[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/common-operator.h

Index: src/compiler/common-operator.h
diff --git a/src/compiler/common-operator.h b/src/compiler/common-operator.h
index 53debe1f5a6871e77ccea385bc9931aab8f045bb..044784fa3af7b4a5bdf5b6142e9c511bd1902be4 100644
--- a/src/compiler/common-operator.h
+++ b/src/compiler/common-operator.h
@@ -183,6 +183,8 @@ 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 {
@@ -248,6 +250,7 @@ class CommonOperatorBuilder final : public ZoneObject {
   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.