Improve and simplify removal of unreachable code

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 703 matching lines @@
   static const int kNoRedefinedOperand = -1;
   virtual int RedefinedOperandIndex() { return kNoRedefinedOperand; }
   bool IsInformativeDefinition() {
     return RedefinedOperandIndex() != kNoRedefinedOperand;
   }
   HValue* RedefinedOperand() {
     int index = RedefinedOperandIndex();
     return index == kNoRedefinedOperand ? NULL : OperandAt(index);
   }
 
+  bool CanReplaceWithDummyUses();
+
   // A purely informative definition is an idef that will not emit code and
   // should therefore be removed from the graph in the RestoreActualValues
   // phase (so that live ranges will be shorter).
   virtual bool IsPurelyInformativeDefinition() { return false; }
 
   // This method must always return the original HValue SSA definition,
   // regardless of any chain of iDefs of this value.
   HValue* ActualValue() {
     HValue* value = this;
     int index;
@@ skipping 442 matching lines @@
 
 
 class HControlInstruction : public HInstruction {
  public:
   virtual HBasicBlock* SuccessorAt(int i) = 0;
   virtual int SuccessorCount() = 0;
   virtual void SetSuccessorAt(int i, HBasicBlock* block) = 0;
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
+  virtual bool KnownSuccessorBlock(HBasicBlock** block) V8_OVERRIDE {
+    *block = NULL;
+    return false;
+  }
+
   HBasicBlock* FirstSuccessor() {
     return SuccessorCount() > 0 ? SuccessorAt(0) : NULL;
   }
   HBasicBlock* SecondSuccessor() {
     return SuccessorCount() > 1 ? SuccessorAt(1) : NULL;
   }
 
   void Not() {
     HBasicBlock* swap = SuccessorAt(0);
     SetSuccessorAt(0, SuccessorAt(1));
@@ skipping 69 matching lines @@
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     return Representation::None();
   }
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   DECLARE_CONCRETE_INSTRUCTION(DummyUse);
 };
 
 
-class HDeoptimize V8_FINAL : public HTemplateInstruction<0> {
- public:
-  DECLARE_INSTRUCTION_FACTORY_P2(HDeoptimize, const char*,
-                                 Deoptimizer::BailoutType);
-
-  virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
-    return Representation::None();
-  }
-
-  const char* reason() const { return reason_; }
-  Deoptimizer::BailoutType type() { return type_; }
-
-  DECLARE_CONCRETE_INSTRUCTION(Deoptimize)
-
- private:
-  explicit HDeoptimize(const char* reason, Deoptimizer::BailoutType type)
-      : reason_(reason), type_(type) {}
-
-  const char* reason_;
-  Deoptimizer::BailoutType type_;
-};
-
-
 // Inserts an int3/stop break instruction for debugging purposes.
 class HDebugBreak V8_FINAL : public HTemplateInstruction<0> {
  public:
   DECLARE_INSTRUCTION_FACTORY_P0(HDebugBreak);
 
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     return Representation::None();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(DebugBreak)
 };
 
 
 class HGoto V8_FINAL : public HTemplateControlInstruction<1, 0> {
  public:
   explicit HGoto(HBasicBlock* target) {
     SetSuccessorAt(0, target);
   }
 
+  virtual bool KnownSuccessorBlock(HBasicBlock** block) V8_OVERRIDE {
+    *block = FirstSuccessor();
+    return true;
+  }
+
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     return Representation::None();
   }
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   DECLARE_CONCRETE_INSTRUCTION(Goto)
 };
 
 
+class HDeoptimize V8_FINAL : public HTemplateControlInstruction<1, 0> {
+ public:
+  static HInstruction* New(Zone* zone,
+                           HValue* context,
+                           const char* reason,
+                           Deoptimizer::BailoutType type,
+                           HBasicBlock* unreachable_continuation) {
+    return new(zone) HDeoptimize(reason, type, unreachable_continuation);
+  }
+
+  virtual bool KnownSuccessorBlock(HBasicBlock** block) {
+    *block = NULL;
+    return true;
+  }
+
+  virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
+    return Representation::None();
+  }
+
+  const char* reason() const { return reason_; }
+  Deoptimizer::BailoutType type() { return type_; }
+
+  DECLARE_CONCRETE_INSTRUCTION(Deoptimize)
+
+ private:
+  explicit HDeoptimize(const char* reason,
+                       Deoptimizer::BailoutType type,
+                       HBasicBlock* unreachable_continuation)
+      : reason_(reason), type_(type) {
+    SetSuccessorAt(0, unreachable_continuation);
+  }
+
+  const char* reason_;
+  Deoptimizer::BailoutType type_;
+};
+
+
 class HUnaryControlInstruction : public HTemplateControlInstruction<2, 1> {
  public:
   HUnaryControlInstruction(HValue* value,
                            HBasicBlock* true_target,
                            HBasicBlock* false_target) {
     SetOperandAt(0, value);
     SetSuccessorAt(0, true_target);
     SetSuccessorAt(1, false_target);
   }
 
