diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
@@ -2183,20 +2183,17 @@ class Sema final {
       const FunctionProtoType *Old, SourceLocation OldLoc,
       const FunctionProtoType *New, SourceLocation NewLoc);
   bool handlerCanCatch(QualType HandlerType, QualType ExceptionType);
-  bool CheckExceptionSpecSubset(const PartialDiagnostic &DiagID,
-                                const PartialDiagnostic &NestedDiagID,
-                                const PartialDiagnostic &NoteID,
-                                const PartialDiagnostic &NoThrowDiagID,
-                                const FunctionProtoType *Superset,
-                                SourceLocation SuperLoc,
-                                const FunctionProtoType *Subset,
-                                SourceLocation SubLoc);
-  bool CheckParamExceptionSpec(const PartialDiagnostic &NestedDiagID,
-                               const PartialDiagnostic &NoteID,
-                               const FunctionProtoType *Target,
-                               SourceLocation TargetLoc,
-                               const FunctionProtoType *Source,
-                               SourceLocation SourceLoc);
+  bool CheckExceptionSpecSubset(
+      const PartialDiagnostic &DiagID, const PartialDiagnostic &NestedDiagID,
+      const PartialDiagnostic &NoteID, const PartialDiagnostic &NoThrowDiagID,
+      const FunctionProtoType *Superset, bool SkipSupersetFirstParameter,
+      SourceLocation SuperLoc, const FunctionProtoType *Subset,
+      bool SkipSubsetFirstParameter, SourceLocation SubLoc);
+  bool CheckParamExceptionSpec(
+      const PartialDiagnostic &NestedDiagID, const PartialDiagnostic &NoteID,
+      const FunctionProtoType *Target, bool SkipTargetFirstParameter,
+      SourceLocation TargetLoc, const FunctionProtoType *Source,
+      bool SkipSourceFirstParameter, SourceLocation SourceLoc);
 
   TypeResult ActOnTypeName(Scope *S, Declarator &D);
 
@@ -3023,7 +3020,8 @@ class Sema final {
   Attr *getImplicitCodeSegOrSectionAttrForFunction(const FunctionDecl *FD,
                                                    bool IsDefinition);
   void CheckFunctionOrTemplateParamDeclarator(Scope *S, Declarator &D);
-  Decl *ActOnParamDeclarator(Scope *S, Declarator &D);
+  Decl *ActOnParamDeclarator(Scope *S, Declarator &D,
+                             SourceLocation ExplicitThisLoc = {});
   ParmVarDecl *BuildParmVarDeclForTypedef(DeclContext *DC,
                                           SourceLocation Loc,
                                           QualType T);
@@ -3797,8 +3795,12 @@ class Sema final {
                              NamedDecl *&OldDecl,
                              bool UseMemberUsingDeclRules);
   bool IsOverload(FunctionDecl *New, FunctionDecl *Old,
-                  bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true,
-                  bool ConsiderRequiresClauses = true);
+                  bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
+
+  // Checks whether MD constitutes an override the base class method BaseMD.
+  // When checking for overrides, the object object members are ignored.
+  bool IsOverride(FunctionDecl *MD, FunctionDecl *BaseMD,
+                  bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
 
   // Calculates whether the expression Constraint depends on an enclosing
   // template, for the purposes of [temp.friend] p9.
@@ -3856,6 +3858,12 @@ class Sema final {
                                  QualType &ConvertedType);
   bool IsBlockPointerConversion(QualType FromType, QualType ToType,
                                 QualType& ConvertedType);
+
+  bool FunctionParamTypesAreEqual(ArrayRef<QualType> Old,
+                                  ArrayRef<QualType> New,
+                                  unsigned *ArgPos = nullptr,
+                                  bool Reversed = false);
+
   bool FunctionParamTypesAreEqual(const FunctionProtoType *OldType,
                                   const FunctionProtoType *NewType,
                                   unsigned *ArgPos = nullptr,
@@ -3896,10 +3904,11 @@ class Sema final {
                                        ExprResult Init,
                                        bool TopLevelOfInitList = false,
                                        bool AllowExplicit = false);
-  ExprResult PerformObjectArgumentInitialization(Expr *From,
-                                                 NestedNameSpecifier *Qualifier,
-                                                 NamedDecl *FoundDecl,
-                                                 CXXMethodDecl *Method);
+  ExprResult InitializeExplicitObjectArgument(Sema &S, Expr *Obj,
+                                              FunctionDecl *Fun);
+  ExprResult PerformImplicitObjectArgumentInitialization(
+      Expr *From, NestedNameSpecifier *Qualifier, NamedDecl *FoundDecl,
+      CXXMethodDecl *Method);
 
   /// Check that the lifetime of the initializer (and its subobjects) is
   /// sufficient for initializing the entity, and perform lifetime extension
@@ -4221,9 +4230,8 @@ class Sema final {
       QualType DestTypeForComplaining = QualType(),
       unsigned DiagIDForComplaining = 0);
 
-  Expr *FixOverloadedFunctionReference(Expr *E,
-                                       DeclAccessPair FoundDecl,
-                                       FunctionDecl *Fn);
+  ExprResult FixOverloadedFunctionReference(Expr *E, DeclAccessPair FoundDecl,
+                                            FunctionDecl *Fn);
   ExprResult FixOverloadedFunctionReference(ExprResult,
                                             DeclAccessPair FoundDecl,
                                             FunctionDecl *Fn);
@@ -4799,8 +4807,8 @@ class Sema final {
   /// Adjust the calling convention of a method to be the ABI default if it
   /// wasn't specified explicitly.  This handles method types formed from
   /// function type typedefs and typename template arguments.
-  void adjustMemberFunctionCC(QualType &T, bool IsStatic, bool IsCtorOrDtor,
-                              SourceLocation Loc);
+  void adjustMemberFunctionCC(QualType &T, bool HasThisPointer,
+                              bool IsCtorOrDtor, SourceLocation Loc);
 
   // Check if there is an explicit attribute, but only look through parens.
   // The intent is to look for an attribute on the current declarator, but not
@@ -5796,6 +5804,10 @@ class Sema final {
                           Expr *Input, bool IsAfterAmp = false);
 
   bool isQualifiedMemberAccess(Expr *E);
+  bool CheckUseOfCXXMethodAsAddressOfOperand(SourceLocation OpLoc,
+                                             const Expr *Op,
+                                             const CXXMethodDecl *MD);
+
   QualType CheckAddressOfOperand(ExprResult &Operand, SourceLocation OpLoc);
 
   bool CheckTypeTraitArity(unsigned Arity, SourceLocation Loc, size_t N);
@@ -7236,6 +7248,8 @@ class Sema final {
       StorageClass SC, ArrayRef<ParmVarDecl *> Params,
       bool HasExplicitResultType);
 
+  void DiagnoseInvalidExplicitObjectParameterInLambda(CXXMethodDecl *Method);
+
   /// Perform initialization analysis of the init-capture and perform
   /// any implicit conversions such as an lvalue-to-rvalue conversion if
   /// not being used to initialize a reference.
@@ -7916,6 +7930,13 @@ class Sema final {
   void DefineDefaultedComparison(SourceLocation Loc, FunctionDecl *FD,
                                  DefaultedComparisonKind DCK);
 
+  void CheckExplicitObjectMemberFunction(Declarator &D, DeclarationName Name,
+                                         QualType R, bool IsLambda,
+                                         DeclContext *DC = nullptr);
+  void CheckExplicitObjectMemberFunction(DeclContext *DC, Declarator &D,
+                                         DeclarationName Name, QualType R);
+  void CheckExplicitObjectLambda(Declarator &D);
+
   //===--------------------------------------------------------------------===//
   // C++ Derived Classes
   //
@@ -7967,6 +7988,10 @@ class Sema final {
   bool CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
                                          const CXXMethodDecl *Old);
 
+  // Check that the overriding method has no explicit object parameter.
+  bool CheckExplicitObjectOverride(CXXMethodDecl *New,
+                                   const CXXMethodDecl *Old);
+
   /// CheckOverridingFunctionExceptionSpec - Checks whether the exception
   /// spec is a subset of base spec.
   bool CheckOverridingFunctionExceptionSpec(const CXXMethodDecl *New,
@@ -9210,6 +9235,7 @@ class Sema final {
       TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
       FunctionDecl *&Specialization, sema::TemplateDeductionInfo &Info,
       bool PartialOverloading, bool AggregateDeductionCandidate,
+      QualType ObjectType, Expr::Classification ObjectClassification,
       llvm::function_ref<bool(ArrayRef<QualType>)> CheckNonDependent);
 
   TemplateDeductionResult
@@ -9220,11 +9246,10 @@ class Sema final {
                           sema::TemplateDeductionInfo &Info,
                           bool IsAddressOfFunction = false);
 
-  TemplateDeductionResult
-  DeduceTemplateArguments(FunctionTemplateDecl *FunctionTemplate,
-                          QualType ToType,
-                          CXXConversionDecl *&Specialization,
-                          sema::TemplateDeductionInfo &Info);
+  TemplateDeductionResult DeduceTemplateArguments(
+      FunctionTemplateDecl *FunctionTemplate, QualType ObjectType,
+      Expr::Classification ObjectClassification, QualType ToType,
+      CXXConversionDecl *&Specialization, sema::TemplateDeductionInfo &Info);
 
   TemplateDeductionResult
   DeduceTemplateArguments(FunctionTemplateDecl *FunctionTemplate,

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
@@ -4521,6 +4521,8 @@ ExpectedDecl ASTNodeImporter::VisitImplicitParamDecl(ImplicitParamDecl *D) {
 Error ASTNodeImporter::ImportDefaultArgOfParmVarDecl(
     const ParmVarDecl *FromParam, ParmVarDecl *ToParam) {
   ToParam->setHasInheritedDefaultArg(FromParam->hasInheritedDefaultArg());
+  ToParam->setExplicitObjectParameterLoc(
+      FromParam->getExplicitObjectParamThisLoc());
   ToParam->setKNRPromoted(FromParam->isKNRPromoted());
 
   if (FromParam->hasUninstantiatedDefaultArg()) {

diff --git a/clang/lib/AST/ASTStructuralEquivalence.cpp b/clang/lib/AST/ASTStructuralEquivalence.cpp
@@ -1403,6 +1403,8 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
       Method1->getAccess() == Method2->getAccess() &&
       Method1->getOverloadedOperator() == Method2->getOverloadedOperator() &&
       Method1->isStatic() == Method2->isStatic() &&
+      Method1->isImplicitObjectMemberFunction() ==
+          Method2->isImplicitObjectMemberFunction() &&
       Method1->isConst() == Method2->isConst() &&
       Method1->isVolatile() == Method2->isVolatile() &&
       Method1->isVirtual() == Method2->isVirtual() &&

diff --git a/clang/lib/AST/ComputeDependence.cpp b/clang/lib/AST/ComputeDependence.cpp
@@ -484,6 +484,10 @@ ExprDependence clang::computeDependence(DeclRefExpr *E, const ASTContext &Ctx) {
 
   //    - an identifier associated by name lookup with one or more declarations
   //      declared with a dependent type
+  //    - an identifier associated by name lookup with an entity captured by
+  //    copy ([expr.prim.lambda.capture])
+  //      in a lambda-expression that has an explicit object parameter whose
+  //      type is dependent ([dcl.fct]),
   //
   // [The "or more" case is not modeled as a DeclRefExpr. There are a bunch
   // more bullets here that we handle by treating the declaration as having a
@@ -493,6 +497,11 @@ ExprDependence clang::computeDependence(DeclRefExpr *E, const ASTContext &Ctx) {
   else if (Type->isInstantiationDependentType())
     Deps |= ExprDependence::Instantiation;
 
+  //    - an identifier associated by name lookup with an entity captured by
+  //    copy ([expr.prim.lambda.capture])
+  if (E->isCapturedByCopyInLambdaWithExplicitObjectParameter())
+    Deps |= ExprDependence::Type;
+
   //    - a conversion-function-id that specifies a dependent type
   if (Decl->getDeclName().getNameKind() ==
       DeclarationName::CXXConversionFunctionName) {

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
@@ -3652,6 +3652,20 @@ unsigned FunctionDecl::getMinRequiredArguments() const {
   return NumRequiredArgs;
 }
 
+bool FunctionDecl::hasCXXExplicitFunctionObjectParameter() const {
+  return getNumParams() != 0 && getParamDecl(0)->isExplicitObjectParameter();
+}
+
+unsigned FunctionDecl::getNumNonObjectParams() const {
+  return getNumParams() -
+         static_cast<unsigned>(hasCXXExplicitFunctionObjectParameter());
+}
+
+unsigned FunctionDecl::getMinRequiredExplicitArguments() const {
+  return getMinRequiredArguments() -
+         static_cast<unsigned>(hasCXXExplicitFunctionObjectParameter());
+}
+
 bool FunctionDecl::hasOneParamOrDefaultArgs() const {
   return getNumParams() == 1 ||
          (getNumParams() > 1 &&

diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
@@ -838,7 +838,7 @@ void CXXRecordDecl::addedMember(Decl *D) {
       SMKind |= SMF_CopyAssignment;
 
       const auto *ParamTy =
-          Method->getParamDecl(0)->getType()->getAs<ReferenceType>();
+          Method->getNonObjectParameter(0)->getType()->getAs<ReferenceType>();
       if (!ParamTy || ParamTy->getPointeeType().isConstQualified())
         data().HasDeclaredCopyAssignmentWithConstParam = true;
     }
@@ -2409,18 +2409,30 @@ bool CXXMethodDecl::isUsualDeallocationFunction(
   return Result;
 }
 
