Subzero: Improve performance of liveness analysis and live range construction.

src/IceCfgNode.h

Index: src/IceCfgNode.h
diff --git a/src/IceCfgNode.h b/src/IceCfgNode.h
index cc97ae412955b98be3167f6ca84490ba91ba641a..e5661cc617454538e04943e7229a37dca47829ca 100644
--- a/src/IceCfgNode.h
+++ b/src/IceCfgNode.h
@@ -51,6 +51,11 @@ public:
   InstList &getInsts() { return Insts; }
   void appendInst(Inst *Inst);
   void renumberInstructions();
+  // Rough and generally conservative estimate of the number of
+  // instructions in the block.  It is updated when an instruction is
+  // added, but not when deleted.  It is recomputed during
+  // renumberInstructions().
+  InstNumberT getInstCountEstimate() const { return InstCountEstimate; }
 
   // Add a predecessor edge to the InEdges list for each of this
   // node's successors.
@@ -77,6 +82,7 @@ private:
   const SizeT Number; // label index
   IceString Name;     // for dumping only
   bool HasReturn;     // does this block need an epilog?
+  InstNumberT InstCountEstimate; // rough instruction count estimate
   NodeList InEdges;   // in no particular order
   NodeList OutEdges;  // in no particular order
   PhiList Phis;       // unordered set of phi instructions