SemaExpr.cpp

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//===--- SemaExpr.cpp - Semantic Analysis for Expressions -----------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file implements semantic analysis for expressions.
//
//===----------------------------------------------------------------------===//

#include "TreeTransform.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/ASTMutationListener.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/EvaluatedExprVisitor.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ExprOpenMP.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/TypeLoc.h"
#include "clang/Basic/FixedPoint.h"
#include "clang/Basic/PartialDiagnostic.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Lex/LiteralSupport.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/AnalysisBasedWarnings.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/DelayedDiagnostic.h"
#include "clang/Sema/Designator.h"
#include "clang/Sema/Initialization.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/Overload.h"
#include "clang/Sema/ParsedTemplate.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/ScopeInfo.h"
#include "clang/Sema/SemaFixItUtils.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Sema/Template.h"
#include "llvm/Support/ConvertUTF.h"
using namespace clang;
using namespace sema;

/// Determine whether the use of this declaration is valid, without
/// emitting diagnostics.
bool Sema::CanUseDecl(NamedDecl *D, bool TreatUnavailableAsInvalid) {
  // See if this is an auto-typed variable whose initializer we are parsing.
  if (ParsingInitForAutoVars.count(D))
    return false;

  // See if this is a deleted function.
  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
    if (FD->isDeleted())
      return false;

    // If the function has a deduced return type, and we can't deduce it,
    // then we can't use it either.
    if (getLangOpts().CPlusPlus14 && FD->getReturnType()->isUndeducedType() &&
        DeduceReturnType(FD, SourceLocation(), /*Diagnose*/ false))
      return false;

    // See if this is an aligned allocation/deallocation function that is
    // unavailable.
    if (TreatUnavailableAsInvalid &&
        isUnavailableAlignedAllocationFunction(*FD))
      return false;
  }

  // See if this function is unavailable.
  if (TreatUnavailableAsInvalid && D->getAvailability() == AR_Unavailable &&
      cast<Decl>(CurContext)->getAvailability() != AR_Unavailable)
    return false;

  return true;
}

static void DiagnoseUnusedOfDecl(Sema &S, NamedDecl *D, SourceLocation Loc) {
  // Warn if this is used but marked unused.
  if (const auto *A = D->getAttr<UnusedAttr>()) {
    // [[maybe_unused]] should not diagnose uses, but __attribute__((unused))
    // should diagnose them.
    if (A->getSemanticSpelling() != UnusedAttr::CXX11_maybe_unused &&
        A->getSemanticSpelling() != UnusedAttr::C2x_maybe_unused) {
      const Decl *DC = cast_or_null<Decl>(S.getCurObjCLexicalContext());
      if (DC && !DC->hasAttr<UnusedAttr>())
        S.Diag(Loc, diag::warn_used_but_marked_unused) << D->getDeclName();
    }
  }
}

/// Emit a note explaining that this function is deleted.
void Sema::NoteDeletedFunction(FunctionDecl *Decl) {
  assert(Decl->isDeleted());

  CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Decl);

  if (Method && Method->isDeleted() && Method->isDefaulted()) {
    // If the method was explicitly defaulted, point at that declaration.
    if (!Method->isImplicit())
      Diag(Decl->getLocation(), diag::note_implicitly_deleted);

    // Try to diagnose why this special member function was implicitly
    // deleted. This might fail, if that reason no longer applies.
    CXXSpecialMember CSM = getSpecialMember(Method);
    if (CSM != CXXInvalid)
      ShouldDeleteSpecialMember(Method, CSM, nullptr, /*Diagnose=*/true);

    return;
  }

  auto *Ctor = dyn_cast<CXXConstructorDecl>(Decl);
  if (Ctor && Ctor->isInheritingConstructor())
    return NoteDeletedInheritingConstructor(Ctor);

  Diag(Decl->getLocation(), diag::note_availability_specified_here)
    << Decl << 1;
}

/// Determine whether a FunctionDecl was ever declared with an
/// explicit storage class.
static bool hasAnyExplicitStorageClass(const FunctionDecl *D) {
  for (auto I : D->redecls()) {
    if (I->getStorageClass() != SC_None)
      return true;
  }
  return false;
}

