Index: lib/AST/DeclObjC.cpp
===================================================================
--- lib/AST/DeclObjC.cpp
+++ lib/AST/DeclObjC.cpp
@@ -1577,8 +1577,10 @@
           data().IvarList = layout[0].Ivar; Ix++;
           curIvar = data().IvarList;
         }
-        for ( ; Ix != EIx; curIvar = layout[Ix].Ivar, Ix++)
+        for ( ; Ix != EIx; curIvar = layout[Ix].Ivar, Ix++) {
+          assert(curIvar && "instance variable is NULL, stop iterating through layout");
           curIvar->setNextIvar(layout[Ix].Ivar);
+        }
       }
     }
   }
Index: lib/Frontend/CompilerInstance.cpp
===================================================================
--- lib/Frontend/CompilerInstance.cpp
+++ lib/Frontend/CompilerInstance.cpp
@@ -742,7 +742,7 @@
 
   // Figure out where to get and map in the main file.
   if (InputFile != "-") {
-    const FileEntry *File;
+    const FileEntry *File = nullptr;
     if (Opts.FindPchSource.empty()) {
       File = FileMgr.getFile(InputFile, /*OpenFile=*/true);
     } else {
@@ -760,13 +760,14 @@
       SmallVector<std::pair<const FileEntry *, const DirectoryEntry *>, 16>
           Includers;
       Includers.push_back(std::make_pair(FindFile, FindFile->getDir()));
-      File = HS->LookupFile(InputFile, SourceLocation(), /*isAngled=*/false,
-                            /*FromDir=*/nullptr,
-                            /*CurDir=*/UnusedCurDir, Includers,
-                            /*SearchPath=*/nullptr,
-                            /*RelativePath=*/nullptr,
-                            /*RequestingModule=*/nullptr,
-                            /*SuggestedModule=*/nullptr, /*SkipCache=*/true);
+      if (HS)
+        File = HS->LookupFile(InputFile, SourceLocation(), /*isAngled=*/false,
+                              /*FromDir=*/nullptr,
+                              /*CurDir=*/UnusedCurDir, Includers,
+                              /*SearchPath=*/nullptr,
+                              /*RelativePath=*/nullptr,
+                              /*RequestingModule=*/nullptr,
+                              /*SuggestedModule=*/nullptr, /*SkipCache=*/true);
       // Also add the header to /showIncludes output.
       if (File)
         DepOpts.ShowIncludesPretendHeader = File->getName();
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp
+++ lib/Sema/SemaExprCXX.cpp
@@ -398,8 +398,10 @@
                                 SourceLocation TypeidLoc,
                                 Expr *E,
                                 SourceLocation RParenLoc) {
+  assert(E && "expression operand is NULL, cannot build C++ typeid expression");
+
   bool WasEvaluated = false;
-  if (E && !E->isTypeDependent()) {
+  if (!E->isTypeDependent()) {
     if (E->getType()->isPlaceholderType()) {
       ExprResult result = CheckPlaceholderExpr(E);
       if (result.isInvalid()) return ExprError();
Index: lib/Sema/SemaLookup.cpp
===================================================================
--- lib/Sema/SemaLookup.cpp
+++ lib/Sema/SemaLookup.cpp
@@ -3744,6 +3744,7 @@
   bool AnyVisibleDecls = !NewDecls.empty();
 
   for (/**/; DI != DE; ++DI) {
+    assert(*DI && "TypoCorrection iterator cannot be NULL");
     NamedDecl *VisibleDecl = *DI;
     if (!LookupResult::isVisible(SemaRef, *DI))
       VisibleDecl = findAcceptableDecl(SemaRef, *DI);
Index: lib/StaticAnalyzer/Core/PlistDiagnostics.cpp
===================================================================
--- lib/StaticAnalyzer/Core/PlistDiagnostics.cpp
+++ lib/StaticAnalyzer/Core/PlistDiagnostics.cpp
@@ -297,6 +297,7 @@
   if (!Diags.empty())
     SM = &Diags.front()->path.front()->getLocation().getManager();
 
+  assert(SM && "SourceManager is NULL, cannot iterate through the diagnostics");
 
   for (std::vector<const PathDiagnostic*>::iterator DI = Diags.begin(),
        DE = Diags.end(); DI != DE; ++DI) {