+bool CXXMethodDecl::isExplicitObjectMemberFunction() const {
+  // C++2b [dcl.fct]p6:
+  // An explicit object member function is a non-static member
+  // function with an explicit object parameter
+  return !isStatic() && hasCXXExplicitFunctionObjectParameter();
+}
+
+bool CXXMethodDecl::isImplicitObjectMemberFunction() const {
+  return !isStatic() && !hasCXXExplicitFunctionObjectParameter();
+}
+
 bool CXXMethodDecl::isCopyAssignmentOperator() const {
   // C++0x [class.copy]p17:
   //  A user-declared copy assignment operator X::operator= is a non-static
   //  non-template member function of class X with exactly one parameter of
   //  type X, X&, const X&, volatile X& or const volatile X&.
   if (/*operator=*/getOverloadedOperator() != OO_Equal ||
       /*non-static*/ isStatic() ||
-      /*non-template*/getPrimaryTemplate() || getDescribedFunctionTemplate() ||
-      getNumParams() != 1)
+
+      /*non-template*/ getPrimaryTemplate() || getDescribedFunctionTemplate() ||
+      getNumExplicitParams() != 1)
     return false;
 
-  QualType ParamType = getParamDecl(0)->getType();
+  QualType ParamType = getNonObjectParameter(0)->getType();
   if (const auto *Ref = ParamType->getAs<LValueReferenceType>())
     ParamType = Ref->getPointeeType();
 
@@ -2437,10 +2449,10 @@ bool CXXMethodDecl::isMoveAssignmentOperator() const {
   //  X&&, const X&&, volatile X&&, or const volatile X&&.
   if (getOverloadedOperator() != OO_Equal || isStatic() ||
       getPrimaryTemplate() || getDescribedFunctionTemplate() ||
-      getNumParams() != 1)
+      getNumExplicitParams() != 1)
     return false;
 
-  QualType ParamType = getParamDecl(0)->getType();
+  QualType ParamType = getNonObjectParameter(0)->getType();
   if (!ParamType->isRValueReferenceType())
     return false;
   ParamType = ParamType->getPointeeType();
@@ -2496,12 +2508,6 @@ QualType CXXMethodDecl::getThisType(const FunctionProtoType *FPT,
                               : C.getPointerType(ObjectTy);
 }
 
-QualType CXXMethodDecl::getThisObjectType(const FunctionProtoType *FPT,
-                                          const CXXRecordDecl *Decl) {
-  ASTContext &C = Decl->getASTContext();
-  return ::getThisObjectType(C, FPT, Decl);
-}
-
 QualType CXXMethodDecl::getThisType() const {
   // C++ 9.3.2p1: The type of this in a member function of a class X is X*.
   // If the member function is declared const, the type of this is const X*,
@@ -2513,11 +2519,17 @@ QualType CXXMethodDecl::getThisType() const {
                                     getParent());
 }
 
-QualType CXXMethodDecl::getThisObjectType() const {
-  // Ditto getThisType.
-  assert(isInstance() && "No 'this' for static methods!");
-  return CXXMethodDecl::getThisObjectType(
-      getType()->castAs<FunctionProtoType>(), getParent());
+QualType CXXMethodDecl::getFunctionObjectParameterReferenceType() const {
+  if (isExplicitObjectMemberFunction())
+    return parameters()[0]->getType();
+
+  ASTContext &C = getParentASTContext();
+  const FunctionProtoType *FPT = getType()->castAs<FunctionProtoType>();
+  QualType Type = ::getThisObjectType(C, FPT, getParent());
+  RefQualifierKind RK = FPT->getRefQualifier();
+  if (RK == RefQualifierKind::RQ_RValue)
+    return C.getRValueReferenceType(Type);
+  return C.getLValueReferenceType(Type);
 }
 
 bool CXXMethodDecl::hasInlineBody() const {

diff --git a/clang/lib/AST/DeclPrinter.cpp b/clang/lib/AST/DeclPrinter.cpp
@@ -962,6 +962,10 @@ void DeclPrinter::VisitLabelDecl(LabelDecl *D) {
 void DeclPrinter::VisitVarDecl(VarDecl *D) {
   prettyPrintPragmas(D);
 
+  if (const auto *Param = dyn_cast<ParmVarDecl>(D);
+      Param && Param->isExplicitObjectParameter())
+    Out << "this ";
+
   std::string LeftSide;
   llvm::raw_string_ostream LeftSideStream(LeftSide);
 

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
@@ -491,6 +491,7 @@ DeclRefExpr::DeclRefExpr(const ASTContext &Ctx, ValueDecl *D,
   DeclRefExprBits.HadMultipleCandidates = false;
   DeclRefExprBits.RefersToEnclosingVariableOrCapture =
       RefersToEnclosingVariableOrCapture;
+  DeclRefExprBits.CapturedByCopyInLambdaWithExplicitObjectParameter = false;
   DeclRefExprBits.NonOdrUseReason = NOUR;
   DeclRefExprBits.IsImmediateEscalating = false;
   DeclRefExprBits.Loc = L;
@@ -518,6 +519,7 @@ DeclRefExpr::DeclRefExpr(const ASTContext &Ctx,
     = (TemplateArgs || TemplateKWLoc.isValid()) ? 1 : 0;
   DeclRefExprBits.RefersToEnclosingVariableOrCapture =
       RefersToEnclosingVariableOrCapture;
+  DeclRefExprBits.CapturedByCopyInLambdaWithExplicitObjectParameter = false;
   DeclRefExprBits.NonOdrUseReason = NOUR;
   if (TemplateArgs) {
     auto Deps = TemplateArgumentDependence::None;

diff --git a/clang/lib/AST/ExprClassification.cpp b/clang/lib/AST/ExprClassification.cpp
@@ -465,8 +465,13 @@ static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
   // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
   // special-case this.
 
-  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
-    return Cl::CL_MemberFunction;
+  if (const auto *M = dyn_cast<CXXMethodDecl>(D)) {
+    if (M->isImplicitObjectMemberFunction())
+      return Cl::CL_MemberFunction;
+    if (M->isStatic())
+      return Cl::CL_LValue;
+    return Cl::CL_PRValue;
+  }
 
   bool islvalue;
   if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
@@ -551,8 +556,13 @@ static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
   //      -- If it refers to a static member function [...], then E1.E2 is an
   //         lvalue; [...]
   //      -- Otherwise [...] E1.E2 is a prvalue.
-  if (const auto *Method = dyn_cast<CXXMethodDecl>(Member))
-    return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
+  if (const auto *Method = dyn_cast<CXXMethodDecl>(Member)) {
+    if (Method->isStatic())
+      return Cl::CL_LValue;
+    if (Method->isImplicitObjectMemberFunction())
+      return Cl::CL_MemberFunction;
+    return Cl::CL_PRValue;
+  }
 
   //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
   // So is everything else we haven't handled yet.

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
@@ -1945,9 +1945,9 @@ APValue *EvalInfo::createHeapAlloc(const Expr *E, QualType T, LValue &LV) {
 /// Produce a string describing the given constexpr call.
 void CallStackFrame::describe(raw_ostream &Out) const {
   unsigned ArgIndex = 0;
-  bool IsMemberCall = isa<CXXMethodDecl>(Callee) &&
-                      !isa<CXXConstructorDecl>(Callee) &&
-                      cast<CXXMethodDecl>(Callee)->isInstance();
+  bool IsMemberCall =
+      isa<CXXMethodDecl>(Callee) && !isa<CXXConstructorDecl>(Callee) &&
+      cast<CXXMethodDecl>(Callee)->isImplicitObjectMemberFunction();
 
   if (!IsMemberCall)
     Callee->getNameForDiagnostic(Out, Info.Ctx.getPrintingPolicy(),
@@ -4711,6 +4711,9 @@ static bool EvaluateObjectArgument(EvalInfo &Info, const Expr *Object,
   if (Object->getType()->isLiteralType(Info.Ctx))
     return EvaluateTemporary(Object, This, Info);
 
+  if (Object->getType()->isRecordType() && Object->isPRValue())
+    return EvaluateTemporary(Object, This, Info);
+
   Info.FFDiag(Object, diag::note_constexpr_nonliteral) << Object->getType();
   return false;
 }
@@ -7789,15 +7792,18 @@ class ExprEvaluatorBase
       if (OCE && OCE->isAssignmentOp()) {
         assert(Args.size() == 2 && "wrong number of arguments in assignment");
         Call = Info.CurrentCall->createCall(FD);
-        if (!EvaluateArgs(isa<CXXMethodDecl>(FD) ? Args.slice(1) : Args, Call,
-                          Info, FD, /*RightToLeft=*/true))
+        bool HasThis = false;
+        if (const auto *MD = dyn_cast<CXXMethodDecl>(FD))
+          HasThis = MD->isImplicitObjectMemberFunction();
+        if (!EvaluateArgs(HasThis ? Args.slice(1) : Args, Call, Info, FD,
+                          /*RightToLeft=*/true))
           return false;
       }
 
       // Overloaded operator calls to member functions are represented as normal
       // calls with '*this' as the first argument.
       const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
-      if (MD && !MD->isStatic()) {
+      if (MD && MD->isImplicitObjectMemberFunction()) {
         // FIXME: When selecting an implicit conversion for an overloaded
         // operator delete, we sometimes try to evaluate calls to conversion
         // operators without a 'this' parameter!
@@ -7881,7 +7887,7 @@ class ExprEvaluatorBase
                                    CovariantAdjustmentPath);
         if (!FD)
           return false;
-      } else {
+      } else if (NamedMember && NamedMember->isImplicitObjectMemberFunction()) {
         // Check that the 'this' pointer points to an object of the right type.
         // FIXME: If this is an assignment operator call, we may need to change
         // the active union member before we check this.
@@ -16284,7 +16290,8 @@ bool Expr::EvaluateWithSubstitution(APValue &Value, ASTContext &Ctx,
 #ifndef NDEBUG
     auto *MD = dyn_cast<CXXMethodDecl>(Callee);
     assert(MD && "Don't provide `this` for non-methods.");
-    assert(!MD->isStatic() && "Don't provide `this` for static methods.");
+    assert(MD->isImplicitObjectMemberFunction() &&
+           "Don't provide `this` for methods without an implicit object.");
 #endif
     if (!This->isValueDependent() &&
         EvaluateObjectArgument(Info, This, ThisVal) &&
@@ -16379,9 +16386,10 @@ bool Expr::isPotentialConstantExpr(const FunctionDecl *FD,
     HandleConstructorCall(&VIE, This, Args, CD, Info, Scratch);
   } else {
     SourceLocation Loc = FD->getLocation();
-    HandleFunctionCall(Loc, FD, (MD && MD->isInstance()) ? &This : nullptr,
-                       &VIE, Args, CallRef(), FD->getBody(), Info, Scratch,
-                       /*ResultSlot=*/nullptr);
+    HandleFunctionCall(
+        Loc, FD, (MD && MD->isImplicitObjectMemberFunction()) ? &This : nullptr,
+        &VIE, Args, CallRef(), FD->getBody(), Info, Scratch,
+        /*ResultSlot=*/nullptr);
   }
 
   return Diags.empty();

diff --git a/clang/lib/AST/Interp/ByteCodeEmitter.cpp b/clang/lib/AST/Interp/ByteCodeEmitter.cpp
@@ -44,7 +44,7 @@ ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl) {
   // InterpStack when calling the function.
   bool HasThisPointer = false;
   if (const auto *MD = dyn_cast<CXXMethodDecl>(FuncDecl)) {
-    if (MD->isInstance()) {
+    if (MD->isImplicitObjectMemberFunction()) {
       HasThisPointer = true;
       ParamTypes.push_back(PT_Ptr);
       ParamOffsets.push_back(ParamOffset);

diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
@@ -1721,7 +1721,7 @@ void CXXNameMangler::mangleUnqualifiedName(
 
       // If we have a member function, we need to include the 'this' pointer.
       if (const auto *MD = dyn_cast<CXXMethodDecl>(ND))
-        if (!MD->isStatic())
+        if (MD->isImplicitObjectMemberFunction())
           Arity++;
     }
     [[fallthrough]];
@@ -1781,6 +1781,8 @@ void CXXNameMangler::mangleNestedName(GlobalDecl GD,
     Qualifiers MethodQuals = Method->getMethodQualifiers();
     // We do not consider restrict a distinguishing attribute for overloading
     // purposes so we must not mangle it.
+    if (Method->isExplicitObjectMemberFunction())
+      Out << 'H';
     MethodQuals.removeRestrict();
     mangleQualifiers(MethodQuals);
     mangleRefQualifier(Method->getRefQualifier());

diff --git a/clang/lib/AST/JSONNodeDumper.cpp b/clang/lib/AST/JSONNodeDumper.cpp
@@ -876,6 +876,9 @@ void JSONNodeDumper::VisitUsingShadowDecl(const UsingShadowDecl *USD) {
 void JSONNodeDumper::VisitVarDecl(const VarDecl *VD) {
   VisitNamedDecl(VD);
   JOS.attribute("type", createQualType(VD->getType()));
+  if (const auto *P = dyn_cast<ParmVarDecl>(VD))
+    attributeOnlyIfTrue("explicitObjectParameter",
+                        P->isExplicitObjectParameter());
 