/// Check whether we're in an extern inline function and referring to a
/// variable or function with internal linkage (C11 6.7.4p3).
///
/// This is only a warning because we used to silently accept this code, but
/// in many cases it will not behave correctly. This is not enabled in C++ mode
/// because the restriction language is a bit weaker (C++11 [basic.def.odr]p6)
/// and so while there may still be user mistakes, most of the time we can't
/// prove that there are errors.
static void diagnoseUseOfInternalDeclInInlineFunction(Sema &S,
                                                      const NamedDecl *D,
                                                      SourceLocation Loc) {
  // This is disabled under C++; there are too many ways for this to fire in
  // contexts where the warning is a false positive, or where it is technically
  // correct but benign.
  if (S.getLangOpts().CPlusPlus)
    return;

  // Check if this is an inlined function or method.
  FunctionDecl *Current = S.getCurFunctionDecl();
  if (!Current)
    return;
  if (!Current->isInlined())
    return;
  if (!Current->isExternallyVisible())
    return;

  // Check if the decl has internal linkage.
  if (D->getFormalLinkage() != InternalLinkage)
    return;

  // Downgrade from ExtWarn to Extension if
  //  (1) the supposedly external inline function is in the main file,
  //      and probably won't be included anywhere else.
  //  (2) the thing we're referencing is a pure function.
  //  (3) the thing we're referencing is another inline function.
  // This last can give us false negatives, but it's better than warning on
  // wrappers for simple C library functions.
  const FunctionDecl *UsedFn = dyn_cast<FunctionDecl>(D);
  bool DowngradeWarning = S.getSourceManager().isInMainFile(Loc);
  if (!DowngradeWarning && UsedFn)
    DowngradeWarning = UsedFn->isInlined() || UsedFn->hasAttr<ConstAttr>();

  S.Diag(Loc, DowngradeWarning ? diag::ext_internal_in_extern_inline_quiet
                               : diag::ext_internal_in_extern_inline)
    << /*IsVar=*/!UsedFn << D;

  S.MaybeSuggestAddingStaticToDecl(Current);

  S.Diag(D->getCanonicalDecl()->getLocation(), diag::note_entity_declared_at)
      << D;
}

void Sema::MaybeSuggestAddingStaticToDecl(const FunctionDecl *Cur) {
  const FunctionDecl *First = Cur->getFirstDecl();

  // Suggest "static" on the function, if possible.
  if (!hasAnyExplicitStorageClass(First)) {
    SourceLocation DeclBegin = First->getSourceRange().getBegin();
    Diag(DeclBegin, diag::note_convert_inline_to_static)
      << Cur << FixItHint::CreateInsertion(DeclBegin, "static ");
  }
}

/// Determine whether the use of this declaration is valid, and
/// emit any corresponding diagnostics.
///
/// This routine diagnoses various problems with referencing
/// declarations that can occur when using a declaration. For example,
/// it might warn if a deprecated or unavailable declaration is being
/// used, or produce an error (and return true) if a C++0x deleted
/// function is being used.
///
/// \returns true if there was an error (this declaration cannot be
/// referenced), false otherwise.
///
bool Sema::DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                             const ObjCInterfaceDecl *UnknownObjCClass,
                             bool ObjCPropertyAccess,
                             bool AvoidPartialAvailabilityChecks,
                             ObjCInterfaceDecl *ClassReceiver) {
  SourceLocation Loc = Locs.front();
  if (getLangOpts().CPlusPlus && isa<FunctionDecl>(D)) {
    // If there were any diagnostics suppressed by template argument deduction,
    // emit them now.
    auto Pos = SuppressedDiagnostics.find(D->getCanonicalDecl());
    if (Pos != SuppressedDiagnostics.end()) {
      for (const PartialDiagnosticAt &Suppressed : Pos->second)
        Diag(Suppressed.first, Suppressed.second);

      // Clear out the list of suppressed diagnostics, so that we don't emit
      // them again for this specialization. However, we don't obsolete this
      // entry from the table, because we want to avoid ever emitting these
      // diagnostics again.
      Pos->second.clear();
    }

    // C++ [basic.start.main]p3:
    //   The function 'main' shall not be used within a program.
    if (cast<FunctionDecl>(D)->isMain())
      Diag(Loc, diag::ext_main_used);

    diagnoseUnavailableAlignedAllocation(*cast<FunctionDecl>(D), Loc);
  }

  // See if this is an auto-typed variable whose initializer we are parsing.
  if (ParsingInitForAutoVars.count(D)) {
    if (isa<BindingDecl>(D)) {
      Diag(Loc, diag::err_binding_cannot_appear_in_own_initializer)
        << D->getDeclName();
    } else {
      Diag(Loc, diag::err_auto_variable_cannot_appear_in_own_initializer)
        << D->getDeclName() << cast<VarDecl>(D)->getType();
    }
    return true;
  }

