Index: lib/Sema/SemaDeclCXX.cpp
===================================================================
--- lib/Sema/SemaDeclCXX.cpp
+++ lib/Sema/SemaDeclCXX.cpp
@@ -434,6 +434,9 @@
 /// error, false otherwise.
 bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old,
                                 Scope *S) {
+  assert(New && "New function declaration is NULL, aborting merge.");
+  assert(Old && "Old function declaration is NULL, aborting merge.");
+
   bool Invalid = false;
 
   // The declaration context corresponding to the scope is the semantic
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/SemaInit.cpp
===================================================================
--- lib/Sema/SemaInit.cpp
+++ lib/Sema/SemaInit.cpp
@@ -4862,6 +4862,8 @@
                                        InitializationSequence &Sequence,
                                        const InitializedEntity &Entity,
                                        Expr *Initializer) {
+  assert(Initializer && "Initializer needs to be not NULL");
+
   bool ArrayDecay = false;
   QualType ArgType = Initializer->getType();
   QualType ArgPointee;
@@ -5237,11 +5239,11 @@
     DeclAccessPair dap;
     if (isLibstdcxxPointerReturnFalseHack(S, Entity, Initializer)) {
       AddZeroInitializationStep(Entity.getType());
-    } else if (Initializer->getType() == Context.OverloadTy &&
+    } else if (Initializer && Initializer->getType() == Context.OverloadTy &&
                !S.ResolveAddressOfOverloadedFunction(Initializer, DestType,
                                                      false, dap))
       SetFailed(InitializationSequence::FK_AddressOfOverloadFailed);
-    else if (Initializer->getType()->isFunctionType() &&
+    else if (Initializer && Initializer->getType()->isFunctionType() &&
              isExprAnUnaddressableFunction(S, Initializer))
       SetFailed(InitializationSequence::FK_AddressOfUnaddressableFunction);
     else
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/Sema/SemaOpenMP.cpp
===================================================================
--- lib/Sema/SemaOpenMP.cpp
+++ lib/Sema/SemaOpenMP.cpp
@@ -985,6 +985,7 @@
         (VD && DSAStack->isForceVarCapturing()))
       return VD ? VD : Info.second;
     auto DVarPrivate = DSAStack->getTopDSA(D, DSAStack->isClauseParsingMode());
+    assert(DVarPrivate.PrivateCopy && "DSAStackTy object must be not NULL");
     if (DVarPrivate.CKind != OMPC_unknown && isOpenMPPrivate(DVarPrivate.CKind))
       return VD ? VD : cast<VarDecl>(DVarPrivate.PrivateCopy->getDecl());
     DVarPrivate = DSAStack->hasDSA(D, isOpenMPPrivate, MatchesAlways(),
@@ -3994,6 +3995,7 @@
 static ExprResult
 tryBuildCapture(Sema &SemaRef, Expr *Capture,
                 llvm::MapVector<Expr *, DeclRefExpr *> &Captures) {
+  assert(Capture && "cannot build capture if expression is NULL");
   if (Capture->isEvaluatable(SemaRef.Context, Expr::SE_AllowSideEffects))
     return SemaRef.PerformImplicitConversion(
         Capture->IgnoreImpCasts(), Capture->getType(), Sema::AA_Converting,
@@ -4251,7 +4253,7 @@
         SemaRef.Diag(CollapseLoopCountExpr->getExprLoc(),
                      diag::note_omp_collapse_ordered_expr)
             << 0 << CollapseLoopCountExpr->getSourceRange();
-      else
+      else if (OrderedLoopCountExpr)
         SemaRef.Diag(OrderedLoopCountExpr->getExprLoc(),
                      diag::note_omp_collapse_ordered_expr)
             << 1 << OrderedLoopCountExpr->getSourceRange();
Index: lib/Sema/SemaOverload.cpp
===================================================================
--- lib/Sema/SemaOverload.cpp
+++ lib/Sema/SemaOverload.cpp
@@ -8705,6 +8705,7 @@
 
 void Sema::diagnoseEquivalentInternalLinkageDeclarations(
     SourceLocation Loc, const NamedDecl *D, ArrayRef<const NamedDecl *> Equiv) {
+  assert(D && "named declaration must be not NULL");
   Diag(Loc, diag::ext_equivalent_internal_linkage_decl_in_modules) << D;
 
   Module *M = getOwningModule(const_cast<NamedDecl*>(D));
@@ -9185,7 +9186,9 @@
         !ToRefTy->getPointeeType()->isIncompleteType() &&
         S.IsDerivedFrom(SourceLocation(), ToRefTy->getPointeeType(), FromTy)) {
       BaseToDerivedConversion = 3;
-    } else if (ToTy->isLValueReferenceType() && !FromExpr->isLValue() &&
+    } else if (FromExpr &&
+               !FromExpr->isLValue() &&
+               ToTy->isLValueReferenceType() &&
                ToTy.getNonReferenceType().getCanonicalType() ==
                FromTy.getNonReferenceType().getCanonicalType()) {
       S.Diag(Fn->getLocation(), diag::note_ovl_candidate_bad_lvalue)