   StorageClass SC = VD->getStorageClass();
   if (SC != SC_None)

diff --git a/clang/lib/AST/Mangle.cpp b/clang/lib/AST/Mangle.cpp
@@ -225,7 +225,7 @@ void MangleContext::mangleName(GlobalDecl GD, raw_ostream &Out) {
   assert(!Proto->isVariadic());
   unsigned ArgWords = 0;
   if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD))
-    if (!MD->isStatic())
+    if (MD->isImplicitObjectMemberFunction())
       ++ArgWords;
   uint64_t DefaultPtrWidth = TI.getPointerWidth(LangAS::Default);
   for (const auto &AT : Proto->param_types()) {

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
@@ -2636,7 +2636,7 @@ void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
   if (const CXXMethodDecl *MD = dyn_cast_or_null<CXXMethodDecl>(D)) {
     if (MD->getParent()->isLambda())
       IsInLambda = true;
-    if (MD->isInstance())
+    if (MD->isImplicitObjectMemberFunction())
       HasThisQuals = true;
     if (isa<CXXDestructorDecl>(MD)) {
       IsStructor = true;
@@ -2745,6 +2745,10 @@ void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
   } else {
     // Happens for function pointer type arguments for example.
     for (unsigned I = 0, E = Proto->getNumParams(); I != E; ++I) {
+      // Explicit object parameters are prefixed by "_V".
+      if (I == 0 && D && D->getParamDecl(I)->isExplicitObjectParameter())
+        Out << "_V";
+
       mangleFunctionArgumentType(Proto->getParamType(I), Range);
       // Mangle each pass_object_size parameter as if it's a parameter of enum
       // type passed directly after the parameter with the pass_object_size
@@ -2810,23 +2814,23 @@ void MicrosoftCXXNameMangler::mangleFunctionClass(const FunctionDecl *FD) {
       case AS_none:
         llvm_unreachable("Unsupported access specifier");
       case AS_private:
-        if (MD->isStatic())
+        if (!MD->isImplicitObjectMemberFunction())
           Out << 'C';
         else if (IsVirtual)
           Out << 'E';
         else
           Out << 'A';
         break;
       case AS_protected:
-        if (MD->isStatic())
+        if (!MD->isImplicitObjectMemberFunction())
           Out << 'K';
         else if (IsVirtual)
           Out << 'M';
         else
           Out << 'I';
         break;
       case AS_public:
-        if (MD->isStatic())
+        if (!MD->isImplicitObjectMemberFunction())
           Out << 'S';
         else if (IsVirtual)
           Out << 'U';

diff --git a/clang/lib/AST/TextNodeDumper.cpp b/clang/lib/AST/TextNodeDumper.cpp
@@ -1949,6 +1949,10 @@ void TextNodeDumper::VisitFieldDecl(const FieldDecl *D) {
 void TextNodeDumper::VisitVarDecl(const VarDecl *D) {
   dumpNestedNameSpecifier(D->getQualifier());
   dumpName(D);
+  if (const auto *P = dyn_cast<ParmVarDecl>(D);
+      P && P->isExplicitObjectParameter())
+    OS << " this";
+
   dumpType(D->getType());
   dumpTemplateSpecializationKind(D->getTemplateSpecializationKind());
   StorageClass SC = D->getStorageClass();

diff --git a/clang/lib/Analysis/Consumed.cpp b/clang/lib/Analysis/Consumed.cpp
@@ -771,7 +771,7 @@ void ConsumedStmtVisitor::VisitCXXBindTemporaryExpr(
 void ConsumedStmtVisitor::VisitCXXConstructExpr(const CXXConstructExpr *Call) {
   CXXConstructorDecl *Constructor = Call->getConstructor();
 
-  QualType ThisType = Constructor->getThisObjectType();
+  QualType ThisType = Constructor->getFunctionObjectParameterType();
 
   if (!isConsumableType(ThisType))
     return;
@@ -1199,7 +1199,7 @@ void ConsumedAnalyzer::determineExpectedReturnState(AnalysisDeclContext &AC,
                                                     const FunctionDecl *D) {
   QualType ReturnType;
   if (const auto *Constructor = dyn_cast<CXXConstructorDecl>(D)) {
-    ReturnType = Constructor->getThisObjectType();
+    ReturnType = Constructor->getFunctionObjectParameterType();
   } else
     ReturnType = D->getCallResultType();
 

diff --git a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
@@ -452,8 +452,8 @@ Environment::Environment(DataflowAnalysisContext &DACtx,
       MethodDecl = dyn_cast<CXXMethodDecl>(Parent->getDeclContext());
 
     // FIXME: Initialize the ThisPointeeLoc of lambdas too.
-    if (MethodDecl && !MethodDecl->isStatic()) {
-      QualType ThisPointeeType = MethodDecl->getThisObjectType();
+    if (MethodDecl && MethodDecl->isImplicitObjectMemberFunction()) {
+      QualType ThisPointeeType = MethodDecl->getFunctionObjectParameterType();
       ThisPointeeLoc =
           &cast<RecordValue>(createValue(ThisPointeeType))->getLoc();
     }

diff --git a/clang/lib/Analysis/FlowSensitive/Transfer.cpp b/clang/lib/Analysis/FlowSensitive/Transfer.cpp
@@ -525,7 +525,9 @@ class TransferVisitor : public ConstStmtVisitor<TransferVisitor> {
       // The assignment operators are different from the type of the destination
       // in this model (i.e. in one of their base classes). This must be very
       // rare and we just bail.
-      if (Method->getThisObjectType().getCanonicalType().getUnqualifiedType() !=
+      if (Method->getFunctionObjectParameterType()
+              .getCanonicalType()
+              .getUnqualifiedType() !=
           LocDst->getType().getCanonicalType().getUnqualifiedType())
         return;
 

diff --git a/clang/lib/Analysis/ThreadSafetyCommon.cpp b/clang/lib/Analysis/ThreadSafetyCommon.cpp
@@ -154,7 +154,9 @@ CapabilityExpr SExprBuilder::translateAttrExpr(const Expr *AttrExp,
     // If the attribute has no arguments, then assume the argument is "this".
     if (!AttrExp)
       return CapabilityExpr(
-          Self, ClassifyDiagnostic(cast<CXXMethodDecl>(D)->getThisObjectType()),
+          Self,
+          ClassifyDiagnostic(
+              cast<CXXMethodDecl>(D)->getFunctionObjectParameterType()),
           false);
     else  // For most attributes.
       return translateAttrExpr(AttrExp, &Ctx);

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
@@ -298,7 +298,7 @@ CodeGenTypes::arrangeCXXMethodDeclaration(const CXXMethodDecl *MD) {
   setCUDAKernelCallingConvention(FT, CGM, MD);
   auto prototype = FT.getAs<FunctionProtoType>();
 
-  if (MD->isInstance()) {
+  if (MD->isImplicitObjectMemberFunction()) {
     // The abstract case is perfectly fine.
     const CXXRecordDecl *ThisType = TheCXXABI.getThisArgumentTypeForMethod(MD);
     return arrangeCXXMethodType(ThisType, prototype.getTypePtr(), MD);
@@ -448,7 +448,7 @@ CodeGenTypes::arrangeCXXConstructorCall(const CallArgList &args,
 const CGFunctionInfo &
 CodeGenTypes::arrangeFunctionDeclaration(const FunctionDecl *FD) {
   if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD))
-    if (MD->isInstance())
+    if (MD->isImplicitObjectMemberFunction())
       return arrangeCXXMethodDeclaration(MD);
 
   CanQualType FTy = FD->getType()->getCanonicalTypeUnqualified();

diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
@@ -138,7 +138,7 @@ Address CodeGenFunction::LoadCXXThisAddress() {
     CXXThisAlignment = CGM.getClassPointerAlignment(MD->getParent());
   }
 
-  llvm::Type *Ty = ConvertType(MD->getThisObjectType());
+  llvm::Type *Ty = ConvertType(MD->getFunctionObjectParameterType());
   return Address(LoadCXXThis(), Ty, CXXThisAlignment, KnownNonNull);
 }
 
@@ -510,7 +510,7 @@ namespace {
       const CXXDestructorDecl *D = BaseClass->getDestructor();
       // We are already inside a destructor, so presumably the object being
       // destroyed should have the expected type.
-      QualType ThisTy = D->getThisObjectType();
+      QualType ThisTy = D->getFunctionObjectParameterType();
       Address Addr =
         CGF.GetAddressOfDirectBaseInCompleteClass(CGF.LoadCXXThisAddress(),
                                                   DerivedClass, BaseClass,
@@ -1456,7 +1456,7 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
     RunCleanupsScope DtorEpilogue(*this);
     EnterDtorCleanups(Dtor, Dtor_Deleting);
     if (HaveInsertPoint()) {
-      QualType ThisTy = Dtor->getThisObjectType();
+      QualType ThisTy = Dtor->getFunctionObjectParameterType();
       EmitCXXDestructorCall(Dtor, Dtor_Complete, /*ForVirtualBase=*/false,
                             /*Delegating=*/false, LoadCXXThisAddress(), ThisTy);
     }
@@ -1490,7 +1490,7 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
     EnterDtorCleanups(Dtor, Dtor_Complete);
 
     if (!isTryBody) {
-      QualType ThisTy = Dtor->getThisObjectType();
+      QualType ThisTy = Dtor->getFunctionObjectParameterType();
       EmitCXXDestructorCall(Dtor, Dtor_Base, /*ForVirtualBase=*/false,
                             /*Delegating=*/false, LoadCXXThisAddress(), ThisTy);
       break;
@@ -2114,7 +2114,7 @@ void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
   CallArgList Args;
   Address This = ThisAVS.getAddress();
   LangAS SlotAS = ThisAVS.getQualifiers().getAddressSpace();
-  LangAS ThisAS = D->getThisObjectType().getAddressSpace();
+  LangAS ThisAS = D->getFunctionObjectParameterType().getAddressSpace();
   llvm::Value *ThisPtr = This.getPointer();
 
   if (SlotAS != ThisAS) {
@@ -2453,7 +2453,7 @@ namespace {
     void Emit(CodeGenFunction &CGF, Flags flags) override {
       // We are calling the destructor from within the constructor.
       // Therefore, "this" should have the expected type.
-      QualType ThisTy = Dtor->getThisObjectType();
+      QualType ThisTy = Dtor->getFunctionObjectParameterType();
       CGF.EmitCXXDestructorCall(Dtor, Type, /*ForVirtualBase=*/false,
                                 /*Delegating=*/true, Addr, ThisTy);
     }

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -2130,14 +2130,14 @@ CGDebugInfo::CollectTemplateParams(std::optional<TemplateArgs> OArgs,
       // attribute, i.e. that value is not available at the host side.
       if (!CGM.getLangOpts().CUDA || CGM.getLangOpts().CUDAIsDevice ||
           !D->hasAttr<CUDADeviceAttr>()) {
-        const CXXMethodDecl *MD;
         // Variable pointer template parameters have a value that is the address
         // of the variable.
         if (const auto *VD = dyn_cast<VarDecl>(D))
           V = CGM.GetAddrOfGlobalVar(VD);
         // Member function pointers have special support for building them,
         // though this is currently unsupported in LLVM CodeGen.
-        else if ((MD = dyn_cast<CXXMethodDecl>(D)) && MD->isInstance())
+        else if (const auto *MD = dyn_cast<CXXMethodDecl>(D);
+                 MD && MD->isImplicitObjectMemberFunction())
           V = CGM.getCXXABI().EmitMemberFunctionPointer(MD);
         else if (const auto *FD = dyn_cast<FunctionDecl>(D))
           V = CGM.GetAddrOfFunction(FD);

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
@@ -2647,9 +2647,8 @@ static LValue EmitFunctionDeclLValue(CodeGenFunction &CGF, const Expr *E,
 
 static LValue EmitCapturedFieldLValue(CodeGenFunction &CGF, const FieldDecl *FD,
                                       llvm::Value *ThisValue) {
-  QualType TagType = CGF.getContext().getTagDeclType(FD->getParent());
-  LValue LV = CGF.MakeNaturalAlignAddrLValue(ThisValue, TagType);
-  return CGF.EmitLValueForField(LV, FD);
+
+  return CGF.EmitLValueForLambdaField(FD, ThisValue);
 }
 
 /// Named Registers are named metadata pointing to the register name
@@ -4262,17 +4261,38 @@ LValue CodeGenFunction::EmitMemberExpr(const MemberExpr *E) {
 
 /// Given that we are currently emitting a lambda, emit an l-value for
 /// one of its members.
-LValue CodeGenFunction::EmitLValueForLambdaField(const FieldDecl *Field) {
-  if (CurCodeDecl) {
-    assert(cast<CXXMethodDecl>(CurCodeDecl)->getParent()->isLambda());
-    assert(cast<CXXMethodDecl>(CurCodeDecl)->getParent() == Field->getParent());
+///
+LValue CodeGenFunction::EmitLValueForLambdaField(const FieldDecl *Field,
+                                                 llvm::Value *ThisValue) {
+  bool HasExplicitObjectParameter = false;
+  if (const auto *MD = dyn_cast_if_present<CXXMethodDecl>(CurCodeDecl)) {
+    HasExplicitObjectParameter = MD->isExplicitObjectMemberFunction();
+    assert(MD->getParent()->isLambda());
+    assert(MD->getParent() == Field->getParent());
+  }
+  LValue LambdaLV;
+  if (HasExplicitObjectParameter) {
+    const VarDecl *D = cast<CXXMethodDecl>(CurCodeDecl)->getParamDecl(0);
+    auto It = LocalDeclMap.find(D);
+    assert(It != LocalDeclMap.end() && "explicit parameter not loaded?");
+    Address AddrOfExplicitObject = It->getSecond();
+    if (D->getType()->isReferenceType())
+      LambdaLV = EmitLoadOfReferenceLValue(AddrOfExplicitObject, D->getType(),
+                                           AlignmentSource::Decl);
+    else
+      LambdaLV = MakeNaturalAlignAddrLValue(AddrOfExplicitObject.getPointer(),
+                                            D->getType().getNonReferenceType());
+  } else {
+    QualType LambdaTagType = getContext().getTagDeclType(Field->getParent());
+    LambdaLV = MakeNaturalAlignAddrLValue(ThisValue, LambdaTagType);
   }
-  QualType LambdaTagType =
-    getContext().getTagDeclType(Field->getParent());
-  LValue LambdaLV = MakeNaturalAlignAddrLValue(CXXABIThisValue, LambdaTagType);
   return EmitLValueForField(LambdaLV, Field);
 }
 