  // See if this is a deleted function.
  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
    if (FD->isDeleted()) {
      auto *Ctor = dyn_cast<CXXConstructorDecl>(FD);
      if (Ctor && Ctor->isInheritingConstructor())
        Diag(Loc, diag::err_deleted_inherited_ctor_use)
            << Ctor->getParent()
            << Ctor->getInheritedConstructor().getConstructor()->getParent();
      else
        Diag(Loc, diag::err_deleted_function_use);
      NoteDeletedFunction(FD);
      return true;
    }

    // If the function has a deduced return type, and we can't deduce it,
    // then we can't use it either.
    if (getLangOpts().CPlusPlus14 && FD->getReturnType()->isUndeducedType() &&
        DeduceReturnType(FD, Loc))
      return true;

    if (getLangOpts().CUDA && !CheckCUDACall(Loc, FD))
      return true;
  }

  if (auto *MD = dyn_cast<CXXMethodDecl>(D)) {
    // Lambdas are only default-constructible or assignable in C++2a onwards.
    if (MD->getParent()->isLambda() &&
        ((isa<CXXConstructorDecl>(MD) &&
          cast<CXXConstructorDecl>(MD)->isDefaultConstructor()) ||
         MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator())) {
      Diag(Loc, diag::warn_cxx17_compat_lambda_def_ctor_assign)
        << !isa<CXXConstructorDecl>(MD);
    }
  }

  auto getReferencedObjCProp = [](const NamedDecl *D) ->
                                      const ObjCPropertyDecl * {
    if (const auto *MD = dyn_cast<ObjCMethodDecl>(D))
      return MD->findPropertyDecl();
    return nullptr;
  };
  if (const ObjCPropertyDecl *ObjCPDecl = getReferencedObjCProp(D)) {
    if (diagnoseArgIndependentDiagnoseIfAttrs(ObjCPDecl, Loc))
      return true;
  } else if (diagnoseArgIndependentDiagnoseIfAttrs(D, Loc)) {
      return true;
  }

  // [OpenMP 4.0], 2.15 declare reduction Directive, Restrictions
  // Only the variables omp_in and omp_out are allowed in the combiner.
  // Only the variables omp_priv and omp_orig are allowed in the
  // initializer-clause.
  auto *DRD = dyn_cast<OMPDeclareReductionDecl>(CurContext);
  if (LangOpts.OpenMP && DRD && !CurContext->containsDecl(D) &&
      isa<VarDecl>(D)) {
    Diag(Loc, diag::err_omp_wrong_var_in_declare_reduction)
        << getCurFunction()->HasOMPDeclareReductionCombiner;
    Diag(D->getLocation(), diag::note_entity_declared_at) << D;
    return true;
  }

  // [OpenMP 5.0], 2.19.7.3. declare mapper Directive, Restrictions
  //  List-items in map clauses on this construct may only refer to the declared
  //  variable var and entities that could be referenced by a procedure defined
  //  at the same location
  auto *DMD = dyn_cast<OMPDeclareMapperDecl>(CurContext);
  if (LangOpts.OpenMP && DMD && !CurContext->containsDecl(D) &&
      isa<VarDecl>(D)) {
    Diag(Loc, diag::err_omp_declare_mapper_wrong_var)
        << DMD->getVarName().getAsString();
    Diag(D->getLocation(), diag::note_entity_declared_at) << D;
    return true;
  }

  DiagnoseAvailabilityOfDecl(D, Locs, UnknownObjCClass, ObjCPropertyAccess,
                             AvoidPartialAvailabilityChecks, ClassReceiver);

  DiagnoseUnusedOfDecl(*this, D, Loc);

  diagnoseUseOfInternalDeclInInlineFunction(*this, D, Loc);

  return false;
}

/// DiagnoseSentinelCalls - This routine checks whether a call or
/// message-send is to a declaration with the sentinel attribute, and
/// if so, it checks that the requirements of the sentinel are
/// satisfied.
void Sema::DiagnoseSentinelCalls(NamedDecl *D, SourceLocation Loc,
                                 ArrayRef<Expr *> Args) {
  const SentinelAttr *attr = D->getAttr<SentinelAttr>();
  if (!attr)
    return;

  // The number of formal parameters of the declaration.
  unsigned numFormalParams;

