diff --git a/clang/include/clang/Analysis/Analyses/PostOrderCFGView.h b/clang/include/clang/Analysis/Analyses/PostOrderCFGView.h
index 0b306d14be4d8..8964481ee66c5 100644
--- a/clang/include/clang/Analysis/Analyses/PostOrderCFGView.h
+++ b/clang/include/clang/Analysis/Analyses/PostOrderCFGView.h
@@ -54,11 +54,12 @@ class PostOrderCFGView : public ManagedAnalysis {
       // occasionally hand out null pointers for pruned edges, so we catch those
       // here.
       if (!Block)
-        return std::make_pair(None, false); // if an edge is trivially false.
+        return std::make_pair(std::nullopt,
+                              false); // if an edge is trivially false.
       if (VisitedBlockIDs.test(Block->getBlockID()))
-        return std::make_pair(None, false);
+        return std::make_pair(std::nullopt, false);
       VisitedBlockIDs.set(Block->getBlockID());
-      return std::make_pair(None, true);
+      return std::make_pair(std::nullopt, true);
     }
 
     /// Check if the bit for a CFGBlock has been already set.
diff --git a/clang/include/clang/Analysis/Analyses/ThreadSafetyTIL.h b/clang/include/clang/Analysis/Analyses/ThreadSafetyTIL.h
index 48593516d8534..385cd02f882c0 100644
--- a/clang/include/clang/Analysis/Analyses/ThreadSafetyTIL.h
+++ b/clang/include/clang/Analysis/Analyses/ThreadSafetyTIL.h
@@ -1464,7 +1464,7 @@ class Return : public Terminator {
   static bool classof(const SExpr *E) { return E->opcode() == COP_Return; }
 
   /// Return an empty list.
-  ArrayRef<BasicBlock *> successors() { return None; }
+  ArrayRef<BasicBlock *> successors() { return std::nullopt; }
 
   SExpr *returnValue() { return Retval; }
   const SExpr *returnValue() const { return Retval; }
@@ -1490,7 +1490,7 @@ inline ArrayRef<BasicBlock*> Terminator::successors() {
     case COP_Branch: return cast<Branch>(this)->successors();
     case COP_Return: return cast<Return>(this)->successors();
     default:
-      return None;
+      return std::nullopt;
   }
 }
 
diff --git a/clang/include/clang/Analysis/AnyCall.h b/clang/include/clang/Analysis/AnyCall.h
index 6e5e019ce2632..876d423a21f2d 100644
--- a/clang/include/clang/Analysis/AnyCall.h
+++ b/clang/include/clang/Analysis/AnyCall.h
@@ -123,7 +123,7 @@ class AnyCall {
     } else if (const auto *CXCIE = dyn_cast<CXXInheritedCtorInitExpr>(E)) {
       return AnyCall(CXCIE);
     } else {
-      return None;
+      return std::nullopt;
     }
   }
 
@@ -136,13 +136,13 @@ class AnyCall {
     } else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
       return AnyCall(MD);
     }
-    return None;
+    return std::nullopt;
   }
 
   /// \returns formal parameters for direct calls (including virtual calls)
   ArrayRef<ParmVarDecl *> parameters() const {
     if (!D)
-      return None;
+      return std::nullopt;
 
     if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
       return FD->parameters();
@@ -151,7 +151,7 @@ class AnyCall {
     } else if (const auto *BD = dyn_cast<BlockDecl>(D)) {
       return BD->parameters();
     } else {
-      return None;
+      return std::nullopt;
     }
   }
 
