<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/99135>99135</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Implement the `lit` 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 `lit` clang builtin,
- [ ] Link `lit` clang builtin with `hlsl_intrinsics.h`
- [ ] Add sema checks for `lit` to `CheckHLSLBuiltinFunctionCall` in `SemaChecking.cpp`
- [ ] Add codegen for `lit` to `EmitHLSLBuiltinExpr` in `CGBuiltin.cpp`
- [ ] Add codegen tests to `clang/test/CodeGenHLSL/builtins/lit.hlsl`
- [ ] Add sema tests to `clang/test/SemaHLSL/BuiltIns/lit-errors.hlsl`
- [ ] Create the `int_dx_lit` intrinsic in `IntrinsicsDirectX.td`
- [ ] Create the `DXILOpMapping` of `int_dx_lit` to `23` in `DXIL.td`
- [ ] Create the `lit.ll` and `lit_errors.ll` tests in `llvm/test/CodeGen/DirectX/`
- [ ] Create the `int_spv_lit` intrinsic in `IntrinsicsSPIRV.td`
- [ ] In SPIRVInstructionSelector.cpp create the `lit` lowering and map it to `int_spv_lit` in `SPIRVInstructionSelector::selectIntrinsic`.
- [ ] Create SPIR-V backend test case in `llvm/test/CodeGen/SPIRV/hlsl-intrinsics/lit.ll`
## DirectX
| DXIL Opcode | DXIL OpName | Shader Model | Shader Stages |
| ----------- | ----------- | ------------ | ------------- |
| 23 | Log | 6.0 | () |
## SPIR-V
# FMax:
## Description:
**FMax**
Result is *y* if *x* \< *y*; otherwise result is *x*. Which operand is
the result is undefined if one of the operands is a NaN.
The operands must all be a scalar or vector whose component type is
floating-point.
*Result Type* and the type of all operands must be the same type.
Results are computed per component.
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<th>Operand 2</th>
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<th>Operand 4</th>
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<td
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<em>x</em></p></td>
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<em>y</em></p></td>
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## Test Case(s)
### Example 1
```hlsl
//dxc lit_test.hlsl -T lib_6_8 -enable-16bit-types -O0
export float4 fn(float p1, float p2, float p3) {
return lit(p1, p2, p3);
}
```
## HLSL:
Returns a lighting coefficient vector.
| *ret* lit(*n\_dot\_l*, *n\_dot\_h*, *m*) |
|------------------------------------------|
This function returns a lighting coefficient vector (ambient, diffuse, specular, 1) where:
- ambient = 1
- diffuse = n · l < 0 ? 0 : n · l
- specular = n · l < 0 \|\| n · h < 0 ? 0 : (n · h) ^ m
Where the vector n is the normal vector, l is the direction to light and h is the half vector.
## Parameters
| Item | Description |
|----------------------------------------------------------------------------|------------------------------------------------------------------------------------------|
| <span id="n_dot_l"></span><span id="N_DOT_L"></span>*n\_dot\_l*<br/> | \[in\] The dot product of the normalized surface normal and the light vector.<br/> |
| <span id="n_dot_h"></span><span id="N_DOT_H"></span>*n\_dot\_h*<br/> | \[in\] The dot product of the half-angle vector and the surface normal.<br/> |
| <span id="m"></span><span id="M"></span>*m*<br/> | \[in\] A specular exponent.<br/> |
## Return Value
The lighting coefficient vector.
## Type Description
| Name | [**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 |
|-------------|-------------------------------------------------------------------------------------|----------------------------------------------------------------|------|
| *n\_dot\_l* | [**scalar**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md) | [**float**](/windows/desktop/WinProg/windows-data-types) | 1 |
| *n\_dot\_h* | [**scalar**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md) | [**float**](/windows/desktop/WinProg/windows-data-types) | 1 |
| *m* | [**scalar**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md) | [**float**](/windows/desktop/WinProg/windows-data-types) | 1 |
| *ret* | [**vector**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md) | [**float**](/windows/desktop/WinProg/windows-data-types) | 4 |
## 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) |
## 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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