[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 bcd25b2eb87fb2df4fbd8783bfc25107680fb6ac..21734470919f475b63e71ce57e4507f4210fe78d 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 +524,17 @@ class Instruction : public ZoneObject {
 
   void operator delete(void* pointer, void* location) { UNREACHABLE(); }
 
+  void OverwriteWithNop() {
+    opcode_ = ArchOpcodeField::encode(kArchNop);
+    bit_field_ = 0;
+    pointer_map_ = NULL;
+  }
+
+  bool IsNop() const {
+    return arch_opcode() == kArchNop && InputCount() == 0 &&
+           OutputCount() == 0 && TempCount() == 0;
+  }
+
  protected:
   explicit Instruction(InstructionCode opcode)
       : opcode_(opcode),
@@ -599,6 +614,8 @@ 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);
@@ -893,12 +910,16 @@ 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.
   const BasicBlock::RpoNumber rpo_number_;
   const BasicBlock::RpoNumber loop_header_;
   const BasicBlock::RpoNumber loop_end_;
@@ -991,6 +1012,8 @@ class InstructionSequence FINAL : public ZoneObject {
   void EndBlock(BasicBlock::RpoNumber rpo);
 
   int AddConstant(int virtual_register, Constant constant) {
+    // TODO(titzer): allow RPO numbers as constants?
+    DCHECK(constant.type() != Constant::kRpoNumber);
     DCHECK(virtual_register >= 0 && virtual_register < next_virtual_register_);
     DCHECK(constants_.find(virtual_register) == constants_.end());
     constants_.insert(std::make_pair(virtual_register, constant));
@@ -1003,8 +1026,8 @@ class InstructionSequence FINAL : public ZoneObject {
     return it->second;
   }
 
-  typedef ConstantDeque Immediates;
-  const Immediates& immediates() const { return immediates_; }
+  typedef ZoneVector<Constant> Immediates;
+  Immediates& immediates() { return immediates_; }
 
   int AddImmediate(Constant constant) {
     int index = static_cast<int>(immediates_.size());
@@ -1031,6 +1054,13 @@ class InstructionSequence FINAL : public ZoneObject {
   FrameStateDescriptor* GetFrameStateDescriptor(StateId deoptimization_id);
   int GetFrameStateDescriptorCount();
 
+  BasicBlock::RpoNumber InputRpo(Instruction* instr, size_t index) {
+    InstructionOperand* operand = instr->InputAt(index);
+    Constant constant = operand->IsImmediate() ? GetImmediate(operand->index())
+                                               : GetConstant(operand->index());
+    return constant.ToRpoNumber();
+  }
+
  private:
   friend std::ostream& operator<<(std::ostream& os,
                                   const PrintableInstructionSequence& code);
@@ -1041,7 +1071,7 @@ class InstructionSequence FINAL : public ZoneObject {
   InstructionBlocks* const instruction_blocks_;
   IntVector block_starts_;
   ConstantMap constants_;
-  ConstantDeque immediates_;
+  Immediates immediates_;
   InstructionDeque instructions_;
   int next_virtual_register_;
   PointerMapDeque pointer_maps_;