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

src/IceCfg.h

Index: src/IceCfg.h
diff --git a/src/IceCfg.h b/src/IceCfg.h
index e6c5a4a43c7708f9fb42f2b028312c2a8f1e8800..3c8972df6ad80f58b1b22035a38636aff4a2fe6f 100644
--- a/src/IceCfg.h
+++ b/src/IceCfg.h
@@ -86,7 +86,9 @@ public:
   /// @{
   void setEntryNode(CfgNode *EntryNode) { Entry = EntryNode; }
   CfgNode *getEntryNode() const { return Entry; }
-  /// Create a node and append it to the end of the linearized list.
+  /// Create a node and append it to the end of the linearized list. The loop
+  /// nest depth of the new node may not be valid if it is created after
+  /// computeLoopNestDepth.
   CfgNode *makeNode();
   SizeT getNumNodes() const { return Nodes.size(); }
   const NodeList &getNodes() const { return Nodes; }
@@ -189,6 +191,7 @@ public:
   void doNopInsertion();
   void genCode();
   void genFrame();
+  void computeLoopNestDepth();
   void livenessLightweight();
   void liveness(LivenessMode Mode);
   bool validateLiveness() const;