+LValue CodeGenFunction::EmitLValueForLambdaField(const FieldDecl *Field) {
+  return EmitLValueForLambdaField(Field, CXXABIThisValue);
+}
+
 /// Get the field index in the debug info. The debug info structure/union
 /// will ignore the unnamed bitfields.
 unsigned CodeGenFunction::getDebugInfoFIndex(const RecordDecl *Rec,
@@ -4987,9 +5007,12 @@ RValue CodeGenFunction::EmitCallExpr(const CallExpr *E,
   if (const auto *CE = dyn_cast<CUDAKernelCallExpr>(E))
     return EmitCUDAKernelCallExpr(CE, ReturnValue);
 
+  // A CXXOperatorCallExpr is created even for explicit object methods, but
+  // these should be treated like static function call.
   if (const auto *CE = dyn_cast<CXXOperatorCallExpr>(E))
-    if (const CXXMethodDecl *MD =
-          dyn_cast_or_null<CXXMethodDecl>(CE->getCalleeDecl()))
+    if (const auto *MD =
+            dyn_cast_if_present<CXXMethodDecl>(CE->getCalleeDecl());
+        MD && MD->isImplicitObjectMemberFunction())
       return EmitCXXOperatorMemberCallExpr(CE, MD, ReturnValue);
 
   CGCallee callee = EmitCallee(E->getCallee());

diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -41,7 +41,7 @@ commonEmitCXXMemberOrOperatorCall(CodeGenFunction &CGF, GlobalDecl GD,
 
   assert(CE == nullptr || isa<CXXMemberCallExpr>(CE) ||
          isa<CXXOperatorCallExpr>(CE));
-  assert(MD->isInstance() &&
+  assert(MD->isImplicitObjectMemberFunction() &&
          "Trying to emit a member or operator call expr on a static method!");
 
   // Push the this ptr.
@@ -66,7 +66,12 @@ commonEmitCXXMemberOrOperatorCall(CodeGenFunction &CGF, GlobalDecl GD,
     Args.addFrom(*RtlArgs);
   } else if (CE) {
     // Special case: skip first argument of CXXOperatorCall (it is "this").
-    unsigned ArgsToSkip = isa<CXXOperatorCallExpr>(CE) ? 1 : 0;
+    unsigned ArgsToSkip = 0;
+    if (const auto *Op = dyn_cast<CXXOperatorCallExpr>(CE)) {
+      if (const auto *M = dyn_cast<CXXMethodDecl>(Op->getCalleeDecl()))
+        ArgsToSkip =
+            static_cast<unsigned>(!M->isExplicitObjectMemberFunction());
+    }
     CGF.EmitCallArgs(Args, FPT, drop_begin(CE->arguments(), ArgsToSkip),
                      CE->getDirectCallee());
   } else {
@@ -484,7 +489,7 @@ RValue
 CodeGenFunction::EmitCXXOperatorMemberCallExpr(const CXXOperatorCallExpr *E,
                                                const CXXMethodDecl *MD,
                                                ReturnValueSlot ReturnValue) {
-  assert(MD->isInstance() &&
+  assert(MD->isImplicitObjectMemberFunction() &&
          "Trying to emit a member call expr on a static method!");
   return EmitCXXMemberOrOperatorMemberCallExpr(
       E, MD, ReturnValue, /*HasQualifier=*/false, /*Qualifier=*/nullptr,

diff --git a/clang/lib/CodeGen/CGOpenMPRuntime.cpp b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
@@ -8260,7 +8260,7 @@ class MappableExprsHandler {
       // of tofrom.
       // Emit this[:1]
       CombinedInfo.Pointers.push_back(PartialStruct.Base.getPointer());
-      QualType Ty = MD->getThisObjectType();
+      QualType Ty = MD->getFunctionObjectParameterType();
       llvm::Value *Size =
           CGF.Builder.CreateIntCast(CGF.getTypeSize(Ty), CGF.Int64Ty,
                                     /*isSigned=*/true);

diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
@@ -201,7 +201,7 @@ CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
   // Find the first store of "this", which will be to the alloca associated
   // with "this".
   Address ThisPtr =
-      Address(&*AI, ConvertTypeForMem(MD->getThisObjectType()),
+      Address(&*AI, ConvertTypeForMem(MD->getFunctionObjectParameterType()),
               CGM.getClassPointerAlignment(MD->getParent()));
   llvm::BasicBlock *EntryBB = &Fn->front();
   llvm::BasicBlock::iterator ThisStore =

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1167,12 +1167,13 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
 
   EmitFunctionProlog(*CurFnInfo, CurFn, Args);
 
-  if (isa_and_nonnull<CXXMethodDecl>(D) &&
-      cast<CXXMethodDecl>(D)->isInstance()) {
-    CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
-    const CXXMethodDecl *MD = cast<CXXMethodDecl>(D);
-    if (MD->getParent()->isLambda() &&
-        MD->getOverloadedOperator() == OO_Call) {
+  if (const CXXMethodDecl *MD = dyn_cast_if_present<CXXMethodDecl>(D);
+      MD && !MD->isStatic()) {
+    bool IsInLambda =
+        MD->getParent()->isLambda() && MD->getOverloadedOperator() == OO_Call;
+    if (MD->isImplicitObjectMemberFunction())
+      CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
+    if (IsInLambda) {
       // We're in a lambda; figure out the captures.
       MD->getParent()->getCaptureFields(LambdaCaptureFields,
                                         LambdaThisCaptureField);
@@ -1202,7 +1203,7 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
           VLASizeMap[VAT->getSizeExpr()] = ExprArg;
         }
       }
-    } else {
+    } else if (MD->isImplicitObjectMemberFunction()) {
       // Not in a lambda; just use 'this' from the method.
       // FIXME: Should we generate a new load for each use of 'this'?  The
       // fast register allocator would be happier...
@@ -1313,7 +1314,7 @@ QualType CodeGenFunction::BuildFunctionArgList(GlobalDecl GD,
   QualType ResTy = FD->getReturnType();
 
   const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
-  if (MD && MD->isInstance()) {
+  if (MD && MD->isImplicitObjectMemberFunction()) {
     if (CGM.getCXXABI().HasThisReturn(GD))
       ResTy = MD->getThisType();
     else if (CGM.getCXXABI().hasMostDerivedReturn(GD))

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
@@ -4017,6 +4017,8 @@ class CodeGenFunction : public CodeGenTypeCache {
                                            const ObjCIvarDecl *Ivar);
   LValue EmitLValueForField(LValue Base, const FieldDecl* Field);
   LValue EmitLValueForLambdaField(const FieldDecl *Field);
+  LValue EmitLValueForLambdaField(const FieldDecl *Field,
+                                  llvm::Value *ThisValue);
 
   /// EmitLValueForFieldInitialization - Like EmitLValueForField, except that
   /// if the Field is a reference, this will return the address of the reference

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2246,8 +2246,8 @@ static bool requiresMemberFunctionPointerTypeMetadata(CodeGenModule &CGM,
 
   // Only functions whose address can be taken with a member function pointer
   // need this sort of type metadata.
-  return !MD->isStatic() && !MD->isVirtual() && !isa<CXXConstructorDecl>(MD) &&
-         !isa<CXXDestructorDecl>(MD);
+  return MD->isImplicitObjectMemberFunction() && !MD->isVirtual() &&
+         !isa<CXXConstructorDecl, CXXDestructorDecl>(MD);
 }
 
 SmallVector<const CXXRecordDecl *, 0>

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
@@ -5835,8 +5835,7 @@ bool Parser::isDeclarationSpecifier(
 bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
                                      DeclSpec::FriendSpecified IsFriend,
                                      const ParsedTemplateInfo *TemplateInfo) {
-  TentativeParsingAction TPA(*this);
-
+  RevertingTentativeParsingAction TPA(*this);
   // Parse the C++ scope specifier.
   CXXScopeSpec SS;
   if (TemplateInfo && TemplateInfo->TemplateParams)
@@ -5845,7 +5844,6 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
   if (ParseOptionalCXXScopeSpecifier(SS, /*ObjectType=*/nullptr,
                                      /*ObjectHasErrors=*/false,
                                      /*EnteringContext=*/true)) {
-    TPA.Revert();
     return false;
   }
 
@@ -5857,7 +5855,6 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
   } else if (Tok.is(tok::annot_template_id)) {
     ConsumeAnnotationToken();
   } else {
-    TPA.Revert();
     return false;
   }
 
@@ -5867,7 +5864,6 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
 
   // Current class name must be followed by a left parenthesis.
   if (Tok.isNot(tok::l_paren)) {
-    TPA.Revert();
     return false;
   }
   ConsumeParen();
@@ -5876,7 +5872,6 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
   // that we have a constructor.
   if (Tok.is(tok::r_paren) ||
       (Tok.is(tok::ellipsis) && NextToken().is(tok::r_paren))) {
-    TPA.Revert();
     return true;
   }
 
@@ -5885,7 +5880,6 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
   if (getLangOpts().CPlusPlus11 &&
       isCXX11AttributeSpecifier(/*Disambiguate*/ false,
                                 /*OuterMightBeMessageSend*/ true)) {
-    TPA.Revert();
     return true;
   }
 
@@ -5906,9 +5900,17 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
   // If we parsed a scope specifier as well as friend,
   // we might be parsing a friend constructor.
   bool IsConstructor = false;
-  if (isDeclarationSpecifier(IsFriend && !SS.isSet()
-                                 ? ImplicitTypenameContext::No
-                                 : ImplicitTypenameContext::Yes))
+  ImplicitTypenameContext ITC = IsFriend && !SS.isSet()
+                                    ? ImplicitTypenameContext::No
+                                    : ImplicitTypenameContext::Yes;
+  // Constructors cannot have this parameters, but we support that scenario here
+  // to improve diagnostic.
+  if (Tok.is(tok::kw_this)) {
+    ConsumeToken();
+    return isDeclarationSpecifier(ITC);
+  }
+
+  if (isDeclarationSpecifier(ITC))
     IsConstructor = true;
   else if (Tok.is(tok::identifier) ||
            (Tok.is(tok::annot_cxxscope) && NextToken().is(tok::identifier))) {
@@ -5977,8 +5979,6 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
       break;
     }
   }
-
-  TPA.Revert();
   return IsConstructor;
 }
 
@@ -7356,6 +7356,7 @@ void Parser::ParseFunctionDeclaratorIdentifierList(
 ///           '=' assignment-expression
 /// [GNU]   declaration-specifiers abstract-declarator[opt] attributes
 /// [C++11] attribute-specifier-seq parameter-declaration
+/// [C++2b] attribute-specifier-seq 'this' parameter-declaration
 ///
 void Parser::ParseParameterDeclarationClause(
     DeclaratorContext DeclaratorCtx, ParsedAttributes &FirstArgAttrs,
@@ -7420,9 +7421,16 @@ void Parser::ParseParameterDeclarationClause(
 
     SourceLocation DSStart = Tok.getLocation();
 
+    // Parse a C++23 Explicit Object Parameter
+    // We do that in all language modes to produce a better diagnostic.
+    SourceLocation ThisLoc;
+    if (getLangOpts().CPlusPlus && Tok.is(tok::kw_this))
+      ThisLoc = ConsumeToken();
+
     ParseDeclarationSpecifiers(DS, /*TemplateInfo=*/ParsedTemplateInfo(),
                                AS_none, DeclSpecContext::DSC_normal,
                                /*LateAttrs=*/nullptr, AllowImplicitTypename);
+
     DS.takeAttributesFrom(ArgDeclSpecAttrs);
 
     // Parse the declarator.  This is "PrototypeContext" or
@@ -7436,6 +7444,9 @@ void Parser::ParseParameterDeclarationClause(
                                   : DeclaratorContext::Prototype);
     ParseDeclarator(ParmDeclarator);
 
+    if (ThisLoc.isValid())
+      ParmDeclarator.SetRangeBegin(ThisLoc);
+
     // Parse GNU attributes, if present.
     MaybeParseGNUAttributes(ParmDeclarator);
     if (getLangOpts().HLSL)
@@ -7505,7 +7516,8 @@ void Parser::ParseParameterDeclarationClause(
       }
       // Inform the actions module about the parameter declarator, so it gets
       // added to the current scope.
-      Decl *Param = Actions.ActOnParamDeclarator(getCurScope(), ParmDeclarator);
+      Decl *Param =
+          Actions.ActOnParamDeclarator(getCurScope(), ParmDeclarator, ThisLoc);
       // Parse the default argument, if any. We parse the default
       // arguments in all dialects; the semantic analysis in
       // ActOnParamDefaultArgument will reject the default argument in

diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
@@ -1571,6 +1571,17 @@ Parser::isCXXDeclarationSpecifier(ImplicitTypenameContext AllowImplicitTypename,
   case tok::kw___vector:
     return TPResult::True;
 
