diff --git a/include/clang/AST/ExprCXX.h b/include/clang/AST/ExprCXX.h
index 7665dbc..cc12d05 100644
--- a/include/clang/AST/ExprCXX.h
+++ b/include/clang/AST/ExprCXX.h
@@ -3373,7 +3373,7 @@
     if (NumExpansions)
       return NumExpansions - 1;
 
-    return Optional<unsigned>();
+    return None;
   }
 
   SourceLocation getLocStart() const LLVM_READONLY {
diff --git a/include/clang/AST/ExprObjC.h b/include/clang/AST/ExprObjC.h
index 2b88dfd..b6bf006 100644
--- a/include/clang/AST/ExprObjC.h
+++ b/include/clang/AST/ExprObjC.h
@@ -300,8 +300,7 @@
   ObjCDictionaryElement getKeyValueElement(unsigned Index) const {
     assert((Index < NumElements) && "Arg access out of range!");
     const KeyValuePair &KV = getKeyValues()[Index];
-    ObjCDictionaryElement Result = { KV.Key, KV.Value, SourceLocation(),
-                                     Optional<unsigned>() };
+    ObjCDictionaryElement Result = { KV.Key, KV.Value, SourceLocation(), None };
     if (HasPackExpansions) {
       const ExpansionData &Expansion = getExpansionData()[Index];
       Result.EllipsisLoc = Expansion.EllipsisLoc;
diff --git a/include/clang/AST/Type.h b/include/clang/AST/Type.h
index f0a7ae8..2026b22 100644
--- a/include/clang/AST/Type.h
+++ b/include/clang/AST/Type.h
@@ -4155,7 +4155,7 @@
     if (NumExpansions)
       return NumExpansions - 1;
 
-    return Optional<unsigned>();
+    return None;
   }
 
   bool isSugared() const { return false; }
diff --git a/include/clang/Basic/LLVM.h b/include/clang/Basic/LLVM.h
index abeec15..eb47597 100644
--- a/include/clang/Basic/LLVM.h
+++ b/include/clang/Basic/LLVM.h
@@ -16,9 +16,13 @@
 #ifndef CLANG_BASIC_LLVM_H
 #define CLANG_BASIC_LLVM_H
 
-// This should be the only #include, force #includes of all the others on
-// clients.
+// Do not proliferate #includes here, require clients to #include their
+// dependencies.
+// Casting.h has complex templates that cannot be easily forward declared.
 #include "llvm/Support/Casting.h"
+// None.h includes an enumerant that is desired & cannot be forward declared
+// without a definition of NoneType.
+#include "llvm/ADT/None.h"
 
 namespace llvm {
   // ADT's.
@@ -54,6 +58,7 @@
   using llvm::cast_or_null;
   
   // ADT's.
+  using llvm::None;
   using llvm::Optional;
   using llvm::StringRef;
   using llvm::Twine;
diff --git a/include/clang/Basic/VersionTuple.h b/include/clang/Basic/VersionTuple.h
index 059b7f7..ff06a5c 100644
--- a/include/clang/Basic/VersionTuple.h
+++ b/include/clang/Basic/VersionTuple.h
@@ -57,14 +57,14 @@
   /// \brief Retrieve the minor version number, if provided.
   Optional<unsigned> getMinor() const {
     if (!HasMinor)
-      return Optional<unsigned>();
+      return None;
     return Minor;
   }
 
   /// \brief Retrieve the subminor version number, if provided.
   Optional<unsigned> getSubminor() const {
     if (!HasSubminor)
-      return Optional<unsigned>();
+      return None;
     return Subminor;
   }
 
diff --git a/include/clang/Lex/PreprocessingRecord.h b/include/clang/Lex/PreprocessingRecord.h
index 926da52..535e0ca 100644
--- a/include/clang/Lex/PreprocessingRecord.h
+++ b/include/clang/Lex/PreprocessingRecord.h
@@ -279,7 +279,7 @@
     /// entity with index \p Index came from file \p FID.
     virtual Optional<bool> isPreprocessedEntityInFileID(unsigned Index,
                                                         FileID FID) {
-      return Optional<bool>();
+      return None;
     }
   };
   
diff --git a/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h b/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h
index 0e0108c..31d02f5 100644
--- a/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h
+++ b/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h
@@ -85,7 +85,7 @@
   template<typename T>
   Optional<T> getAs() const {
     if (!T::isKind(*this))
-      return Optional<T>();
+      return None;
     T t;
     SVal& sv = t;
     sv = *this;
diff --git a/lib/AST/ASTImporter.cpp b/lib/AST/ASTImporter.cpp
index 98ef237..bdf2bbc 100644
--- a/lib/AST/ASTImporter.cpp
+++ b/lib/AST/ASTImporter.cpp
@@ -908,7 +908,7 @@
 
