[turbofan] Split ControlEquivalence implementation and add trace flag.

src/compiler/control-equivalence.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_CONTROL_EQUIVALENCE_H_
 #define V8_COMPILER_CONTROL_EQUIVALENCE_H_
 
 #include "src/compiler/graph.h"
 #include "src/compiler/node.h"
-#include "src/compiler/node-properties.h"
 #include "src/zone-containers.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
-#define TRACE(...)                                       \
-  do {                                                   \
-    if (FLAG_trace_turbo_scheduler) PrintF(__VA_ARGS__); \
-  } while (false)
-
 // Determines control dependence equivalence classes for control nodes. Any two
 // nodes having the same set of control dependences land in one class. These
 // classes can in turn be used to:
 //  - Build a program structure tree (PST) for controls in the graph.
 //  - Determine single-entry single-exit (SESE) regions within the graph.
 //
 // Note that this implementation actually uses cycle equivalence to establish
 // class numbers. Any two nodes are cycle equivalent if they occur in the same
 // set of cycles. It can be shown that control dependence equivalence reduces
 // to undirected cycle equivalence for strongly connected control flow graphs.
 //
 // The algorithm is based on the paper, "The program structure tree: computing
 // control regions in linear time" by Johnson, Pearson & Pingali (PLDI94) which
 // also contains proofs for the aforementioned equivalence. References to line
 // numbers in the algorithm from figure 4 have been added [line:x].
-class ControlEquivalence : public ZoneObject {
+class ControlEquivalence FINAL : public ZoneObject {
  public:
   ControlEquivalence(Zone* zone, Graph* graph)
       : zone_(zone),
         graph_(graph),
         dfs_number_(0),
         class_number_(1),
         node_data_(graph->NodeCount(), EmptyData(), zone) {}
 
   // Run the main algorithm starting from the {exit} control node. This causes
   // the following iterations over control edges of the graph:
   //  1) A breadth-first backwards traversal to determine the set of nodes that
   //     participate in the next step. Takes O(E) time and O(N) space.
   //  2) An undirected depth-first backwards traversal that determines class
   //     numbers for all participating nodes. Takes O(E) time and O(N) space.
-  void Run(Node* exit) {
-    if (GetClass(exit) != kInvalidClass) return;
-    DetermineParticipation(exit);
-    RunUndirectedDFS(exit);
-  }
+  void Run(Node* exit);
 
   // Retrieves a previously computed class number.
   size_t ClassOf(Node* node) {
-    DCHECK(GetClass(node) != kInvalidClass);
+    DCHECK_NE(kInvalidClass, GetClass(node));
     return GetClass(node);
   }
 
  private:
   static const size_t kInvalidClass = static_cast<size_t>(-1);
   typedef enum { kInputDirection, kUseDirection } DFSDirection;
 
   struct Bracket {
     DFSDirection direction;  // Direction in which this bracket was added.
     size_t recent_class;     // Cached class when bracket was topmost.
@@ skipping 22 matching lines @@
     bool visited;         // Indicates node has already been visited.
     bool on_stack;        // Indicates node is on DFS stack during walk.
     bool participates;    // Indicates node participates in DFS walk.
     BracketList blist;    // List of brackets per node.
   };
 
   // The per-node data computed during the DFS walk.
   typedef ZoneVector<NodeData> Data;
 
   // Called at pre-visit during DFS walk.
-  void VisitPre(Node* node) {
-    TRACE("CEQ: Pre-visit of #%d:%s\n", node->id(), node->op()->mnemonic());
-
-    // Dispense a new pre-order number.
-    SetNumber(node, NewDFSNumber());
-    TRACE("  Assigned DFS number is %zu\n", GetNumber(node));
-  }
+  void VisitPre(Node* node);
 
   // Called at mid-visit during DFS walk.
-  void VisitMid(Node* node, DFSDirection direction) {
-    TRACE("CEQ: Mid-visit of #%d:%s\n", node->id(), node->op()->mnemonic());
-    BracketList& blist = GetBracketList(node);
-
-    // Remove brackets pointing to this node [line:19].
-    BracketListDelete(blist, node, direction);
-
-    // Potentially introduce artificial dependency from start to end.
-    if (blist.empty()) {
-      DCHECK_EQ(kInputDirection, direction);
-      VisitBackedge(node, graph_->end(), kInputDirection);
-    }
-
-    // Potentially start a new equivalence class [line:37].
-    BracketListTRACE(blist);
-    Bracket* recent = &blist.back();
-    if (recent->recent_size != blist.size()) {
-      recent->recent_size = blist.size();
-      recent->recent_class = NewClassNumber();
-    }
-
-    // Assign equivalence class to node.
-    SetClass(node, recent->recent_class);
-    TRACE("  Assigned class number is %zu\n", GetClass(node));
-  }
+  void VisitMid(Node* node, DFSDirection direction);
 
