RelayTextPrinter is now non-recursive. ExpandDataflow refactored

RelayTextPrinter is now non-recursive to allow printing larger
graphs. ExpandDataflow is generalised to have separate node expander.

Change-Id: Id5a3a470fbc8b90822502fbc8d24d534df1ea355

include/tvm/relay/expr_functor.h

@@ -32,11 +32,12 @@
 #include <tvm/relay/function.h>
 #include <tvm/relay/op.h>
 
+#include <deque>
 #include <stack>
 #include <string>
 #include <unordered_map>
 #include <utility>
-
+#include <vector>
 namespace tvm {
 namespace relay {
 
@@ -276,7 +277,9 @@ class MixedModeVisitor : public ::tvm::relay::ExprVisitor {
  */
 class MixedModeMutator : public ::tvm::relay::ExprMutator {
  public:
+  MixedModeMutator(bool pre = false) : pre_{pre} {};
   Expr VisitExpr(const Expr& expr) final;
+
   virtual Expr DispatchVisitExpr(const Expr& expr);
   Expr VisitExpr_(const TupleNode* op) final { return Rewrite(op); };
   Expr VisitExpr_(const CallNode* call_node) final { return Rewrite(call_node); };
@@ -294,6 +297,7 @@ class MixedModeMutator : public ::tvm::relay::ExprMutator {
   virtual Expr Rewrite_(const TupleGetItemNode* pre, const Expr& post) { return post; }
 
  protected:
+  bool pre_;
   /*! \brief Implement Rewrite API by calling ExprMutator's VisitExpr_(op) to get a `post` node with
    * changed inputs.
    */
@@ -410,72 +414,82 @@ Expr PostOrderRewrite(const Expr& expr, ExprRewriter* rewriter);
  */
 void PostOrderVisit(const Expr& node, std::function<void(const Expr&)> fvisit);
 
