Cache common constants before lowering.

src/IceTargetLoweringX8664.cpp

 //===- subzero/src/IceTargetLoweringX8664.cpp - x86-64 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 180 matching lines @@
   }
 
   Variable *r15 =
       getPhysicalRegister(Traits::RegisterSet::Reg_r15, IceType_i64);
   _add(rsp, r15);
 }
 
 void TargetX8664::_push_rbp() {
   assert(NeedSandboxing);
 
-  Constant *_0 = Ctx->getConstantZero(IceType_i32);
+  Constant *_0 = getConstantZero(IceType_i32);
   Variable *ebp =
       getPhysicalRegister(Traits::RegisterSet::Reg_ebp, IceType_i32);
   Variable *rsp =
       getPhysicalRegister(Traits::RegisterSet::Reg_rsp, IceType_i64);
   auto *TopOfStack = llvm::cast<X86OperandMem>(
       legalize(X86OperandMem::create(Func, IceType_i32, rsp, _0),
                Legal_Reg | Legal_Mem));
 
   // Emits a sequence:
   //
@@ skipping 593 matching lines @@
 #define X(tag, sizeLog2, align, elts, elty, str, rcstr)                        \
   static_assert(_table1_##tag == _table2_##tag,                                \
                 "Inconsistency between ICETYPEX8664_TABLE and ICETYPE_TABLE");
 ICETYPE_TABLE
 #undef X
 } // end of namespace dummy3
 } // end of anonymous namespace
 
 } // end of namespace X8664
 } // end of namespace Ice