diff --git a/clang/include/clang/Analysis/CFG.h b/clang/include/clang/Analysis/CFG.h
index f3e005b890662..ecf5906fa1dca 100644
--- a/clang/include/clang/Analysis/CFG.h
+++ b/clang/include/clang/Analysis/CFG.h
@@ -108,7 +108,7 @@ class CFGElement {
   template<typename T>
   Optional<T> getAs() const {
     if (!T::isKind(*this))
-      return None;
+      return std::nullopt;
     T t;
     CFGElement& e = t;
     e = *this;
diff --git a/clang/include/clang/Analysis/ProgramPoint.h b/clang/include/clang/Analysis/ProgramPoint.h
index 680713a52f2f0..81a1288f61c7b 100644
--- a/clang/include/clang/Analysis/ProgramPoint.h
+++ b/clang/include/clang/Analysis/ProgramPoint.h
@@ -149,7 +149,7 @@ class ProgramPoint {
   template<typename T>
   Optional<T> getAs() const {
     if (!T::isKind(*this))
-      return None;
+      return std::nullopt;
     T t;
     ProgramPoint& PP = t;
     PP = *this;
diff --git a/clang/lib/Analysis/BodyFarm.cpp b/clang/lib/Analysis/BodyFarm.cpp
index 38f100ae0a4fc..b242008865cc4 100644
--- a/clang/lib/Analysis/BodyFarm.cpp
+++ b/clang/lib/Analysis/BodyFarm.cpp
@@ -541,7 +541,7 @@ static Stmt *create_dispatch_once(ASTContext &C, const FunctionDecl *D) {
   CallExpr *CE = CallExpr::Create(
       /*ASTContext=*/C,
       /*StmtClass=*/M.makeLvalueToRvalue(/*Expr=*/Block),
-      /*Args=*/None,
+      /*Args=*/std::nullopt,
       /*QualType=*/C.VoidTy,
       /*ExprValueType=*/VK_PRValue,
       /*SourceLocation=*/SourceLocation(), FPOptionsOverride());
@@ -609,7 +609,7 @@ static Stmt *create_dispatch_sync(ASTContext &C, const FunctionDecl *D) {
   ASTMaker M(C);
   DeclRefExpr *DR = M.makeDeclRefExpr(PV);
   ImplicitCastExpr *ICE = M.makeLvalueToRvalue(DR, Ty);
-  CallExpr *CE = CallExpr::Create(C, ICE, None, C.VoidTy, VK_PRValue,
+  CallExpr *CE = CallExpr::Create(C, ICE, std::nullopt, C.VoidTy, VK_PRValue,
                                   SourceLocation(), FPOptionsOverride());
   return CE;
 }
diff --git a/clang/lib/Analysis/CFG.cpp b/clang/lib/Analysis/CFG.cpp
index 233af415b71e0..c3b774fafadfb 100644
--- a/clang/lib/Analysis/CFG.cpp
+++ b/clang/lib/Analysis/CFG.cpp
@@ -1044,14 +1044,14 @@ class CFGBuilder {
           return llvm::APInt(Context->getTypeSize(Context->IntTy), !Value);
         default:
           assert(false && "Unexpected unary operator!");
-          return llvm::None;
+          return std::nullopt;
         }
       }
     } else if (const auto *IntLiteral =
                    dyn_cast<IntegerLiteral>(E->IgnoreParens()))
       return IntLiteral->getValue();
 
-    return llvm::None;
+    return std::nullopt;
   }
 
   TryResult analyzeLogicOperatorCondition(BinaryOperatorKind Relation,
diff --git a/clang/lib/Analysis/CalledOnceCheck.cpp b/clang/lib/Analysis/CalledOnceCheck.cpp
index ce760d22405e6..705a736861986 100644
--- a/clang/lib/Analysis/CalledOnceCheck.cpp
+++ b/clang/lib/Analysis/CalledOnceCheck.cpp
@@ -513,7 +513,7 @@ class NotCalledClarifier
     if (const Stmt *Terminator = Conditional->getTerminatorStmt()) {
       return NotCalledClarifier{Conditional, SuccWithoutCall}.Visit(Terminator);
     }
-    return llvm::None;
+    return std::nullopt;
   }
 
   llvm::Optional<Clarification> VisitIfStmt(const IfStmt *If) {
@@ -563,7 +563,7 @@ class NotCalledClarifier
 
   llvm::Optional<Clarification> VisitBinaryOperator(const BinaryOperator *) {
     // We don't want to report on short-curcuit logical operations.
-    return llvm::None;
+    return std::nullopt;
   }
 
   llvm::Optional<Clarification> VisitStmt(const Stmt *Terminator) {
@@ -1008,7 +1008,7 @@ class CalledOnceChecker : public ConstStmtVisitor<CalledOnceChecker> {
 
       return A->getCompletionHandlerIndex().getASTIndex() == ParamIndex;
     }
-    return llvm::None;
+    return std::nullopt;
   }
 