   RecordDecl *Owner = dyn_cast<RecordDecl>(Anon->getDeclContext());
   if (!Owner)
-    return Optional<unsigned>();
+    return None;
 
   unsigned Index = 0;
   for (DeclContext::decl_iterator D = Owner->noload_decls_begin(),
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 3ce2f44..3124261 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -180,7 +180,7 @@
         return DefaultVisibility;
   }
 
-  return Optional<Visibility>();
+  return None;
 }
 
 static LinkageInfo getLVForType(QualType T) {
@@ -893,7 +893,7 @@
         return getVisibilityOf(InstantiatedFrom, kind);
     }
 
-    return Optional<Visibility>();
+    return None;
   }
   // Use the most recent declaration of a function, and also handle
   // function template specializations.
@@ -914,7 +914,7 @@
     if (InstantiatedFrom)
       return getVisibilityOf(InstantiatedFrom, kind);
 
-    return Optional<Visibility>();
+    return None;
   }
 
   // Otherwise, just check the declaration itself first.
@@ -941,7 +941,7 @@
       return getVisibilityOf(InstantiatedFrom, kind);
   }
 
-  return Optional<Visibility>();
+  return None;
 }
 
 static LinkageInfo getLVForLocalDecl(const NamedDecl *D,
diff --git a/lib/AST/DeclTemplate.cpp b/lib/AST/DeclTemplate.cpp
index 49ef5a3..5e25536 100644
--- a/lib/AST/DeclTemplate.cpp
+++ b/lib/AST/DeclTemplate.cpp
@@ -184,7 +184,7 @@
     if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(*Param)) {
       QualType ArgType = Context.getTypeDeclType(TTP);
       if (TTP->isParameterPack())
-        ArgType = Context.getPackExpansionType(ArgType, Optional<unsigned>());
+        ArgType = Context.getPackExpansionType(ArgType, None);
 
       Arg = TemplateArgument(ArgType);
     } else if (NonTypeTemplateParmDecl *NTTP =
@@ -195,8 +195,8 @@
                                           NTTP->getLocation());
       
       if (NTTP->isParameterPack())
-        E = new (Context) PackExpansionExpr(
-            Context.DependentTy, E, NTTP->getLocation(), Optional<unsigned>());
+        E = new (Context) PackExpansionExpr(Context.DependentTy, E,
+                                            NTTP->getLocation(), None);
       Arg = TemplateArgument(E);
     } else {
       TemplateTemplateParmDecl *TTP = cast<TemplateTemplateParmDecl>(*Param);
diff --git a/lib/AST/NSAPI.cpp b/lib/AST/NSAPI.cpp
index b06769e..a862630 100644
--- a/lib/AST/NSAPI.cpp
+++ b/lib/AST/NSAPI.cpp
@@ -75,7 +75,7 @@
       return MK;
   }
 
-  return Optional<NSStringMethodKind>();
+  return None;
 }
 
 Selector NSAPI::getNSArraySelector(NSArrayMethodKind MK) const {
@@ -133,7 +133,7 @@
       return MK;
   }
 
-  return Optional<NSArrayMethodKind>();
+  return None;
 }
 
 Selector NSAPI::getNSDictionarySelector(
@@ -219,7 +219,7 @@
       return MK;
   }
 
-  return Optional<NSDictionaryMethodKind>();
+  return None;
 }
 
 Selector NSAPI::getNSNumberLiteralSelector(NSNumberLiteralMethodKind MK,
@@ -282,14 +282,14 @@
       return MK;
   }
 
-  return Optional<NSNumberLiteralMethodKind>();
+  return None;
 }
 
 Optional<NSAPI::NSNumberLiteralMethodKind>
 NSAPI::getNSNumberFactoryMethodKind(QualType T) const {
   const BuiltinType *BT = T->getAs<BuiltinType>();
   if (!BT)
-    return Optional<NSAPI::NSNumberLiteralMethodKind>();
+    return None;
 
   const TypedefType *TDT = T->getAs<TypedefType>();
   if (TDT) {
@@ -363,7 +363,7 @@
     break;
   }
   