   // Called at post-visit during DFS walk.
-  void VisitPost(Node* node, Node* parent_node, DFSDirection direction) {
-    TRACE("CEQ: Post-visit of #%d:%s\n", node->id(), node->op()->mnemonic());
-    BracketList& blist = GetBracketList(node);
-
-    // Remove brackets pointing to this node [line:19].
-    BracketListDelete(blist, node, direction);
-
-    // Propagate bracket list up the DFS tree [line:13].
-    if (parent_node != NULL) {
-      BracketList& parent_blist = GetBracketList(parent_node);
-      parent_blist.splice(parent_blist.end(), blist);
-    }
-  }
+  void VisitPost(Node* node, Node* parent_node, DFSDirection direction);
 
   // Called when hitting a back edge in the DFS walk.
-  void VisitBackedge(Node* from, Node* to, DFSDirection direction) {
-    TRACE("CEQ: Backedge from #%d:%s to #%d:%s\n", from->id(),
-          from->op()->mnemonic(), to->id(), to->op()->mnemonic());
-
-    // Push backedge onto the bracket list [line:25].
-    Bracket bracket = {direction, kInvalidClass, 0, from, to};
-    GetBracketList(from).push_back(bracket);
-  }
+  void VisitBackedge(Node* from, Node* to, DFSDirection direction);
 
   // Performs and undirected DFS walk of the graph. Conceptually all nodes are
   // expanded, splitting "input" and "use" out into separate nodes. During the
   // traversal, edges towards the representative nodes are preferred.
   //
   //   \ /        - Pre-visit: When N1 is visited in direction D the preferred
   //    x   N1      edge towards N is taken next, calling VisitPre(N).
   //    |         - Mid-visit: After all edges out of N2 in direction D have
   //    |   N       been visited, we switch the direction and start considering
   //    |           edges out of N1 now, and we call VisitMid(N).
   //    x   N2    - Post-visit: After all edges out of N1 in direction opposite
   //   / \          to D have been visited, we pop N and call VisitPost(N).
   //
   // This will yield a true spanning tree (without cross or forward edges) and
   // also discover proper back edges in both directions.
-  void RunUndirectedDFS(Node* exit) {
-    ZoneStack<DFSStackEntry> stack(zone_);
-    DFSPush(stack, exit, NULL, kInputDirection);
-    VisitPre(exit);
+  void RunUndirectedDFS(Node* exit);
 
-    while (!stack.empty()) {  // Undirected depth-first backwards traversal.
-      DFSStackEntry& entry = stack.top();
-      Node* node = entry.node;
-
-      if (entry.direction == kInputDirection) {
-        if (entry.input != node->input_edges().end()) {
-          Edge edge = *entry.input;
-          Node* input = edge.to();
-          ++(entry.input);
-          if (NodeProperties::IsControlEdge(edge)) {
-            // Visit next control input.
-            if (!GetData(input)->participates) continue;
-            if (GetData(input)->visited) continue;
-            if (GetData(input)->on_stack) {
-              // Found backedge if input is on stack.
-              if (input != entry.parent_node) {
-                VisitBackedge(node, input, kInputDirection);
-              }
-            } else {
-              // Push input onto stack.
-              DFSPush(stack, input, node, kInputDirection);
-              VisitPre(input);
-            }
-          }
-          continue;
-        }
-        if (entry.use != node->use_edges().end()) {
-          // Switch direction to uses.
-          entry.direction = kUseDirection;
-          VisitMid(node, kInputDirection);
-          continue;
-        }
-      }
-
-      if (entry.direction == kUseDirection) {
-        if (entry.use != node->use_edges().end()) {
-          Edge edge = *entry.use;
-          Node* use = edge.from();
-          ++(entry.use);
-          if (NodeProperties::IsControlEdge(edge)) {
-            // Visit next control use.
-            if (!GetData(use)->participates) continue;
-            if (GetData(use)->visited) continue;
-            if (GetData(use)->on_stack) {
-              // Found backedge if use is on stack.
-              if (use != entry.parent_node) {
-                VisitBackedge(node, use, kUseDirection);
-              }
-            } else {
-              // Push use onto stack.
-              DFSPush(stack, use, node, kUseDirection);
-              VisitPre(use);
-            }
-          }
-          continue;
-        }
-        if (entry.input != node->input_edges().end()) {
-          // Switch direction to inputs.
-          entry.direction = kInputDirection;
-          VisitMid(node, kUseDirection);
-          continue;
-        }
-      }
-
-      // Pop node from stack when done with all inputs and uses.
-      DCHECK(entry.input == node->input_edges().end());
-      DCHECK(entry.use == node->use_edges().end());
-      DFSPop(stack, node);
-      VisitPost(node, entry.parent_node, entry.direction);
-    }
-  }
-
-  void DetermineParticipationEnqueue(ZoneQueue<Node*>& queue, Node* node) {
-    if (!GetData(node)->participates) {
-      GetData(node)->participates = true;
-      queue.push(node);
-    }
-  }
-
-  void DetermineParticipation(Node* exit) {
-    ZoneQueue<Node*> queue(zone_);
-    DetermineParticipationEnqueue(queue, exit);
-    while (!queue.empty()) {  // Breadth-first backwards traversal.
-      Node* node = queue.front();
-      queue.pop();
-      int max = NodeProperties::PastControlIndex(node);
-      for (int i = NodeProperties::FirstControlIndex(node); i < max; i++) {
-        DetermineParticipationEnqueue(queue, node->InputAt(i));
-      }
-    }
-  }
+  void DetermineParticipationEnqueue(ZoneQueue<Node*>& queue, Node* node);
+  void DetermineParticipation(Node* exit);
 