+  case tok::kw_this: {
+    // Try to parse a C++23 Explicit Object Parameter
+    // We do that in all language modes to produce a better diagnostic.
+    if (getLangOpts().CPlusPlus) {
+      RevertingTentativeParsingAction PA(*this);
+      ConsumeToken();
+      return isCXXDeclarationSpecifier(AllowImplicitTypename, BracedCastResult,
+                                       InvalidAsDeclSpec);
+    }
+    return TPResult::False;
+  }
   case tok::annot_template_id: {
     TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
     // If lookup for the template-name found nothing, don't assume we have a

diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
@@ -420,6 +420,18 @@ bool Declarator::isStaticMember() {
               getName().OperatorFunctionId.Operator));
 }
 
+bool Declarator::isExplicitObjectMemberFunction() {
+  if (!isFunctionDeclarator())
+    return false;
+  DeclaratorChunk::FunctionTypeInfo &Fun = getFunctionTypeInfo();
+  if (Fun.NumParams) {
+    auto *P = dyn_cast_or_null<ParmVarDecl>(Fun.Params[0].Param);
+    if (P && P->isExplicitObjectParameter())
+      return true;
+  }
+  return false;
+}
+
 bool Declarator::isCtorOrDtor() {
   return (getName().getKind() == UnqualifiedIdKind::IK_ConstructorName) ||
          (getName().getKind() == UnqualifiedIdKind::IK_DestructorName);

diff --git a/clang/lib/Sema/HLSLExternalSemaSource.cpp b/clang/lib/Sema/HLSLExternalSemaSource.cpp
@@ -175,8 +175,8 @@ struct BuiltinTypeDeclBuilder {
                                   SourceLocation(), FPOptionsOverride());
 
     CXXThisExpr *This = CXXThisExpr::Create(
-        AST, SourceLocation(),
-        Constructor->getThisObjectType(), true);
+        AST, SourceLocation(), Constructor->getFunctionObjectParameterType(),
+        true);
     Expr *Handle = MemberExpr::CreateImplicit(AST, This, false, Fields["h"],
                                               Fields["h"]->getType(), VK_LValue,
                                               OK_Ordinary);
@@ -260,9 +260,9 @@ struct BuiltinTypeDeclBuilder {
     auto FnProtoLoc = TSInfo->getTypeLoc().getAs<FunctionProtoTypeLoc>();
     FnProtoLoc.setParam(0, IdxParam);
 
-    auto *This = CXXThisExpr::Create(
-        AST, SourceLocation(),
-        MethodDecl->getThisObjectType(), true);
+    auto *This =
+        CXXThisExpr::Create(AST, SourceLocation(),
+                            MethodDecl->getFunctionObjectParameterType(), true);
     auto *HandleAccess = MemberExpr::CreateImplicit(
         AST, This, false, Handle, Handle->getType(), VK_LValue, OK_Ordinary);
 

diff --git a/clang/lib/Sema/ScopeInfo.cpp b/clang/lib/Sema/ScopeInfo.cpp
@@ -248,6 +248,14 @@ void LambdaScopeInfo::visitPotentialCaptures(
   }
 }
 
+bool LambdaScopeInfo::lambdaCaptureShouldBeConst() const {
+  if (ExplicitObjectParameter)
+    return ExplicitObjectParameter->getType()
+        .getNonReferenceType()
+        .isConstQualified();
+  return !Mutable;
+}
+
 FunctionScopeInfo::~FunctionScopeInfo() { }
 BlockScopeInfo::~BlockScopeInfo() { }
 CapturedRegionScopeInfo::~CapturedRegionScopeInfo() { }
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
@@ -126,7 +126,7 @@ static bool checkArgCountAtLeast(Sema &S, CallExpr *Call,
 
   return S.Diag(Call->getEndLoc(), diag::err_typecheck_call_too_few_args)
          << 0 /*function call*/ << MinArgCount << ArgCount
-         << Call->getSourceRange();
+         << /*is non object*/ 0 << Call->getSourceRange();
 }
 
 /// Checks that a call expression's argument count is at most the desired
@@ -139,7 +139,7 @@ static bool checkArgCountAtMost(Sema &S, CallExpr *Call, unsigned MaxArgCount) {
   return S.Diag(Call->getEndLoc(),
                 diag::err_typecheck_call_too_many_args_at_most)
          << 0 /*function call*/ << MaxArgCount << ArgCount
-         << Call->getSourceRange();
+         << /*is non object*/ 0 << Call->getSourceRange();
 }
 
 /// Checks that a call expression's argument count is in the desired range. This
@@ -168,7 +168,7 @@ static bool checkArgCount(Sema &S, CallExpr *Call, unsigned DesiredArgCount) {
 
   return S.Diag(Range.getBegin(), diag::err_typecheck_call_too_many_args)
          << 0 /*function call*/ << DesiredArgCount << ArgCount
-         << Call->getArg(1)->getSourceRange();
+         << /*is non object*/ 0 << Call->getArg(1)->getSourceRange();
 }
 
 static bool convertArgumentToType(Sema &S, Expr *&Value, QualType Ty) {
@@ -217,7 +217,7 @@ static bool SemaBuiltinMSVCAnnotation(Sema &S, CallExpr *TheCall) {
   // We need at least one argument.
   if (TheCall->getNumArgs() < 1) {
     S.Diag(TheCall->getEndLoc(), diag::err_typecheck_call_too_few_args_at_least)
-        << 0 << 1 << TheCall->getNumArgs()
+        << 0 << 1 << TheCall->getNumArgs() << /*is non object*/ 0
         << TheCall->getCallee()->getSourceRange();
     return true;
   }
@@ -1578,7 +1578,7 @@ static bool SemaOpenCLBuiltinEnqueueKernel(Sema &S, CallExpr *TheCall) {
   if (NumArgs < 4) {
     S.Diag(TheCall->getBeginLoc(),
            diag::err_typecheck_call_too_few_args_at_least)
-        << 0 << 4 << NumArgs;
+        << 0 << 4 << NumArgs << /*is non object*/ 0;
     return true;
   }
 
@@ -6924,8 +6924,9 @@ void Sema::CheckConstructorCall(FunctionDecl *FDecl, QualType ThisType,
       Proto->isVariadic() ? VariadicConstructor : VariadicDoesNotApply;
 
   auto *Ctor = cast<CXXConstructorDecl>(FDecl);
-  CheckArgAlignment(Loc, FDecl, "'this'", Context.getPointerType(ThisType),
-                    Context.getPointerType(Ctor->getThisObjectType()));
+  CheckArgAlignment(
+      Loc, FDecl, "'this'", Context.getPointerType(ThisType),
+      Context.getPointerType(Ctor->getFunctionObjectParameterType()));
 
   checkCall(FDecl, Proto, /*ThisArg=*/nullptr, Args, /*IsMemberFunction=*/true,
             Loc, SourceRange(), CallType);
@@ -6945,14 +6946,16 @@ bool Sema::CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall,
   unsigned NumArgs = TheCall->getNumArgs();
 
   Expr *ImplicitThis = nullptr;
-  if (IsMemberOperatorCall && !FDecl->isStatic()) {
+  if (IsMemberOperatorCall && !FDecl->isStatic() &&
+      !FDecl->hasCXXExplicitFunctionObjectParameter()) {
     // If this is a call to a non-static member operator, hide the first
     // argument from checkCall.
     // FIXME: Our choice of AST representation here is less than ideal.
     ImplicitThis = Args[0];
     ++Args;
     --NumArgs;
-  } else if (IsMemberFunction && !FDecl->isStatic())
+  } else if (IsMemberFunction && !FDecl->isStatic() &&
+             !FDecl->hasCXXExplicitFunctionObjectParameter())
     ImplicitThis =
         cast<CXXMemberCallExpr>(TheCall)->getImplicitObjectArgument();
 
@@ -6965,8 +6968,8 @@ bool Sema::CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall,
       ThisType = Context.getPointerType(ThisType);
     }
 
-    QualType ThisTypeFromDecl =
-        Context.getPointerType(cast<CXXMethodDecl>(FDecl)->getThisObjectType());
+    QualType ThisTypeFromDecl = Context.getPointerType(
+        cast<CXXMethodDecl>(FDecl)->getFunctionObjectParameterType());
 
     CheckArgAlignment(TheCall->getRParenLoc(), FDecl, "'this'", ThisType,
                       ThisTypeFromDecl);
@@ -7293,13 +7296,13 @@ ExprResult Sema::BuildAtomicExpr(SourceRange CallRange, SourceRange ExprRange,
   if (Args.size() < AdjustedNumArgs) {
     Diag(CallRange.getEnd(), diag::err_typecheck_call_too_few_args)
         << 0 << AdjustedNumArgs << static_cast<unsigned>(Args.size())
-        << ExprRange;
+        << /*is non object*/ 0 << ExprRange;
     return ExprError();
   } else if (Args.size() > AdjustedNumArgs) {
     Diag(Args[AdjustedNumArgs]->getBeginLoc(),
          diag::err_typecheck_call_too_many_args)
         << 0 << AdjustedNumArgs << static_cast<unsigned>(Args.size())
-        << ExprRange;
+        << /*is non object*/ 0 << ExprRange;
     return ExprError();
   }
 
@@ -7662,7 +7665,8 @@ bool Sema::BuiltinWasmRefNullExtern(CallExpr *TheCall) {
 bool Sema::BuiltinWasmRefNullFunc(CallExpr *TheCall) {
   if (TheCall->getNumArgs() != 0) {
     Diag(TheCall->getBeginLoc(), diag::err_typecheck_call_too_many_args)
-         << 0 /*function call*/ << 0 << TheCall->getNumArgs();
+        << 0 /*function call*/ << /*expected*/ 0 << TheCall->getNumArgs()
+        << /*is non object*/ 0;
     return true;
   }
 
@@ -7695,7 +7699,8 @@ Sema::SemaBuiltinAtomicOverloaded(ExprResult TheCallResult) {
   // Ensure that we have at least one argument to do type inference from.
   if (TheCall->getNumArgs() < 1) {
     Diag(TheCall->getEndLoc(), diag::err_typecheck_call_too_few_args_at_least)
-        << 0 << 1 << TheCall->getNumArgs() << Callee->getSourceRange();
+        << 0 << 1 << TheCall->getNumArgs() << /*is non object*/ 0
+        << Callee->getSourceRange();
     return ExprError();
   }
 
@@ -7971,7 +7976,7 @@ Sema::SemaBuiltinAtomicOverloaded(ExprResult TheCallResult) {
   // have at least that many.
   if (TheCall->getNumArgs() < 1+NumFixed) {
     Diag(TheCall->getEndLoc(), diag::err_typecheck_call_too_few_args_at_least)
-        << 0 << 1 + NumFixed << TheCall->getNumArgs()
+        << 0 << 1 + NumFixed << TheCall->getNumArgs() << /*is non object*/ 0
         << Callee->getSourceRange();
     return ExprError();
   }
@@ -8361,7 +8366,8 @@ bool Sema::SemaBuiltinVAStartARMMicrosoft(CallExpr *Call) {
   if (Call->getNumArgs() < 3)
     return Diag(Call->getEndLoc(),
                 diag::err_typecheck_call_too_few_args_at_least)
-           << 0 /*function call*/ << 3 << Call->getNumArgs();
+           << 0 /*function call*/ << 3 << Call->getNumArgs()
+           << /*is non object*/ 0;
 
   // Type-check the first argument normally.
   if (checkBuiltinArgument(*this, Call, 0))
@@ -8622,7 +8628,7 @@ ExprResult Sema::SemaBuiltinShuffleVector(CallExpr *TheCall) {
     return ExprError(Diag(TheCall->getEndLoc(),
                           diag::err_typecheck_call_too_few_args_at_least)
                      << 0 /*function call*/ << 2 << TheCall->getNumArgs()
-                     << TheCall->getSourceRange());
+                     << /*is non object*/ 0 << TheCall->getSourceRange());
 
   // Determine which of the following types of shufflevector we're checking:
   // 1) unary, vector mask: (lhs, mask)
@@ -8742,7 +8748,8 @@ bool Sema::SemaBuiltinPrefetch(CallExpr *TheCall) {
   if (NumArgs > 3)
     return Diag(TheCall->getEndLoc(),
                 diag::err_typecheck_call_too_many_args_at_most)
-           << 0 /*function call*/ << 3 << NumArgs << TheCall->getSourceRange();
+           << 0 /*function call*/ << 3 << NumArgs << /*is non object*/ 0
+           << TheCall->getSourceRange();
 
