diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp
@@ -34,7 +34,9 @@
     }
     if (auto *call = dyn_cast<CallExpr>(E)) {
       if (auto *memberCall = dyn_cast<CXXMemberCallExpr>(call)) {
-        if (isGetterOfRefCounted(memberCall->getMethodDecl())) {
+        Optional<bool> IsGetterOfRefCt =
+            isGetterOfRefCounted(memberCall->getMethodDecl());
+        if (IsGetterOfRefCt && *IsGetterOfRefCt) {
           E = memberCall->getImplicitObjectArgument();
           if (StopAtFirstRefCountedObj) {
             return {E, true};
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/NoUncountedMembersChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/NoUncountedMembersChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/NoUncountedMembersChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/NoUncountedMembersChecker.cpp
@@ -76,8 +76,11 @@
 
       if (auto *MemberCXXRD = MemberType->getPointeeCXXRecordDecl()) {
         // If we don't see the definition we just don't know.
-        if (MemberCXXRD->hasDefinition() && isRefCountable(MemberCXXRD))
-          reportBug(Member, MemberType, MemberCXXRD, RD);
+        if (MemberCXXRD->hasDefinition()) {
+          llvm::Optional<bool> isRCAble = isRefCountable(MemberCXXRD);
+          if (isRCAble && *isRCAble)
+            reportBug(Member, MemberType, MemberCXXRD, RD);
+        }
       }
     }
   }
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h
@@ -9,6 +9,8 @@
 #ifndef LLVM_CLANG_ANALYZER_WEBKIT_PTRTYPESEMANTICS_H
 #define LLVM_CLANG_ANALYZER_WEBKIT_PTRTYPESEMANTICS_H
 
+#include "llvm/ADT/APInt.h"
+
 namespace clang {
 class CXXBaseSpecifier;
 class CXXMethodDecl;
@@ -25,30 +27,31 @@
 // Ref<T>.
 
 /// \returns CXXRecordDecl of the base if the type is ref-countable, nullptr if
-/// not.
-const clang::CXXRecordDecl *isRefCountable(const clang::CXXBaseSpecifier *Base);
+/// not, None if inconclusive.
+llvm::Optional<const clang::CXXRecordDecl *>
+isRefCountable(const clang::CXXBaseSpecifier *Base);
 
-/// \returns true if \p Class is ref-countable, false if not.
-/// Asserts that \p Class IS a definition.
-bool isRefCountable(const clang::CXXRecordDecl *Class);
+/// \returns true if \p Class is ref-countable, false if not, None if
+/// inconclusive.
+llvm::Optional<bool> isRefCountable(const clang::CXXRecordDecl *Class);
 
 /// \returns true if \p Class is ref-counted, false if not.
 bool isRefCounted(const clang::CXXRecordDecl *Class);
 
 /// \returns true if \p Class is ref-countable AND not ref-counted, false if
-/// not. Asserts that \p Class IS a definition.
-bool isUncounted(const clang::CXXRecordDecl *Class);
+/// not, None if inconclusive.
+llvm::Optional<bool> isUncounted(const clang::CXXRecordDecl *Class);
 
 /// \returns true if \p T is either a raw pointer or reference to an uncounted
-/// class, false if not.
-bool isUncountedPtr(const clang::Type *T);
+/// class, false if not, None if inconclusive.
+llvm::Optional<bool> isUncountedPtr(const clang::Type *T);
 
 /// \returns true if \p F creates ref-countable object from uncounted parameter,
 /// false if not.
 bool isCtorOfRefCounted(const clang::FunctionDecl *F);
 
 /// \returns true if \p M is getter of a ref-counted class, false if not.
-bool isGetterOfRefCounted(const clang::CXXMethodDecl *Method);
+llvm::Optional<bool> isGetterOfRefCounted(const clang::CXXMethodDecl *Method);
 
 /// \returns true if \p F is a conversion between ref-countable or ref-counted
 /// pointer types.
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
@@ -12,6 +12,7 @@
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/ExprCXX.h"
+#include "llvm/ADT/Optional.h"
 
 using llvm::Optional;
 using namespace clang;
@@ -20,6 +21,7 @@
 
 bool hasPublicRefAndDeref(const CXXRecordDecl *R) {
   assert(R);
+  assert(R->hasDefinition());
 
   bool hasRef = false;
   bool hasDeref = false;
@@ -43,25 +45,29 @@
 
 namespace clang {
 
-const CXXRecordDecl *isRefCountable(const CXXBaseSpecifier *Base) {
+llvm::Optional<const clang::CXXRecordDecl *>
+isRefCountable(const CXXBaseSpecifier *Base) {
   assert(Base);
 
   const Type *T = Base->getType().getTypePtrOrNull();
   if (!T)
-    return nullptr;
+    return llvm::None;
 
   const CXXRecordDecl *R = T->getAsCXXRecordDecl();
   if (!R)
-    return nullptr;
+    return llvm::None;
+  if (!R->hasDefinition())
+    return llvm::None;
 
   return hasPublicRefAndDeref(R) ? R : nullptr;
 }
 
-bool isRefCountable(const CXXRecordDecl *R) {
+llvm::Optional<bool> isRefCountable(const CXXRecordDecl *R) {
   assert(R);
 
   R = R->getDefinition();
-  assert(R);
+  if (!R)
+    return llvm::None;
 
   if (hasPublicRefAndDeref(R))
     return true;
@@ -69,13 +75,24 @@
   CXXBasePaths Paths;
   Paths.setOrigin(const_cast<CXXRecordDecl *>(R));
 
