Compute the loop nest depth of each CfgNode and weight Variables by it.

src/IceCfgNode.h

 //===- subzero/src/IceCfgNode.h - Control flow graph node -------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 28 matching lines @@
   void setName(const IceString &NewName) {
     // Make sure that the name can only be set once.
     assert(NameIndex == Cfg::IdentifierIndexInvalid);
     if (!NewName.empty())
       NameIndex = Func->addIdentifierName(NewName);
   }
   IceString getAsmName() const {
     return ".L" + Func->getFunctionName() + "$" + getName();
   }
 
+  void incrementLoopNestDepth() { ++LoopNestDepth; }
+  void setLoopNestDepth(SizeT NewDepth) { LoopNestDepth = NewDepth; }
+  SizeT getLoopNestDepth() const { return LoopNestDepth; }
+
   /// The HasReturn flag indicates that this node contains a return
   /// instruction and therefore needs an epilog.
   void setHasReturn() { HasReturn = true; }
   bool getHasReturn() const { return HasReturn; }
 
   void setNeedsPlacement(bool Value) { NeedsPlacement = Value; }
   bool needsPlacement() const { return NeedsPlacement; }
 
   void setNeedsAlignment() { NeedsAlignment = true; }
   bool needsAlignment() const { return NeedsAlignment; }
@@ skipping 45 matching lines @@
   void dump(Cfg *Func) const;
 
   void profileExecutionCount(VariableDeclaration *Var);
 
 private:
   CfgNode(Cfg *Func, SizeT LabelIndex);
   Cfg *const Func;
   SizeT Number; /// label index
   Cfg::IdentifierIndexType NameIndex =
       Cfg::IdentifierIndexInvalid; /// index into Cfg::NodeNames table
+  SizeT LoopNestDepth = 0;         /// the loop nest depth of this node
   bool HasReturn = false;          /// does this block need an epilog?
   bool NeedsPlacement = false;
   bool NeedsAlignment = false;       /// is sandboxing required?
   InstNumberT InstCountEstimate = 0; /// rough instruction count estimate
   NodeList InEdges;                  /// in no particular order
   NodeList OutEdges;                 /// in no particular order
   PhiList Phis;                      /// unordered set of phi instructions
   InstList Insts;                    /// ordered list of non-phi instructions
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICECFGNODE_H