[Relay][Frontend][TFLite] Add parser support for squared difference (#4652)

* [Relay][Frontend][TFLite] Add parser support for squared difference

* fix some error

* fix exp_type

* add comment

python/tvm/relay/frontend/tflite.py

@@ -111,6 +111,7 @@ class OperatorConverter(object):
             'SPACE_TO_BATCH_ND': self.convert_space_to_batch_nd,
             'PRELU': self.convert_prelu,
             'TRANSPOSE_CONV': self.convert_transpose_conv,
+            'SQUARED_DIFFERENCE': self.convert_squared_difference,
         }
 
     def check_unsupported_ops(self):
@@ -735,6 +736,17 @@ class OperatorConverter(object):
                 'TFlite quantized greater operator is not supported yet.')
         return self._convert_elemwise(_op.greater, op)
 
+    def convert_squared_difference(self, op):
+        # Check if the input tensor is quantized, call QNN op
+        if self.is_quantized(op):
+            raise tvm.error.OpNotImplemented(
+                'TFlite quantized squared difference operator is not supported yet.')
+        difference = self._convert_elemwise(_op.subtract, op)
+        # _convert_elemwise has guaranteed only have one output tensor
+        exp_type = self.get_tensor_type_str(self.get_output_tensors(op)[0].tensor.Type())
+        out = _op.power(difference, relay.const(2, exp_type))
+        return out
+
     def convert_zeros_like(self, op):
         """Convert TFLite ZEROS LIKE"""
         try:

tests/python/frontend/tflite/test_forward.py

@@ -864,6 +864,14 @@ def _test_greater(data):
     """ One iteration of greater """
     return _test_elemwise(math_ops.greater, data)
 
+#######################################################################
+# Squared_difference
+# ------------------
+
+def _test_squared_difference(data):
+    """ One iteration of squared difference """
+    return _test_elemwise(math_ops.squared_difference, data)
+
 def _test_forward_elemwise(testop):
     """ Elewise"""
     testop([np.arange(6.0, dtype=np.float32).reshape((2, 1, 1, 3)),
@@ -906,6 +914,7 @@ def test_all_elemwise():
     _test_forward_elemwise(_test_maximum)
     _test_forward_elemwise(_test_minimum)
     _test_forward_elemwise(_test_greater)
+    _test_forward_elemwise(_test_squared_difference)
 
 #######################################################################
 # Zeros like