[TFLite] QNN support for TFLite 2.1.0 quantized models (apache#5848)

* [TFLite] TFLite 2.x parser quantization support.

* Address comments. Fix a bug for depthwise conv

* Added tests for relu, conv, quantize. Address comments.

* Using web-data. Minor refactoring.

* Removing TF hub package

* Trigger CI.

* Handle TFLite input layer naming.

* Addressing reviews.

* Retrigger CI.

python/tvm/relay/frontend/tflite.py

@@ -244,42 +244,92 @@ def get_tensors(self, tensors_idx_list):
             qnn_params = None
             tflite_qnn_params = tensor.Quantization()
             if tflite_qnn_params is not None:
-                scale = float(tflite_qnn_params.ScaleAsNumpy())
-                zero_point = int(tflite_qnn_params.ZeroPointAsNumpy())
+                # TFLite supports both per-tensor and per-axis (aka channel) quantization.  For
+                # per-tensor quantization, scale and zero points are scalar values.  For per-axis
+                # quantization, scale and zero points for the weights are tensors (activations are
+                # per-tensor quantized). However, the TFLite quantization spec puts restrictions on
+                # zero points for per-axis quantization.  Specifically, the zero point is a tensor
+                # but all values are 0. More information can be found here -
+                # https://www.tensorflow.org/lite/performance/quantization_spec
+
+                tflite_scale = tflite_qnn_params.ScaleAsNumpy()
+                tflite_zero_point = tflite_qnn_params.ZeroPointAsNumpy()
+                is_qnn_params_valid = True
+
+                # Handle Per-axis and per-tensor cases
+                if isinstance(tflite_scale, np.ndarray):
+                    assert isinstance(tflite_zero_point, np.ndarray)
+
+                    # Tensor - Per-axis quantization
+                    if tflite_scale.size != 1 and tflite_zero_point.size != 1:
+                        scale = tflite_scale
+                        # Ensure that all zero points are zeros
+                        zero_point = tflite_zero_point
+                        if not np.all(zero_point == 0):
+                            raise tvm.error.OpAttributeInvalid(\
+                                    "TFLite per-axis quantization restricts all zero points to be"
+                                    + " 0, but a non-zero value is observed")
+                        zero_point = int(zero_point[0])
+
+                    # Scalar - Per-tensor quantization
+                    elif tflite_scale.size == 1 and tflite_zero_point.size == 1:
+                        scale = float(tflite_scale[0])
+                        zero_point = int(tflite_zero_point[0])
+
+                    else:
+                        raise NotImplementedError(\
+                                "Quantized type {} (scale) and  {} (zero point) not supported"
+                                .format(type(tflite_scale), type(tflite_zero_point)))
+                elif tflite_scale == 0 and tflite_zero_point == 0:
+                    # Handle corner case for ops like quantized reshape whose second operand (shape)
+                    # has zero scale and zero zero point. This is not used.
+                    is_qnn_params_valid = False
+                else:
+                    raise NotImplementedError("Quantized type {} not supported"
+                                              .format(type(tflite_scale)))
+
                 # Check that the scale and zero points are valid.
-                if scale != 0 or zero_point != 0:
+                if is_qnn_params_valid:
                     qnn_params = dict()
                     qnn_params['scale'] = relay.const(scale, 'float32')
                     qnn_params['zero_point'] = relay.const(zero_point, 'int32')
             return_list.append(TensorWrapper(tensor_idx, tensor, buffer, qnn_params))
         return return_list
 
-    def get_tensor_value(self, tensor_wrapper):
-        """Get tensor buffer value from given tensor wrapper"""
+
+    def get_tensor_type_as_numpy(self, tensor_wrapper):
+        """Returns np.dtype out of TensorType"""
         assert isinstance(tensor_wrapper, TensorWrapper)
 
