Add parses support for zeros_like tflite operator (#4042)

The tensorflow zeros_like operation provided in array_ops.py produces directly a tensor with zeros
without a graph, using only the shape and type of the input. This imposes the use of gen_array_ops.py
that produces both a tensor and a graph so a comparison between tflite and tvm can be done.

python/tvm/relay/frontend/tflite.py

@@ -75,6 +75,7 @@ class OperatorConverter(object):
             'MAXIMUM': self.convert_maximum,
             'MINIMUM': self.convert_minimum,
             'GREATER': self.convert_greater,
+            'ZEROS_LIKE': self.convert_zeros_like,
             'REDUCE_MIN': self._convert_reduce_min,
             'REDUCE_MAX': self._convert_reduce_max,
             'MEAN': self._convert_reduce_mean,
@@ -478,6 +479,23 @@ class OperatorConverter(object):
     def convert_greater(self, op):
         return self._convert_elemwise(_op.greater, op)
 
+    def convert_zeros_like(self, op):
+        """Convert TFLite ZEROS LIKE"""
+        try:
+            from tflite.Operator import Operator
+        except ImportError:
+            raise ImportError("The tflite package must be installed")
+
+        assert isinstance(op, Operator)
+        input_tensors = self.get_input_tensors(op)
+        assert len(input_tensors) == 1, "input tensors length should be 1"
+
+        input_tensor = input_tensors[0]
+        in_expr = self.get_expr(input_tensor.tensor_idx)
+        out = _op.zeros_like(in_expr)
+
+        return out
+
     def _convert_reduce(self, relay_op, op):
         """Generic method to Convert TFLite MEAN operators"""
         try:

tests/python/frontend/tflite/test_forward.py

@@ -31,6 +31,7 @@ from tensorflow.python.framework import ops
 from tensorflow.python.ops import math_ops
 from tensorflow.python.ops import nn_ops
 from tensorflow.python.ops import array_ops
+from tensorflow.python.ops import gen_array_ops
 from tensorflow.python.ops import variables
 try:
     from tensorflow import lite as interpreter_wrapper
@@ -633,6 +634,21 @@ def test_all_elemwise():
     _test_forward_elemwise(_test_greater)
 
 #######################################################################
+# Zeros like
+# --------
+
+def _test_zeros_like(data):
+    """ One iteration of ZEROS LIKE """
+    with tf.Graph().as_default():
+        in_data = array_ops.placeholder(shape=data.shape, dtype=data.dtype)
+        out = gen_array_ops.zeros_like(in_data)
+        compare_tflite_with_tvm(data, 'Placeholder:0', [in_data], [out])
+
+def test_forward_zeros_like():
+    """ ZEROS LIKE """
+    _test_zeros_like(np.arange(6.0, dtype=np.float32).reshape((1, 6)))
+
+#######################################################################
 # Reduce
 # ------
 
@@ -1020,6 +1036,9 @@ if __name__ == '__main__':
     # Elemwise
     test_all_elemwise()
 
+    # Zeros Like
+    test_forward_zeros_like()
+
     # Reduce
     test_all_reduce()