-  return Optional<NSAPI::NSNumberLiteralMethodKind>();
+  return None;
 }
 
 /// \brief Returns true if \param T is a typedef of "BOOL" in objective-c.
diff --git a/lib/AST/TemplateBase.cpp b/lib/AST/TemplateBase.cpp
index 520ca25..2b50681 100644
--- a/lib/AST/TemplateBase.cpp
+++ b/lib/AST/TemplateBase.cpp
@@ -229,7 +229,7 @@
   if (TemplateArg.NumExpansions)
     return TemplateArg.NumExpansions - 1;
   
-  return Optional<unsigned>();
+  return None; 
 }
 
 void TemplateArgument::Profile(llvm::FoldingSetNodeID &ID,
diff --git a/lib/Analysis/FormatString.cpp b/lib/Analysis/FormatString.cpp
index 10bb9f3..ad0dce4 100644
--- a/lib/Analysis/FormatString.cpp
+++ b/lib/Analysis/FormatString.cpp
@@ -533,7 +533,7 @@
   
   switch (getKind()) {
   default:
-    return Optional<ConversionSpecifier>();
+    return None;
   case DArg:
     NewKind = dArg;
     break;
@@ -766,7 +766,7 @@
     }
   }
 
-  return Optional<LengthModifier>();
+  return None;
 }
 
 bool FormatSpecifier::namedTypeToLengthModifier(QualType QT,
diff --git a/lib/Analysis/UninitializedValues.cpp b/lib/Analysis/UninitializedValues.cpp
index cf2533c..13af435 100644
--- a/lib/Analysis/UninitializedValues.cpp
+++ b/lib/Analysis/UninitializedValues.cpp
@@ -77,7 +77,7 @@
 Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
   llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
   if (I == map.end())
-    return Optional<unsigned>();
+    return None;
   return I->second;
 }
 
diff --git a/lib/Basic/SourceManager.cpp b/lib/Basic/SourceManager.cpp
index 550e82c..901d3a6 100644
--- a/lib/Basic/SourceManager.cpp
+++ b/lib/Basic/SourceManager.cpp
@@ -1462,11 +1462,11 @@
 /// in non-performance-critical code.
 static Optional<ino_t> getActualFileInode(const FileEntry *File) {
   if (!File)
-    return Optional<ino_t>();
+    return None;
   
   struct stat StatBuf;
   if (::stat(File->getName(), &StatBuf))
-    return Optional<ino_t>();
+    return None;
     
   return StatBuf.st_ino;
 }
diff --git a/lib/Parse/ParseObjc.cpp b/lib/Parse/ParseObjc.cpp
index 27eeb05..ddb6a70 100644
--- a/lib/Parse/ParseObjc.cpp
+++ b/lib/Parse/ParseObjc.cpp
@@ -2730,7 +2730,7 @@
     // We have a valid expression. Collect it in a vector so we can
     // build the argument list.
     ObjCDictionaryElement Element = { 
-      KeyExpr.get(), ValueExpr.get(), EllipsisLoc, Optional<unsigned>()
+      KeyExpr.get(), ValueExpr.get(), EllipsisLoc, None 
     };
     Elements.push_back(Element);
     
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index c3e3149..61fd826 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -3036,7 +3036,7 @@
       return TTP->getNumExpansionTemplateParameters();
   }
 
-  return Optional<unsigned>();
+  return None;
 }
 
 /// \brief Check that the given template argument list is well-formed
diff --git a/lib/Sema/SemaTemplateInstantiate.cpp b/lib/Sema/SemaTemplateInstantiate.cpp
index bbf2a98..c8f0372 100644
--- a/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/lib/Sema/SemaTemplateInstantiate.cpp
@@ -628,7 +628,7 @@
     case ActiveTemplateInstantiation::DefaultFunctionArgumentInstantiation:
     case ActiveTemplateInstantiation::ExceptionSpecInstantiation:
       // This is a template instantiation, so there is no SFINAE.
-      return Optional<TemplateDeductionInfo *>();
+      return None;
 
     case ActiveTemplateInstantiation::DefaultTemplateArgumentInstantiation:
     case ActiveTemplateInstantiation::PriorTemplateArgumentSubstitution:
@@ -647,7 +647,7 @@
     }
   }
 
-  return Optional<TemplateDeductionInfo *>();
+  return None;
 }
 
 /// \brief Retrieve the depth and index of a parameter pack.
diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index b971a04..1515a35 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1638,9 +1638,8 @@
 }
 