@@ skipping 10 matching lines @@
                                  ToBooleanStub::Types);
   DECLARE_INSTRUCTION_FACTORY_P4(HBranch, HValue*,
                                  ToBooleanStub::Types,
                                  HBasicBlock*, HBasicBlock*);
 
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     return Representation::None();
   }
   virtual Representation observed_input_representation(int index) V8_OVERRIDE;
 
+  virtual bool KnownSuccessorBlock(HBasicBlock** block) V8_OVERRIDE;
+
   ToBooleanStub::Types expected_input_types() const {
     return expected_input_types_;
   }
 
   DECLARE_CONCRETE_INSTRUCTION(Branch)
 
  private:
   HBranch(HValue* value,
           ToBooleanStub::Types expected_input_types = ToBooleanStub::Types(),
           HBasicBlock* true_target = NULL,
@@ skipping 2114 matching lines @@
           int32_value_ == other_constant->int32_value_;
     } else if (has_double_value_) {
       return other_constant->has_double_value_ &&
           BitCast<int64_t>(double_value_) ==
           BitCast<int64_t>(other_constant->double_value_);
     } else if (has_external_reference_value_) {
       return other_constant->has_external_reference_value_ &&
           external_reference_value_ ==
           other_constant->external_reference_value_;
     } else {
+      if (other_constant->has_int32_value_ ||
+          other_constant->has_double_value_ ||
+          other_constant->has_external_reference_value_) {
+        return false;
+      }
       ASSERT(!object_.handle().is_null());
       return other_constant->object_ == object_;
     }
   }
 
  private:
   friend class HGraph;
   HConstant(Handle<Object> handle, Representation r = Representation::None());
   HConstant(int32_t value,
             Representation r = Representation::None(),
@@ skipping 583 matching lines @@
                         HBasicBlock* false_target = NULL)
       : HUnaryControlInstruction(value, true_target, false_target) {
     SetFlag(kFlexibleRepresentation);
     SetFlag(kAllowUndefinedAsNaN);
   }
 };
 
 
 class HCompareObjectEqAndBranch : public HTemplateControlInstruction<2, 2> {
  public:
+  HCompareObjectEqAndBranch(HValue* left,
+                            HValue* right,
+                            HBasicBlock* true_target = NULL,
+                            HBasicBlock* false_target = NULL) {
+    // TODO(danno): make this private when the IfBuilder properly constructs
+    // control flow instructions.
+    ASSERT(!left->IsConstant() ||
+           (!HConstant::cast(left)->HasInteger32Value() ||
+            HConstant::cast(left)->HasSmiValue()));
+    ASSERT(!right->IsConstant() ||
+           (!HConstant::cast(right)->HasInteger32Value() ||
+            HConstant::cast(right)->HasSmiValue()));
+    SetOperandAt(0, left);
+    SetOperandAt(1, right);
+    SetSuccessorAt(0, true_target);
+    SetSuccessorAt(1, false_target);
+  }
+
   DECLARE_INSTRUCTION_FACTORY_P2(HCompareObjectEqAndBranch, HValue*, HValue*);
   DECLARE_INSTRUCTION_FACTORY_P4(HCompareObjectEqAndBranch, HValue*, HValue*,
                                  HBasicBlock*, HBasicBlock*);
 
+  virtual bool KnownSuccessorBlock(HBasicBlock** block) V8_OVERRIDE;
+
   HValue* left() { return OperandAt(0); }
   HValue* right() { return OperandAt(1); }
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     return Representation::Tagged();
   }
 
   virtual Representation observed_input_representation(int index) V8_OVERRIDE {
     return Representation::Tagged();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(CompareObjectEqAndBranch)
-
- private:
-  HCompareObjectEqAndBranch(HValue* left,
-                            HValue* right,
-                            HBasicBlock* true_target = NULL,
-                            HBasicBlock* false_target = NULL) {
-    SetOperandAt(0, left);
-    SetOperandAt(1, right);
-    SetSuccessorAt(0, true_target);
-    SetSuccessorAt(1, false_target);
-  }
 };
 
 
 class HIsObjectAndBranch V8_FINAL : public HUnaryControlInstruction {
  public:
   DECLARE_INSTRUCTION_FACTORY_P1(HIsObjectAndBranch, HValue*);
   DECLARE_INSTRUCTION_FACTORY_P3(HIsObjectAndBranch, HValue*,
                                  HBasicBlock*, HBasicBlock*);
 
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
@@ skipping 2931 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_