Remove num dim usages in xnnpack flatbuffer (#19013)

There's some redundancy here where num_dims is serialized into the
flatbuffer. Use size from the dims array directly, as if we use
num_dims, we have to check it matches up with the dims array size.

Hopefully prevent some security issues down the line.

Co-authored-by: Github Executorch <github_executorch@arm.com>

Author: lucylq

backends/xnnpack/runtime/XNNCompiler.cpp

@@ -319,24 +319,9 @@ Error defineTensor(
   ET_CHECK_OR_RETURN_ERROR(
       tensor_value != nullptr, InvalidProgram, "Deserialized tensor is null");
 
-  ET_CHECK_OR_RETURN_ERROR(
-      tensor_value->num_dims() == 0 || tensor_value->dims() != nullptr,
-      InvalidProgram,
-      "Tensor dims is null but num_dims is %u",
-      tensor_value->num_dims());
-
-  if (tensor_value->dims() != nullptr) {
-    ET_CHECK_OR_RETURN_ERROR(
-        tensor_value->num_dims() == tensor_value->dims()->size(),
-        InvalidProgram,
-        "Tensor num_dims %u does not match dims array size %u",
-        tensor_value->num_dims(),
-        tensor_value->dims()->size());
-  }
-
-  // Get tensor dims, here we need to use a vector in order
-  // to properly convert the uint32_t* to size_t*. For scalar tensors
-  // (num_dims == 0), dims() is permitted to be null per the check above.
+  // Get tensor dims, here we need to use a vector in order to properly
+  // convert the uint32_t* to size_t*. Scalar tensors (rank 0) are permitted
+  // to have a null dims vector; in that case dims_data is empty.
   std::vector<size_t> dims_data;
   if (tensor_value->dims() != nullptr) {
     dims_data = flatbufferDimsToVector(tensor_value->dims());
@@ -386,7 +371,7 @@ Error defineTensor(
       status = xnn_define_tensor_value(
           /*subgraph=*/subgraph_ptr,
           /*datatype=*/getDataType(tensor_value->datatype()),
-          /*num_dims=*/tensor_value->num_dims(),
+          /*num_dims=*/dims_data.size(),
           /*dims=*/dims_data.data(),
           /*data=*/buffer_ptr,
           /*external_id=*/tensor_value->external_id(),
@@ -421,7 +406,7 @@ Error defineTensor(
           status = xnn_define_dynamically_quantized_tensor_value(
               /*subgraph=*/subgraph_ptr,
               /*datatype=*/xnn_datatype_qdint8,
-              /*num_dims=*/tensor_value->num_dims(),
+              /*num_dims=*/dims_data.size(),
               /*num_nonbatch_dims=*/1, // always do per token quantization
               /*dims=*/dims_data.data(),
               /*external_id=*/XNN_INVALID_VALUE_ID, // always internal value id
@@ -435,7 +420,7 @@ Error defineTensor(
           status = xnn_define_tensor_value(
               /*subgraph=*/subgraph_ptr,
               /*datatype=*/fp_datatype,
-              /*num_dims=*/tensor_value->num_dims(),
+              /*num_dims=*/dims_data.size(),
               /*dims=*/dims_data.data(),
               /*data=*/buffer_ptr,
               /*external_id=*/tensor_value->external_id(),
@@ -476,7 +461,7 @@ Error defineTensor(
             /*datatype=*/getDataType(tensor_value->datatype()),
             /*zero_point=*/qparams->zero_point(),
             /*scale=*/qparams->scale(),
-            /*num_dims=*/tensor_value->num_dims(),
+            /*num_dims=*/dims_data.size(),
             /*dims=*/dims_data.data(),
             /*data=*/buffer_ptr,
             /*external_id=*/tensor_value->external_id(),
@@ -521,7 +506,7 @@ Error defineTensor(
             /*datatype=*/dtype,
             /*zero_point=*/zero_point,
             /*scale=*/scale,
-            /*num_dims=*/tensor_value->num_dims(),
+            /*num_dims=*/dims_data.size(),
             /*channel_dim*/ qparams->channel_dim(),
             /*dims=*/dims_data.data(),
             /*data=*/buffer_ptr,
@@ -599,7 +584,7 @@ Error defineTensor(
             /*datatype=*/datatype,
             /*zero_point=*/zero_point,
             /*scale=*/scale_data,
-            /*num_dims=*/tensor_value->num_dims(),
+            /*num_dims=*/dims_data.size(),
             /*channel_dim=*/qparams->channel_dim(),
             /*block_size=*/qparams->group_size(),
             /*dims=*/dims_data.data(),
@@ -613,8 +598,8 @@ Error defineTensor(
         auto qparams = qtensor_value->quant_params_as_PerTokenDynamicQuant();
         ET_LOG(
             Debug,
-            "define quant tensor (dynamic): num_dims: %i, num_nonbatch_dims: %i\n",
-            tensor_value->num_dims(),
+            "define quant tensor (dynamic): num_dims: %zu, num_nonbatch_dims: %i\n",
+            dims_data.size(),
             qparams->num_nonbatch_dims());
         ET_CHECK_OR_RETURN_ERROR(
             buffer_ptr == nullptr,
@@ -623,7 +608,7 @@ Error defineTensor(
         status = xnn_define_dynamically_quantized_tensor_value(
             /*subgraph=*/subgraph_ptr,
             /*datatype=*/getDataType(tensor_value->datatype()),
-            /*num_dims=*/tensor_value->num_dims(),
+            /*num_dims=*/dims_data.size(),
             /*num_nonbatch_dims*/ qparams->num_nonbatch_dims(),
             /*dims=*/dims_data.data(),
             /*external_id=*/tensor_value->external_id(),