Skip to content
Switch branches/tags
Go to file

* add ALv2 to missed files and remove leftover MIT licenses

Signed-off-by: Sheng Zha <>

* update proto files

Signed-off-by: Sheng Zha <>
23 contributors

Users who have contributed to this file

@linkerzhang @ezyang @bddppq @gramalingam @wschin @marcelolr @NiklasGustafsson @postrational @yuslepukhin @TMVector @tjingrant @tbennun
717 lines (619 sloc) 29.3 KB
// WARNING: This file is automatically generated! Please edit
// SPDX-License-Identifier: Apache-2.0
syntax = "proto3";
package onnx;
// Overview
// ONNX is an open specification that is comprised of the following components:
// 1) A definition of an extensible computation graph model.
// 2) Definitions of standard data types.
// 3) Definitions of built-in operators.
// This document describes the syntax of models and their computation graphs,
// as well as the standard data types. Together, they are referred to as the ONNX
// Intermediate Representation, or 'IR' for short.
// The normative semantic specification of the ONNX IR is found in docs/
// Definitions of the built-in neural network operators may be found in docs/
// Notes
// Release
// We are still in the very early stage of defining ONNX. The current
// version of ONNX is a starting point. While we are actively working
// towards a complete spec, we would like to get the community involved
// by sharing our working version of ONNX.
// Protobuf compatibility
// To simplify framework compatibility, ONNX is defined using the subset of protobuf
// that is compatible with both protobuf v2 and v3. This means that we do not use any
// protobuf features that are only available in one of the two versions.
// Here are the most notable contortions we have to carry out to work around
// these limitations:
// - No 'map' (added protobuf 3.0). We instead represent mappings as lists
// of key-value pairs, where order does not matter and duplicates
// are not allowed.
// Versioning
// ONNX versioning is specified in docs/ and elaborated on in docs/
// To be compatible with both proto2 and proto3, we will use a version number
// that is not defined by the default value but an explicit enum number.
enum Version {
// proto3 requires the first enum value to be zero.
// We add this just to appease the compiler.
// The version field is always serialized and we will use it to store the
// version that the graph is generated from. This helps us set up version
// control.
// For the IR, we are using simple numbers starting with 0x00000001,
// which was the version we published on Oct 10, 2017.
IR_VERSION_2017_10_10 = 0x0000000000000001;
// IR_VERSION 2 published on Oct 30, 2017
// - Added type discriminator to AttributeProto to support proto3 users
IR_VERSION_2017_10_30 = 0x0000000000000002;
// IR VERSION 3 published on Nov 3, 2017
// - For operator versioning:
// - Added new message OperatorSetIdProto
// - Added opset_import in ModelProto
// - For vendor extensions, added domain in NodeProto
IR_VERSION_2017_11_3 = 0x0000000000000003;
// IR VERSION 4 published on Jan 22, 2019
// - Relax constraint that initializers should be a subset of graph inputs
// - Add type BFLOAT16
IR_VERSION_2019_1_22 = 0x0000000000000004;
// IR VERSION 5 published on March 18, 2019
// - Add message TensorAnnotation.
// - Add quantization annotation in GraphProto to map tensor with its scale and zero point quantization parameters.
IR_VERSION_2019_3_18 = 0x0000000000000005;
// IR VERSION 6 published on Sep 19, 2019
// - Add support for sparse tensor constants stored in model.
// - Add message SparseTensorProto
// - Add sparse initializers
IR_VERSION_2019_9_19 = 0x0000000000000006;
// IR VERSION 7 published on <TBD>
// - Add support to allow function body graph to rely on multiple external opreator sets.
// - Add a list to promote inference graph's initializers to global and
// mutable variables. Global variables are visible in all graphs of the
// stored models.
// - Add message TrainingInfoProto to store initialization
// method and training algorithm. The execution of TrainingInfoProto
// can modify the values of mutable variables.
// - Implicitly add inference graph into each TrainingInfoProto's algorithm.
IR_VERSION = 0x0000000000000007;
// Attributes
// A named attribute containing either singular float, integer, string, graph,
// and tensor values, or repeated float, integer, string, graph, and tensor values.
