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/Analysis/BasicAliasAnalysis.cpp

@@ -1238,6 +1238,17 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
       return NoAlias;
     if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
       return NoAlias;
+
+    // If one object is a global variable without address taken, the other one
+    // is a different object, they will not alias because the global variable
+    // in question cannot be indirectly accessed.
+    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(O1))
+      if (!GV->AddressMaybeTaken())
+        return NoAlias;
+
+    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(O2))
+      if (!GV->AddressMaybeTaken())
+        return NoAlias;
   }
 
   // If the size of one access is larger than the entire object on the other