Subzero: Use CFG-local arena allocation for relevant containers.

src/IceOperand.cpp

 //===- subzero/src/IceOperand.cpp - High-level operand implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the Operand class and its target-independent
@@ skipping 108 matching lines @@
   while (TrimmedBegin != Range.end() && TrimmedBegin->second <= Lower)
     ++TrimmedBegin;
 }
 
 IceString Variable::getName(const Cfg *Func) const {
   if (Func && NameIndex >= 0)
     return Func->getIdentifierName(NameIndex);
   return "__" + std::to_string(getIndex());
 }
 
-Variable Variable::asType(Type Ty) {
+Variable *Variable::asType(Type Ty) {
   // Note: This returns a Variable, even if the "this" object is a
   // subclass of Variable.
-  Variable V(kVariable, Ty, Number);
-  V.NameIndex = NameIndex;
-  V.RegNum = RegNum;
-  V.StackOffset = StackOffset;
+  if (!ALLOW_DUMP || getType() == Ty)
+    return this;
+  Variable *V = new (getCurrentCfgAllocator()->Allocate<Variable>())
+      Variable(kVariable, Ty, Number);
+  V->NameIndex = NameIndex;
+  V->RegNum = RegNum;
+  V->StackOffset = StackOffset;
   return V;
 }
 
 void VariableTracking::markUse(MetadataKind TrackingKind, const Inst *Instr,
                                const CfgNode *Node, bool IsFromDef,
                                bool IsImplicit) {
   (void)TrackingKind;
   if (MultiBlock == MBS_MultiBlock)
     return;
   // TODO(stichnot): If the use occurs as a source operand in the
@@ skipping 334 matching lines @@
   if (!ALLOW_DUMP)
     return Str;
   if (W.getWeight() == RegWeight::Inf)
     Str << "Inf";
   else
     Str << W.getWeight();
   return Str;
 }
 
 } // end of namespace Ice