[Relay][Pass] Fix CombineParallelConv2D

[vinx13]

Fix the issue mentioned in #2163

• It is possible that conv2d has parallel branches that are not conv2d, so a condition check is added.
• When grouping branches, ensure branches with different root to be placed in different groups (even if they are compatible)

Please review @masahi @tqchen

[masahi]

even with this change, VGG and Resnet tests in tests/python/frontend/mxnet/test_forward.py don't work if I enable CombineParallelConv2D pass. @vinx13 can you take a look?

The weird thing is that I am getting slightly different errors every time I run test_forward_vgg() and test_forward_resnet().

[masahi]

@vinx13 is CombineParallelConv2DPass supposed to change residual block? When I run test_forward_resnet(), it sometimes finishes without error, but I am seeing a log like the one below. This is not a standard workload in resnet.

WARNING:autotvm:Cannot find config for target=llvm, workload=('conv2d', (1, 128, 28, 28, 'float32'), (2944, 128, 3, 3, 'float32'), (1, 1), (1, 1), (1, 1), 'NCHW', 'float32'). A fallback configuration is used, which may bring great performance regression.
WARNING:autotvm:Cannot find config for target=llvm, workload=('conv2d', (1, 64, 56, 56, 'float32'), (896, 64, 1, 1, 'float32'), (2, 2), (0, 0), (1, 1), 'NCHW', 'float32'). A fallback configuration is used, which may bring great performance regression.

[vinx13]

@masahi It shouldn't. Fixed, please review again.

[masahi]

OK, I confirmed locally that test_forward.py is working with CombineParallelConv2D enabled. You can roll back OPT_PASS_LEVEL to 1 if you want. This way we can test CombineParallelConv2D pass on other end to end compilation test cases for free.

[tqchen]

@vinx13 Let us set the CombineParallelConv2D to opt_level=3

[tqchen]

@vinx13 can you also follow up to check the current status on the inception style models to see the actual benefit of this pass? since we already support inception models

[tqchen]

@masahi please https://docs.tvm.ai/contribute/code_review.html#approve-and-request-changes-explicitly

[masahi]

OK, I thought Inception test was coming. The fix looks good.

[tqchen]

Thanks, @vinx13 ! can you confirm the inception perf and post a followup?

[tqchen]

Thanks, @masahi @vinx13 , this is merged