[Onnx简化库深度剖析] OnnxSimplifier和OnnxOptimizer解读-(2)

简介

上篇重点介绍了OnnxSimplifier的库，其中的FixedPointFn迭代优化函数利用到了OnnxOptimizer这个官方的优化库，大部分的优化细节是在OnnxOptimizer内的。因此本篇重点介绍一下OnnxOptimizer库的内部优化细节和逐个介绍每个优化pass和手段。

OnnxOptimizer基本概念原理

Pass

含义：所有优化项的基类，每个优化项必须拥有唯一的名字，用来注册和管理。
概念：
- 优化类型(PassType)：
  - Fuse: 会融合算子的优化项
  - Nop: 会移除无用的算子的优化项
  - Separate：
  - Immutable：
  - Replace：会进行节点替换的优化项
  - Other：其他
- (PassAnalysisType)：
  - Empty
  - CountBased
- (PassEfficiency):
  - Partial
  - Complete
- (PassOptimizationType):
  - None
  - Compute: 针对计算优化
  - Memory：针对内存优化
  - ComputeMemory：针对计算和内存优化
  - Stability：稳定
基类的代码：

class Pass {PassType pass_type;PassEfficiency pass_efficiency;PassOptimizationType pass_optimization_type;public:Pass(PassType pass_type, PassEfficiency pass_efficiency,PassOptimizationType pass_optimization_type);virtual ~Pass();PassType getPassType() const {return this->pass_type;}PassEfficiency getPassEfficiency() const {return this->pass_efficiency;}PassOptimizationType getPassOptimizationType() const {return this->pass_optimization_type;}virtual PassAnalysisType getPassAnalysisType() const = 0; // virtual std::string getPassName() const = 0; // 返回优化项的名字virtual bool initializePass(Graph &) { // 可有可无的函数实现return false;}virtual bool finalizePass(Graph &) { // 可有可无的函数实现return false;}virtual std::shared_ptr<PostPassAnalysis> runPass(Graph &graph) = 0; // 子类必须实现该函数，用于运行模型优化protected:// Iterates through the elements in the graph and counts the number of times// the transform is successfully run.unsigned int DescendOnGraphAttributesAndCount(Node *n, std::function<unsigned int(Graph &)> fn);// A more general version of the function above that doesn't constrain the// return type of fn.void DescendOnGraphAttributesUnconstrained(Node *n,std::function<void(Graph &)> fn);
};

具体的Pass实现和细节罗列

Pass	PassName	PassType	PassEfficiency	PassOptimizationType	描述
AdjustAdd	adjust_add	Immutable	Complete	Compute	交换add第一个constant_input到第二位置上
RenameInputOutput	rename_input_output	Other	Complete	None	修改模型输入/输出为统一的预设的或者默认的格式:input_%d/output_%d
SetUniqueNameForNodes	set_unique_name_for_nodes	Other	Complete	None	为name为空的node设置唯一的node_name
EliminateNopCast	eliminate_nop_cast	Nop	Complete	Compute	移除那些目标输出数据类型等于输入数据类型的cast算子
EliminateNopDropout	eliminate_nop_dropout	Nop	Complete	Compute	移除那些ratio=0.0的dropout算子
EliminateNopFlatten	eliminate_nop_flatten	Nop	Complete	Compute	移除那些对shape无影响的Flatten算子
ExtractConstantToInitializer	extract_constant_to_initializer	Nop	Complete	Memory	移除Constant算子，放置到Initializer内
EliminateConsecutiveIdempotentOps	eliminate_consecutive_idempotent_ops	Fuse	Complete	Compute	融合连续的op,比如"Ceil", “Floor”, “Round”, “Relu”, "Reshape"等
EliminateIfWithConstCond	eliminate_if_with_const_cond	Nop	Complete	Compute	消除输入条件cond为常量的if算子
EliminateNopMonotoneArgmax	eliminate_nop_monotone_argmax	Nop	Partial	Compute	消除输入条件cond为常量的if算子