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md) | Size |
|------|--------|----------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------|------------------------------|
| x | in | [**scalar**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md), **vector**, or **matrix** | [**float**](/windows/desktop/WinProg/windows-data-types), [**int**](/windows/desktop/WinProg/windows-data-types) | any |
| ip | out | same as input x | [**float**](/windows/desktop/WinProg/windows-data-types), [**int**](/windows/desktop/WinProg/windows-data-types) | same dimension(s) as input x |
| ret | out | same as input x | [**float**](/windows/desktop/WinProg/windows-data-types), [**int**](/windows/desktop/WinProg/windows-data-types) | 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)](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-sm2.md) and higher shader models | yes |
| [Shader Model 1 (DirectX HLSL)](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-sm1.md) | yes (vs\_1\_1 only) |
## Requirements
| Requirement | Value |
|-------------------|--------------------------------------------------------------------------------------------|
| Header<br/> | <dl> <dt>Corecrt\_math.h</dt> </dl> |
## See also
<dl> <dt>
[**Intrinsic Functions (DirectX HLSL)**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md)
</dt> </dl>
</pre>
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