         try:
             from tflite.TensorType import TensorType
+            return {TensorType.UINT8: np.uint8,
+                    TensorType.INT8: np.int8,
+                    TensorType.FLOAT32: np.float32,
+                    TensorType.INT32: np.int32,
+                    TensorType.INT64: np.int64,
+                    TensorType.BOOL: np.bool_}[tensor_wrapper.tensor.Type()]
         except ImportError:
             raise ImportError("The tflite package must be installed")
+        except KeyError:
+            raise NotImplementedError("Tensor type '{}' currently not supported"
+                                      .format(tensor_wrapper.tensor.Type()))
+
+
+    def get_tensor_value(self, tensor_wrapper):
+        """Get tensor buffer value from given tensor wrapper"""
+        assert isinstance(tensor_wrapper, TensorWrapper)
+
+        dtype = self.get_tensor_type_as_numpy(tensor_wrapper)
+        data = tensor_wrapper.buffer.DataAsNumpy()
+
+        if tensor_wrapper.tensor.ShapeLength() != 0:
+            shape = tensor_wrapper.tensor.ShapeAsNumpy()
+        else:
+            shape = []
+
+        return np.frombuffer(data, dtype=dtype).reshape(shape)
 
-        if tensor_wrapper.tensor.Type() == TensorType.UINT8:
-            return np.frombuffer(tensor_wrapper.buffer.DataAsNumpy(), dtype=np.uint8).reshape(
-                tensor_wrapper.tensor.ShapeAsNumpy())
-        if tensor_wrapper.tensor.Type() == TensorType.FLOAT32:
-            return np.frombuffer(tensor_wrapper.buffer.DataAsNumpy(), dtype=np.float32).reshape(
-                tensor_wrapper.tensor.ShapeAsNumpy())
-        if tensor_wrapper.tensor.Type() == TensorType.INT32:
-            return np.frombuffer(tensor_wrapper.buffer.DataAsNumpy(), dtype=np.int32).reshape(
-                tensor_wrapper.tensor.ShapeAsNumpy())
-        if tensor_wrapper.tensor.Type() == TensorType.INT64:
-            return np.frombuffer(tensor_wrapper.buffer.DataAsNumpy(), dtype=np.int64).reshape(
-                tensor_wrapper.tensor.ShapeAsNumpy())
-        if tensor_wrapper.tensor.Type() == TensorType.BOOL:
-            return np.frombuffer(tensor_wrapper.buffer.DataAsNumpy(), dtype=np.bool_).reshape(
-                tensor_wrapper.tensor.ShapeAsNumpy())
-        raise NotImplementedError("Tensor type {} is currently not supported"
-                                  .format(str(tensor_wrapper.tensor.Type())))
 
     def get_tensor_type_str(self, tensor_type):
         """Get tensor type string representation when given TFLite tensor type"""
@@ -651,12 +701,43 @@ def convert_shape(self, op):
 
     def convert_relu(self, op):
         """Convert TFLite ReLU"""
+        try:
+            from tflite.ActivationFunctionType import ActivationFunctionType
+        except ImportError:
+            raise ImportError("The tflite package must be installed")
+
         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.nn.relu(in_expr)
+
+        output_tensors = self.get_output_tensors(op)
+        assert len(output_tensors) == 1, "output tensors length should be 1"
+        output_tensor = output_tensors[0]
+
+        if input_tensor.qnn_params:
+            # Quantize a float value to an quantized integer value
+            scale_val = get_scalar_from_constant(input_tensor.qnn_params['scale'])
+            zero_point_val = get_scalar_from_constant(input_tensor.qnn_params['zero_point'])
+
+            output_tensor_type_str = self.get_tensor_type_str(output_tensor.tensor.Type())
+            out = self.convert_qnn_fused_activation_function(\
+                    expr=in_expr,
+                    fused_activation_fn=ActivationFunctionType.RELU,
+                    scale=scale_val,
+                    zero_point=zero_point_val,
+                    dtype=output_tensor_type_str)
+        else:
+            out = _op.nn.relu(in_expr)
+
+        if output_tensor.qnn_params:
+            output_tensor_type_str = self.get_tensor_type_str(output_tensor.tensor.Type())
+            out = _qnn.op.requantize(out,
+                                     input_scale=input_tensor.qnn_params['scale'],
+                                     input_zero_point=input_tensor.qnn_params['zero_point'],
+                                     output_scale=output_tensor.qnn_params['scale'],
+                                     output_zero_point=output_tensor.qnn_params['zero_point'],
+                                     out_dtype=output_tensor_type_str)
 
         return out
 
@@ -692,6 +773,11 @@ def _hard_swish(data):
 
     def convert_relu6(self, op):
         """Convert TFLite ReLU6"""
+        try:
+            from tflite.ActivationFunctionType import ActivationFunctionType
+        except ImportError:
+            raise ImportError("The tflite package must be installed")
+
         input_tensors = self.get_input_tensors(op)
         assert len(input_tensors) == 1, "input tensors length should be 1"
         input_tensor = input_tensors[0]
@@ -705,17 +791,14 @@ def convert_relu6(self, op):
             # Quantize a float value to an quantized integer value
             scale_val = get_scalar_from_constant(input_tensor.qnn_params['scale'])
             zero_point_val = get_scalar_from_constant(input_tensor.qnn_params['zero_point'])
-            quantize = lambda x: float(int(round(x / scale_val)) + zero_point_val)
 
