add converter for MXNet slice in nnvm

Author: haojin2

nnvm/python/nnvm/frontend/mxnet.py

@@ -189,6 +189,19 @@ def _reshape(inputs, attrs):
     new_attrs['shape'] = _required_attr(attrs, 'shape')
     return _get_nnvm_op(op_name)(*inputs, **new_attrs)
 
+def _slice(inputs, attrs):
+    begin = attrs.get('begin', None)
+    end = attrs.get('end', None)
+    stride = attrs.get('step', None)
+    if begin is None or end is None:
+        raise RuntimeError('begin and end are required params')
+    if 'None' in begin or 'None' in end:
+        raise RuntimeError('None in begin or end not supported yet...')
+    new_attrs = {'begin': begin, 'end': end}
+    if stride is not None:
+        new_attrs['stride'] = stride
+    return _get_nnvm_op('strided_slice')(inputs[0], **new_attrs)
+
 def _split(inputs, attrs):
     op_name, new_attrs = 'split', {}
     axis = attrs.get('axis', 1)
@@ -337,6 +350,7 @@ def _argmin(inputs, attrs):
     'Pooling'       : _pooling,
     'Pooling_v1'    : _pooling,
     'Reshape'       : _reshape,
+    'slice'         : _slice,
     'SliceChannel'  : _split,
     'split'         : _split,
     'Softmax'       : _rename('softmax'),

nnvm/tests/python/frontend/mxnet/test_forward.py

@@ -220,6 +220,14 @@ def test_forward_where():
         tvm_out = m.get_output(0, tvm.nd.empty(out_shape, dtype)).asnumpy()
         tvm.testing.assert_allclose(mx_out, tvm_out, rtol=1e-5, atol=1e-5)
 
+def test_forward_slice():
+    data = mx.sym.var('data')
+    mx_sym = mx.sym.slice(data, begin=(0, 1), end=(2, 4))
+    verify_mxnet_frontend_impl(mx_sym, (3, 4), (2, 3))
+    mx_sym = mx.sym.slice(data, begin=(-1, 1), end=(-3, 4), step=(-1, 2))
+    verify_mxnet_frontend_impl(mx_sym, (3, 4), (2, 2))
+
+
 if __name__ == '__main__':
     test_forward_mlp()
     test_forward_vgg()
@@ -242,4 +250,5 @@ def test_forward_where():
     test_forward_argmax()
     test_forward_argmin()
     test_forward_where()
+    test_forward_slice()