MLBEDSW-7408: MLCE: Crash when serialising model LSTM

 - Added checking and reporting of missing operator attributes when
reading and writing TFLite file
 - Added a TFLite semantic check to ensure that all required attribute
fields of builtin operators are read
 - Added some sanity checks for RESHAPE operators that run on the
Ethos-U
 - Stopped CPU operators from having their attributes modified

Change-Id: I05700681acdb09554f5945819717c08a9457295c
Signed-off-by: Tim Hall <tim.hall@arm.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/ethosu/vela/tflite_reader.py b/ethosu/vela/tflite_reader.py
index 2325ff65..2f3192b7 100644
--- a/ethosu/vela/tflite_reader.py
+++ b/ethosu/vela/tflite_reader.py
@@ -41,6 +41,7 @@ from .tflite_mapping import builtin_operator_map
 from .tflite_mapping import DataType
 from .tflite_mapping import datatype_map
 from .tflite_mapping import datatype_map_numpy
+from .tflite_mapping import optype_to_builtintype
 
 
 class TFLiteSubgraph:
@@ -180,9 +181,11 @@ class TFLiteSubgraph:
                 init_subgraph_index = op.attrs["init_subgraph_index"]
                 op.attrs["subgraph"] = (self.graph.nng.subgraphs[init_subgraph_index],)
 
-            if op_type == Op.Reshape and "new_shape" not in op.attrs:
-                # Reshape should have an attrib "new_shape" but if it is missing, add it based on the output shape
-                op.attrs["new_shape"] = outputs[0].shape
+            if op_type == Op.Reshape:
+                if "new_shape" in op.attrs["attribute_read_error"] and len(inputs) > 1:
+                    # the "new_shape" attribute is optional if the new_shape tensor (inputs[1]) is specified. therefore,
+                    # remove the attribute read error
+                    op.attrs["attribute_read_error"].remove("new_shape")
 
             if op_type == Op.Cast:
                 # Cast op should have "in/out_data_type" attribs add if missing
@@ -212,6 +215,14 @@ class TFLiteSubgraph:
             if custom_code is not None:
                 op.attrs["custom_code"] = custom_code
 
+            # finally, report any missing attributes that could not be read during deserialize()
+            attribute_read_error = op.attrs["attribute_read_error"]
+            if len(attribute_read_error) != 0:
+                print(
+                    f"Warning: Could not read the following attributes from {optype_to_builtintype(op.type)}"
+                    f" '{op.name}' {opt_serializer.name} field: {', '.join(attribute_read_error)}"
+                )
+
     @staticmethod
     def len1_array_to_scalar(arr):
         # The following flatbuffer quantisation fields all return a scalar value of 0 if they are not definied in