  // The kind of declaration.  This is also an index into a %select in
  // the diagnostic.
  enum CalleeType { CT_Function, CT_Method, CT_Block } calleeType;

  if (ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(D)) {
    numFormalParams = MD->param_size();
    calleeType = CT_Method;
  } else if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
    numFormalParams = FD->param_size();
    calleeType = CT_Function;
  } else if (isa<VarDecl>(D)) {
    QualType type = cast<ValueDecl>(D)->getType();
    const FunctionType *fn = nullptr;
    if (const PointerType *ptr = type->getAs<PointerType>()) {
      fn = ptr->getPointeeType()->getAs<FunctionType>();
      if (!fn) return;
      calleeType = CT_Function;
    } else if (const BlockPointerType *ptr = type->getAs<BlockPointerType>()) {
      fn = ptr->getPointeeType()->castAs<FunctionType>();
      calleeType = CT_Block;
    } else {
      return;
    }

    if (const FunctionProtoType *proto = dyn_cast<FunctionProtoType>(fn)) {
      numFormalParams = proto->getNumParams();
    } else {
      numFormalParams = 0;
    }
  } else {
    return;
  }

  // "nullPos" is the number of formal parameters at the end which
  // effectively count as part of the variadic arguments.  This is
  // useful if you would prefer to not have *any* formal parameters,
  // but the language forces you to have at least one.
  unsigned nullPos = attr->getNullPos();
  assert((nullPos == 0 || nullPos == 1) && "invalid null position on sentinel");
  numFormalParams = (nullPos > numFormalParams ? 0 : numFormalParams - nullPos);

  // The number of arguments which should follow the sentinel.
  unsigned numArgsAfterSentinel = attr->getSentinel();

  // If there aren't enough arguments for all the formal parameters,
  // the sentinel, and the args after the sentinel, complain.
  if (Args.size() < numFormalParams + numArgsAfterSentinel + 1) {
    Diag(Loc, diag::warn_not_enough_argument) << D->getDeclName();
    Diag(D->getLocation(), diag::note_sentinel_here) << int(calleeType);
    return;
  }

  // Otherwise, find the sentinel expression.
  Expr *sentinelExpr = Args[Args.size() - numArgsAfterSentinel - 1];
  if (!sentinelExpr) return;
  if (sentinelExpr->isValueDependent()) return;
  if (Context.isSentinelNullExpr(sentinelExpr)) return;

  // Pick a reasonable string to insert.  Optimistically use 'nil', 'nullptr',
  // or 'NULL' if those are actually defined in the context.  Only use
  // 'nil' for ObjC methods, where it's much more likely that the
  // variadic arguments form a list of object pointers.
  SourceLocation MissingNilLoc = getLocForEndOfToken(sentinelExpr->getEndLoc());
  std::string NullValue;
  if (calleeType == CT_Method && PP.isMacroDefined("nil"))
    NullValue = "nil";
  else if (getLangOpts().CPlusPlus11)
    NullValue = "nullptr";
  else if (PP.isMacroDefined("NULL"))
    NullValue = "NULL";
  else
    NullValue = "(void*) 0";

  if (MissingNilLoc.isInvalid())
    Diag(Loc, diag::warn_missing_sentinel) << int(calleeType);
  else
    Diag(MissingNilLoc, diag::warn_missing_sentinel)
      << int(calleeType)
      << FixItHint::CreateInsertion(MissingNilLoc, ", " + NullValue);
  Diag(D->getLocation(), diag::note_sentinel_here) << int(calleeType);
}

SourceRange Sema::getExprRange(Expr *E) const {
  return E ? E->getSourceRange() : SourceRange();
}

//===----------------------------------------------------------------------===//
//  Standard Promotions and Conversions
//===----------------------------------------------------------------------===//

/// DefaultFunctionArrayConversion (C99 6.3.2.1p3, C99 6.3.2.1p4).
ExprResult Sema::DefaultFunctionArrayConversion(Expr *E, bool Diagnose) {
  // Handle any placeholder expressions which made it here.
  if (E->getType()->isPlaceholderType()) {
    ExprResult result = CheckPlaceholderExpr(E);
    if (result.isInvalid()) return ExprError();
    E = result.get();
  }

  QualType Ty = E->getType();
  assert(!Ty.isNull() && "DefaultFunctionArrayConversion - missing type");

  if (Ty->isFunctionType()) {
    if (auto *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenCasts()))
      if (auto *FD = dyn_cast<FunctionDecl>(DRE->getDecl()))
        if (!checkAddressOfFunctionIsAvailable(FD, Diagnose, E->getExprLoc()))
          return ExprError();

