<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/99191>99191</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Implement the `RayTMin` 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 `RayTMin` clang builtin,
- [ ] Link `RayTMin` clang builtin with `hlsl_intrinsics.h`
- [ ] Add sema checks for `RayTMin` to `CheckHLSLBuiltinFunctionCall` in `SemaChecking.cpp`
- [ ] Add codegen for `RayTMin` to `EmitHLSLBuiltinExpr` in `CGBuiltin.cpp`
- [ ] Add codegen tests to `clang/test/CodeGenHLSL/builtins/RayTMin.hlsl`
- [ ] Add sema tests to `clang/test/SemaHLSL/BuiltIns/RayTMin-errors.hlsl`
- [ ] Create the `int_dx_RayTMin` intrinsic in `IntrinsicsDirectX.td`
- [ ] Create the `DXILOpMapping` of `int_dx_RayTMin` to  `153` in `DXIL.td`
- [ ] Create the `RayTMin.ll` and `RayTMin_errors.ll` tests in `llvm/test/CodeGen/DirectX/`
- [ ] Create the `int_spv_RayTMin` intrinsic in `IntrinsicsSPIRV.td`
- [ ] In SPIRVInstructionSelector.cpp create the `RayTMin` lowering and map  it to `int_spv_RayTMin` in `SPIRVInstructionSelector::selectIntrinsic`.
- [ ] Create SPIR-V backend test case in `llvm/test/CodeGen/SPIRV/hlsl-intrinsics/RayTMin.ll`

## DirectX

| DXIL Opcode | DXIL OpName | Shader Model | Shader Stages |
| ----------- | ----------- | ------------ | ------------- |
| 153 | RayTMin | 6.3 | ('library', 'intersection', 'anyhit', 'closesthit', 'miss') |

## SPIR-V

<div id="header">

# [RayTminKHR](https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/RayTminKHR.html)

## Short Description

<div class="sectionbody">

RayTminKHR - Minimum T value of a ray

</div>

</div>

<div id="content" class="loadable">

<div class="sect1">

## <a href="#_description" class="anchor"></a> Description

<div class="sectionbody">

<div class="dlist">

` RayTminKHR `  
A variable decorated with the ` RayTminKHR ` decoration will contain the
parametric <span class="eq"> t _min </span> value of the ray
being processed. The value is independent of the space in which the ray
origin and direction exist. The value is the parameter passed into the
<a
href="https://registry.khronos.org/vulkan/specs/1.3-extensions/html/vkspec.html#glossary-pipeline-trace-ray"
rel="noopener" target="_blank">pipeline trace ray</a> instruction.

<div class="paragraph">

The <span class="eq"> t _min </span> value remains constant
for the duration of the ray query.

</div>

</div>

<div class="sidebarblock">

<div class="content">

<div class="title">

Valid Usage

</div>

<div class="ulist">

- <a href="#VUID-RayTminKHR-RayTminKHR-04351"
 id="VUID-RayTminKHR-RayTminKHR-04351"></a> <span class="vuid">
 VUID-RayTminKHR-RayTminKHR-04351 </span>  
  The ` RayTminKHR ` decoration **must** be used only within the
  ` IntersectionKHR ` , ` AnyHitKHR ` , ` ClosestHitKHR ` , or
  ` MissKHR ` ` Execution ` ` Model `

- <a href="#VUID-RayTminKHR-RayTminKHR-04352"
 id="VUID-RayTminKHR-RayTminKHR-04352"></a> <span class="vuid">
 VUID-RayTminKHR-RayTminKHR-04352 </span>  
  The variable decorated with ` RayTminKHR ` **must** be declared using
  the ` Input ` ` Storage ` ` Class `

- <a href="#VUID-RayTminKHR-RayTminKHR-04353"
 id="VUID-RayTminKHR-RayTminKHR-04353"></a> <span class="vuid">
 VUID-RayTminKHR-RayTminKHR-04353 </span>  
  The variable decorated with ` RayTminKHR ` **must** be declared as a
  scalar 32-bit floating-point value

</div>

</div>

</div>

</div>

</div>

</div>


## Test Case(s)

 
 ### Example 1
```hlsl
//dxc RayTMin_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export float fn() {
    return RayTMin();
}
```
 ### SPIRV Example(s):

 ### Example 2
```hlsl
//dxc RayTMin_spirv_test.hlsl -T lib_6_8 -E fn -enable-16bit-types -spirv -fspv-target-env=universal1.5 -fcgl -O0

[shader("intersection")]
void fn() {
float   ret = RayTMin();
}
```
## HLSL:

A float representing the current parametric starting point for the ray. 

## Syntax

```
float RayTMin();

```

## Remarks

**RayTMin** defines the starting point of the ray according to the following formula: Origin + (Direction * RayTMin).  *Origin* and *Direction* may be in either world or object space, which results in either a world or an object space starting point.

**RayTMin** is specified in the call to [**TraceRay**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/traceray-function.md), and is constant for the duration of that call.




This function can be called from the following raytracing shader types:

* [**Any Hit Shader**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/any-hit-shader.md)
* [**Closest Hit Shader**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/closest-hit-shader.md)
* [**Intersection Shader**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/intersection-shader.md)
* [**Miss Shader**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/miss-shader.md)





## See also

<dl> <dt>

[Direct3D 12 Raytracing HLSL Reference](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/direct3d-12-raytracing-hlsl-reference.md)
</dt> </dl>
</pre>
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