Subzero: Slight improvement to phi lowering.

src/IceLiveness.h

 //===- subzero/src/IceLiveness.h - Liveness analysis ------------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 78 matching lines @@
   LiveBeginEndMap *getLiveBegin(const CfgNode *Node) {
     SizeT Index = Node->getIndex();
     resize(Index);
     return &Nodes[Index].LiveBegin;
   }
   LiveBeginEndMap *getLiveEnd(const CfgNode *Node) {
     SizeT Index = Node->getIndex();
     resize(Index);
     return &Nodes[Index].LiveEnd;
   }
+  bool getRangeMask(SizeT Index) const { return RangeMask[Index]; }
 
 private:
   void initInternal(NodeList::const_iterator FirstNode,
                     VarList::const_iterator FirstVar, bool IsFullInit);
   /// Resize Nodes so that Nodes[Index] is valid.
   void resize(SizeT Index) {
     if (Index >= Nodes.size())
       Nodes.resize(Index + 1);
   }
   Cfg *Func;
   LivenessMode Mode;
   SizeT NumGlobals = 0;
   /// Size of Nodes is Cfg::Nodes.size().
   std::vector<LivenessNode> Nodes;
   /// VarToLiveMap maps a Variable's Variable::Number to its live index
   /// within its basic block.
   std::vector<SizeT> VarToLiveMap;
   /// LiveToVarMap is analogous to LivenessNode::LiveToVarMap, but for
   /// non-local variables.
   std::vector<Variable *> LiveToVarMap;
+  /// RangeMask[Variable::Number] indicates whether we want to track that
+  /// Variable's live range.
+  llvm::BitVector RangeMask;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICELIVENESS_H