[turbofan] Induction variable bound analysis.

src/compiler/loop-variable-optimizer.cc

+// Copyright 2016 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/loop-variable-optimizer.h"
+
+#include "src/compiler/common-operator.h"
+#include "src/compiler/graph.h"
+#include "src/compiler/node-marker.h"
+#include "src/compiler/node-properties.h"
+#include "src/compiler/node.h"
+#include "src/zone-containers.h"
+#include "src/zone.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Macro for outputting trace information from representation inference.
+#define TRACE(...)                                  \
+  do {                                              \
+    if (FLAG_trace_turbo_loop) PrintF(__VA_ARGS__); \
+  } while (false)
+
+LoopVariableOptimizer::LoopVariableOptimizer(Graph* graph,
+                                             CommonOperatorBuilder* common,
+                                             Zone* zone)
+    : graph_(graph),
+      common_(common),
+      zone_(zone),
+      limits_(zone),
+      induction_vars_(zone) {}
+
+void LoopVariableOptimizer::Run() {
+  ZoneQueue<Node*> queue(zone());
+  queue.push(graph()->start());
+  NodeMarker<bool> queued(graph(), 2);
+  while (!queue.empty()) {
+    Node* node = queue.front();
+    queue.pop();
+    queued.Set(node, false);
+
+    DCHECK(limits_.find(node->id()) == limits_.end());
+    bool all_inputs_visited = true;
+    int inputs_end = (node->opcode() == IrOpcode::kLoop)
+                         ? kFirstBackedge
+                         : node->op()->ControlInputCount();
+    for (int i = 0; i < inputs_end; i++) {
+      auto input = limits_.find(NodeProperties::GetControlInput(node, i)->id());
+      if (input == limits_.end()) {
+        all_inputs_visited = false;
+        break;
+      }
+    }
+    if (!all_inputs_visited) continue;
+
+    VisitNode(node);
+    DCHECK(limits_.find(node->id()) != limits_.end());
+
+    // Queue control outputs.
+    for (Edge edge : node->use_edges()) {
+      if (NodeProperties::IsControlEdge(edge) &&
+          edge.from()->op()->ControlOutputCount() > 0) {
+        Node* use = edge.from();
+        if (use->opcode() == IrOpcode::kLoop &&
+            edge.index() != kAssumedLoopEntryIndex) {
+          VisitBackedge(node, use);
+        } else if (!queued.Get(use)) {
+          queue.push(use);
+          queued.Set(use, true);
+        }
+      }
+    }
+  }
+}
+
+class LoopVariableOptimizer::Constraint : public ZoneObject {
+ public:
+  InductionVariable::ConstraintKind kind() const { return kind_; }
+  Node* left() const { return left_; }
+  Node* right() const { return right_; }
+
+  const Constraint* next() const { return next_; }
+
+  Constraint(Node* left, InductionVariable::ConstraintKind kind, Node* right,
+             const Constraint* next)
+      : left_(left), right_(right), kind_(kind), next_(next) {}
+
+ private:
+  Node* left_;
+  Node* right_;
+  InductionVariable::ConstraintKind kind_;
+  const Constraint* next_;
+};
+
+class LoopVariableOptimizer::VariableLimits : public ZoneObject {
+ public:
+  static VariableLimits* Empty(Zone* zone) {
+    return new (zone) VariableLimits();
+  }
+
+  VariableLimits* Copy(Zone* zone) const {
+    return new (zone) VariableLimits(this);
+  }
+
+  void Add(Node* left, InductionVariable::ConstraintKind kind, Node* right,
+           Zone* zone) {
+    head_ = new (zone) Constraint(left, kind, right, head_);
+    limit_count_++;
+  }
+
+  void Merge(const VariableLimits* other) {
+    // Change the current condition list to a longest common tail
+    // of this condition list and the other list. (The common tail
+    // should correspond to the list from the common dominator.)
+
+    // First, we throw away the prefix of the longer list, so that
+    // we have lists of the same length.
+    size_t other_size = other->limit_count_;
+    const Constraint* other_limit = other->head_;
+    while (other_size > limit_count_) {
+      other_limit = other_limit->next();
+      other_size--;
+    }
+    while (limit_count_ > other_size) {
+      head_ = head_->next();
+      limit_count_--;
+    }
+
+    // Then we go through both lists in lock-step until we find
+    // the common tail.