   /// Return true if the specified selector represents init method.
@@ -1644,7 +1644,7 @@ class CalledOnceChecker : public ConstStmtVisitor<CalledOnceChecker> {
       return getIndex(*Parameter);
     }
 
-    return llvm::None;
+    return std::nullopt;
   }
 
   llvm::Optional<unsigned> getIndex(const ParmVarDecl &Parameter) const {
@@ -1662,7 +1662,7 @@ class CalledOnceChecker : public ConstStmtVisitor<CalledOnceChecker> {
       return It - TrackedParams.begin();
     }
 
-    return llvm::None;
+    return std::nullopt;
   }
 
   const ParmVarDecl *getParameter(unsigned Index) const {
diff --git a/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp b/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp
index 1a41cfaa5fa13..2ae6cd16f2d11 100644
--- a/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp
+++ b/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp
@@ -56,7 +56,7 @@ auto hasOptionalType() { return hasType(optionalOrAliasType()); }
 
 auto isOptionalMemberCallWithName(
     llvm::StringRef MemberName,
-    llvm::Optional<StatementMatcher> Ignorable = llvm::None) {
+    llvm::Optional<StatementMatcher> Ignorable = std::nullopt) {
   auto Exception = unless(Ignorable ? expr(anyOf(*Ignorable, cxxThisExpr()))
                                     : cxxThisExpr());
   return cxxMemberCallExpr(
@@ -66,7 +66,7 @@ auto isOptionalMemberCallWithName(
 
 auto isOptionalOperatorCallWithName(
     llvm::StringRef operator_name,
-    llvm::Optional<StatementMatcher> Ignorable = llvm::None) {
+    llvm::Optional<StatementMatcher> Ignorable = std::nullopt) {
   return cxxOperatorCallExpr(
       hasOverloadedOperatorName(operator_name),
       callee(cxxMethodDecl(ofClass(optionalClass()))),
@@ -540,7 +540,7 @@ ignorableOptional(const UncheckedOptionalAccessModelOptions &Options) {
         cxxOperatorCallExpr(anyOf(hasOverloadedOperatorName("->"),
                                   hasOverloadedOperatorName("*")),
                             unless(hasArgument(0, expr(hasOptionalType())))))));
-  return llvm::None;
+  return std::nullopt;
 }
 
 StatementMatcher
diff --git a/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp b/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp
index 04d6de3b6c6d5..8f0df9e51c093 100644
--- a/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp
+++ b/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp
@@ -414,7 +414,7 @@ runTypeErasedDataflowAnalysis(
   ForwardDataflowWorklist Worklist(CFCtx.getCFG(), &POV);
 
   std::vector<llvm::Optional<TypeErasedDataflowAnalysisState>> BlockStates(
-      CFCtx.getCFG().size(), llvm::None);
+      CFCtx.getCFG().size(), std::nullopt);
 
   // The entry basic block doesn't contain statements so it can be skipped.
   const CFGBlock &Entry = CFCtx.getCFG().getEntry();
diff --git a/clang/lib/Analysis/MacroExpansionContext.cpp b/clang/lib/Analysis/MacroExpansionContext.cpp
index 290510691891c..489cdfcbbc043 100644
--- a/clang/lib/Analysis/MacroExpansionContext.cpp
+++ b/clang/lib/Analysis/MacroExpansionContext.cpp
@@ -99,11 +99,11 @@ void MacroExpansionContext::registerForPreprocessor(Preprocessor &NewPP) {
 Optional<StringRef>
 MacroExpansionContext::getExpandedText(SourceLocation MacroExpansionLoc) const {
   if (MacroExpansionLoc.isMacroID())
-    return llvm::None;
+    return std::nullopt;
 
