[turbofan] Implement jump threading after register allocation.

src/compiler/instruction.h

Index: src/compiler/instruction.h
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index 1740dfbf25b970054417d75c533ba95e8ea65366..8e2192fb86b1f06761296be612946f5feb762798 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -441,6 +441,10 @@ class Instruction : public ZoneObject {
     DCHECK(i < InputCount());
     return operands_[OutputCount() + i];
   }
+  void SetInputAt(size_t i, InstructionOperand* operand) {
+    DCHECK(i < InputCount());
+    operands_[OutputCount() + i] = operand;
+  }
 
   size_t TempCount() const { return TempCountField::decode(bit_field_); }
   InstructionOperand* TempAt(size_t i) const {
@@ -520,6 +524,12 @@ class Instruction : public ZoneObject {
 
   void operator delete(void* pointer, void* location) { UNREACHABLE(); }
 
+  void OverwriteWithNop() {
+    opcode_ = ArchOpcodeField::encode(kArchNop);
+    bit_field_ = 0;
+    pointer_map_ = NULL;
+  }
+
  protected:
   explicit Instruction(InstructionCode opcode)
       : opcode_(opcode),
@@ -599,6 +609,8 @@ class GapInstruction : public Instruction {
     return parallel_moves_[pos];
   }
 
+  bool IsRedundant() const;
+
   static GapInstruction* New(Zone* zone) {
     void* buffer = zone->New(sizeof(GapInstruction));
     return new (buffer) GapInstruction(kGapInstruction);
@@ -885,12 +897,16 @@ class InstructionBlock FINAL : public ZoneObject {
   const PhiInstructions& phis() const { return phis_; }
   void AddPhi(PhiInstruction* phi) { phis_.push_back(phi); }
 
+  void set_ao_number(BasicBlock::RpoNumber ao_number) {
+    ao_number_ = ao_number;
+  }
+
  private:
   Successors successors_;
   Predecessors predecessors_;
   PhiInstructions phis_;
   const BasicBlock::Id id_;
-  const BasicBlock::RpoNumber ao_number_;  // Assembly order number.
+  BasicBlock::RpoNumber ao_number_;  // Assembly order number.
   // TODO(dcarney): probably dont't need this.
   const BasicBlock::RpoNumber rpo_number_;
   const BasicBlock::RpoNumber loop_header_;
@@ -1024,6 +1040,15 @@ class InstructionSequence FINAL : public ZoneObject {
   FrameStateDescriptor* GetFrameStateDescriptor(StateId deoptimization_id);
   int GetFrameStateDescriptorCount();
 
+  BasicBlock::RpoNumber InputRpo(Instruction* instr, int index) {
+    InstructionOperand* operand = instr->InputAt(index);
+    Constant constant = operand->IsImmediate() ? GetImmediate(operand->index())
+                                               : GetConstant(operand->index());
+    int rpo = constant.ToInt32();
+    DCHECK(rpo >= 0 && rpo < static_cast<int>(instruction_blocks_->size()));
+    return BasicBlock::RpoNumber::FromInt(rpo);
+  }
+
  private:
   friend std::ostream& operator<<(std::ostream& os,
                                   const PrintableInstructionSequence& code);