    E = ImpCastExprToType(E, Context.getPointerType(Ty),
                          CK_FunctionToPointerDecay).get();
  } else if (Ty->isArrayType()) {
    // In C90 mode, arrays only promote to pointers if the array expression is
    // an lvalue.  The relevant legalese is C90 6.2.2.1p3: "an lvalue that has
    // type 'array of type' is converted to an expression that has type 'pointer
    // to type'...".  In C99 this was changed to: C99 6.3.2.1p3: "an expression
    // that has type 'array of type' ...".  The relevant change is "an lvalue"
    // (C90) to "an expression" (C99).
    //
    // C++ 4.2p1:
    // An lvalue or rvalue of type "array of N T" or "array of unknown bound of
    // T" can be converted to an rvalue of type "pointer to T".
    //
    if (getLangOpts().C99 || getLangOpts().CPlusPlus || E->isLValue())
      E = ImpCastExprToType(E, Context.getArrayDecayedType(Ty),
                            CK_ArrayToPointerDecay).get();
  }
  return E;
}

static void CheckForNullPointerDereference(Sema &S, Expr *E) {
  // Check to see if we are dereferencing a null pointer.  If so,
  // and if not volatile-qualified, this is undefined behavior that the
  // optimizer will delete, so warn about it.  People sometimes try to use this
  // to get a deterministic trap and are surprised by clang's behavior.  This
  // only handles the pattern "*null", which is a very syntactic check.
  if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E->IgnoreParenCasts()))
    if (UO->getOpcode() == UO_Deref &&
        UO->getSubExpr()->IgnoreParenCasts()->
          isNullPointerConstant(S.Context, Expr::NPC_ValueDependentIsNotNull) &&
        !UO->getType().isVolatileQualified()) {
    S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
                          S.PDiag(diag::warn_indirection_through_null)
                            << UO->getSubExpr()->getSourceRange());
    S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
                        S.PDiag(diag::note_indirection_through_null));
  }
}

static void DiagnoseDirectIsaAccess(Sema &S, const ObjCIvarRefExpr *OIRE,
                                    SourceLocation AssignLoc,
                                    const Expr* RHS) {
  const ObjCIvarDecl *IV = OIRE->getDecl();
  if (!IV)
    return;

  DeclarationName MemberName = IV->getDeclName();
  IdentifierInfo *Member = MemberName.getAsIdentifierInfo();
  if (!Member || !Member->isStr("isa"))
    return;

  const Expr *Base = OIRE->getBase();
  QualType BaseType = Base->getType();
  if (OIRE->isArrow())
    BaseType = BaseType->getPointeeType();
  if (const ObjCObjectType *OTy = BaseType->getAs<ObjCObjectType>())
    if (ObjCInterfaceDecl *IDecl = OTy->getInterface()) {
      ObjCInterfaceDecl *ClassDeclared = nullptr;
      ObjCIvarDecl *IV = IDecl->lookupInstanceVariable(Member, ClassDeclared);
      if (!ClassDeclared->getSuperClass()
          && (*ClassDeclared->ivar_begin()) == IV) {
        if (RHS) {
          NamedDecl *ObjectSetClass =
            S.LookupSingleName(S.TUScope,
                               &S.Context.Idents.get("object_setClass"),
                               SourceLocation(), S.LookupOrdinaryName);
          if (ObjectSetClass) {
            SourceLocation RHSLocEnd = S.getLocForEndOfToken(RHS->getEndLoc());
            S.Diag(OIRE->getExprLoc(), diag::warn_objc_isa_assign)
                << FixItHint::CreateInsertion(OIRE->getBeginLoc(),
                                              "object_setClass(")
                << FixItHint::CreateReplacement(
                       SourceRange(OIRE->getOpLoc(), AssignLoc), ",")
                << FixItHint::CreateInsertion(RHSLocEnd, ")");
          }
          else
            S.Diag(OIRE->getLocation(), diag::warn_objc_isa_assign);
        } else {
          NamedDecl *ObjectGetClass =
            S.LookupSingleName(S.TUScope,
                               &S.Context.Idents.get("object_getClass"),
                               SourceLocation(), S.LookupOrdinaryName);
          if (ObjectGetClass)
            S.Diag(OIRE->getExprLoc(), diag::warn_objc_isa_use)
                << FixItHint::CreateInsertion(OIRE->getBeginLoc(),
                                              "object_getClass(")
                << FixItHint::CreateReplacement(
                       SourceRange(OIRE->getOpLoc(), OIRE->getEndLoc()), ")");
          else
            S.Diag(OIRE->getLocation(), diag::warn_objc_isa_use);
        }
        S.Diag(IV->getLocation(), diag::note_ivar_decl);
      }
    }
}

