Subzero: Convert a few getName() methods to return a const string ref.

src/IceOperand.h

 //===- subzero/src/IceOperand.h - High-level operands -----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the Operand class and its target-independent
@@ skipping 205 matching lines @@
   static ConstantRelocatable *create(GlobalContext *Ctx, Type Ty,
                                      const RelocatableTuple &Tuple,
                                      uint32_t PoolEntryID) {
     assert(!Ctx->isIRGenerationDisabled() &&
            "Attempt to build relocatable constant when IR generation disabled");
     return new (Ctx->allocate<ConstantRelocatable>()) ConstantRelocatable(
         Ty, Tuple.Offset, Tuple.Name, Tuple.SuppressMangling, PoolEntryID);
   }
 
   RelocOffsetT getOffset() const { return Offset; }
-  IceString getName() const { return Name; }
+  const IceString &getName() const { return Name; }
   void setSuppressMangling(bool Value) { SuppressMangling = Value; }
   bool getSuppressMangling() const { return SuppressMangling; }
   using Constant::emit;
   using Constant::dump;
   void emit(GlobalContext *Ctx) const override;
   void emitWithoutDollar(GlobalContext *Ctx) const;
   void dump(const Cfg *Func, Ostream &Str) const override;
 
   static bool classof(const Operand *Operand) {
     OperandKind Kind = Operand->getKind();
@@ skipping 384 matching lines @@
 private:
   const Cfg *Func;
   MetadataKind Kind;
   std::vector<VariableTracking> Metadata;
   const static InstDefList NoDefinitions;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEOPERAND_H