  private:
   NodeData* GetData(Node* node) { return &node_data_[node->id()]; }
   int NewClassNumber() { return class_number_++; }
   int NewDFSNumber() { return dfs_number_++; }
 
   // Template used to initialize per-node data.
   NodeData EmptyData() {
     return {kInvalidClass, 0, false, false, false, BracketList(zone_)};
   }
@@ skipping 10 matching lines @@
     GetData(node)->class_number = number;
   }
 
   // Accessors for the bracket list stored within the per-node data.
   BracketList& GetBracketList(Node* node) { return GetData(node)->blist; }
   void SetBracketList(Node* node, BracketList& list) {
     GetData(node)->blist = list;
   }
 
   // Mutates the DFS stack by pushing an entry.
-  void DFSPush(DFSStack& stack, Node* node, Node* from, DFSDirection dir) {
-    DCHECK(GetData(node)->participates);
-    DCHECK(!GetData(node)->visited);
-    GetData(node)->on_stack = true;
-    Node::InputEdges::iterator input = node->input_edges().begin();
-    Node::UseEdges::iterator use = node->use_edges().begin();
-    stack.push({dir, input, use, from, node});
-  }
+  void DFSPush(DFSStack& stack, Node* node, Node* from, DFSDirection dir);
 
   // Mutates the DFS stack by popping an entry.
-  void DFSPop(DFSStack& stack, Node* node) {
-    DCHECK_EQ(stack.top().node, node);
-    GetData(node)->on_stack = false;
-    GetData(node)->visited = true;
-    stack.pop();
-  }
+  void DFSPop(DFSStack& stack, Node* node);
 
-  // TODO(mstarzinger): Optimize this to avoid linear search.
-  void BracketListDelete(BracketList& blist, Node* to, DFSDirection direction) {
-    for (BracketList::iterator i = blist.begin(); i != blist.end(); /*nop*/) {
-      if (i->to == to && i->direction != direction) {
-        TRACE("  BList erased: {%d->%d}\n", i->from->id(), i->to->id());
-        i = blist.erase(i);
-      } else {
-        ++i;
-      }
-    }
-  }
+  void BracketListDelete(BracketList& blist, Node* to, DFSDirection direction);
+  void BracketListTRACE(BracketList& blist);
 
-  void BracketListTRACE(BracketList& blist) {
-    if (FLAG_trace_turbo_scheduler) {
-      TRACE("  BList: ");
-      for (Bracket bracket : blist) {
-        TRACE("{%d->%d} ", bracket.from->id(), bracket.to->id());
-      }
-      TRACE("\n");
-    }
-  }
-
-  Zone* zone_;
-  Graph* graph_;
+  Zone* const zone_;
+  Graph* const graph_;
   int dfs_number_;    // Generates new DFS pre-order numbers on demand.
   int class_number_;  // Generates new equivalence class numbers on demand.
   Data node_data_;    // Per-node data stored as a side-table.
 };
 
-#undef TRACE
-
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_CONTROL_EQUIVALENCE_H_