   // Argument 0 is checked for us and the remaining arguments must be
   // constant integers.
@@ -8881,13 +8888,13 @@ bool Sema::SemaBuiltinOSLogFormat(CallExpr *TheCall) {
   if (NumArgs < NumRequiredArgs) {
     return Diag(TheCall->getEndLoc(), diag::err_typecheck_call_too_few_args)
            << 0 /* function call */ << NumRequiredArgs << NumArgs
-           << TheCall->getSourceRange();
+           << /*is non object*/ 0 << TheCall->getSourceRange();
   }
   if (NumArgs >= NumRequiredArgs + 0x100) {
     return Diag(TheCall->getEndLoc(),
                 diag::err_typecheck_call_too_many_args_at_most)
            << 0 /* function call */ << (NumRequiredArgs + 0xff) << NumArgs
-           << TheCall->getSourceRange();
+           << /*is non object*/ 0 << TheCall->getSourceRange();
   }
   unsigned i = 0;
 

diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
@@ -70,15 +70,15 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
   // If the function is a non-static member function, add the type
   // of the implicit object parameter before the formal parameters.
   if (auto *MD = dyn_cast<CXXMethodDecl>(FD)) {
-    if (MD->isInstance()) {
+    if (MD->isImplicitObjectMemberFunction()) {
       // [over.match.funcs]4
       // For non-static member functions, the type of the implicit object
       // parameter is
       //  -- "lvalue reference to cv X" for functions declared without a
       //      ref-qualifier or with the & ref-qualifier
       //  -- "rvalue reference to cv X" for functions declared with the &&
       //      ref-qualifier
-      QualType T = MD->getThisObjectType();
+      QualType T = MD->getFunctionObjectParameterType();
       T = FnType->getRefQualifier() == RQ_RValue
               ? S.Context.getRValueReferenceType(T)
               : S.Context.getLValueReferenceType(T, /*SpelledAsLValue*/ true);
@@ -564,10 +564,10 @@ VarDecl *Sema::buildCoroutinePromise(SourceLocation Loc) {
   assert(isa<FunctionDecl>(CurContext) && "not in a function scope");
   auto *FD = cast<FunctionDecl>(CurContext);
   bool IsThisDependentType = [&] {
-    if (auto *MD = dyn_cast_or_null<CXXMethodDecl>(FD))
-      return MD->isInstance() && MD->getThisObjectType()->isDependentType();
-    else
-      return false;
+    if (const auto *MD = dyn_cast_if_present<CXXMethodDecl>(FD))
+      return MD->isImplicitObjectMemberFunction() &&
+             MD->getThisType()->isDependentType();
+    return false;
   }();
 
   QualType T = FD->getType()->isDependentType() || IsThisDependentType
@@ -592,7 +592,7 @@ VarDecl *Sema::buildCoroutinePromise(SourceLocation Loc) {
 
   // Add implicit object parameter.
   if (auto *MD = dyn_cast<CXXMethodDecl>(FD)) {
-    if (MD->isInstance() && !isLambdaCallOperator(MD)) {
+    if (MD->isImplicitObjectMemberFunction() && !isLambdaCallOperator(MD)) {
       ExprResult ThisExpr = ActOnCXXThis(Loc);
       if (ThisExpr.isInvalid())
         return nullptr;
@@ -1367,7 +1367,7 @@ bool CoroutineStmtBuilder::makeReturnOnAllocFailure() {
 static bool collectPlacementArgs(Sema &S, FunctionDecl &FD, SourceLocation Loc,
                                  SmallVectorImpl<Expr *> &PlacementArgs) {
   if (auto *MD = dyn_cast<CXXMethodDecl>(&FD)) {
-    if (MD->isInstance() && !isLambdaCallOperator(MD)) {
+    if (MD->isImplicitObjectMemberFunction() && !isLambdaCallOperator(MD)) {
       ExprResult ThisExpr = S.ActOnCXXThis(Loc);
       if (ThisExpr.isInvalid())
         return false;

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
@@ -8924,13 +8924,11 @@ bool Sema::AddOverriddenMethods(CXXRecordDecl *DC, CXXMethodDecl *MD) {
       CXXMethodDecl *BaseMD =
           dyn_cast<CXXMethodDecl>(BaseND->getCanonicalDecl());
       if (!BaseMD || !BaseMD->isVirtual() ||
-          IsOverload(MD, BaseMD, /*UseMemberUsingDeclRules=*/false,
-                     /*ConsiderCudaAttrs=*/true,
-                     // C++2a [class.virtual]p2 does not consider requires
-                     // clauses when overriding.
-                     /*ConsiderRequiresClauses=*/false))
+          IsOverride(MD, BaseMD, /*UseMemberUsingDeclRules=*/false,
+                     /*ConsiderCudaAttrs=*/true))
+        continue;
+      if (!CheckExplicitObjectOverride(MD, BaseMD))
         continue;
-
       if (Overridden.insert(BaseMD).second) {
         MD->addOverriddenMethod(BaseMD);
         CheckOverridingFunctionReturnType(MD, BaseMD);
@@ -9265,6 +9263,8 @@ static FunctionDecl *CreateNewFunctionDecl(Sema &SemaRef, Declarator &D,
   }
   Expr *TrailingRequiresClause = D.getTrailingRequiresClause();
 
+  SemaRef.CheckExplicitObjectMemberFunction(DC, D, Name, R);
+
   if (Name.getNameKind() == DeclarationName::CXXConstructorName) {
     // This is a C++ constructor declaration.
     assert(DC->isRecord() &&
@@ -9766,8 +9766,9 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
       << DeclSpec::getSpecifierName(TSCS);
 
   if (D.isFirstDeclarationOfMember())
-    adjustMemberFunctionCC(R, D.isStaticMember(), D.isCtorOrDtor(),
-                           D.getIdentifierLoc());
+    adjustMemberFunctionCC(
+        R, !(D.isStaticMember() || D.isExplicitObjectMemberFunction()),
+        D.isCtorOrDtor(), D.getIdentifierLoc());
 
   bool isFriend = false;
   FunctionTemplateDecl *FunctionTemplate = nullptr;
@@ -11971,7 +11972,7 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
       // struct B { struct Y { ~Y(); }; using X = Y; };
       // template struct A<B>;
       if (NewFD->getFriendObjectKind() == Decl::FriendObjectKind::FOK_None ||
-          !Destructor->getThisObjectType()->isDependentType()) {
+          !Destructor->getFunctionObjectParameterType()->isDependentType()) {
         CXXRecordDecl *Record = Destructor->getParent();
         QualType ClassType = Context.getTypeDeclType(Record);
 
@@ -14918,9 +14919,32 @@ void Sema::CheckFunctionOrTemplateParamDeclarator(Scope *S, Declarator &D) {
   }
 }
 
+static void CheckExplicitObjectParameter(Sema &S, ParmVarDecl *P,
+                                         SourceLocation ExplicitThisLoc) {
+  if (!ExplicitThisLoc.isValid())
+    return;
+  assert(S.getLangOpts().CPlusPlus &&
+         "explicit parameter in non-cplusplus mode");
+  if (!S.getLangOpts().CPlusPlus23)
+    S.Diag(ExplicitThisLoc, diag::err_cxx20_deducing_this)
+        << P->getSourceRange();
+
+  // C++2b [dcl.fct/7] An explicit object parameter shall not be a function
+  // parameter pack.
+  if (P->isParameterPack()) {
+    S.Diag(P->getBeginLoc(), diag::err_explicit_object_parameter_pack)
+        << P->getSourceRange();
+    return;
+  }
+  P->setExplicitObjectParameterLoc(ExplicitThisLoc);
+  if (LambdaScopeInfo *LSI = S.getCurLambda())
+    LSI->ExplicitObjectParameter = P;
+}
+
 /// ActOnParamDeclarator - Called from Parser::ParseFunctionDeclarator()
 /// to introduce parameters into function prototype scope.
-Decl *Sema::ActOnParamDeclarator(Scope *S, Declarator &D) {
+Decl *Sema::ActOnParamDeclarator(Scope *S, Declarator &D,
+                                 SourceLocation ExplicitThisLoc) {
   const DeclSpec &DS = D.getDeclSpec();
 
   // Verify C99 6.7.5.3p2: The only SCS allowed is 'register'.
@@ -14998,6 +15022,8 @@ Decl *Sema::ActOnParamDeclarator(Scope *S, Declarator &D) {
   if (D.isInvalidType())
     New->setInvalidDecl();
 
+  CheckExplicitObjectParameter(*this, New, ExplicitThisLoc);
+
   assert(S->isFunctionPrototypeScope());
   assert(S->getFunctionPrototypeDepth() >= 1);
   New->setScopeInfo(S->getFunctionPrototypeDepth() - 1,
@@ -15395,6 +15421,8 @@ LambdaScopeInfo *Sema::RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator) {
 
   LSI->IntroducerRange = DNI.getCXXOperatorNameRange();
   LSI->Mutable = !CallOperator->isConst();
+  if (CallOperator->isExplicitObjectMemberFunction())
+    LSI->ExplicitObjectParameter = CallOperator->getParamDecl(0);
 
   // Add the captures to the LSI so they can be noted as already
   // captured within tryCaptureVar.
@@ -18781,10 +18809,13 @@ static bool AreSpecialMemberFunctionsSameKind(ASTContext &Context,
   if (CSM == Sema::CXXDefaultConstructor)
     return bool(M1->getDescribedFunctionTemplate()) ==
            bool(M2->getDescribedFunctionTemplate());
-  if (!Context.hasSameType(M1->getParamDecl(0)->getType(),
-                           M2->getParamDecl(0)->getType()))
+  // FIXME: better resolve CWG
+  // https://cplusplus.github.io/CWG/issues/2787.html
+  if (!Context.hasSameType(M1->getNonObjectParameter(0)->getType(),
+                           M2->getNonObjectParameter(0)->getType()))
     return false;
-  if (!Context.hasSameType(M1->getThisType(), M2->getThisType()))
+  if (!Context.hasSameType(M1->getFunctionObjectParameterReferenceType(),
+                           M2->getFunctionObjectParameterReferenceType()))
     return false;
 
   return true;

diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1234,7 +1234,7 @@ static void handleConsumableAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
 
 static bool checkForConsumableClass(Sema &S, const CXXMethodDecl *MD,
                                     const ParsedAttr &AL) {
-  QualType ThisType = MD->getThisObjectType();
+  QualType ThisType = MD->getFunctionObjectParameterType();
 
   if (const CXXRecordDecl *RD = ThisType->getAsCXXRecordDecl()) {
     if (!RD->hasAttr<ConsumableAttr>()) {
@@ -1336,23 +1336,23 @@ static void handleReturnTypestateAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   // FIXME: This check is currently being done in the analysis.  It can be
   //        enabled here only after the parser propagates attributes at
   //        template specialization definition, not declaration.
-  //QualType ReturnType;
+  // QualType ReturnType;
   //
-  //if (const ParmVarDecl *Param = dyn_cast<ParmVarDecl>(D)) {
+  // if (const ParmVarDecl *Param = dyn_cast<ParmVarDecl>(D)) {
   //  ReturnType = Param->getType();
   //
   //} else if (const CXXConstructorDecl *Constructor =
   //             dyn_cast<CXXConstructorDecl>(D)) {
-  //  ReturnType = Constructor->getThisObjectType();
+  //  ReturnType = Constructor->getFunctionObjectParameterType();
   //
   //} else {
   //
   //  ReturnType = cast<FunctionDecl>(D)->getCallResultType();
   //}
   //
-  //const CXXRecordDecl *RD = ReturnType->getAsCXXRecordDecl();
+  // const CXXRecordDecl *RD = ReturnType->getAsCXXRecordDecl();
   //
-  //if (!RD || !RD->hasAttr<ConsumableAttr>()) {
+  // if (!RD || !RD->hasAttr<ConsumableAttr>()) {
   //    S.Diag(Attr.getLoc(), diag::warn_return_state_for_unconsumable_type) <<
   //      ReturnType.getAsString();
   //    return;

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -769,14 +769,12 @@ bool Sema::handlerCanCatch(QualType HandlerType, QualType ExceptionType) {
 /// CheckExceptionSpecSubset - Check whether the second function type's
 /// exception specification is a subset (or equivalent) of the first function
 /// type. This is used by override and pointer assignment checks.
-bool Sema::CheckExceptionSpecSubset(const PartialDiagnostic &DiagID,
-                                    const PartialDiagnostic &NestedDiagID,
-                                    const PartialDiagnostic &NoteID,
-                                    const PartialDiagnostic &NoThrowDiagID,
-                                    const FunctionProtoType *Superset,
-                                    SourceLocation SuperLoc,
-                                    const FunctionProtoType *Subset,
-                                    SourceLocation SubLoc) {
+bool Sema::CheckExceptionSpecSubset(
+    const PartialDiagnostic &DiagID, const PartialDiagnostic &NestedDiagID,
+    const PartialDiagnostic &NoteID, const PartialDiagnostic &NoThrowDiagID,
+    const FunctionProtoType *Superset, bool SkipSupersetFirstParameter,
+    SourceLocation SuperLoc, const FunctionProtoType *Subset,
+    bool SkipSubsetFirstParameter, SourceLocation SubLoc) {
 
   // Just auto-succeed under -fno-exceptions.
   if (!getLangOpts().CXXExceptions)
@@ -816,8 +814,9 @@ bool Sema::CheckExceptionSpecSubset(const PartialDiagnostic &DiagID,
   // done.
   if ((SuperCanThrow == CT_Can && SuperEST != EST_Dynamic) ||
       SubCanThrow == CT_Cannot)
-    return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset, SuperLoc,
-                                   Subset, SubLoc);
+    return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset,
+                                   SkipSupersetFirstParameter, SuperLoc, Subset,
+                                   SkipSubsetFirstParameter, SubLoc);
 
