<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/99130>99130</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Implement the `InterlockedCompareExchange` 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 `InterlockedCompareExchange` clang builtin,
- [ ] Link `InterlockedCompareExchange` clang builtin with `hlsl_intrinsics.h`
- [ ] Add sema checks for `InterlockedCompareExchange` to `CheckHLSLBuiltinFunctionCall` in `SemaChecking.cpp`
- [ ] Add codegen for `InterlockedCompareExchange` to `EmitHLSLBuiltinExpr` in `CGBuiltin.cpp`
- [ ] Add codegen tests to `clang/test/CodeGenHLSL/builtins/InterlockedCompareExchange.hlsl`
- [ ] Add sema tests to `clang/test/SemaHLSL/BuiltIns/InterlockedCompareExchange-errors.hlsl`
- [ ] Create the `int_dx_InterlockedCompareExchange` intrinsic in `IntrinsicsDirectX.td`
- [ ] Create the `DXILOpMapping` of `int_dx_InterlockedCompareExchange` to `160` in `DXIL.td`
- [ ] Create the `InterlockedCompareExchange.ll` and `InterlockedCompareExchange_errors.ll` tests in `llvm/test/CodeGen/DirectX/`
- [ ] Create the `int_spv_InterlockedCompareExchange` intrinsic in `IntrinsicsSPIRV.td`
- [ ] In SPIRVInstructionSelector.cpp create the `InterlockedCompareExchange` lowering and map it to `int_spv_InterlockedCompareExchange` in `SPIRVInstructionSelector::selectIntrinsic`.
- [ ] Create SPIR-V backend test case in `llvm/test/CodeGen/SPIRV/hlsl-intrinsics/InterlockedCompareExchange.ll`
## DirectX
| DXIL Opcode | DXIL OpName | Shader Model | Shader Stages |
| ----------- | ----------- | ------------ | ------------- |
| 160 | CreateHandleForLib | 6.3 | () |
## SPIR-V
# [OpAtomicCompareExchange](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#OpAtomicCompareExchange):
## Description:
Perform the following steps atomically with respect to any other atomic
accesses within *Scope* to the same location:
1) load through *Pointer* to get an *Original Value*,
2) get a *New Value* from *Value* only if *Original Value* equals
*Comparator*, and
3) store the *New Value* back through *Pointer* only if *Original Value*
equaled *Comparator*.
The instruction’s result is the *Original Value*.
*Result Type* must be an [*integer type*](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#Integer) scalar.
Use *Equal* for the memory semantics of this instruction when *Value*
and *Original Value* compare equal.
Use *Unequal* for the memory semantics of this instruction when *Value*
and *Original Value* compare unequal. *Unequal* must not be set to
**Release** or **Acquire and Release**. In addition, *Unequal* cannot be
set to a stronger memory-order then *Equal*.
The type of *Value* must be the same as *Result Type*. The type of the
value pointed to by *Pointer* must be the same as *Result Type*. This
type must also match the type of *Comparator*.
*Memory* is a memory [*Scope*](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#Scope_-id-).
