[Apache TVM Discuss] [Questions] Questions about codegen?

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Hi, everyone ! I have a few questions about the following code in `include/tvm/tir/stmt_functor.h`
```
template <typename TNode>
  TSelf& set_dispatch(FPointer f) {  // NOLINT(*)
    uint32_t tindex = TNode::RuntimeTypeIndex();
    if (func_.size() <= tindex) {
      func_.resize(tindex + 1, nullptr);
    }
    ICHECK(func_[tindex] == nullptr) << "Dispatch for " << TNode::_type_key << " is already set";
    func_[tindex] = f;
    return *this;
  }

#define IR_STMT_FUNCTOR_DISPATCH(OP)                                                       \
  vtable.template set_dispatch<OP>([](const ObjectRef& n, TSelf* self, Args... args) {     \
    return self->VisitStmt_(static_cast<const OP*>(n.get()), std::forward<Args>(args)...); \
  });

static FType InitVTable() {
    FType vtable;
    IR_STMT_FUNCTOR_DISPATCH(LetStmtNode);
    IR_STMT_FUNCTOR_DISPATCH(AttrStmtNode);
    IR_STMT_FUNCTOR_DISPATCH(IfThenElseNode);
    IR_STMT_FUNCTOR_DISPATCH(ForNode);
    IR_STMT_FUNCTOR_DISPATCH(AllocateNode);
    IR_STMT_FUNCTOR_DISPATCH(StoreNode);
    IR_STMT_FUNCTOR_DISPATCH(AssertStmtNode);
    IR_STMT_FUNCTOR_DISPATCH(ProducerStoreNode);
    IR_STMT_FUNCTOR_DISPATCH(ProducerRealizeNode);
    IR_STMT_FUNCTOR_DISPATCH(PrefetchNode);
    IR_STMT_FUNCTOR_DISPATCH(SeqStmtNode);
    IR_STMT_FUNCTOR_DISPATCH(EvaluateNode);
    IR_STMT_FUNCTOR_DISPATCH(BufferStoreNode);
    IR_STMT_FUNCTOR_DISPATCH(BufferRealizeNode);
    IR_STMT_FUNCTOR_DISPATCH(BlockNode);
    IR_STMT_FUNCTOR_DISPATCH(BlockRealizeNode);
    return vtable;
  }

 virtual R VisitStmt(const Stmt& n, Args... args) {                                                                                                                                
           static FType vtable = InitVTable();                                                                                                                                                
           return vtable(n, this, std::forward<Args>(args)...);
}
```
a) I can not find the `template` member in `vtable`, so I can not understand the meaning of `vtable.template` in `IR_STMT_FUNCTOR_DISPATCH`, why not just call for `set_dispatch`;

b)when I step in `vtable(n, this, std::forward<Args>(args)...);` It will find the specific function in `vtable.func_` to run according to `stmt n` index. It should have no more than 20 functions in `vtable.func_` following `InitVTable()`, but when I debug in gdb, it has more than 100 functions,
so why ?

c) I am reading the tvm codegen source code, and I find `VisitStmt` function is used for transform the function body, now I get stuck in `VisitStmt`, I can not find the specific function to finish function body's transforming.

Thanks in advance.





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