// An AttributeProto MUST contain the name field, and *only one* of the
// following content fields, effectively enforcing a C/C++ union equivalent.
message AttributeProto {
// Note: this enum is structurally identical to the OpSchema::AttrType
// enum defined in schema.h. If you rev one, you likely need to rev the other.
enum AttributeType {
FLOAT = 1;
INT = 2;
GRAPH = 5;
INTS = 7;
GRAPHS = 10;
// The name field MUST be present for this version of the IR.
string name = 1; // namespace Attribute
// if ref_attr_name is not empty, ref_attr_name is the attribute name in parent function.
// In this case, this AttributeProto does not contain data, and it's a reference of attribute
// in parent scope.
// NOTE: This should ONLY be used in function (sub-graph). It's invalid to be used in main graph.
string ref_attr_name = 21;
// A human-readable documentation for this attribute. Markdown is allowed.
string doc_string = 13;
// The type field MUST be present for this version of the IR.
// For 0.0.1 versions of the IR, this field was not defined, and
// implementations needed to use has_field heuristics to determine
// which value field was in use. For IR_VERSION 0.0.2 or later, this
// field MUST be set and match the f|i|s|t|... field in use. This
// change was made to accommodate proto3 implementations.
AttributeType type = 20; // discriminator that indicates which field below is in use
// Exactly ONE of the following fields must be present for this version of the IR
float f = 2; // float
int64 i = 3; // int
bytes s = 4; // UTF-8 string
TensorProto t = 5; // tensor value
GraphProto g = 6; // graph
SparseTensorProto sparse_tensor = 22; // sparse tensor value
// Do not use field below, it's deprecated.
// optional ValueProto v = 12; // value - subsumes everything but graph
repeated float floats = 7; // list of floats
repeated int64 ints = 8; // list of ints
repeated bytes strings = 9; // list of UTF-8 strings
repeated TensorProto tensors = 10; // list of tensors
repeated GraphProto graphs = 11; // list of graph
repeated SparseTensorProto sparse_tensors = 23; // list of sparse tensors
// Defines information on value, including the name, the type, and
// the shape of the value.
message ValueInfoProto {
// This field MUST be present in this version of the IR.
string name = 1; // namespace Value
// This field MUST be present in this version of the IR for
// inputs and outputs of the top-level graph.
TypeProto type = 2;
// A human-readable documentation for this value. Markdown is allowed.
string doc_string = 3;
// Nodes
// Computation graphs are made up of a DAG of nodes, which represent what is
// commonly called a "layer" or "pipeline stage" in machine learning frameworks.
// For example, it can be a node of type "Conv" that takes in an image, a filter
// tensor and a bias tensor, and produces the convolved output.
message NodeProto {
repeated string input = 1; // namespace Value
repeated string output = 2; // namespace Value
// An optional identifier for this node in a graph.
// This field MAY be absent in ths version of the IR.
string name = 3; // namespace Node
// The symbolic identifier of the Operator to execute.
string op_type = 4; // namespace Operator
// The domain of the OperatorSet that specifies the operator named by op_type.
string domain = 7; // namespace Domain
// Additional named attributes.
repeated AttributeProto attribute = 5;
// A human-readable documentation for this node. Markdown is allowed.
string doc_string = 6;
// Training information
// TrainingInfoProto stores information for training a model.
// In particular, this defines two functionalities: an initialization-step
// and a training-algorithm-step. Initialization resets the model
// back to its original state as if no training has been performed.
// Training algorithm improves the model based on input data.
// The semantics of the initialization-step is that the initializers
// in ModelProto.graph and in TrainingInfoProto.algorithm are first
// initialized as specified by the initializers in the graph, and then
// updated by the "initialization_binding" in every instance in
// ModelProto.training_info.
// The field "algorithm" defines a computation graph which represents a
// training algorithm's step. After the execution of a
// TrainingInfoProto.algorithm, the initializers specified by "update_binding"
// may be immediately updated. If the targeted training algorithm contains
// consecutive update steps (such as block coordinate descent methods),
// the user needs to create a TrainingInfoProto for each step.
message TrainingInfoProto {
// This field describes a graph to compute the initial tensors
// upon starting the training process. Initialization graph has no input
// and can have multiple outputs. Usually, trainable tensors in neural
// networks are randomly initialized. To achieve that, for each tensor,
// the user can put a random number operator such as RandomNormal or
// RandomUniform in TrainingInfoProto.initialization.node and assign its
// random output to the specific tensor using "initialization_binding".
