Subzero: Manage each Cfg as a std::unique_ptr<Cfg>.

src/IceCfg.cpp

 //===- subzero/src/IceCfg.cpp - Control flow graph 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 Cfg class, including constant pool
@@ skipping 31 matching lines @@
       TargetAssembler(
           TargetLowering::createAssembler(Ctx->getTargetArch(), this)),
       CurrentNode(nullptr) {
   assert(!Ctx->isIRGenerationDisabled() &&
          "Attempt to build cfg when IR generation disabled");
 }
 
 Cfg::~Cfg() {
   assert(ICE_TLS_GET_FIELD(CurrentCfg) == this);
   // Reset the thread-local CurrentCfg pointer.
-  ICE_TLS_SET_FIELD(CurrentCfg, nullptr);
+  updateTLS(nullptr);
 }
 
 void Cfg::setError(const IceString &Message) {
   HasError = true;
   ErrorMessage = Message;
 }
 
 CfgNode *Cfg::makeNode() {
   SizeT LabelIndex = Nodes.size();
   CfgNode *Node = CfgNode::create(this, LabelIndex);
@@ skipping 456 matching lines @@
     }
   }
   // Print each basic block
   for (CfgNode *Node : Nodes)
     Node->dump(this);
   if (isVerbose(IceV_Instructions))
     Str << "}\n";
 }
 
 } // end of namespace Ice