-            # Get min/max of the input dtype. This will be used to ensure that
-            # clip a_min/a_max are not beyond the dtype range.
-            input_tensor_type_str = self.get_tensor_type_str(input_tensor.tensor.Type())
-            qmin = float(tvm.tir.op.min_value(input_tensor_type_str).value)
-            qmax = float(tvm.tir.op.max_value(input_tensor_type_str).value)
-
-            out = _op.clip(in_expr,
-                           a_min=max(qmin, quantize(0)),
-                           a_max=min(qmax, quantize(6.0)))
+            output_tensor_type_str = self.get_tensor_type_str(output_tensor.tensor.Type())
+            out = self.convert_qnn_fused_activation_function(\
+                    expr=in_expr,
+                    fused_activation_fn=ActivationFunctionType.RELU6,
+                    scale=scale_val,
+                    zero_point=zero_point_val,
+                    dtype=output_tensor_type_str)
         else:
             out = _op.clip(in_expr, a_min=0, a_max=6)
 
@@ -1604,9 +1687,9 @@ def convert_fully_connected(self, op):
         fully_connected_options.Init(op_options.Bytes, op_options.Pos)
         fused_activation_fn = fully_connected_options.FusedActivationFunction()
 
-        # weight tensor type should be UINT8 (quantization) or FLOAT32
+        # weight tensor type should be INT8/UINT8 (quantization) or FLOAT32
         weight_tensor_type = weight_tensor.tensor.Type()
-        assert weight_tensor_type in (TensorType.UINT8, TensorType.FLOAT32)
+        assert weight_tensor_type in (TensorType.INT8, TensorType.UINT8, TensorType.FLOAT32)
         weight_tensor_type_str = self.get_tensor_type_str(weight_tensor_type)
 
         if self.has_expr(weight_tensor.tensor_idx):
@@ -1795,9 +1878,9 @@ def convert_conv(self, op, conv_type):
             params['channels'] = int(output_channels)
             params['kernel_layout'] = 'HWIO'
 
-        # weight tensor type should be UINT8 (quantization) or FLOAT32
+        # weight tensor type should be INT8/UINT8 (quantization) or FLOAT32
         weight_tensor_type = weight_tensor.tensor.Type()
-        assert weight_tensor_type in (TensorType.UINT8, TensorType.FLOAT32)
+        assert weight_tensor_type in (TensorType.INT8, TensorType.UINT8, TensorType.FLOAT32)
         weight_tensor_type_str = self.get_tensor_type_str(weight_tensor_type)
 
         in_expr = self.get_expr(input_tensor_idx)
@@ -1856,9 +1939,15 @@ def convert_conv(self, op, conv_type):
         if output_tensor.qnn_params:
             # Calculate the intermediate scale and zero point of the int32 output.
             data_scale = input_tensor.qnn_params['scale']
-            weight_scale = weight_tensor.qnn_params['scale']
             data_scale_val = get_scalar_from_constant(data_scale)
-            weight_scale_val = get_scalar_from_constant(weight_scale)
+
+            weight_scale = weight_tensor.qnn_params['scale']
+            # If weight scale is scalar, it is per-tensor quantization
+            if isinstance(weight_scale, float):
+                weight_scale_val = get_scalar_from_constant(weight_scale)
+            else:
+                weight_scale_val = get_tensor_from_constant(weight_scale)
+
             new_input_scale_val = data_scale_val * weight_scale_val
             new_input_scale = relay.const(new_input_scale_val, 'float32')
             new_input_zero_point = relay.const(0, 'int32')
@@ -1869,7 +1958,8 @@ def convert_conv(self, op, conv_type):
                                      input_zero_point=new_input_zero_point,
                                      output_scale=output_tensor.qnn_params['scale'],
                                      output_zero_point=output_tensor.qnn_params['zero_point'],
-                                     out_dtype=output_tensor_type_str)
+                                     out_dtype=output_tensor_type_str,
+                                     axis=3)
 