// This graph can also set the initializers in "algorithm" in the same
// TrainingInfoProto; a use case is resetting the number of training
// iteration to zero.
// By default, this field is an empty graph and its evaluation does not
// produce any output. Thus, no initializer would be changed by default.
GraphProto initialization = 1;
// This field represents a training algorithm step. Given required inputs,
// it computes outputs to update initializers in its own or inference graph's
// initializer lists. In general, this field contains loss node, gradient node,
// optimizer node, increment of iteration count.
// An execution of the training algorithm step is performed by executing the
// graph obtained by combining the inference graph (namely "ModelProto.graph")
// and the "algorithm" graph. That is, the actual the actual
// input/initializer/output/node/value_info/sparse_initializer list of
// the training graph is the concatenation of
// "ModelProto.graph.input/initializer/output/node/value_info/sparse_initializer"
// and "algorithm.input/initializer/output/node/value_info/sparse_initializer"
// in that order. This combined graph must satisfy the normal ONNX conditions.
// Now, let's provide a visualization of graph combination for clarity.
// Let the inference graph (i.e., "ModelProto.graph") be
// tensor_a, tensor_b -> MatMul -> tensor_c -> Sigmoid -> tensor_d
// and the "algorithm" graph be
// tensor_d -> Add -> tensor_e
// The combination process results
// tensor_a, tensor_b -> MatMul -> tensor_c -> Sigmoid -> tensor_d -> Add -> tensor_e
// Notice that an input of a node in the "algorithm" graph may reference the
// output of a node in the inference graph (but not the other way round). Also, inference
// node cannot reference inputs of "algorithm". With these restrictions, inference graph
// can always be run independently without training information.
// By default, this field is an empty graph and its evaluation does not
// produce any output. Evaluating the default training step never
// update any initializers.
GraphProto algorithm = 2;
// This field specifies the bindings from the outputs of "initialization" to
// some initializers in "ModelProto.graph.initializer" and
// the "algorithm.initializer" in the same TrainingInfoProto.
// See "update_binding" below for details.
// By default, this field is empty and no initializer would be changed
// by the execution of "initialization".
repeated StringStringEntryProto initialization_binding = 3;
// Gradient-based training is usually an iterative procedure. In one gradient
// descent iteration, we apply
// x = x - r * g
// where "x" is the optimized tensor, "r" stands for learning rate, and "g" is
// gradient of "x" with respect to a chosen loss. To avoid adding assignments
// into the training graph, we split the update equation into
// y = x - r * g
// x = y
// The user needs to save "y = x - r * g" into TrainingInfoProto.algorithm. To
// tell that "y" should be assigned to "x", the field "update_binding" may
// contain a key-value pair of strings, "x" (key of StringStringEntryProto)
// and "y" (value of StringStringEntryProto).
// For a neural network with multiple trainable (mutable) tensors, there can
// be multiple key-value pairs in "update_binding".
// The initializers appears as keys in "update_binding" are considered
// mutable variables. This implies some behaviors
// as described below.
// 1. We have only unique keys in all "update_binding"s so that two
// variables may not have the same name. This ensures that one
// variable is assigned up to once.
// 2. The keys must appear in names of "ModelProto.graph.initializer" or
// "TrainingInfoProto.algorithm.initializer".
// 3. The values must be output names of "algorithm" or "ModelProto.graph.output".
// 4. Mutable variables are initialized to the value specified by the
// corresponding initializer, and then potentially updated by
// "initializer_binding"s and "update_binding"s in "TrainingInfoProto"s.
// This field usually contains names of trainable tensors
// (in ModelProto.graph), optimizer states such as momentums in advanced
// stochastic gradient methods (in TrainingInfoProto.graph),
// and number of training iterations (in TrainingInfoProto.graph).
// By default, this field is empty and no initializer would be changed
// by the execution of "algorithm".
repeated StringStringEntryProto update_binding = 4;
// Models
// ModelProto is a top-level file/container format for bundling a ML model and
// associating its computation graph with metadata.
// The semantics of the model are described by the associated GraphProto's.
message ModelProto {
// The version of the IR this model targets. See Version enum above.
// This field MUST be present.
int64 ir_version = 1;
// The OperatorSets this model relies on.
// All ModelProtos MUST have at least one entry that
// specifies which version of the ONNX OperatorSet is
// being imported.