 ParmVarDecl *TemplateDeclInstantiator::VisitParmVarDecl(ParmVarDecl *D) {
-  return SemaRef.SubstParmVarDecl(D, TemplateArgs, /*indexAdjustment*/ 0,
-                                  Optional<unsigned>(),
-                                  /*ExpectParameterPack=*/false);
+  return SemaRef.SubstParmVarDecl(D, TemplateArgs, /*indexAdjustment*/ 0, None,
+                                  /*ExpectParameterPack=*/ false);
 }
 
 Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
diff --git a/lib/Sema/SemaTemplateVariadic.cpp b/lib/Sema/SemaTemplateVariadic.cpp
index 2cff7aa..c0ad2be 100644
--- a/lib/Sema/SemaTemplateVariadic.cpp
+++ b/lib/Sema/SemaTemplateVariadic.cpp
@@ -443,8 +443,7 @@
   if (!TSInfo)
     return true;
 
-  TypeSourceInfo *TSResult =
-      CheckPackExpansion(TSInfo, EllipsisLoc, Optional<unsigned>());
+  TypeSourceInfo *TSResult = CheckPackExpansion(TSInfo, EllipsisLoc, None);
   if (!TSResult)
     return true;
   
@@ -490,7 +489,7 @@
 }
 
 ExprResult Sema::ActOnPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc) {
-  return CheckPackExpansion(Pattern, EllipsisLoc, Optional<unsigned>());
+  return CheckPackExpansion(Pattern, EllipsisLoc, None);
 }
 
 ExprResult Sema::CheckPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc,
@@ -662,7 +661,7 @@
         if (Instantiation->is<Decl*>())
           // The pattern refers to an unexpanded pack. We're not ready to expand
           // this pack yet.
-          return Optional<unsigned>();
+          return None;
 
         unsigned Size = Instantiation->get<DeclArgumentPack *>()->size();
         assert((!Result || *Result == Size) && "inconsistent pack sizes");
@@ -676,7 +675,7 @@
         !TemplateArgs.hasTemplateArgument(Depth, Index))
       // The pattern refers to an unknown template argument. We're not ready to
       // expand this pack yet.
-      return Optional<unsigned>();
+      return None;
     
     // Determine the size of the argument pack.
     unsigned Size = TemplateArgs(Depth, Index).pack_size();
diff --git a/lib/Sema/SemaType.cpp b/lib/Sema/SemaType.cpp
index d4d42cd..209699f 100644
--- a/lib/Sema/SemaType.cpp
+++ b/lib/Sema/SemaType.cpp
@@ -2889,7 +2889,7 @@
           << T <<  D.getSourceRange();
         D.setEllipsisLoc(SourceLocation());
       } else {
-        T = Context.getPackExpansionType(T, Optional<unsigned>());
+        T = Context.getPackExpansionType(T, None);
       }
       break;
 
@@ -2903,7 +2903,7 @@
       // parameter packs in the type of the non-type template parameter, then
       // it expands those parameter packs.
       if (T->containsUnexpandedParameterPack())
-        T = Context.getPackExpansionType(T, Optional<unsigned>());
+        T = Context.getPackExpansionType(T, None);
       else
         S.Diag(D.getEllipsisLoc(),
                LangOpts.CPlusPlus11
diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index 0832a24..438d06a 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -4098,8 +4098,7 @@
                                                   /*ExpectParameterPack=*/true);
       } else {
         NewParm = getDerived().TransformFunctionTypeParam(
-            OldParm, indexAdjustment, Optional<unsigned>(),
-            /*ExpectParameterPack=*/ false);
+            OldParm, indexAdjustment, None, /*ExpectParameterPack=*/ false);
       }
 
       if (!NewParm)
@@ -8565,7 +8564,7 @@
       ArgChanged = true;
 
     ObjCDictionaryElement Element = {
-      Key.get(), Value.get(), SourceLocation(), Optional<unsigned>()
+      Key.get(), Value.get(), SourceLocation(), None
     };
     Elements.push_back(Element);
   }
diff --git a/lib/StaticAnalyzer/Checkers/BasicObjCFoundationChecks.cpp b/lib/StaticAnalyzer/Checkers/BasicObjCFoundationChecks.cpp
index ae33a8a..85b9305 100644
--- a/lib/StaticAnalyzer/Checkers/BasicObjCFoundationChecks.cpp
+++ b/lib/StaticAnalyzer/Checkers/BasicObjCFoundationChecks.cpp
@@ -217,7 +217,7 @@
     case kCFNumberCGFloatType:
       // FIXME: We need a way to map from names to Type*.
     default:
-      return Optional<uint64_t>();
+      return None;
   }
 
