Use address-taken to disambiguate global variable and indirect memops.

Major steps include:
 1). introduces a not-addr-taken bit-field in GlobalVariable
 2). GlobalOpt pass sets "not-address-taken" if it proves a global varirable 
    dosen't have its address taken.
 3). AA use this info for disambiguation. 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193251 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/AsmWriter.cpp

@@ -1459,6 +1459,7 @@ void AssemblyWriter::printGlobal(const GlobalVariable *GV) {
   if (GV->hasUnnamedAddr()) Out << "unnamed_addr ";
   if (GV->isExternallyInitialized()) Out << "externally_initialized ";
   Out << (GV->isConstant() ? "constant " : "global ");
+  if (!GV->AddressMaybeTaken()) Out << "notaddrtaken ";
   TypePrinter.print(GV->getType()->getElementType(), Out);
 
   if (GV->hasInitializer()) {