// All nodes in the ModelProto's graph will bind against the operator
// with the same-domain/same-op_type operator with the HIGHEST version
// in the referenced operator sets.
repeated OperatorSetIdProto opset_import = 8;
// The name of the framework or tool used to generate this model.
// This field SHOULD be present to indicate which implementation/tool/framework
// emitted the model.
string producer_name = 2;
// The version of the framework or tool used to generate this model.
// This field SHOULD be present to indicate which implementation/tool/framework
// emitted the model.
string producer_version = 3;
// Domain name of the model.
// We use reverse domain names as name space indicators. For example:
// `com.facebook.fair` or ``
// Together with `model_version` and, this forms the unique identity of
// the graph.
string domain = 4;
// The version of the graph encoded. See Version enum below.
int64 model_version = 5;
// A human-readable documentation for this model. Markdown is allowed.
string doc_string = 6;
// The parameterized graph that is evaluated to execute the model.
GraphProto graph = 7;
// Named metadata values; keys should be distinct.
repeated StringStringEntryProto metadata_props = 14;
// Training-specific information. Sequentially executing all stored
// `TrainingInfoProto.algorithm`s and assigning their outputs following
// the corresponding `TrainingInfoProto.update_binding`s is one training
// iteration. Similarly, to initialize the model
// (as if training hasn't happened), the user should sequentially execute
// all stored `TrainingInfoProto.initialization`s and assigns their outputs
// using `TrainingInfoProto.initialization_binding`s.
// If this field is empty, the training behavior of the model is undefined.
repeated TrainingInfoProto training_info = 20;
// StringStringEntryProto follows the pattern for cross-proto-version maps.
// See
message StringStringEntryProto {
string key = 1;
string value= 2;
message TensorAnnotation {
string tensor_name = 1;
// <key, value> pairs to annotate tensor specified by <tensor_name> above.
// The keys used in the mapping below must be pre-defined in ONNX spec.
// For example, for 8-bit linear quantization case, 'SCALE_TENSOR', 'ZERO_POINT_TENSOR' will be pre-defined as
// quantization parameter keys.
repeated StringStringEntryProto quant_parameter_tensor_names = 2;
// Graphs
// A graph defines the computational logic of a model and is comprised of a parameterized
// list of nodes that form a directed acyclic graph based on their inputs and outputs.
// This is the equivalent of the "network" or "graph" in many deep learning
// frameworks.
message GraphProto {
// The nodes in the graph, sorted topologically.
repeated NodeProto node = 1;
// The name of the graph.
string name = 2; // namespace Graph
// A list of named tensor values, used to specify constant inputs of the graph.
// Each initializer (both TensorProto as well SparseTensorProto) MUST have a name.
// The name MUST be unique across both initializer and sparse_initializer,
// but the name MAY also appear in the input list.
repeated TensorProto initializer = 5;
// Initializers (see above) stored in sparse format.
repeated SparseTensorProto sparse_initializer = 15;
// A human-readable documentation for this graph. Markdown is allowed.
string doc_string = 10;
// The inputs and outputs of the graph.
repeated ValueInfoProto input = 11;
repeated ValueInfoProto output = 12;
// Information for the values in the graph. The's
// must be distinct. It is optional for a value to appear in value_info list.
repeated ValueInfoProto value_info = 13;
// This field carries information to indicate the mapping among a tensor and its
// quantization parameter tensors. For example:
// For tensor 'a', it may have {'SCALE_TENSOR', 'a_scale'} and {'ZERO_POINT_TENSOR', 'a_zero_point'} annotated,
// which means, tensor 'a_scale' and tensor 'a_zero_point' are scale and zero point of tensor 'a' in the model.
repeated TensorAnnotation quantization_annotation = 14;
// DO NOT USE the following fields, they were deprecated from earlier versions.
// repeated string input = 3;
// repeated string output = 4;
// optional int64 ir_version = 6;
// optional int64 producer_version = 7;
// optional string producer_tag = 8;
// optional string domain = 9;
// Tensors
// A serialized tensor value.
message TensorProto {
enum DataType {
// Basic types.
FLOAT = 1; // float
UINT8 = 2; // uint8_t
INT8 = 3; // int8_t
UINT16 = 4; // uint16_t
INT16 = 5; // int16_t
INT32 = 6; // int32_t
INT64 = 7; // int64_t
STRING = 8; // string
BOOL = 9; // bool
// IEEE754 half-precision floating-point format (16 bits wide).
