Subzero: Don't store std::string objects inside Variable.

src/IceOperand.h

Index: src/IceOperand.h
diff --git a/src/IceOperand.h b/src/IceOperand.h
index 99bbd39dbcb442bc8d5ebb3d8bf05e429f44361a..e4f6bba5350d04a5f0155eb43a8c16e039bbaf63 100644
--- a/src/IceOperand.h
+++ b/src/IceOperand.h
@@ -388,18 +388,17 @@ class Variable : public Operand {
   Variable(Variable &&V) = default;
 
 public:
-  static Variable *create(Cfg *Func, Type Ty, SizeT Index,
-                          const IceString &Name) {
-    return new (Func->allocate<Variable>())
-        Variable(kVariable, Ty, Index, Name);
+  static Variable *create(Cfg *Func, Type Ty, SizeT Index) {
+    return new (Func->allocate<Variable>()) Variable(kVariable, Ty, Index);
   }
 
   SizeT getIndex() const { return Number; }
-  IceString getName() const;
-  void setName(IceString &NewName) {
+  IceString getName(const Cfg *Func) const;
+  void setName(Cfg *Func, const IceString &NewName) {
     // Make sure that the name can only be set once.
-    assert(Name.empty());
-    Name = NewName;
+    assert(NameIndex < 0);
+    if (!NewName.empty())
+      NameIndex = Func->addIdentifierName(NewName);
   }
 
   bool getIsArg() const { return IsArgument; }
@@ -484,8 +483,8 @@ public:
   ~Variable() override {}
 
 protected:
-  Variable(OperandKind K, Type Ty, SizeT Index, const IceString &Name)
-      : Operand(K, Ty), Number(Index), Name(Name), IsArgument(false),
+  Variable(OperandKind K, Type Ty, SizeT Index)
+      : Operand(K, Ty), Number(Index), NameIndex(-1), IsArgument(false),
         IsImplicitArgument(false), IgnoreLiveness(false), StackOffset(0),
         RegNum(NoRegister), RegNumTmp(NoRegister), Weight(1), LoVar(NULL),
         HiVar(NULL) {
@@ -496,8 +495,7 @@ protected:
   // Number is unique across all variables, and is used as a
   // (bit)vector index for liveness analysis.
   const SizeT Number;
-  // Name is optional.
-  IceString Name;
+  int32_t NameIndex;
   bool IsArgument;
   bool IsImplicitArgument;
   // IgnoreLiveness means that the variable should be ignored when