   // If there was no macro expansion at that location, return None.
   if (ExpansionRanges.find_as(MacroExpansionLoc) == ExpansionRanges.end())
-    return llvm::None;
+    return std::nullopt;
 
   // There was macro expansion, but resulted in no tokens, return empty string.
   const auto It = ExpandedTokens.find_as(MacroExpansionLoc);
@@ -117,11 +117,11 @@ MacroExpansionContext::getExpandedText(SourceLocation MacroExpansionLoc) const {
 Optional<StringRef>
 MacroExpansionContext::getOriginalText(SourceLocation MacroExpansionLoc) const {
   if (MacroExpansionLoc.isMacroID())
-    return llvm::None;
+    return std::nullopt;
 
   const auto It = ExpansionRanges.find_as(MacroExpansionLoc);
   if (It == ExpansionRanges.end())
-    return llvm::None;
+    return std::nullopt;
 
   assert(It->getFirst() != It->getSecond() &&
          "Every macro expansion must cover a non-empty range.");
diff --git a/clang/lib/Analysis/PathDiagnostic.cpp b/clang/lib/Analysis/PathDiagnostic.cpp
index bb5f116d69405..c6303ccc2666d 100644
--- a/clang/lib/Analysis/PathDiagnostic.cpp
+++ b/clang/lib/Analysis/PathDiagnostic.cpp
@@ -239,7 +239,7 @@ compareControlFlow(const PathDiagnosticControlFlowPiece &X,
   FullSourceLoc YEL = Y.getEndLocation().asLocation();
   if (XEL != YEL)
     return XEL.isBeforeInTranslationUnitThan(YEL);
-  return None;
+  return std::nullopt;
 }
 
 static Optional<bool> compareMacro(const PathDiagnosticMacroPiece &X,
@@ -305,7 +305,7 @@ static Optional<bool> comparePiece(const PathDiagnosticPiece &X,
     case PathDiagnosticPiece::Event:
     case PathDiagnosticPiece::Note:
     case PathDiagnosticPiece::PopUp:
-      return None;
+      return std::nullopt;
   }
   llvm_unreachable("all cases handled");
 }
@@ -323,7 +323,7 @@ static Optional<bool> comparePath(const PathPieces &X, const PathPieces &Y) {
       return b.value();
   }
 
-  return None;
+  return std::nullopt;
 }
 
 static bool compareCrossTUSourceLocs(FullSourceLoc XL, FullSourceLoc YL) {
@@ -367,7 +367,7 @@ static bool compare(const PathDiagnostic &X, const PathDiagnostic &Y) {
     return X.getShortDescription() < Y.getShortDescription();
   auto CompareDecls = [&XL](const Decl *D1, const Decl *D2) -> Optional<bool> {
     if (D1 == D2)
-      return None;
+      return std::nullopt;
     if (!D1)
       return true;
     if (!D2)
@@ -379,7 +379,7 @@ static bool compare(const PathDiagnostic &X, const PathDiagnostic &Y) {
       return compareCrossTUSourceLocs(FullSourceLoc(D1L, SM),
                                       FullSourceLoc(D2L, SM));
     }
-    return None;
+    return std::nullopt;
   };
   if (auto Result = CompareDecls(X.getDeclWithIssue(), Y.getDeclWithIssue()))
     return *Result;
diff --git a/clang/lib/Analysis/RetainSummaryManager.cpp b/clang/lib/Analysis/RetainSummaryManager.cpp
index 143c037dda9f6..f17ad9100ce44 100644
--- a/clang/lib/Analysis/RetainSummaryManager.cpp
+++ b/clang/lib/Analysis/RetainSummaryManager.cpp
@@ -71,7 +71,7 @@ Optional<ObjKind> RetainSummaryManager::hasAnyEnabledAttrOf(const Decl *D,
   if (isOneOf<T, CFConsumedAttr, CFReturnsRetainedAttr,
               CFReturnsNotRetainedAttr>()) {
     if (!TrackObjCAndCFObjects)
-      return None;
+      return std::nullopt;
 
