[turbofan] Split ControlEquivalence implementation and add trace flag.

Split interface and implementation of ControlEquivalence and add a
dedicated trace flag --trace-turbo-ceq to make it reusable outside the
scheduler.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1056093005

Cr-Commit-Position: refs/heads/master@{#27862}

BUILD.gn

@@ -561,6 +561,7 @@ source_set("v8_base") {
     "src/compiler/common-operator.h",
     "src/compiler/control-builders.cc",
     "src/compiler/control-builders.h",
+    "src/compiler/control-equivalence.cc",
     "src/compiler/control-equivalence.h",
     "src/compiler/control-flow-optimizer.cc",
     "src/compiler/control-flow-optimizer.h",

src/compiler/control-equivalence.cc

+// Copyright 2015 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.
+
+#include "src/compiler/control-equivalence.h"
+#include "src/compiler/node-properties.h"
+
+#define TRACE(...)                                 \
+  do {                                             \
+    if (FLAG_trace_turbo_ceq) PrintF(__VA_ARGS__); \
+  } while (false)
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+void ControlEquivalence::Run(Node* exit) {
+  if (GetClass(exit) == kInvalidClass) {
+    DetermineParticipation(exit);
+    RunUndirectedDFS(exit);
+  }
+}
+
+
+// static
+STATIC_CONST_MEMBER_DEFINITION const size_t ControlEquivalence::kInvalidClass;
+
+
+void ControlEquivalence::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 ControlEquivalence::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 ControlEquivalence::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 ControlEquivalence::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 ControlEquivalence::RunUndirectedDFS(Node* exit) {
+  ZoneStack<DFSStackEntry> stack(zone_);
+  DFSPush(stack, exit, NULL, kInputDirection);
+  VisitPre(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 ControlEquivalence::DetermineParticipationEnqueue(ZoneQueue<Node*>& queue,
+                                                       Node* node) {
+  if (!GetData(node)->participates) {
+    GetData(node)->participates = true;
+    queue.push(node);
+  }
+}
+
+
+void ControlEquivalence::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 ControlEquivalence::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 ControlEquivalence::DFSPop(DFSStack& stack, Node* node) {
+  DCHECK_EQ(stack.top().node, node);
+  GetData(node)->on_stack = false;
+  GetData(node)->visited = true;
+  stack.pop();
+}
+
+
+void ControlEquivalence::BracketListDelete(BracketList& blist, Node* to,
+                                           DFSDirection direction) {
+  // TODO(mstarzinger): Optimize this to avoid linear search.
+  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 ControlEquivalence::BracketListTRACE(BracketList& blist) {
+  if (FLAG_trace_turbo_ceq) {
+    TRACE("  BList: ");
+    for (Bracket bracket : blist) {
+      TRACE("{%d->%d} ", bracket.from->id(), bracket.to->id());
+    }
+    TRACE("\n");
+  }
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8

src/flag-definitions.h

@@ -390,6 +390,7 @@ DEFINE_BOOL(trace_turbo_types, true, "trace TurboFan's types")
 DEFINE_BOOL(trace_turbo_scheduler, false, "trace TurboFan's scheduler")
 DEFINE_BOOL(trace_turbo_reduction, false, "trace TurboFan's various reducers")
 DEFINE_BOOL(trace_turbo_jt, false, "trace TurboFan's jump threading")
+DEFINE_BOOL(trace_turbo_ceq, false, "trace TurboFan's control equivalence")
 DEFINE_BOOL(turbo_asm, true, "enable TurboFan for asm.js code")
 DEFINE_BOOL(turbo_verify, DEBUG_BOOL, "verify TurboFan graphs at each phase")
 DEFINE_BOOL(turbo_stats, false, "print TurboFan statistics")

tools/gyp/v8.gyp

@@ -447,6 +447,7 @@
         '../../src/compiler/common-operator.h',
         '../../src/compiler/control-builders.cc',
         '../../src/compiler/control-builders.h',
+        '../../src/compiler/control-equivalence.cc',
         '../../src/compiler/control-equivalence.h',
         '../../src/compiler/control-flow-optimizer.cc',
         '../../src/compiler/control-flow-optimizer.h',