+/*!
+ * \brief A struct to keep info of traversed expr in ExpandDataflow function
+ */
+struct v_info {
+  explicit v_info(Expr node_) : node{node_} {}
+  v_info(Expr node_, bool children_expanded_)
+      : node{node_}, children_expanded{children_expanded_} {};
+  Expr node{};
+  bool children_expanded{false};
+};
+
 /*!
  * \brief A function to iteratively traverse dataflow regions of a graph
  *
  * ExpandDataflow manually manages a stack and performs DFS to determine the processing
  * order of nodes in an input graph.
  *
- * If it finds a dataflow node (Call, Tuple, TupleGetItem), it checks if the arguments to that node
- * need to be processed via fcheck_visited. If so, the function pushes those arguments to the stack
- * and continues iteratively to process the top of the stack. When it finds a node that doesn't
- * match the dataflow types, or a node who's inputs have all been processed, it visits the current
- * leaf via fvisit_leaf.
+ * By default fexpand_expr implemented in a way that if it finds a dataflow node (Call, Tuple,
+ * TupleGetItem), it checks if the arguments to that node need to be processed via fcheck_visited.
+ * If so, the function pushes those arguments to the stack and continues iteratively to process
+ * the top of the stack. When it finds a node that doesn't match the dataflow types, or a node who's
+ * inputs have all been processed, it visits the current leaf via fvisit_leaf.
  *
  * This function should be used internally to other classes to implement mixed-mode traversals. The
  * expectation is that fvisit_leaf will perform recursive analysis within mixed-mode traversal if it
  * hits a non-dataflow node.
  *
- * fcheck_visited and fvisit_leaf are templated to encourage compiler inlining.
+ * fcheck_visited, fvisit_leaf and fexpand_expr are templated to encourage reusing.
  */
-template <typename FCheckVisited, typename FVisitLeaf>
-void ExpandDataflow(Expr expr, FCheckVisited fcheck_visited, FVisitLeaf fvisit_leaf) {
-  std::stack<std::pair<Expr, bool>> stack;
+template <typename FCheckVisited, typename FVisitLeaf, typename FExpandExpr>
+void ExpandDataflow(Expr expr, FCheckVisited fcheck_visited, FVisitLeaf fvisit_leaf,
+                    FExpandExpr fexpand_expr) {
+  std::deque<v_info> stack;
   auto fpush_to_stack = [&fcheck_visited, &stack](const Expr& expr) {
-    // The second state of the stack indicate whether the child has been
-    // expanded in the pre-order.
-    // NOTE: function will be inlined.
     if (!fcheck_visited(expr)) {
-      stack.push({expr, false});
+      stack.push_front(std::move(v_info(expr)));
     }
   };
+
   fpush_to_stack(expr);
   while (stack.size() > 0) {
-    auto node = stack.top().first;
-    if (fcheck_visited(node)) {
-      // if this node was visited through another path
-      // after being added to the stack ignore it.
-      stack.pop();
-    } else if (stack.top().second) {
-      // all the children have already been expanded.
-      // we can just run post order visit on it.
-      fvisit_leaf(node);
-      stack.pop();
-    } else if (const CallNode* op = node.as<CallNode>()) {
-      // mark expanded = true
-      stack.top().second = true;
-      // push the children to the stack in reverse order
-      // to match recursive processing order
+    v_info* front = &stack.front();
+    if (fcheck_visited(front->node)) {
+      stack.pop_front();
+    } else if (front->children_expanded) {
+      fvisit_leaf(front->node);
+      // TODO(d-smirnov): this is for compatibility with current implementation of MixedModeVisitor
+      stack.pop_front();
+    } else {
+      front->children_expanded = true;
+      for (auto e : fexpand_expr(front->node)) {
+        fpush_to_stack(e);
+      }
+    }
+  }
+}
+
+template <typename FCheckVisited, typename FVisitLeaf>
+void ExpandDataflow(Expr expr, FCheckVisited fcheck_visited, FVisitLeaf fvisit_leaf) {
+  auto fexpand_expr = [](const Expr& expr) {
+    std::vector<Expr> result;
+    if (const CallNode* op = expr.as<CallNode>()) {
       for (auto it = op->args.rbegin(); it != op->args.rend(); ++it) {
-        fpush_to_stack(*it);
+        result.push_back(*it);
       }
-      fpush_to_stack(op->op);
-    } else if (const TupleNode* op = node.as<TupleNode>()) {
-      stack.top().second = true;
-      // push the children to the stack in reverse order
-      // to match recursive processing order
+      result.push_back(op->op);
+    } else if (const TupleNode* op = expr.as<TupleNode>()) {
       for (auto it = op->fields.rbegin(); it != op->fields.rend(); ++it) {
-        fpush_to_stack(*it);
+        result.push_back(*it);
       }
-    } else if (const TupleGetItemNode* op = node.as<TupleGetItemNode>()) {
-      stack.top().second = true;
-      fpush_to_stack(op->tuple);
-    } else {
-      // No need to expand the children directly run visit.
-      fvisit_leaf(node);
-      stack.pop();
+    } else if (const TupleGetItemNode* op = expr.as<TupleGetItemNode>()) {
+      result.push_back(op->tuple);
     }
-  }
+    return std::move(result);
+  };
+  ExpandDataflow(expr, fcheck_visited, fvisit_leaf, fexpand_expr);
 }
 
 void ExpandANormalForm(const LetNode* op, std::function<void(const LetNode*)> pre_visit,

src/printer/relay_text_printer.cc

@@ -236,6 +236,34 @@ bool RelayTextPrinter::AlwaysInline(const Expr& expr) {
          expr.as<VarNode>() || expr.as<ConstructorNode>();
 }
 
+Doc RelayTextPrinter::VisitLeaf(const Expr& expr) {
+  if (!CheckVisited(expr)) {
+    Doc result = ExprFunctor<Doc(const Expr&)>::VisitExpr(expr);
+    // Add if not added after visiting
+    if (!CheckVisited(expr)) {
+      memo_[expr] = result;
+    } else {
+      result_memo_[expr] = result;
+    }
+    return result;
+  }
+  return memo_[expr];
+}
+
+bool RelayTextPrinter::CheckVisited(const Expr& expr) { return (memo_.count(expr)); }
+
+Doc RelayTextPrinter::VisitExpr(const Expr& expr) {
+  auto fcheck_visited = [this](const Expr& expr) { return this->CheckVisited(expr); };
+  auto fvisit_leaf = [this](const Expr& expr) { return this->VisitLeaf(expr); };
+
+  if (fcheck_visited(expr)) {
+    return memo_[expr];
+  } else {
+    ExpandDataflow(expr, fcheck_visited, fvisit_leaf);
+    return memo_[expr];
+  }
+}
+
 //------------------------------------
 // Overload of Expr printing functions
 //------------------------------------
@@ -252,9 +280,6 @@ Doc RelayTextPrinter::PrintExpr(const Expr& expr, bool meta, bool try_inline, bo
     inline_expr |= IsUnique(expr);
   }
 