             # Call activation function
             output_scale_val = get_scalar_from_constant(output_tensor.qnn_params['scale'])
@@ -1882,7 +1972,6 @@ def convert_conv(self, op, conv_type):
                     dtype=output_tensor_type_str)
         else:
             out = self.convert_fused_activation_function(out, fused_activation_fn)
-
         return out
 
     def convert_split(self, op):
@@ -2594,17 +2683,27 @@ def convert_quantize(self, op):
         input_tensors = self.get_input_tensors(op)
         assert len(input_tensors) == 1, "input tensors length should be 1"
         input_tensor = input_tensors[0]
+        input_tensor_type_str = self.get_tensor_type_str(input_tensor.tensor.Type())
         in_expr = self.get_expr(input_tensor.tensor_idx)
 
         output_tensors = self.get_output_tensors(op)
         assert len(output_tensors) == 1, "output tensors length should be 1"
         output_tensor = output_tensors[0]
+        output_tensor_type_str = self.get_tensor_type_str(output_tensor.tensor.Type())
 
         # The output must be quantized
         assert output_tensor.qnn_params
-        # Quantize the input
-        out = self.quantize(in_expr, output_tensor)
 
+        # TFLite Quantize op can also act as Requantize op
+        if input_tensor_type_str == "float32":
+            out = self.quantize(in_expr, output_tensor)
+        else:
+            out = _qnn.op.requantize(in_expr,
+                                     input_scale=input_tensor.qnn_params['scale'],
+                                     input_zero_point=input_tensor.qnn_params['zero_point'],
+                                     output_scale=output_tensor.qnn_params['scale'],
+                                     output_zero_point=output_tensor.qnn_params['zero_point'],
+                                     out_dtype=output_tensor_type_str)
         return out
 
     def convert_dequantize(self, op):
@@ -2734,7 +2833,6 @@ def get_tensor_expr(self, tensor):
         else:
             type_str = self.get_tensor_type_str(tensor.tensor.Type())
             expr = self.exp_tab.new_const(self.get_tensor_value(tensor), dtype=type_str)
-
         return expr
 
 
@@ -2747,6 +2845,13 @@ def get_scalar_from_constant(expr):
         "value must be float32/int32"
     return np.asscalar(value)
 
+def get_tensor_from_constant(expr):
+    """ Returns tensor of values from Relay constant node. """
+    assert isinstance(expr, _expr.Constant)
+    value = expr.data.asnumpy()
+    assert value.dtype == np.dtype(np.int32) or value.dtype == np.dtype(np.float32), \
+        "value must be float32/int32"
+    return value
 
 def build_str_map(obj):
     """Build string map of TFLite enum int value

src/relay/qnn/op/convolution.cc

@@ -61,9 +61,19 @@ bool QnnConv2DRel(const Array<Type>& types, int num_inputs, const Attrs& attrs,
   CHECK(IsScalarType(types[3], DataType::Int(32)));    // kernel_zero_point
   CHECK(IsScalarType(types[4], DataType::Float(32)));  // input_scale
   // Kernel scale can be a vector of length output_channels or a scalar.
-  size_t axis = param->kernel_layout.find('O');
-  CHECK(axis != std::string::npos) << "Kernel layout attribute is not defined";
-  AssignType(types[5], DataType::Float(32), weight->shape[axis], reporter);  // kernel scale
+  if (param->groups == 1) {
+    size_t axis = param->kernel_layout.find('O');
+    CHECK(axis != std::string::npos) << "Kernel layout attribute is not defined";
+    AssignType(types[5], DataType::Float(32), weight->shape[axis], reporter);  // kernel scale
+  } else {
+    // Here, total number of output channels depend on depth multiplier.
+    size_t o_axis = param->kernel_layout.find('O');
+    size_t i_axis = param->kernel_layout.find('I');
+    CHECK(o_axis != std::string::npos || i_axis != std::string::npos)
+        << "Kernel layout attribute is not defined";
+    AssignType(types[5], DataType::Float(32), weight->shape[i_axis] * weight->shape[o_axis],
+               reporter);  // kernel scale
+  }
 
   // Collect the input tensor and output tensor devoid of scale and zero points to reuse Relay
   // Conv2D infer type function.