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..18bd11bb8afc4964ce26c8b9016b189096b0cf40 100644
--- a/src/IceCfg.h
+++ b/src/IceCfg.h
@@ -189,6 +189,7 @@ public:
   void doNopInsertion();
   void genCode();
   void genFrame();
+  void computeLoopNestDepth();
   void livenessLightweight();
   void liveness(LivenessMode Mode);
   bool validateLiveness() const;