[turbofan] Induction variable decrement bound analysis.

src/compiler/loop-variable-optimizer.h

 // 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.
 
 #ifndef V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_
 #define V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_
 
 #include "src/zone-containers.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class CommonOperatorBuilder;
 class Graph;
 class Node;
 
 class InductionVariable : public ZoneObject {
  public:
   Node* phi() const { return phi_; }
   Node* arith() const { return arith_; }
   Node* increment() const { return increment_; }
   Node* init_value() const { return init_value_; }
 
   enum ConstraintKind { kStrict, kNonStrict };
+  enum ArithmeticType { kAddition, kSubtraction };
   struct Bound {
     Bound(Node* bound, ConstraintKind kind) : bound(bound), kind(kind) {}
 
     Node* bound;
     ConstraintKind kind;
   };
 
   const ZoneVector<Bound>& lower_bounds() { return lower_bounds_; }
   const ZoneVector<Bound>& upper_bounds() { return upper_bounds_; }
 
+  ArithmeticType Type() { return arithmeticType_; }
+
  private:
   friend class LoopVariableOptimizer;
 
   InductionVariable(Node* phi, Node* arith, Node* increment, Node* init_value,
-                    Zone* zone)
+                    Zone* zone, ArithmeticType arithmeticType)
       : phi_(phi),
         arith_(arith),
         increment_(increment),
         init_value_(init_value),
         lower_bounds_(zone),
-        upper_bounds_(zone) {}
+        upper_bounds_(zone),
+        arithmeticType_(arithmeticType) {}
 
   void AddUpperBound(Node* bound, ConstraintKind kind);
   void AddLowerBound(Node* bound, ConstraintKind kind);
 
   Node* phi_;
   Node* arith_;
   Node* increment_;
   Node* init_value_;
   ZoneVector<Bound> lower_bounds_;
   ZoneVector<Bound> upper_bounds_;
+  ArithmeticType arithmeticType_;
 };
 
 class LoopVariableOptimizer {
  public:
   void Run();
 
   LoopVariableOptimizer(Graph* graph, CommonOperatorBuilder* common,
                         Zone* zone);
 
   const ZoneMap<int, InductionVariable*>& induction_variables() {
@@ skipping 36 matching lines @@
   Zone* zone_;
   ZoneMap<int, const VariableLimits*> limits_;
   ZoneMap<int, InductionVariable*> induction_vars_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_