-  auto it = memo_.find(expr);
-  if (it != memo_.end()) return it->second;
-
   Doc printed_expr;
 
   if (meta) {
@@ -277,13 +302,19 @@ Doc RelayTextPrinter::PrintExpr(const Expr& expr, bool meta, bool try_inline, bo
   if (expr.as<VarNode>()) {
     // This is our first time visiting the var and we hit the VarNode case
     // in the visitor. Thus the variable is free.
-    doc_stack_.back() << "free_var " << printed_expr << ";" << Doc::NewLine();
+    if (var_memo_.insert(expr).second && result_memo_.count(expr)) {
+      doc_stack_.back() << "free_var " << result_memo_[expr] << ";" << Doc::NewLine();
+    }
     // Memoization is done in AllocVar.
     return memo_[expr];
   } else if (inline_expr) {
     memo_[expr] = printed_expr;
     return printed_expr;
   } else {
+    // Already exists. Reuse
+    if (!var_memo_.insert(expr).second) {
+      return memo_[expr];
+    }
     Doc temp_var = AllocTemp();
     memo_[expr] = temp_var;
     doc_stack_.back() << temp_var << " = " << printed_expr << ";" << Doc::NewLine();

src/printer/text_printer.h

@@ -37,6 +37,7 @@
 
 #include <string>
 #include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 #include "../ir/attr_functor.h"
@@ -60,6 +61,9 @@ class RelayTextPrinter : public ExprFunctor<Doc(const Expr&)>,
   explicit RelayTextPrinter(bool show_meta_data, TextMetaDataContext* meta,
                             runtime::TypedPackedFunc<std::string(ObjectRef)> annotate)
       : show_meta_data_(show_meta_data), annotate_(annotate), meta_(meta) {}
+  Doc VisitExpr(const Expr& expr) override;
+  virtual Doc VisitLeaf(const Expr& expr);
+  virtual bool CheckVisited(const Expr& expr);
 
   /*!
    * \brief Print additional info about expr in comment.
@@ -170,6 +174,10 @@ class RelayTextPrinter : public ExprFunctor<Doc(const Expr&)>,
   runtime::TypedPackedFunc<std::string(ObjectRef)> annotate_;
   /*! \brief Stack of docs to implement scoped GNFing. */
   std::vector<Doc> doc_stack_{};
+  /*! \brief Set for introduced vars */
+  std::unordered_set<Expr, ObjectPtrHash, ObjectPtrEqual> var_memo_;
+  /*! \brief Map for result and memo_ diffs for visited expression */
+  std::unordered_map<Expr, Doc, ObjectPtrHash, ObjectPtrEqual> result_memo_;
   /*! \brief Map from Expr to Doc */
   std::unordered_map<Expr, Doc, ObjectPtrHash, ObjectPtrEqual> memo_;
   /*! \brief Map from Type to Doc */

src/relay/analysis/dependency_graph.cc

@@ -32,7 +32,7 @@ namespace tvm {
 namespace relay {
 
 // Creator of DependencyGraph
-class DependencyGraph::Creator : private ExprFunctor<void(const Expr& e)> {
+class DependencyGraph::Creator : private MixedModeVisitor {
  public:
   explicit Creator(support::Arena* arena) : arena_(arena) {}
 
@@ -73,13 +73,13 @@ class DependencyGraph::Creator : private ExprFunctor<void(const Expr& e)> {
     return ret;
   }
 
-  void VisitExpr(const Expr& e) final {
+  void VisitLeaf(const Expr& e) override {
     if (visited_.count(e) == 0) {
       if (graph_.expr_node.count(e) == 0) {
         graph_.expr_node[e] = NewNode(false);
       }
       visited_.insert(e);
-      ExprFunctor<void(const Expr&)>::VisitExpr(e);
+      MixedModeVisitor::VisitLeaf(e);
       graph_.post_dfs_order.push_back(graph_.expr_node[e]);
     }
   }