   return Ctx.getTypeSize(T);
diff --git a/lib/StaticAnalyzer/Core/PathDiagnostic.cpp b/lib/StaticAnalyzer/Core/PathDiagnostic.cpp
index bbf2db3..69a4e27 100644
--- a/lib/StaticAnalyzer/Core/PathDiagnostic.cpp
+++ b/lib/StaticAnalyzer/Core/PathDiagnostic.cpp
@@ -225,7 +225,7 @@
   FullSourceLoc YEL = Y.getEndLocation().asLocation();
   if (XEL != YEL)
     return XEL.isBeforeInTranslationUnitThan(YEL);
-  return Optional<bool>();
+  return None;
 }
 
 static Optional<bool> compareMacro(const PathDiagnosticMacroPiece &X,
@@ -283,7 +283,7 @@
       return compareControlFlow(cast<PathDiagnosticControlFlowPiece>(X),
                                 cast<PathDiagnosticControlFlowPiece>(Y));
     case clang::ento::PathDiagnosticPiece::Event:
-      return Optional<bool>();
+      return None;
     case clang::ento::PathDiagnosticPiece::Macro:
       return compareMacro(cast<PathDiagnosticMacroPiece>(X),
                           cast<PathDiagnosticMacroPiece>(Y));
@@ -302,7 +302,7 @@
     if (b.hasValue())
       return b.getValue();
   }
-  return Optional<bool>();
+  return None;
 }
 
 static bool compare(const PathDiagnostic &X, const PathDiagnostic &Y) {
diff --git a/lib/StaticAnalyzer/Core/RegionStore.cpp b/lib/StaticAnalyzer/Core/RegionStore.cpp
index 3bd624b..09bbcef 100644
--- a/lib/StaticAnalyzer/Core/RegionStore.cpp
+++ b/lib/StaticAnalyzer/Core/RegionStore.cpp
@@ -227,7 +227,7 @@
 Optional<SVal> RegionBindingsRef::getDirectBinding(const MemRegion *R) const {
   if (const SVal *V = lookup(R, BindingKey::Direct))
     return *V;
-  return Optional<SVal>();
+  return None;
 }
 
 Optional<SVal> RegionBindingsRef::getDefaultBinding(const MemRegion *R) const {
@@ -237,7 +237,7 @@
         return UnknownVal();
   if (const SVal *V = lookup(R, BindingKey::Default))
     return *V;
-  return Optional<SVal>();
+  return None;
 }
 
 RegionBindingsRef RegionBindingsRef::addBinding(BindingKey K, SVal V) const {
@@ -1448,12 +1448,12 @@
 
     // Lazy bindings are handled later.
     if (val.getAs<nonloc::LazyCompoundVal>())
-      return Optional<SVal>();
+      return None;
 
     llvm_unreachable("Unknown default value");
   }
 
-  return Optional<SVal>();
+  return None;
 }
 
 SVal RegionStoreManager::getLazyBinding(const SubRegion *LazyBindingRegion,
@@ -1574,11 +1574,11 @@
 static Optional<SVal> getConstValue(SValBuilder &SVB, const VarDecl *VD) {
   ASTContext &Ctx = SVB.getContext();
   if (!VD->getType().isConstQualified())
-    return Optional<SVal>();
+    return None;
 
   const Expr *Init = VD->getInit();
   if (!Init)
-    return Optional<SVal>();
+    return None;
 
   llvm::APSInt Result;
   if (Init->EvaluateAsInt(Result, Ctx))
@@ -1588,7 +1588,7 @@
     return SVB.makeNull();
 
   // FIXME: Handle other possible constant expressions.
-  return Optional<SVal>();
+  return None;
 }
 
 SVal RegionStoreManager::getBindingForVar(RegionBindingsConstRef B,
diff --git a/tools/libclang/CIndex.cpp b/tools/libclang/CIndex.cpp
index 8cbb172..669bb87 100644
--- a/tools/libclang/CIndex.cpp
+++ b/tools/libclang/CIndex.cpp
@@ -561,12 +561,12 @@
   if (RegionOfInterest.isValid()) {
     SourceRange Range = getFullCursorExtent(Cursor, AU->getSourceManager());
     if (Range.isInvalid())
-      return Optional<bool>();
+      return None;
     
     switch (CompareRegionOfInterest(Range)) {
     case RangeBefore:
       // This declaration comes before the region of interest; skip it.
-      return Optional<bool>();
+      return None;
 
     case RangeAfter:
       // This declaration comes after the region of interest; we're done.