     K = ObjKind::CF;
   } else if (isOneOf<T, NSConsumedAttr, NSConsumesSelfAttr,
@@ -79,19 +79,19 @@ Optional<ObjKind> RetainSummaryManager::hasAnyEnabledAttrOf(const Decl *D,
                      NSReturnsNotRetainedAttr, NSConsumesSelfAttr>()) {
 
     if (!TrackObjCAndCFObjects)
-      return None;
+      return std::nullopt;
 
     if (isOneOf<T, NSReturnsRetainedAttr, NSReturnsAutoreleasedAttr,
                 NSReturnsNotRetainedAttr>() &&
         !cocoa::isCocoaObjectRef(QT))
-      return None;
+      return std::nullopt;
     K = ObjKind::ObjC;
   } else if (isOneOf<T, OSConsumedAttr, OSConsumesThisAttr,
                      OSReturnsNotRetainedAttr, OSReturnsRetainedAttr,
                      OSReturnsRetainedOnZeroAttr,
                      OSReturnsRetainedOnNonZeroAttr>()) {
     if (!TrackOSObjects)
-      return None;
+      return std::nullopt;
     K = ObjKind::OS;
   } else if (isOneOf<T, GeneralizedReturnsNotRetainedAttr,
                      GeneralizedReturnsRetainedAttr,
@@ -102,7 +102,7 @@ Optional<ObjKind> RetainSummaryManager::hasAnyEnabledAttrOf(const Decl *D,
   }
   if (D->hasAttr<T>())
     return K;
-  return None;
+  return std::nullopt;
 }
 
 template <class T1, class T2, class... Others>
@@ -724,7 +724,7 @@ RetainSummaryManager::canEval(const CallExpr *CE, const FunctionDecl *FD,
 
   IdentifierInfo *II = FD->getIdentifier();
   if (!II)
-    return None;
+    return std::nullopt;
 
   StringRef FName = II->getName();
   FName = FName.substr(FName.find_first_not_of('_'));
@@ -741,7 +741,7 @@ RetainSummaryManager::canEval(const CallExpr *CE, const FunctionDecl *FD,
         FName == "CMBufferQueueDequeueIfDataReadyAndRetain") {
       // Part of: <rdar://problem/39390714>.
       // These are not retain. They just return something and retain it.
-      return None;
+      return std::nullopt;
     }
     if (CE->getNumArgs() == 1 &&
         (cocoa::isRefType(ResultTy, "CF", FName) ||
@@ -781,7 +781,7 @@ RetainSummaryManager::canEval(const CallExpr *CE, const FunctionDecl *FD,
         return BehaviorSummary::NoOp;
   }
 
-  return None;
+  return std::nullopt;
 }
 
 const RetainSummary *
@@ -885,7 +885,7 @@ RetainSummaryManager::getRetEffectFromAnnotations(QualType RetTy,
       if (auto RE = getRetEffectFromAnnotations(RetTy, PD))
         return RE;
 
-  return None;
+  return std::nullopt;
 }
 
 /// \return Whether the chain of typedefs starting from @c QT
diff --git a/clang/lib/Analysis/UninitializedValues.cpp b/clang/lib/Analysis/UninitializedValues.cpp
index 8f9230c5805c6..566886248bb77 100644
--- a/clang/lib/Analysis/UninitializedValues.cpp
+++ b/clang/lib/Analysis/UninitializedValues.cpp
@@ -90,7 +90,7 @@ void DeclToIndex::computeMap(const DeclContext &dc) {
 Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
   llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
   if (I == map.end())
-    return None;
+    return std::nullopt;
   return I->second;
 }