[Enhance] Adds windows compilation support

[divyanshj16]

fixes #169
Here is the summary of the fixes,

• In windows' compiler variables cannot be passed in the size of initialization of the array, so we have to initialize it something like this. int *xx= new int[variable] - source
• The long datatype in windows and linux are different so the following source suggested it to convert everything to long long .source
• While defining EPS, its scope had to be changed to __device__, otherwise it was throwing errors about undefined EPS.

[CLAassistant]

All committers have signed the CLA.

[Wuziyi616]

@divyanshj16 Hi, we really appreciate your contribution, and this PR seems to be very helpful for us. Can you kindly sign the CLA above and then we will start to review your modifications?

[divyanshj16]

@Wuziyi616 I signed the CLA

[Wuziyi616]

@ZwwWayne Can you have a look at this PR?

[Wuziyi616]

The unit test failed. Seems to because the modified GPU ops can't run successfully on Linux platform?

[divyanshj16]

Almost all of them says operation cancelled. Could it be because of something else?

[Wuziyi616]

If one run failed in CI, all other runs will be canceled. I think we need to find out the reason in that failed run. The error traceback is:

Traceback:
/opt/hostedtoolcache/Python/3.6.13/x64/lib/python3.6/importlib/__init__.py:126: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
tests/test_data/test_datasets/test_dataset_wrappers.py:4: in <module>
    from mmdet3d.datasets.builder import build_dataset
mmdet3d/datasets/__init__.py:3: in <module>
    from .custom_3d import Custom3DDataset
mmdet3d/datasets/custom_3d.py:9: in <module>
    from ..core.bbox import get_box_type
mmdet3d/core/__init__.py:2: in <module>
    from .bbox import *  # noqa: F401, F403
mmdet3d/core/bbox/__init__.py:4: in <module>
    from .iou_calculators import (AxisAlignedBboxOverlaps3D, BboxOverlaps3D,
mmdet3d/core/bbox/iou_calculators/__init__.py:1: in <module>
    from .iou3d_calculator import (AxisAlignedBboxOverlaps3D, BboxOverlaps3D,
mmdet3d/core/bbox/iou_calculators/iou3d_calculator.py:5: in <module>
    from ..structures import get_box_type
mmdet3d/core/bbox/structures/__init__.py:1: in <module>
    from .base_box3d import BaseInstance3DBoxes
mmdet3d/core/bbox/structures/base_box3d.py:5: in <module>
    from mmdet3d.ops.iou3d import iou3d_cuda
mmdet3d/ops/__init__.py:12: in <module>
    from .knn import knn
mmdet3d/ops/knn/__init__.py:1: in <module>
    from .knn import knn
mmdet3d/ops/knn/knn.py:4: in <module>
    from . import knn_ext
E   ImportError: /home/runner/work/mmdetection3d/mmdetection3d/mmdet3d/ops/knn/knn_ext.cpython-36m-x86_64-linux-gnu.so: undefined symbol: _ZNK2at6Tensor8data_ptrIxEEPT_v

I am not very familiar with CUDA. I will let my teammates look into this problem.

[divyanshj16]

@Wuziyi616, @ZwwWayne Is there any update on this?

[ZwwWayne]

Hi @divyanshj16 ,
Thanks for your kind contribution. Could resolve the conflict first? The CI fails due to a weird reason, I just reran it and am waiting for the outcome.

[divyanshj16]

Looks like the conflicts are addressed in different PR. Apologies for delayed response.

[Wuziyi616]

@divyanshj16 No worry! Thank you for pointing us to this solution. Since we have opened a new PR to solve this issue, I will close this PR.

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