Subzero: Use "auto" per (unwritten) auto coding style.

src/IcePhiLoweringImpl.h

 //===------ subzero/src/IcePhiLoweringImpl.h - Phi lowering -----*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 19 matching lines @@
 /// methods. Undef values are also legalized, since loOperand() and hiOperand()
 /// don't expect Undef input.
 template <class TargetT>
 void prelowerPhis32Bit(TargetT *Target, CfgNode *Node, Cfg *Func) {
   for (Inst &I : Node->getPhis()) {
     auto *Phi = llvm::dyn_cast<InstPhi>(&I);
     if (Phi->isDeleted())
       continue;
     Variable *Dest = Phi->getDest();
     if (Dest->getType() == IceType_i64) {
-      Variable *DestLo = llvm::cast<Variable>(Target->loOperand(Dest));
-      Variable *DestHi = llvm::cast<Variable>(Target->hiOperand(Dest));
-      InstPhi *PhiLo = InstPhi::create(Func, Phi->getSrcSize(), DestLo);
-      InstPhi *PhiHi = InstPhi::create(Func, Phi->getSrcSize(), DestHi);
+      auto *DestLo = llvm::cast<Variable>(Target->loOperand(Dest));
+      auto *DestHi = llvm::cast<Variable>(Target->hiOperand(Dest));
+      auto *PhiLo = InstPhi::create(Func, Phi->getSrcSize(), DestLo);
+      auto *PhiHi = InstPhi::create(Func, Phi->getSrcSize(), DestHi);
       for (SizeT I = 0; I < Phi->getSrcSize(); ++I) {
         Operand *Src = Phi->getSrc(I);
         CfgNode *Label = Phi->getLabel(I);
         Src = Target->legalizeUndef(Src);
         PhiLo->addArgument(Target->loOperand(Src), Label);
         PhiHi->addArgument(Target->hiOperand(Src), Label);
       }
       Node->getPhis().push_back(PhiLo);
       Node->getPhis().push_back(PhiHi);
       Phi->setDeleted();
     }
   }
 }
 
 } // end of namespace PhiLowering
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEPHILOWERINGIMPL_H