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

src/IceDefs.h

Index: src/IceDefs.h
diff --git a/src/IceDefs.h b/src/IceDefs.h
index 7ea34be88f1f40415bdd02346193629adfd3b3a0..7bec8e05f6f127952223d50ba0338b2bb5d5b4a8 100644
--- a/src/IceDefs.h
+++ b/src/IceDefs.h
@@ -225,6 +225,7 @@ enum VerboseItem {
   IceV_Random = 1 << 10,
   IceV_Folding = 1 << 11,
   IceV_RMW = 1 << 12,
+  IceV_Loop = 1 << 13,
   IceV_All = ~IceV_None,
   IceV_Most = IceV_All & ~IceV_LinearScan
 };