[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/common-operator.h

 // Copyright 2014 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_COMMON_OPERATOR_H_
 #define V8_COMPILER_COMMON_OPERATOR_H_
 
 #include "src/assembler.h"
 #include "src/compiler/frame-states.h"
 #include "src/deoptimize-reason.h"
@@ skipping 165 matching lines @@
 
 size_t hash_value(RegionObservability);
 
 std::ostream& operator<<(std::ostream&, RegionObservability);
 
 RegionObservability RegionObservabilityOf(Operator const*) WARN_UNUSED_RESULT;
 
 std::ostream& operator<<(std::ostream& os,
                          const ZoneVector<MachineType>* types);
 
+Type* SigmaTypeOf(Operator const*) WARN_UNUSED_RESULT;

[Benedikt Meurer, 2016/08/05 12:54:20]

Nit: Rename to TypeOf

+
 // Interface for building common operators that can be used at any level of IR,
 // including JavaScript, mid-level, and low-level.
 class CommonOperatorBuilder final : public ZoneObject {
  public:
   explicit CommonOperatorBuilder(Zone* zone);
 
   const Operator* Dead();
   const Operator* End(size_t control_input_count);
   const Operator* Branch(BranchHint = BranchHint::kNone);
   const Operator* IfTrue();
@@ skipping 45 matching lines @@
   const Operator* FinishRegion();
   const Operator* StateValues(int arguments);
   const Operator* ObjectState(int pointer_slots, int id);
   const Operator* TypedStateValues(const ZoneVector<MachineType>* types);
   const Operator* FrameState(BailoutId bailout_id,
                              OutputFrameStateCombine state_combine,
                              const FrameStateFunctionInfo* function_info);
   const Operator* Call(const CallDescriptor* descriptor);
   const Operator* TailCall(const CallDescriptor* descriptor);
   const Operator* Projection(size_t index);
+  const Operator* Sigma(Type* type);

[Benedikt Meurer, 2016/08/05 12:54:20]

Nit: Rename to TypeGuard

 
   // Constructs a new merge or phi operator with the same opcode as {op}, but
   // with {size} inputs.
   const Operator* ResizeMergeOrPhi(const Operator* op, int size);
 
   // Constructs function info for frame state construction.
   const FrameStateFunctionInfo* CreateFrameStateFunctionInfo(
       FrameStateType type, int parameter_count, int local_count,
       Handle<SharedFunctionInfo> shared_info);
 
  private:
   Zone* zone() const { return zone_; }
 
   const CommonOperatorGlobalCache& cache_;
   Zone* const zone_;
 
   DISALLOW_COPY_AND_ASSIGN(CommonOperatorBuilder);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_COMMON_OPERATOR_H_