Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -6500,6 +6500,8 @@
           << NewDecl;
       S.Diag(OldDecl->getLocation(), diag::note_previous_declaration);
       NewDecl->dropAttr<DLLImportAttr>();
+
+      assert(NewImportAttr && "!NewImportAttr");
       NewDecl->addAttr(
           DLLExportAttr::CreateImplicit(S.Context, NewImportAttr->getRange()));
     } else {
@@ -10433,7 +10435,7 @@
 
   // Main isn't allowed to become a multiversion function, however it IS
   // permitted to have 'main' be marked with the 'target' optimization hint.
-  if (NewFD->isMain()) {
+  if (NewTA && NewFD->isMain()) {
     if ((MVType == MultiVersionKind::Target && NewTA->isDefaultVersion()) ||
         MVType == MultiVersionKind::CPUDispatch ||
         MVType == MultiVersionKind::CPUSpecific) {
@@ -13199,6 +13201,8 @@
         Deduced = DT->getDeducedType();
         DeducedDecl = D;
       } else if (!Context.hasSameType(DT->getDeducedType(), Deduced)) {
+        assert(DeducedDecl && "!DeducedDecl");
+
         auto *AT = dyn_cast<AutoType>(DT);
         Diag(D->getTypeSourceInfo()->getTypeLoc().getBeginLoc(),
              diag::err_auto_different_deductions)
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -639,6 +639,7 @@
   // C++11 [dcl.constexpr]p1: If any declaration of a function or function
   // template has a constexpr specifier then all its declarations shall
   // contain the constexpr specifier.
+  assert(Old && "!Old");
   if (New->getConstexprKind() != Old->getConstexprKind()) {
     Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
         << New << New->getConstexprKind() << Old->getConstexprKind();
@@ -1293,6 +1294,8 @@
       }
     }
 
+    assert(BestPath && "!BestPath");
+
     //   ... unambiguous ...
     QualType BaseType = BestPath->back().Base->getType();
     if (Paths.isAmbiguous(S.Context.getCanonicalType(BaseType))) {
@@ -2673,7 +2676,7 @@
         const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
         if (Class->isInterface() &&
               (!RD->isInterfaceLike() ||
-               KnownBase->getAccessSpecifier() != AS_public)) {
+               (KnownBase && KnownBase->getAccessSpecifier() != AS_public))) {
           // The Microsoft extension __interface does not permit bases that
           // are not themselves public interfaces.
           Diag(KnownBase->getBeginLoc(), diag::err_invalid_base_in_interface)
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -4556,7 +4556,7 @@
   // resolution for the operator overload should get the first crack
   // at the overload.
   bool IsMSPropertySubscript = false;
-  if (base->getType()->isNonOverloadPlaceholderType()) {
+  if (base && base->getType()->isNonOverloadPlaceholderType()) {
     IsMSPropertySubscript = isMSPropertySubscriptExpr(*this, base);
     if (!IsMSPropertySubscript) {
       ExprResult result = CheckPlaceholderExpr(base);
Index: clang/lib/Sema/SemaExprCXX.cpp
===================================================================
--- clang/lib/Sema/SemaExprCXX.cpp
+++ clang/lib/Sema/SemaExprCXX.cpp
@@ -597,11 +597,11 @@
     }
   }
 
-  if (E->getType()->isVariablyModifiedType())
+  if (E && E->getType()->isVariablyModifiedType())
     return ExprError(Diag(TypeidLoc, diag::err_variably_modified_typeid)
                      << E->getType());
   else if (!inTemplateInstantiation() &&
-           E->HasSideEffects(Context, WasEvaluated)) {
+           E && E->HasSideEffects(Context, WasEvaluated)) {
     // The expression operand for typeid is in an unevaluated expression
     // context, so side effects could result in unintended consequences.
     Diag(E->getExprLoc(), WasEvaluated
Index: clang/lib/Sema/SemaExprObjC.cpp
===================================================================
--- clang/lib/Sema/SemaExprObjC.cpp
+++ clang/lib/Sema/SemaExprObjC.cpp
@@ -589,6 +589,8 @@
       }
 
       BoxingMethod = StringWithUTF8StringMethod;
+      assert(BoxingMethod && "!BoxingMethod");
+
       BoxedType = NSStringPointer;
       // Transfer the nullability from method's return type.
       Optional<NullabilityKind> Nullability =
Index: clang/lib/Sema/SemaInit.cpp
===================================================================
--- clang/lib/Sema/SemaInit.cpp
+++ clang/lib/Sema/SemaInit.cpp
@@ -5912,11 +5912,11 @@
     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: clang/lib/Sema/SemaOverload.cpp
===================================================================
--- clang/lib/Sema/SemaOverload.cpp
+++ clang/lib/Sema/SemaOverload.cpp
@@ -10413,7 +10413,8 @@
         !ToRefTy->getPointeeType()->isIncompleteType() &&
         S.IsDerivedFrom(SourceLocation(), ToRefTy->getPointeeType(), FromTy)) {
       BaseToDerivedConversion = 3;
-    } else if (ToTy->isLValueReferenceType() && !FromExpr->isLValue() &&
+    } else if (ToTy->isLValueReferenceType() && FromExpr &&
+               !FromExpr->isLValue() &&
                ToTy.getNonReferenceType().getCanonicalType() ==
                FromTy.getNonReferenceType().getCanonicalType()) {
       S.Diag(Fn->getLocation(), diag::note_ovl_candidate_bad_lvalue)
Index: clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -5186,7 +5186,7 @@
   LocalEagerInstantiationScope LocalInstantiations(*this);
 
   VarDecl *OldVar = Var;
-  if (Def->isStaticDataMember() && !Def->isOutOfLine()) {
+  if (Def && Def->isStaticDataMember() && !Def->isOutOfLine()) {
     // We're instantiating an inline static data member whose definition was
     // provided inside the class.
     InstantiateVariableInitializer(Var, Def, TemplateArgs);
Index: clang/lib/Sema/SemaTemplateVariadic.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateVariadic.cpp
+++ clang/lib/Sema/SemaTemplateVariadic.cpp
@@ -765,6 +765,8 @@
   // retain an expansion.
   if (NumPartialExpansions) {
     if (NumExpansions && *NumExpansions < *NumPartialExpansions) {
+      assert(CurrentInstantiationScope && "!CurrentInstantiationScope");
+
       NamedDecl *PartialPack =
           CurrentInstantiationScope->getPartiallySubstitutedPack();
       Diag(EllipsisLoc, diag::err_pack_expansion_length_conflict_partial)
Index: clang/lib/Sema/SemaType.cpp
===================================================================
--- clang/lib/Sema/SemaType.cpp
+++ clang/lib/Sema/SemaType.cpp
@@ -8289,7 +8289,7 @@
   // unless it's actually needed.
   if (Tag || IFace) {
     // Avoid diagnosing invalid decls as incomplete.
-    if (Def->isInvalidDecl())
+    if (Def && Def->isInvalidDecl())
       return true;
 
     // Give the external AST source a chance to complete the type.
Index: clang/lib/Sema/TreeTransform.h
===================================================================
--- clang/lib/Sema/TreeTransform.h
+++ clang/lib/Sema/TreeTransform.h
@@ -13921,7 +13921,7 @@
   }
 
   // Determine whether this should be a builtin operation.
-  if (Op == OO_Subscript) {
+  if (Op == OO_Subscript && Second) {
     if (!First->getType()->isOverloadableType() &&
         !Second->getType()->isOverloadableType())
       return getSema().CreateBuiltinArraySubscriptExpr(