// This format has 1 sign bit, 5 exponent bits, and 10 mantissa bits.
FLOAT16 = 10;
DOUBLE = 11;
UINT32 = 12;
UINT64 = 13;
COMPLEX64 = 14; // complex with float32 real and imaginary components
COMPLEX128 = 15; // complex with float64 real and imaginary components
// Non-IEEE floating-point format based on IEEE754 single-precision
// floating-point number truncated to 16 bits.
// This format has 1 sign bit, 8 exponent bits, and 7 mantissa bits.
BFLOAT16 = 16;
// Future extensions go here.
// The shape of the tensor.
repeated int64 dims = 1;
// The data type of the tensor.
// This field MUST have a valid TensorProto.DataType value
int32 data_type = 2;
// For very large tensors, we may want to store them in chunks, in which
// case the following fields will specify the segment that is stored in
// the current TensorProto.
message Segment {
int64 begin = 1;
int64 end = 2;
Segment segment = 3;
// Tensor content must be organized in row-major order.
// Depending on the data_type field, exactly one of the fields below with
// name ending in _data is used to store the elements of the tensor.
// For float and complex64 values
// Complex64 tensors are encoded as a single array of floats,
// with the real components appearing in odd numbered positions,
// and the corresponding imaginary component appearing in the
// subsequent even numbered position. (e.g., [1.0 + 2.0i, 3.0 + 4.0i]
// is encoded as [1.0, 2.0 ,3.0 ,4.0]
// When this field is present, the data_type field MUST be FLOAT or COMPLEX64.
repeated float float_data = 4 [packed = true];
// For int32, uint8, int8, uint16, int16, bool, and float16 values
// float16 values must be bit-wise converted to an uint16_t prior
// to writing to the buffer.
// When this field is present, the data_type field MUST be
// INT32, INT16, INT8, UINT16, UINT8, BOOL, or FLOAT16
repeated int32 int32_data = 5 [packed = true];
// For strings.
// Each element of string_data is a UTF-8 encoded Unicode
// string. No trailing null, no leading BOM. The protobuf "string"
// scalar type is not used to match ML community conventions.
// When this field is present, the data_type field MUST be STRING
repeated bytes string_data = 6;
// For int64.
// When this field is present, the data_type field MUST be INT64
repeated int64 int64_data = 7 [packed = true];
// Optionally, a name for the tensor.
string name = 8; // namespace Value
// A human-readable documentation for this tensor. Markdown is allowed.
string doc_string = 12;
// Serializations can either use one of the fields above, or use this
// raw bytes field. The only exception is the string case, where one is
// required to store the content in the repeated bytes string_data field.
// When this raw_data field is used to store tensor value, elements MUST
// be stored in as fixed-width, little-endian order.
// Floating-point data types MUST be stored in IEEE 754 format.
// Complex64 elements must be written as two consecutive FLOAT values, real component first.
// Complex128 elements must be written as two consecutive DOUBLE values, real component first.
// Boolean type MUST be written one byte per tensor element (00000001 for true, 00000000 for false).
// Note: the advantage of specific field rather than the raw_data field is
// that in some cases (e.g. int data), protobuf does a better packing via
// variable length storage, and may lead to smaller binary footprint.
// When this field is present, the data_type field MUST NOT be STRING or UNDEFINED
bytes raw_data = 9;
// Data can be stored inside the protobuf file using type-specific fields or raw_data.
// Alternatively, raw bytes data can be stored in an external file, using the external_data field.
// external_data stores key-value pairs describing data location. Recognized keys are:
// - "location" (required) - POSIX filesystem path relative to the directory where the ONNX
// protobuf model was stored
// - "offset" (optional) - position of byte at which stored data begins. Integer stored as string.
// Offset values SHOULD be multiples 4096 (page size) to enable mmap support.
// - "length" (optional) - number of bytes containing data. Integer stored as string.
// - "checksum" (optional) - SHA1 digest of file specified in under 'location' key.
repeated StringStringEntryProto external_data = 13;
// Location of the data for this tensor. MUST be one of:
// - DEFAULT - data stored inside the protobuf message. Data is stored in raw_data (if set) otherwise in type-specified field.
