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According to the [APL documentation](https://developer.arm.com/documentation/101004/2404/General-information/Arm-Performance-Libraries-example-programs), libraries ending with _mp are OpenMP multi-threaded libraries.
When a project is compiled with MSVC and the -openmp flag, the vcomp library (Visual C++ implementation of OpenMP) is used for runtime calls.
However, the current APL implementation uses the libomp.dll (LLVM) variant.
As a result, there are unexpected behaviors at runtime.
---
For Example:
```python
import torch
# Create a sparse tensor
# Input (Sparse Tensor):
# [[0, 1],
# [1, 0]]
indices = torch.tensor([[0, 1], [1, 0]])
values = torch.tensor([1, 1], dtype=torch.float32)
size = torch.Size([2, 2])
sparse_tensor = torch.sparse_coo_tensor(indices, values, size)
# Convert sparse tensor to dense tensor
dense_tensor = sparse_tensor.to_dense()
# Expected Output (Dense Tensor):
# [[0, 1],
# [1, 0]]
print("\nDense Tensor:")
print(dense_tensor)
```
However, it prints unexpected outputs such as:
```python
# [[0, 11],
# [10, 0]]
```
The issue arises because the following code does not function as expected at runtime:
https://github.com/pytorch/pytorch/blob/main/aten/src/ATen/ParallelOpenMP.h#L30
```c++
// returns 1 , however since OpenMP is enabled it should return total number of threads
int64_t num_threads = omp_get_num_threads();
```
---
In the runtime, loading multiple OpenMP libraries (in this case `libomp` and `vcomp`) is causing unexpected behaviours.
So, we've changed libraries from `_mp` to non `_mp` versions and we used `vcomp` for OpenMP calls.
Pull Request resolved: #145215
Approved by: https://github.com/ozanMSFT, https://github.com/malfet
Co-authored-by: Ozan Aydin <148207261+ozanMSFT@users.noreply.github.com>
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