Cache common constants before lowering.

src/IceTargetLoweringX8632.h

 //===- subzero/src/IceTargetLoweringX8632.h - x86-32 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 52 matching lines @@
   Inst *emitCallToTarget(Operand *CallTarget, Variable *ReturnReg) override;
   Variable *moveReturnValueToRegister(Operand *Value, Type ReturnType) override;
 
 private:
   ENABLE_MAKE_UNIQUE;
   friend class X8632::TargetX86Base<X8632::Traits>;
 
   explicit TargetX8632(Cfg *Func) : TargetX86Base(Func) {}
 
   Operand *createNaClReadTPSrcOperand() {
-    Constant *Zero = Ctx->getConstantZero(IceType_i32);
+    Constant *Zero = getConstantZero(IceType_i32);
     return Traits::X86OperandMem::create(Func, IceType_i32, nullptr, Zero,
                                          nullptr, 0,
                                          Traits::X86OperandMem::SegReg_GS);
   }
 };
 
 } // end of namespace X8632
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX8632_H