// - EXTERNAL - data stored in an external location as described by external_data field.
enum DataLocation {
// If value not set, data is stored in raw_data (if set) otherwise in type-specified field.
DataLocation data_location = 14;
// For double
// Complex128 tensors are encoded as a single array of doubles,
// with the real components appearing in odd numbered positions,
// and the corresponding imaginary component appearing in the
// subsequent even numbered position. (e.g., [1.0 + 2.0i, 3.0 + 4.0i]
// is encoded as [1.0, 2.0 ,3.0 ,4.0]
// When this field is present, the data_type field MUST be DOUBLE or COMPLEX128
repeated double double_data = 10 [packed = true];
// For uint64 and uint32 values
// When this field is present, the data_type field MUST be
// UINT32 or UINT64
repeated uint64 uint64_data = 11 [packed = true];
// A serialized sparse-tensor value
message SparseTensorProto {
// The sequence of non-default values are encoded as a tensor of shape [NNZ].
// The default-value is zero for numeric tensors, and empty-string for string tensors.
// values must have a non-empty name present which serves as a name for SparseTensorProto
// when used in sparse_initializer list.
TensorProto values = 1;
// The indices of the non-default values, which may be stored in one of two formats.
// (a) Indices can be a tensor of shape [NNZ, rank] with the [i,j]-th value
// corresponding to the j-th index of the i-th value (in the values tensor).
// (b) Indices can be a tensor of shape [NNZ], in which case the i-th value
// must be the linearized-index of the i-th value (in the values tensor).
// The linearized-index can be converted into an index tuple (k_1,...,k_rank)
// using the shape provided below.
// The indices must appear in ascending order without duplication.
// In the first format, the ordering is lexicographic-ordering:
// e.g., index-value [1,4] must appear before [2,1]
TensorProto indices = 2;
// The shape of the underlying dense-tensor: [dim_1, dim_2, ... dim_rank]
repeated int64 dims = 3;
// Defines a tensor shape. A dimension can be either an integer value
// or a symbolic variable. A symbolic variable represents an unknown
// dimension.
message TensorShapeProto {
message Dimension {
oneof value {
int64 dim_value = 1;
string dim_param = 2; // namespace Shape
// Standard denotation can optionally be used to denote tensor
// dimensions with standard semantic descriptions to ensure
// that operations are applied to the correct axis of a tensor.
// Refer to
// for pre-defined dimension denotations.
string denotation = 3;
repeated Dimension dim = 1;
// Types
// The standard ONNX data types.
message TypeProto {
message Tensor {
// This field MUST NOT have the value of UNDEFINED
// This field MUST have a valid TensorProto.DataType value
// This field MUST be present for this version of the IR.
int32 elem_type = 1;
TensorShapeProto shape = 2;
// repeated T
message Sequence {
// The type and optional shape of each element of the sequence.
// This field MUST be present for this version of the IR.
TypeProto elem_type = 1;
// map<K,V>
message Map {
// This field MUST have a valid TensorProto.DataType value
// This field MUST be present for this version of the IR.
// This field MUST refer to an integral type ([U]INT{8|16|32|64}) or STRING
int32 key_type = 1;
// This field MUST be present for this version of the IR.
TypeProto value_type = 2;
oneof value {
// The type of a tensor.
Tensor tensor_type = 1;
// NOTE: DNN-only implementations of ONNX MAY elect to not support non-tensor values
// as input and output to graphs and nodes. These types are needed to naturally
// support classical ML operators. DNN operators SHOULD restrict their input
// and output types to tensors.
// The type of a sequence.
Sequence sequence_type = 4;
// The type of a map.
Map map_type = 5;
// An optional denotation can be used to denote the whole
// type with a standard semantic description as to what is
// stored inside. Refer to
// for pre-defined type denotations.
string denotation = 6;
// Operator Sets
// OperatorSets are uniquely identified by a (domain, opset_version) pair.
message OperatorSetIdProto {
// The domain of the operator set being identified.
// The empty string ("") or absence of this field implies the operator
// set that is defined as part of the ONNX specification.
// This field MUST be present in this version of the IR when referring to any other operator set.
string domain = 1;
// The version of the operator set being identified.
// This field MUST be present in this version of the IR.
int64 version = 2;
// For using protobuf-lite
option optimize_for = LITE_RUNTIME;