[Frontend][TFLite] Add MIRROR_PAD operator (#4822)

python/tvm/relay/frontend/tflite.py

@@ -102,6 +102,7 @@ class OperatorConverter(object):
             'SUM': self._convert_reduce_sum,
             'FULLY_CONNECTED': self.convert_fully_connected,
             'PAD': self.convert_pad,
+            'MIRROR_PAD': self.convert_mirror_pad,
             'PACK': self.convert_pack,
             'UNPACK': self.convert_unpack,
             'LOGISTIC': self.convert_logistic,
@@ -1472,7 +1473,7 @@ class OperatorConverter(object):
         input_tensors = self.get_input_tensors(op)
         assert len(input_tensors) == 2, "input tensors length should be 2"
 
-        # TFLite only support CONSTANT mode and does not support constant_values parameter.
+        # TFLite PAD only support CONSTANT mode and does not support constant_values parameter.
         # tensor
         input_tensor = input_tensors[0]
         in_expr = self.get_expr(input_tensor.tensor_idx)
@@ -1482,10 +1483,48 @@ class OperatorConverter(object):
         # convert list of lists to tuple of tuples
         paddings = tuple(tuple(l) for l in pad_list)
 
-        # Use default pad_value 0 because TFLite does not support constant_values parameter
+        # Use default pad_value 0 because TFLite PAD does not support constant_values parameter
         out = _op.nn.pad(in_expr, paddings)
         return out
 
+    def convert_mirror_pad(self, op):
+        """Convert TFLite MIRROR_PAD"""
+        try:
+            from tflite.Operator import Operator
+            from tflite.BuiltinOptions import BuiltinOptions
+            from tflite.MirrorPadOptions import MirrorPadOptions
+        except ImportError:
+            raise ImportError("The tflite package must be installed")
+
+        # the quantized form MirrorPad is not yet implemented in TFLite.
+        if self.is_quantized(op):
+            raise tvm.error.OpNotImplemented(
+                'TFlite quantized MIRROR_PAD operator is not supported yet.')
+
+        assert isinstance(op, Operator)
+        input_tensors = self.get_input_tensors(op)
+        assert len(input_tensors) == 2, "input tensors length should be 2"
+
+        # tensor
+        input_tensor = input_tensors[0]
+        in_expr = self.get_expr(input_tensor.tensor_idx)
+
+        # paddings
+        pad_list = self.get_tensor_value(input_tensors[1])
+        # convert list of lists to tuple of tuples
+        paddings = tuple(tuple(l) for l in pad_list)
+
+        assert op.BuiltinOptionsType() == BuiltinOptions.MirrorPadOptions
+        op_options = op.BuiltinOptions()
+        mirror_pad_options = MirrorPadOptions()
+        mirror_pad_options.Init(op_options.Bytes, op_options.Pos)
+        mode_byte = mirror_pad_options.Mode()
+
+        mode = "REFLECT" if mode_byte == 0 else "SYMMETRIC"
+        out = _op.nn.mirror_pad(in_expr, paddings, mode)
+
+        return out
+
     def convert_pack(self, op):
         """Convert TFLite pack"""
         try:

tests/python/frontend/tflite/test_forward.py

@@ -1139,7 +1139,7 @@ def test_forward_squeeze():
 # Pad
 # ---
 
-def _test_pad(data):
+def _test_pad(data, mode="CONSTANT"):
     """ One iteration of PAD """
 
     assert len(data) == 2
@@ -1147,7 +1147,7 @@ def _test_pad(data):
     # Test with tensor and constant
     with tf.Graph().as_default():
         in_data = [array_ops.placeholder(shape=data[0].shape, dtype=data[0].dtype, name='in')]
-        out = array_ops.pad(in_data[0], ops.convert_to_tensor(data[1], dtype=data[1].dtype))
+        out = array_ops.pad(in_data[0], ops.convert_to_tensor(data[1], dtype=data[1].dtype), mode=mode)
         compare_tflite_with_tvm([data[0]], ['in:0'], in_data, [out])
 
 
@@ -1161,6 +1161,10 @@ def test_forward_pad():
                np.array([[1, 1], [2, 2]], dtype=np.int32)])
     _test_pad([np.arange(1.0, 4.0, dtype=np.float32).reshape((1, 3)),
                np.array([[1, 1], [2, 2]], dtype=np.int32)])
+    _test_pad([np.arange(1.0, 7.0, dtype=np.float32).reshape((2, 3)),
+               np.array([[1, 1], [2, 2]], dtype=np.int32)], mode="REFLECT")
+    _test_pad([np.arange(1.0, 7.0, dtype=np.float32).reshape((2, 3)),
+               np.array([[1, 1], [2, 2]], dtype=np.int32)], mode="SYMMETRIC")
 
 
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