+    while (head_ != other_limit) {
+      DCHECK(limit_count_ > 0);
+      limit_count_--;
+      other_limit = other_limit->next();
+      head_ = head_->next();
+    }
+  }
+
+  const Constraint* head() const { return head_; }
+
+ private:
+  VariableLimits() {}
+  explicit VariableLimits(const VariableLimits* other)
+      : head_(other->head_), limit_count_(other->limit_count_) {}
+
+  const Constraint* head_ = nullptr;
+  size_t limit_count_ = 0;
+};
+
+void InductionVariable::AddUpperBound(Node* bound,
+                                      InductionVariable::ConstraintKind kind,
+                                      Zone* graph_zone) {
+  if (FLAG_trace_turbo_loop) {
+    OFStream os(stdout);
+    os << "New upper bound for " << phi()->id() << " (loop "
+       << NodeProperties::GetControlInput(phi())->id() << "): " << *bound
+       << std::endl;
+  }
+  upper_bounds_.push_back(Bound(bound, kind));
+}
+
+void InductionVariable::AddLowerBound(Node* bound,
+                                      InductionVariable::ConstraintKind kind,
+                                      Zone* graph_zone) {
+  if (FLAG_trace_turbo_loop) {
+    OFStream os(stdout);
+    os << "New lower bound for " << phi()->id() << " (loop "
+       << NodeProperties::GetControlInput(phi())->id() << "): " << *bound;
+  }
+  lower_bounds_.push_back(Bound(bound, kind));
+}
+
+void LoopVariableOptimizer::VisitBackedge(Node* from, Node* loop) {
+  if (loop->op()->ControlInputCount() != 2) return;
+
+  // Go through the constraints, and update the induction variables in
+  // this loop if they are involved in the constraint.
+  const VariableLimits* limits = limits_[from->id()];
+  for (const Constraint* constraint = limits->head(); constraint != nullptr;
+       constraint = constraint->next()) {
+    if (constraint->left()->opcode() == IrOpcode::kPhi &&
+        NodeProperties::GetControlInput(constraint->left()) == loop) {
+      auto var = induction_vars_.find(constraint->left()->id());
+      if (var != induction_vars_.end()) {
+        var->second->AddUpperBound(constraint->right(), constraint->kind(),
+                                   graph()->zone());
+      }
+    }
+    if (constraint->right()->opcode() == IrOpcode::kPhi &&
+        NodeProperties::GetControlInput(constraint->right()) == loop) {
+      auto var = induction_vars_.find(constraint->right()->id());
+      if (var != induction_vars_.end()) {
+        var->second->AddUpperBound(constraint->left(), constraint->kind(),
+                                   graph()->zone());
+      }
+    }
+  }
+}
+
+void LoopVariableOptimizer::VisitNode(Node* node) {
+  switch (node->opcode()) {
+    case IrOpcode::kMerge:
+      return VisitMerge(node);
+    case IrOpcode::kLoop:
+      return VisitLoop(node);
+    case IrOpcode::kIfFalse:
+      return VisitIf(node, false);
+    case IrOpcode::kIfTrue:
+      return VisitIf(node, true);
+    case IrOpcode::kStart:
+      return VisitStart(node);
+    case IrOpcode::kLoopExit:
+      return VisitLoopExit(node);
+    default:
+      return VisitOtherControl(node);
+  }
+}
+
+void LoopVariableOptimizer::VisitMerge(Node* node) {
+  // Merge the limits of all incoming edges.
+  VariableLimits* merged = limits_[node->InputAt(0)->id()]->Copy(zone());
+  for (int i = 1; i < node->InputCount(); i++) {
+    merged->Merge(limits_[node->InputAt(0)->id()]);
+  }
+  limits_[node->id()] = merged;
+}
+
+void LoopVariableOptimizer::VisitLoop(Node* node) {
+  DetectInductionVariables(node);
+  // Conservatively take the limits from the loop entry here.
+  return TakeConditionsFromFirstControl(node);
+}
+
+void LoopVariableOptimizer::VisitIf(Node* node, bool polarity) {
+  Node* branch = node->InputAt(0);
+  Node* cond = branch->InputAt(0);
+  VariableLimits* limits = limits_[branch->id()]->Copy(zone());
+  // Normalize to less than comparison.
