Polish diagnostics for null dereferences via ObjC ivar accesses.  Finishes up <rdar://problem/6352035>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@113612 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Checker/DereferenceChecker.cpp b/lib/Checker/DereferenceChecker.cpp
index af74c79..50392b2 100644
--- a/lib/Checker/DereferenceChecker.cpp
+++ b/lib/Checker/DereferenceChecker.cpp
@@ -123,6 +123,19 @@
             }
           break;
         }
+        case Stmt::ObjCIvarRefExprClass: {
+          const ObjCIvarRefExpr *IV = cast<ObjCIvarRefExpr>(S);
+          if (const DeclRefExpr *DR =
+              dyn_cast<DeclRefExpr>(IV->getBase()->IgnoreParenCasts())) {
+            if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
+              llvm::raw_svector_ostream os(buf);
+              os << "Instance variable access (via '" << VD->getName()
+                 << "') results in a null pointer dereference";
+            }
+          }
+          Ranges.push_back(IV->getSourceRange());
+          break;
+        }
         default:
           break;
       }