-  const auto isRefCountableBase = [](const CXXBaseSpecifier *Base,
-                                     CXXBasePath &) {
-    return clang::isRefCountable(Base);
-  };
+  bool AnyInconclusiveBase = false;
+  const auto isRefCountableBase =
+      [&AnyInconclusiveBase](const CXXBaseSpecifier *Base, CXXBasePath &) {
+        Optional<const clang::CXXRecordDecl *> IsRefCountable =
+            clang::isRefCountable(Base);
+        if (!IsRefCountable) {
+          AnyInconclusiveBase = true;
+          return false;
+        }
+        return (*IsRefCountable) != nullptr;
+      };
+
+  bool BasesResult = R->lookupInBases(isRefCountableBase, Paths,
+                                      /*LookupInDependent =*/true);
+  if (AnyInconclusiveBase)
+    return llvm::None;
 
-  return R->lookupInBases(isRefCountableBase, Paths,
-                          /*LookupInDependent =*/true);
+  return BasesResult;
 }
 
 bool isCtorOfRefCounted(const clang::FunctionDecl *F) {
@@ -95,12 +112,19 @@
          || FunctionName == "Identifier";
 }
 
-bool isUncounted(const CXXRecordDecl *Class) {
+llvm::Optional<bool> isUncounted(const CXXRecordDecl *Class) {
   // Keep isRefCounted first as it's cheaper.
-  return !isRefCounted(Class) && isRefCountable(Class);
+  if (isRefCounted(Class))
+    return false;
+
+  llvm::Optional<bool> IsRefCountable = isRefCountable(Class);
+  if (!IsRefCountable)
+    return llvm::None;
+
+  return (*IsRefCountable);
 }
 
-bool isUncountedPtr(const Type *T) {
+llvm::Optional<bool> isUncountedPtr(const Type *T) {
   assert(T);
 
   if (T->isPointerType() || T->isReferenceType()) {
@@ -111,7 +135,7 @@
   return false;
 }
 
-bool isGetterOfRefCounted(const CXXMethodDecl *M) {
+Optional<bool> isGetterOfRefCounted(const CXXMethodDecl *M) {
   assert(M);
 
   if (isa<CXXMethodDecl>(M)) {
@@ -133,9 +157,7 @@
       if (auto *maybeRefToRawOperator = dyn_cast<CXXConversionDecl>(M)) {
         if (auto *targetConversionType =
                 maybeRefToRawOperator->getConversionType().getTypePtrOrNull()) {
-          if (isUncountedPtr(targetConversionType)) {
-            return true;
-          }
+          return isUncountedPtr(targetConversionType);
         }
       }
     }
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp
@@ -76,19 +76,15 @@
               (AccSpec == AS_none && RD->isClass()))
             return false;
 
-          llvm::Optional<const clang::CXXRecordDecl *> MaybeRefCntblBaseRD =
+          llvm::Optional<const CXXRecordDecl *> RefCntblBaseRD =
               isRefCountable(Base);
-          if (!MaybeRefCntblBaseRD.hasValue())
+          if (!RefCntblBaseRD || !(*RefCntblBaseRD))
             return false;
 
-          const CXXRecordDecl *RefCntblBaseRD = MaybeRefCntblBaseRD.getValue();
-          if (!RefCntblBaseRD)
-            return false;
-
-          const auto *Dtor = RefCntblBaseRD->getDestructor();
+          const auto *Dtor = (*RefCntblBaseRD)->getDestructor();
           if (!Dtor || !Dtor->isVirtual()) {
             ProblematicBaseSpecifier = Base;
-            ProblematicBaseClass = RefCntblBaseRD;
+            ProblematicBaseClass = *RefCntblBaseRD;
             return true;
           }
 
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedCallArgsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedCallArgsChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedCallArgsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedCallArgsChecker.cpp
@@ -86,7 +86,8 @@
           continue; // FIXME? Should we bail?
 
         // FIXME: more complex types (arrays, references to raw pointers, etc)
-        if (!isUncountedPtr(ArgType))
+        Optional<bool> IsUncounted = isUncountedPtr(ArgType);
+        if (!IsUncounted || !(*IsUncounted))
           continue;
 
         const auto *Arg = CE->getArg(ArgIdx);
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
@@ -59,7 +59,8 @@
       if (C.capturesVariable()) {
         VarDecl *CapturedVar = C.getCapturedVar();
         if (auto *CapturedVarType = CapturedVar->getType().getTypePtrOrNull()) {
-          if (isUncountedPtr(CapturedVarType)) {
+          Optional<bool> IsUncountedPtr = isUncountedPtr(CapturedVarType);
+          if (IsUncountedPtr && *IsUncountedPtr) {
             reportBug(C, CapturedVar, CapturedVarType);
           }
         }
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLocalVarsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLocalVarsChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLocalVarsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLocalVarsChecker.cpp
@@ -169,7 +169,8 @@
     if (!ArgType)
       return;
 
-    if (isUncountedPtr(ArgType)) {
+    Optional<bool> IsUncountedPtr = isUncountedPtr(ArgType);
+    if (IsUncountedPtr && *IsUncountedPtr) {
       const Expr *const InitExpr = V->getInit();
       if (!InitExpr)
         return; // FIXME: later on we might warn on uninitialized vars too