+  switch (cond->opcode()) {
+    case IrOpcode::kJSLessThan:
+      AddCmpToLimits(limits, cond, InductionVariable::kStrict, polarity);
+      break;
+    case IrOpcode::kJSGreaterThan:
+      AddCmpToLimits(limits, cond, InductionVariable::kNonStrict, !polarity);
+      break;
+    case IrOpcode::kJSLessThanOrEqual:
+      AddCmpToLimits(limits, cond, InductionVariable::kNonStrict, polarity);
+      break;
+    case IrOpcode::kJSGreaterThanOrEqual:
+      AddCmpToLimits(limits, cond, InductionVariable::kStrict, !polarity);
+      break;
+    default:
+      break;
+  }
+  limits_[node->id()] = limits;
+}
+
+void LoopVariableOptimizer::AddCmpToLimits(
+    VariableLimits* limits, Node* node, InductionVariable::ConstraintKind kind,
+    bool polarity) {
+  Node* left = node->InputAt(0);
+  Node* right = node->InputAt(1);
+  if (FindInductionVariable(left) || FindInductionVariable(right)) {
+    if (polarity) {
+      limits->Add(left, kind, right, zone());
+    } else {
+      kind = (kind == InductionVariable::kStrict)
+                 ? InductionVariable::kNonStrict
+                 : InductionVariable::kStrict;
+      limits->Add(right, kind, left, zone());
+    }
+  }
+}
+
+void LoopVariableOptimizer::VisitStart(Node* node) {
+  limits_[node->id()] = VariableLimits::Empty(zone());
+}
+
+void LoopVariableOptimizer::VisitLoopExit(Node* node) {
+  return TakeConditionsFromFirstControl(node);
+}
+
+void LoopVariableOptimizer::VisitOtherControl(Node* node) {
+  DCHECK_EQ(1, node->op()->ControlInputCount());
+  return TakeConditionsFromFirstControl(node);
+}
+
+void LoopVariableOptimizer::TakeConditionsFromFirstControl(Node* node) {
+  const VariableLimits* limits =
+      limits_[NodeProperties::GetControlInput(node, 0)->id()];
+  DCHECK_NOT_NULL(limits);
+  limits_[node->id()] = limits;
+}
+
+const InductionVariable* LoopVariableOptimizer::FindInductionVariable(
+    Node* node) {
+  auto var = induction_vars_.find(node->id());
+  if (var != induction_vars_.end()) {
+    return var->second;
+  }
+  return nullptr;
+}
+
+InductionVariable* LoopVariableOptimizer::TryGetInductionVariable(Node* phi) {
+  DCHECK_EQ(2, phi->op()->ValueInputCount());
+  DCHECK_EQ(IrOpcode::kLoop, NodeProperties::GetControlInput(phi)->opcode());
+  Node* initial = phi->InputAt(0);
+  Node* arith = phi->InputAt(1);
+  // TODO(jarin) Support subtraction.
+  if (arith->opcode() != IrOpcode::kJSAdd) {
+    return nullptr;
+  }
+  // TODO(jarin) Support both sides.
+  if (arith->InputAt(0) != phi) {
+    if (arith->InputAt(0)->opcode() != IrOpcode::kJSToNumber ||
+        arith->InputAt(0)->InputAt(0) != phi) {
+      return nullptr;
+    }
+  }
+  Node* incr = arith->InputAt(1);
+  return new (zone()) InductionVariable(phi, arith, incr, initial, zone());
+}
+
+void LoopVariableOptimizer::DetectInductionVariables(Node* loop) {
+  if (loop->op()->ControlInputCount() != 2) return;
+  TRACE("Loop variables for loop %i:", loop->id());
+  for (Edge edge : loop->use_edges()) {
+    if (NodeProperties::IsControlEdge(edge) &&
+        edge.from()->opcode() == IrOpcode::kPhi) {
+      Node* phi = edge.from();
+      InductionVariable* induction_var = TryGetInductionVariable(phi);
+      if (induction_var) {
+        induction_vars_[phi->id()] = induction_var;
+        TRACE(" %i", induction_var->phi()->id());
+      }
+    }
+  }
+  TRACE("\n");
+}
+
+void LoopVariableOptimizer::ChangeToInductionVariablePhis() {
+  for (auto entry : induction_vars_) {
+    // It only make sense to analyze the induction variables if
+    // there is a bound.
+    InductionVariable* induction_var = entry.second;
+    DCHECK_EQ(MachineRepresentation::kTagged,
+              PhiRepresentationOf(induction_var->phi()->op()));
+    if (induction_var->upper_bounds().size() == 0 &&
+        induction_var->lower_bounds().size() == 0) {
+      continue;
+    }
+    // Insert the increment value to the value inputs.
+    induction_var->phi()->InsertInput(graph()->zone(),
+                                      induction_var->phi()->InputCount() - 1,
+                                      induction_var->increment());
+    // Insert the bound inputs to the value inputs.
+    for (auto bound : induction_var->lower_bounds()) {
+      induction_var->phi()->InsertInput(
+          graph()->zone(), induction_var->phi()->InputCount() - 1, bound.bound);
+    }
+    for (auto bound : induction_var->upper_bounds()) {
+      induction_var->phi()->InsertInput(
+          graph()->zone(), induction_var->phi()->InputCount() - 1, bound.bound);
+    }
+    NodeProperties::ChangeOp(
+        induction_var->phi(),
+        common()->InductionVariablePhi(induction_var->phi()->InputCount() - 1));
+  }
+}
+
+void LoopVariableOptimizer::ChangeFromInductionVariablePhis() {
+  for (auto entry : induction_vars_) {
+    InductionVariable* induction_var = entry.second;
+    if (induction_var->phi()->opcode() == IrOpcode::kInductionVariablePhi) {
+      int value_count = 2;
+      Node* control = NodeProperties::GetControlInput(induction_var->phi());
+      DCHECK_EQ(value_count, control->op()->ControlInputCount());
+      induction_var->phi()->TrimInputCount(value_count + 1);
+      induction_var->phi()->ReplaceInput(value_count, control);
+      NodeProperties::ChangeOp(
+          induction_var->phi(),
+          common()->Phi(MachineRepresentation::kTagged, value_count));
+    }
+  }
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8