Subzero: Ignore variables with no actual uses.

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 49 matching lines @@
   };
 
 public:
   Liveness(Cfg *Func, LivenessMode Mode) : Func(Func), Mode(Mode) {}
   void init();
   void initPhiEdgeSplits(NodeList::const_iterator FirstNode,
                          VarList::const_iterator FirstVar);
   Cfg *getFunc() const { return Func; }
   LivenessMode getMode() const { return Mode; }
   Variable *getVariable(SizeT LiveIndex, const CfgNode *Node) const;
-  SizeT getLiveIndex(SizeT VarIndex) const { return VarToLiveMap[VarIndex]; }
+  SizeT getLiveIndex(SizeT VarIndex) const {
+    const SizeT LiveIndex = VarToLiveMap[VarIndex];
+    assert(LiveIndex != InvalidLiveIndex);
+    return LiveIndex;
+  }
   SizeT getNumGlobalVars() const { return NumGlobals; }
   SizeT getNumVarsInNode(const CfgNode *Node) const {
     return NumGlobals + Nodes[Node->getIndex()].NumLocals;
   }
   SizeT &getNumNonDeadPhis(const CfgNode *Node) {
     return Nodes[Node->getIndex()].NumNonDeadPhis;
   }
   LivenessBV &getLiveIn(const CfgNode *Node) {
     SizeT Index = Node->getIndex();
     resize(Index);
@@ skipping 18 matching lines @@
   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);
   }
+  static constexpr SizeT InvalidLiveIndex = -1;
   Cfg *Func;
   LivenessMode Mode;
   SizeT NumGlobals = 0;
   /// Size of Nodes is Cfg::Nodes.size().
   CfgVector<LivenessNode> Nodes;
   /// VarToLiveMap maps a Variable's Variable::Number to its live index within
   /// its basic block.
   CfgVector<SizeT> VarToLiveMap;
   /// LiveToVarMap is analogous to LivenessNode::LiveToVarMap, but for non-local
   /// variables.
   CfgVector<Variable *> LiveToVarMap;
   /// RangeMask[Variable::Number] indicates whether we want to track that
   /// Variable's live range.
   LivenessBV RangeMask;
   /// ScratchBV is a bitvector that can be reused across CfgNode passes, to
   /// avoid having to allocate/deallocate memory so frequently.
   LivenessBV ScratchBV;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICELIVENESS_H