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<thead>
<tr>
<th>Word Count</th>
<th>Opcode</th>
<th>Results</th>
<th>Operands</th>
<th></th>
<th></th>
<th></th>
<th></th>
<th></th>
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<tr>
<td class="tableblock halign-left valign-top"><p>9</p></td>
<td class="tableblock halign-left valign-top"><p>230</p></td>
<td
class="tableblock halign-left valign-top"><p><em><id></em><br />
<em>Result Type</em></p></td>
<td class="tableblock halign-left valign-top"><p><a
href="#ResultId"><em>Result <id></em></a></p></td>
<td
class="tableblock halign-left valign-top"><p><em><id></em><br />
<em>Pointer</em></p></td>
<td class="tableblock halign-left valign-top"><p><a
href="#Scope_-id-"><em>Scope <id></em></a><br />
<em>Memory</em></p></td>
<td class="tableblock halign-left valign-top"><p><a
href="#Memory_Semantics_-id-"><em>Memory Semantics
<id></em></a><br />
<em>Equal</em></p></td>
<td class="tableblock halign-left valign-top"><p><a
href="#Memory_Semantics_-id-"><em>Memory Semantics
<id></em></a><br />
<em>Unequal</em></p></td>
<td
class="tableblock halign-left valign-top"><p><em><id></em><br />
<em>Value</em></p></td>
<td
class="tableblock halign-left valign-top"><p><em><id></em><br />
<em>Comparator</em></p></td>
</tr>
</tbody>
</table>
## Test Case(s)
### Example 1
```hlsl
//dxc InterlockedCompareExchange_test.hlsl -T lib_6_8 -enable-16bit-types -O0
RWStructuredBuffer<int64_t> buffer : register(u0);
[numthreads(1, 1, 1)]
export void fn(uint3 dispatchThreadID : SV_DispatchThreadID, int64_t p1, uint64_t p2, uint64_t p3) {
int index = dispatchThreadID.x;
return InterlockedCompareExchange(buffer[index], p1, p2, p3);
}
```
### Example 2
```hlsl
//dxc InterlockedCompareExchange_1_test.hlsl -T lib_6_8 -enable-16bit-types -O0
RWStructuredBuffer<int> buffer : register(u0);
[numthreads(1, 1, 1)]
export void fn(uint3 dispatchThreadID : SV_DispatchThreadID, int p1, uint p2, uint p3) {
int index = dispatchThreadID.x;
return InterlockedCompareExchange(buffer[index], p1, p2, p3);
}
```
## HLSL:
Atomically compares the destination with the comparison value. If they are identical, the destination is overwritten with the input value. The original value is set to the destination's original value.
## Syntax
``` syntax
void InterlockedCompareExchange(
in R dest,
in T compare_value,
in T value,
out T original_value
);
```
## Parameters
<dl> <dt>
*dest* \[in\]
</dt> <dd>
Type: **R**
The destination address.
</dd> <dt>
*compare\_value* \[in\]
</dt> <dd>
Type: **T**
The comparison value.
</dd> <dt>
*value* \[in\]
</dt> <dd>
Type: **T**
The input value.
</dd> <dt>
*original\_value* \[out\]
</dt> <dd>
Type: **T**
The original value.
</dd> </dl>
## Return value
This function does not return a value.
## Remarks
Atomically compares the value referenced by *dest* with *compare\_value*, stores *value* in the location referenced by *dest* if the values match, returns the original value of *dest* in *original\_value*. This operation can only be performed on **int** or **uint** typed resources and shared memory variables. There are two possible uses for this function. The first is when R is a shared memory variable type. In this case, the function performs the operation on the shared memory register referenced by *dest*. The second scenario is when R is a resource variable type. In this scenario, the function performs the operation on the resource location referenced by *dest*. This operation is only available when R is readable and writable.
Interlocked operations do not imply any memory fence/barrier.
> [!Note]
> If you call **InterlockedCompareExchange** in a [**for**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-for.md) or [**while**](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-while.md) compute shader loop, to properly compile, you must use the **\[allow\_uav\_condition\]** attribute on that loop.
### Minimum Shader Model
This function is supported in the following shader models.
| Shader Model | Supported |
|-----------------------------------------------------------------------------|-----------|
| [Shader Model 5](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/d3d11-graphics-reference-sm5.md) and higher shader models | yes |
This function is supported in the following types of shaders:
| Vertex | Hull | Domain | Geometry | Pixel | Compute |
|--------|------|--------|----------|-------|---------|
| x | x | x | x | x | x |
## See also
<dl> <dt>
[Intrinsic Functions](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/dx-graphics-hlsl-intrinsic-functions.md)
</dt> <dt>
[Shader Model 5](https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src//direct3dhlsl/d3d11-graphics-reference-sm5.md)
</dt> </dl>
</pre>
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