   // Allow __declspec(nothrow) to be missing on redeclaration as an extension in
   // some cases.
@@ -869,8 +868,9 @@ bool Sema::CheckExceptionSpecSubset(const PartialDiagnostic &DiagID,
     }
   }
   // We've run half the gauntlet.
-  return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset, SuperLoc,
-                                 Subset, SubLoc);
+  return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset,
+                                 SkipSupersetFirstParameter, SuperLoc, Subset,
+                                 SkipSupersetFirstParameter, SubLoc);
 }
 
 static bool
@@ -894,12 +894,11 @@ CheckSpecForTypesEquivalent(Sema &S, const PartialDiagnostic &DiagID,
 /// assignment and override compatibility check. We do not check the parameters
 /// of parameter function pointers recursively, as no sane programmer would
 /// even be able to write such a function type.
-bool Sema::CheckParamExceptionSpec(const PartialDiagnostic &DiagID,
-                                   const PartialDiagnostic &NoteID,
-                                   const FunctionProtoType *Target,
-                                   SourceLocation TargetLoc,
-                                   const FunctionProtoType *Source,
-                                   SourceLocation SourceLoc) {
+bool Sema::CheckParamExceptionSpec(
+    const PartialDiagnostic &DiagID, const PartialDiagnostic &NoteID,
+    const FunctionProtoType *Target, bool SkipTargetFirstParameter,
+    SourceLocation TargetLoc, const FunctionProtoType *Source,
+    bool SkipSourceFirstParameter, SourceLocation SourceLoc) {
   auto RetDiag = DiagID;
   RetDiag << 0;
   if (CheckSpecForTypesEquivalent(
@@ -910,14 +909,16 @@ bool Sema::CheckParamExceptionSpec(const PartialDiagnostic &DiagID,
 
   // We shouldn't even be testing this unless the arguments are otherwise
   // compatible.
-  assert(Target->getNumParams() == Source->getNumParams() &&
+  assert((Target->getNumParams() - (unsigned)SkipTargetFirstParameter) ==
+             (Source->getNumParams() - (unsigned)SkipSourceFirstParameter) &&
          "Functions have different argument counts.");
   for (unsigned i = 0, E = Target->getNumParams(); i != E; ++i) {
     auto ParamDiag = DiagID;
     ParamDiag << 1;
     if (CheckSpecForTypesEquivalent(
             *this, ParamDiag, PDiag(),
-            Target->getParamType(i), TargetLoc, Source->getParamType(i),
+            Target->getParamType(i + (SkipTargetFirstParameter ? 1 : 0)),
+            TargetLoc, Source->getParamType(SkipSourceFirstParameter ? 1 : 0),
             SourceLoc))
       return true;
   }
@@ -958,9 +959,10 @@ bool Sema::CheckExceptionSpecCompatibility(Expr *From, QualType ToType) {
   //     void (*q)(void (*) throw(int)) = p;
   //   }
   // ... because it might be instantiated with T=int.
-  return CheckExceptionSpecSubset(
-             PDiag(DiagID), PDiag(NestedDiagID), PDiag(), PDiag(), ToFunc,
-             From->getSourceRange().getBegin(), FromFunc, SourceLocation()) &&
+  return CheckExceptionSpecSubset(PDiag(DiagID), PDiag(NestedDiagID), PDiag(),
+                                  PDiag(), ToFunc, 0,
+                                  From->getSourceRange().getBegin(), FromFunc,
+                                  0, SourceLocation()) &&
          !getLangOpts().CPlusPlus17;
 }
 
@@ -989,14 +991,14 @@ bool Sema::CheckOverridingFunctionExceptionSpec(const CXXMethodDecl *New,
   unsigned DiagID = diag::err_override_exception_spec;
   if (getLangOpts().MSVCCompat)
     DiagID = diag::ext_override_exception_spec;
-  return CheckExceptionSpecSubset(PDiag(DiagID),
-                                  PDiag(diag::err_deep_exception_specs_differ),
-                                  PDiag(diag::note_overridden_virtual_function),
-                                  PDiag(diag::ext_override_exception_spec),
-                                  Old->getType()->castAs<FunctionProtoType>(),
-                                  Old->getLocation(),
-                                  New->getType()->castAs<FunctionProtoType>(),
-                                  New->getLocation());
+  return CheckExceptionSpecSubset(
+      PDiag(DiagID), PDiag(diag::err_deep_exception_specs_differ),
+      PDiag(diag::note_overridden_virtual_function),
+      PDiag(diag::ext_override_exception_spec),
+      Old->getType()->castAs<FunctionProtoType>(),
+      Old->hasCXXExplicitFunctionObjectParameter(), Old->getLocation(),
+      New->getType()->castAs<FunctionProtoType>(),
+      New->hasCXXExplicitFunctionObjectParameter(), New->getLocation());
 }
 
 static CanThrowResult canSubStmtsThrow(Sema &Self, const Stmt *S) {

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
@@ -2444,7 +2444,7 @@ bool Sema::DiagnoseDependentMemberLookup(const LookupResult &R) {
   // FIXME: Is this special case necessary? We could allow the caller to
   // diagnose this.
   if (isDefaultArgument && ((*R.begin())->isCXXInstanceMember())) {
-    Diag(R.getNameLoc(), diag::err_member_call_without_object);
+    Diag(R.getNameLoc(), diag::err_member_call_without_object) << 0;
     return true;
   }
 
@@ -3217,11 +3217,11 @@ Sema::PerformObjectMemberConversion(Expr *From,
       FromRecordType = FromType;
     }
   } else if (const auto *Method = dyn_cast<CXXMethodDecl>(Member)) {
-    if (Method->isStatic())
+    if (!Method->isImplicitObjectMemberFunction())
       return From;
 
     DestType = Method->getThisType().getNonReferenceType();
-    DestRecordType = Method->getThisObjectType();
+    DestRecordType = Method->getFunctionObjectParameterType();
 
     if (FromType->getAs<PointerType>()) {
       FromRecordType = FromType->getPointeeType();
@@ -6503,6 +6503,9 @@ Sema::ConvertArgumentsForCall(CallExpr *Call, Expr *Fn,
 
   // C99 6.5.2.2p7 - the arguments are implicitly converted, as if by
   // assignment, to the types of the corresponding parameter, ...
+  bool HasExplicitObjectParameter =
+      FDecl && FDecl->hasCXXExplicitFunctionObjectParameter();
+  unsigned ExplicitObjectParameterOffset = HasExplicitObjectParameter ? 1 : 0;
   unsigned NumParams = Proto->getNumParams();
   bool Invalid = false;
   unsigned MinArgs = FDecl ? FDecl->getMinRequiredArguments() : NumParams;
@@ -6521,21 +6524,29 @@ Sema::ConvertArgumentsForCall(CallExpr *Call, Expr *Fn,
             MinArgs == NumParams && !Proto->isVariadic()
                 ? diag::err_typecheck_call_too_few_args_suggest
                 : diag::err_typecheck_call_too_few_args_at_least_suggest;
-        diagnoseTypo(TC, PDiag(diag_id) << FnKind << MinArgs
-                                        << static_cast<unsigned>(Args.size())
-                                        << TC.getCorrectionRange());
-      } else if (MinArgs == 1 && FDecl && FDecl->getParamDecl(0)->getDeclName())
+        diagnoseTypo(
+            TC, PDiag(diag_id)
+                    << FnKind << MinArgs - ExplicitObjectParameterOffset
+                    << static_cast<unsigned>(Args.size()) -
+                           ExplicitObjectParameterOffset
+                    << HasExplicitObjectParameter << TC.getCorrectionRange());
+      } else if (MinArgs - ExplicitObjectParameterOffset == 1 && FDecl &&
+                 FDecl->getParamDecl(ExplicitObjectParameterOffset)
+                     ->getDeclName())
         Diag(RParenLoc,
              MinArgs == NumParams && !Proto->isVariadic()
                  ? diag::err_typecheck_call_too_few_args_one
                  : diag::err_typecheck_call_too_few_args_at_least_one)
-            << FnKind << FDecl->getParamDecl(0) << Fn->getSourceRange();
+            << FnKind << FDecl->getParamDecl(ExplicitObjectParameterOffset)
+            << HasExplicitObjectParameter << Fn->getSourceRange();
       else
         Diag(RParenLoc, MinArgs == NumParams && !Proto->isVariadic()
                             ? diag::err_typecheck_call_too_few_args
                             : diag::err_typecheck_call_too_few_args_at_least)
-            << FnKind << MinArgs << static_cast<unsigned>(Args.size())
-            << Fn->getSourceRange();
+            << FnKind << MinArgs - ExplicitObjectParameterOffset
+            << static_cast<unsigned>(Args.size()) -
+                   ExplicitObjectParameterOffset
+            << HasExplicitObjectParameter << Fn->getSourceRange();
 
       // Emit the location of the prototype.
       if (!TC && FDecl && !FDecl->getBuiltinID() && !IsExecConfig)
@@ -6560,26 +6571,34 @@ Sema::ConvertArgumentsForCall(CallExpr *Call, Expr *Fn,
             MinArgs == NumParams && !Proto->isVariadic()
                 ? diag::err_typecheck_call_too_many_args_suggest
                 : diag::err_typecheck_call_too_many_args_at_most_suggest;
-        diagnoseTypo(TC, PDiag(diag_id) << FnKind << NumParams
-                                        << static_cast<unsigned>(Args.size())
-                                        << TC.getCorrectionRange());
-      } else if (NumParams == 1 && FDecl &&
-                 FDecl->getParamDecl(0)->getDeclName())
+        diagnoseTypo(
+            TC, PDiag(diag_id)
+                    << FnKind << NumParams - ExplicitObjectParameterOffset
+                    << static_cast<unsigned>(Args.size()) -
+                           ExplicitObjectParameterOffset
+                    << HasExplicitObjectParameter << TC.getCorrectionRange());
+      } else if (NumParams - ExplicitObjectParameterOffset == 1 && FDecl &&
+                 FDecl->getParamDecl(ExplicitObjectParameterOffset)
+                     ->getDeclName())
         Diag(Args[NumParams]->getBeginLoc(),
              MinArgs == NumParams
                  ? diag::err_typecheck_call_too_many_args_one
                  : diag::err_typecheck_call_too_many_args_at_most_one)
-            << FnKind << FDecl->getParamDecl(0)
-            << static_cast<unsigned>(Args.size()) << Fn->getSourceRange()
+            << FnKind << FDecl->getParamDecl(ExplicitObjectParameterOffset)
+            << static_cast<unsigned>(Args.size()) -
+                   ExplicitObjectParameterOffset
+            << HasExplicitObjectParameter << Fn->getSourceRange()
             << SourceRange(Args[NumParams]->getBeginLoc(),
                            Args.back()->getEndLoc());
       else
         Diag(Args[NumParams]->getBeginLoc(),
              MinArgs == NumParams
                  ? diag::err_typecheck_call_too_many_args
                  : diag::err_typecheck_call_too_many_args_at_most)
-            << FnKind << NumParams << static_cast<unsigned>(Args.size())
-            << Fn->getSourceRange()
+            << FnKind << NumParams - ExplicitObjectParameterOffset
+            << static_cast<unsigned>(Args.size()) -
+                   ExplicitObjectParameterOffset
+            << HasExplicitObjectParameter << Fn->getSourceRange()
             << SourceRange(Args[NumParams]->getBeginLoc(),
                            Args.back()->getEndLoc());
 
@@ -7661,9 +7680,9 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl,
   }
 
   if (CXXMethodDecl *Method = dyn_cast_or_null<CXXMethodDecl>(FDecl))
-    if (!Method->isStatic())
+    if (Method->isImplicitObjectMemberFunction())
       return ExprError(Diag(LParenLoc, diag::err_member_call_without_object)
-        << Fn->getSourceRange());
+                       << Fn->getSourceRange() << 0);
 
   // Check for sentinels
   if (NDecl)
@@ -14955,6 +14974,34 @@ static void diagnoseAddressOfInvalidType(Sema &S, SourceLocation Loc,
   S.Diag(Loc, diag::err_typecheck_address_of) << Type << E->getSourceRange();
 }
 
+bool Sema::CheckUseOfCXXMethodAsAddressOfOperand(SourceLocation OpLoc,
+                                                 const Expr *Op,
+                                                 const CXXMethodDecl *MD) {
+  const auto *DRE = cast<DeclRefExpr>(Op->IgnoreParens());
+
+  if (Op != DRE)
+    return Diag(OpLoc, diag::err_parens_pointer_member_function)
+           << Op->getSourceRange();
+
+  // Taking the address of a dtor is illegal per C++ [class.dtor]p2.
+  if (isa<CXXDestructorDecl>(MD))
+    return Diag(OpLoc, diag::err_typecheck_addrof_dtor)
+           << DRE->getSourceRange();
+
+  if (DRE->getQualifier())
+    return false;
+
+  if (MD->getParent()->getName().empty())
+    return Diag(OpLoc, diag::err_unqualified_pointer_member_function)
+           << DRE->getSourceRange();
+
+  SmallString<32> Str;
+  StringRef Qual = (MD->getParent()->getName() + "::").toStringRef(Str);
+  return Diag(OpLoc, diag::err_unqualified_pointer_member_function)
+         << DRE->getSourceRange()
+         << FixItHint::CreateInsertion(DRE->getSourceRange().getBegin(), Qual);
+}
+
 /// CheckAddressOfOperand - The operand of & must be either a function
 /// designator or an lvalue designating an object. If it is an lvalue, the
 /// object cannot be declared with storage class register or be a bit field.
@@ -15064,28 +15111,7 @@ QualType Sema::CheckAddressOfOperand(ExprResult &OrigOp, SourceLocation OpLoc) {
     DeclRefExpr *DRE = cast<DeclRefExpr>(op);
     CXXMethodDecl *MD = cast<CXXMethodDecl>(DRE->getDecl());
 
-    // The id-expression was parenthesized.
-    if (OrigOp.get() != DRE) {
-      Diag(OpLoc, diag::err_parens_pointer_member_function)
-        << OrigOp.get()->getSourceRange();
-
-    // The method was named without a qualifier.
-    } else if (!DRE->getQualifier()) {
-      if (MD->getParent()->getName().empty())
-        Diag(OpLoc, diag::err_unqualified_pointer_member_function)
-          << op->getSourceRange();
-      else {
-        SmallString<32> Str;
-        StringRef Qual = (MD->getParent()->getName() + "::").toStringRef(Str);
-        Diag(OpLoc, diag::err_unqualified_pointer_member_function)
-          << op->getSourceRange()
-          << FixItHint::CreateInsertion(op->getSourceRange().getBegin(), Qual);
-      }
-    }
-
-    // Taking the address of a dtor is illegal per C++ [class.dtor]p2.
-    if (isa<CXXDestructorDecl>(MD))
-      Diag(OpLoc, diag::err_typecheck_addrof_dtor) << op->getSourceRange();
+    CheckUseOfCXXMethodAsAddressOfOperand(OpLoc, OrigOp.get(), MD);
 
     QualType MPTy = Context.getMemberPointerType(
         op->getType(), Context.getTypeDeclType(MD->getParent()).getTypePtr());
@@ -15105,7 +15131,11 @@ QualType Sema::CheckAddressOfOperand(ExprResult &OrigOp, SourceLocation OpLoc) {
           << op->getType() << op->getSourceRange();
         return QualType();
       }
+    } else if (const auto *DRE = dyn_cast<DeclRefExpr>(op)) {
+      if (const auto *MD = dyn_cast_or_null<CXXMethodDecl>(DRE->getDecl()))
+        CheckUseOfCXXMethodAsAddressOfOperand(OpLoc, OrigOp.get(), MD);
     }
+
   } else if (op->getObjectKind() == OK_BitField) { // C99 6.5.3.2p1
     // The operand cannot be a bit-field
     AddressOfError = AO_Bit_Field;
@@ -16496,7 +16526,7 @@ bool Sema::isQualifiedMemberAccess(Expr *E) {
     if (isa<FieldDecl>(VD) || isa<IndirectFieldDecl>(VD))
       return true;
     if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(VD))
-      return Method->isInstance();
+      return Method->isImplicitObjectMemberFunction();
 
     return false;
   }
@@ -16507,7 +16537,7 @@ bool Sema::isQualifiedMemberAccess(Expr *E) {
 
     for (NamedDecl *D : ULE->decls()) {
       if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D)) {
-        if (Method->isInstance())
+        if (Method->isImplicitObjectMemberFunction())
           return true;
       } else {
         // Overload set does not contain methods.
@@ -19227,7 +19257,8 @@ static bool isVariableAlreadyCapturedInScopeInfo(CapturingScopeInfo *CSI,
     // private instances of the captured declarations.
     const Capture &Cap = CSI->getCapture(Var);
     if (Cap.isCopyCapture() &&
-        !(isa<LambdaScopeInfo>(CSI) && cast<LambdaScopeInfo>(CSI)->Mutable) &&
+        !(isa<LambdaScopeInfo>(CSI) &&
+          !cast<LambdaScopeInfo>(CSI)->lambdaCaptureShouldBeConst()) &&
         !(isa<CapturedRegionScopeInfo>(CSI) &&
           cast<CapturedRegionScopeInfo>(CSI)->CapRegionKind == CR_OpenMP))
       DeclRefType.addConst();
@@ -19544,7 +19575,8 @@ static bool captureInLambda(LambdaScopeInfo *LSI, ValueDecl *Var,
     //   declared const (9.3.1) if and only if the lambda-expression's
     //   parameter-declaration-clause is not followed by mutable.
     DeclRefType = CaptureType.getNonReferenceType();
-    if (!LSI->Mutable && !CaptureType->isReferenceType())
+    bool Const = LSI->lambdaCaptureShouldBeConst();
+    if (Const && !CaptureType->isReferenceType())
       DeclRefType.addConst();
   }
 
@@ -20612,6 +20644,34 @@ void Sema::MarkVariableReferenced(SourceLocation Loc, VarDecl *Var) {
   DoMarkVarDeclReferenced(*this, Loc, Var, nullptr, RefsMinusAssignments);
 }
 
+// C++ [temp.dep.expr]p3:
+//   An id-expression is type-dependent if it contains:
+//     - an identifier associated by name lookup with an entity captured by copy
+//       in a lambda-expression that has an explicit object parameter whose type
+//       is dependent ([dcl.fct]),
+static void FixDependencyOfIdExpressionsInLambdaWithDependentObjectParameter(
+    Sema &SemaRef, ValueDecl *D, Expr *E) {
+  auto *ID = dyn_cast<DeclRefExpr>(E);
+  if (!ID || ID->isTypeDependent())
+    return;
+
+  auto IsDependent = [&]() {
+    const LambdaScopeInfo *LSI = SemaRef.getCurLambda();
+    if (!LSI)
+      return false;
+    if (!LSI->ExplicitObjectParameter ||
+        !LSI->ExplicitObjectParameter->getType()->isDependentType())
+      return false;
+    if (!LSI->CaptureMap.count(D))
+      return false;
+    const Capture &Cap = LSI->getCapture(D);
+    return !Cap.isCopyCapture();
+  }();
+
+  ID->setCapturedByCopyInLambdaWithExplicitObjectParameter(
+      IsDependent, SemaRef.getASTContext());
+}
+
 static void
 MarkExprReferenced(Sema &SemaRef, SourceLocation Loc, Decl *D, Expr *E,
                    bool MightBeOdrUse,
@@ -20621,14 +20681,19 @@ MarkExprReferenced(Sema &SemaRef, SourceLocation Loc, Decl *D, Expr *E,
 
   if (VarDecl *Var = dyn_cast<VarDecl>(D)) {
     DoMarkVarDeclReferenced(SemaRef, Loc, Var, E, RefsMinusAssignments);
+    if (SemaRef.getLangOpts().CPlusPlus)
+      FixDependencyOfIdExpressionsInLambdaWithDependentObjectParameter(SemaRef,
+                                                                       Var, E);
     return;
   }
 
   if (BindingDecl *Decl = dyn_cast<BindingDecl>(D)) {
     DoMarkBindingDeclReferenced(SemaRef, Loc, Decl, E);
+    if (SemaRef.getLangOpts().CPlusPlus)
+      FixDependencyOfIdExpressionsInLambdaWithDependentObjectParameter(SemaRef,
+                                                                       Decl, E);
     return;
   }
-
   SemaRef.MarkAnyDeclReferenced(Loc, D, MightBeOdrUse);
 
   // If this is a call to a method via a cast, also mark the method in the

diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1160,7 +1160,7 @@ static QualType adjustCVQualifiersForCXXThisWithinLambda(
     auto C = CurLSI->getCXXThisCapture();
 
     if (C.isCopyCapture()) {
-      if (!CurLSI->Mutable)
+      if (CurLSI->lambdaCaptureShouldBeConst())
         ClassType.addConst();
       return ASTCtx.getPointerType(ClassType);
     }
@@ -1216,11 +1216,11 @@ QualType Sema::getCurrentThisType() {
   QualType ThisTy = CXXThisTypeOverride;
 
   if (CXXMethodDecl *method = dyn_cast<CXXMethodDecl>(DC)) {
-    if (method && method->isInstance())
+    if (method && method->isImplicitObjectMemberFunction())
       ThisTy = method->getThisType().getNonReferenceType();
   }
 
-  if (ThisTy.isNull() && isLambdaCallOperator(CurContext) &&
+  if (ThisTy.isNull() && isLambdaCallWithImplicitObjectParameter(CurContext) &&
       inTemplateInstantiation() && isa<CXXRecordDecl>(DC)) {
 
     // This is a lambda call operator that is being instantiated as a default
@@ -1398,10 +1398,22 @@ ExprResult Sema::ActOnCXXThis(SourceLocation Loc) {
   /// C++ 9.3.2: In the body of a non-static member function, the keyword this
   /// is a non-lvalue expression whose value is the address of the object for
   /// which the function is called.
-
   QualType ThisTy = getCurrentThisType();
-  if (ThisTy.isNull())
-    return Diag(Loc, diag::err_invalid_this_use);
+
+  if (ThisTy.isNull()) {
+    DeclContext *DC = getFunctionLevelDeclContext();
+
+    if (const auto *Method = dyn_cast<CXXMethodDecl>(DC);
+        Method && Method->isExplicitObjectMemberFunction()) {
+      return Diag(Loc, diag::err_invalid_this_use) << 1;
+    }
+
+    if (isLambdaCallWithExplicitObjectParameter(CurContext))
+      return Diag(Loc, diag::err_invalid_this_use) << 1;
+
+    return Diag(Loc, diag::err_invalid_this_use) << 0;
+  }
+
   return BuildCXXThisExpr(Loc, ThisTy, /*IsImplicit=*/false);
 }
 
@@ -3960,7 +3972,7 @@ void Sema::CheckVirtualDtorCall(CXXDestructorDecl *dtor, SourceLocation Loc,
   if (getSourceManager().isInSystemHeader(PointeeRD->getLocation()))
     return;
 
-  QualType ClassType = dtor->getThisObjectType();
+  QualType ClassType = dtor->getFunctionObjectParameterType();
   if (PointeeRD->isAbstract()) {
     // If the class is abstract, we warn by default, because we're
     // sure the code has undefined behavior.
@@ -4319,15 +4331,17 @@ Sema::PerformImplicitConversion(Expr *From, QualType ToType,
     if (DiagnoseUseOfDecl(Fn, From->getBeginLoc()))
       return ExprError();
 
-    From = FixOverloadedFunctionReference(From, Found, Fn);
+    ExprResult Res = FixOverloadedFunctionReference(From, Found, Fn);
+    if (Res.isInvalid())
+      return ExprError();
 
     // We might get back another placeholder expression if we resolved to a
     // builtin.
-    ExprResult Checked = CheckPlaceholderExpr(From);
-    if (Checked.isInvalid())
+    Res = CheckPlaceholderExpr(Res.get());
+    if (Res.isInvalid())
       return ExprError();
 
-    From = Checked.get();
+    From = Res.get();
     FromType = From->getType();
   }
 
@@ -8052,68 +8066,6 @@ ExprResult Sema::ActOnPseudoDestructorExpr(Scope *S, Expr *Base,
                                    Destructed);
 }
 
-ExprResult Sema::BuildCXXMemberCallExpr(Expr *E, NamedDecl *FoundDecl,
-                                        CXXConversionDecl *Method,
-                                        bool HadMultipleCandidates) {
-  // Convert the expression to match the conversion function's implicit object
-  // parameter.
-  ExprResult Exp = PerformObjectArgumentInitialization(E, /*Qualifier=*/nullptr,
-                                          FoundDecl, Method);
-  if (Exp.isInvalid())
-    return true;
-
-  if (Method->getParent()->isLambda() &&
-      Method->getConversionType()->isBlockPointerType()) {
-    // This is a lambda conversion to block pointer; check if the argument
-    // was a LambdaExpr.
-    Expr *SubE = E;
-    CastExpr *CE = dyn_cast<CastExpr>(SubE);
-    if (CE && CE->getCastKind() == CK_NoOp)
-      SubE = CE->getSubExpr();
-    SubE = SubE->IgnoreParens();
-    if (CXXBindTemporaryExpr *BE = dyn_cast<CXXBindTemporaryExpr>(SubE))
-      SubE = BE->getSubExpr();
-    if (isa<LambdaExpr>(SubE)) {
-      // For the conversion to block pointer on a lambda expression, we
-      // construct a special BlockLiteral instead; this doesn't really make
-      // a difference in ARC, but outside of ARC the resulting block literal
-      // follows the normal lifetime rules for block literals instead of being
-      // autoreleased.
-      PushExpressionEvaluationContext(
-          ExpressionEvaluationContext::PotentiallyEvaluated);
-      ExprResult BlockExp = BuildBlockForLambdaConversion(
-          Exp.get()->getExprLoc(), Exp.get()->getExprLoc(), Method, Exp.get());
-      PopExpressionEvaluationContext();
-
-      // FIXME: This note should be produced by a CodeSynthesisContext.
-      if (BlockExp.isInvalid())
-        Diag(Exp.get()->getExprLoc(), diag::note_lambda_to_block_conv);
-      return BlockExp;
-    }
-  }
-
-  MemberExpr *ME =
-      BuildMemberExpr(Exp.get(), /*IsArrow=*/false, SourceLocation(),
-                      NestedNameSpecifierLoc(), SourceLocation(), Method,
-                      DeclAccessPair::make(FoundDecl, FoundDecl->getAccess()),
-                      HadMultipleCandidates, DeclarationNameInfo(),
-                      Context.BoundMemberTy, VK_PRValue, OK_Ordinary);
-
-  QualType ResultType = Method->getReturnType();
-  ExprValueKind VK = Expr::getValueKindForType(ResultType);
-  ResultType = ResultType.getNonLValueExprType(Context);
-
-  CXXMemberCallExpr *CE = CXXMemberCallExpr::Create(
-      Context, ME, /*Args=*/{}, ResultType, VK, Exp.get()->getEndLoc(),
-      CurFPFeatureOverrides());
-
-  if (CheckFunctionCall(Method, CE,
-                        Method->getType()->castAs<FunctionProtoType>()))
-    return ExprError();
-
-  return CheckForImmediateInvocation(CE, CE->getMethodDecl());
-}
-
 ExprResult Sema::BuildCXXNoexceptExpr(SourceLocation KeyLoc, Expr *Operand,
                                       SourceLocation RParen) {
   // If the operand is an unresolved lookup expression, the expression is ill-