ExprResult Sema::DefaultLvalueConversion(Expr *E) {
  // Handle any placeholder expressions which made it here.
  if (E->getType()->isPlaceholderType()) {
    ExprResult result = CheckPlaceholderExpr(E);
    if (result.isInvalid()) return ExprError();
    E = result.get();
  }

  // C++ [conv.lval]p1:
  //   A glvalue of a non-function, non-array type T can be
  //   converted to a prvalue.
  if (!E->isGLValue()) return E;

  QualType T = E->getType();
  assert(!T.isNull() && "r-value conversion on typeless expression?");

  // We don't want to throw lvalue-to-rvalue casts on top of
  // expressions of certain types in C++.
  if (getLangOpts().CPlusPlus &&
      (E->getType() == Context.OverloadTy ||
       T->isDependentType() ||
       T->isRecordType()))
    return E;

  // The C standard is actually really unclear on this point, and
  // DR106 tells us what the result should be but not why.  It's
  // generally best to say that void types just doesn't undergo
  // lvalue-to-rvalue at all.  Note that expressions of unqualified
  // 'void' type are never l-values, but qualified void can be.
  if (T->isVoidType())
    return E;

  // OpenCL usually rejects direct accesses to values of 'half' type.
  if (getLangOpts().OpenCL && !getOpenCLOptions().isEnabled("cl_khr_fp16") &&
      T->isHalfType()) {
    Diag(E->getExprLoc(), diag::err_opencl_half_load_store)
      << 0 << T;
    return ExprError();
  }

  CheckForNullPointerDereference(*this, E);
  if (const ObjCIsaExpr *OISA = dyn_cast<ObjCIsaExpr>(E->IgnoreParenCasts())) {
    NamedDecl *ObjectGetClass = LookupSingleName(TUScope,
                                     &Context.Idents.get("object_getClass"),
                                     SourceLocation(), LookupOrdinaryName);
    if (ObjectGetClass)
      Diag(E->getExprLoc(), diag::warn_objc_isa_use)
          << FixItHint::CreateInsertion(OISA->getBeginLoc(), "object_getClass(")
          << FixItHint::CreateReplacement(
                 SourceRange(OISA->getOpLoc(), OISA->getIsaMemberLoc()), ")");
    else
      Diag(E->getExprLoc(), diag::warn_objc_isa_use);
  }
  else if (const ObjCIvarRefExpr *OIRE =
            dyn_cast<ObjCIvarRefExpr>(E->IgnoreParenCasts()))
    DiagnoseDirectIsaAccess(*this, OIRE, SourceLocation(), /* Expr*/nullptr);

  // C++ [conv.lval]p1:
  //   [...] If T is a non-class type, the type of the prvalue is the
  //   cv-unqualified version of T. Otherwise, the type of the
  //   rvalue is T.
  //
  // C99 6.3.2.1p2:
  //   If the lvalue has qualified type, the value has the unqualified
  //   version of the type of the lvalue; otherwise, the value has the
  //   type of the lvalue.
  if (T.hasQualifiers())
    T = T.getUnqualifiedType();

  // Under the MS ABI, lock down the inheritance model now.
  if (T->isMemberPointerType() &&
      Context.getTargetInfo().getCXXABI().isMicrosoft())
    (void)isCompleteType(E->getExprLoc(), T);

  ExprResult Res = CheckLValueToRValueConversionOperand(E);
  if (Res.isInvalid())
    return Res;
  E = Res.get();

  // Loading a __weak object implicitly retains the value, so we need a cleanup to
  // balance that.
  if (E->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
    Cleanup.setExprNeedsCleanups(true);

  // C++ [conv.lval]p3:
  //   If T is cv std::nullptr_t, the result is a null pointer constant.
  CastKind CK = T->isNullPtrType() ? CK_NullToPointer : CK_LValueToRValue;
  Res = ImplicitCastExpr::Create(Context, T, CK, E, nullptr, VK_RValue);

  // C11 6.3.2.1p2:
  //   ... if the lvalue has atomic type, the value has the non-atomic version
  //   of the type of the lvalue ...
  if (const AtomicType *Atomic = T->getAs<AtomicType>()) {
    T = Atomic->getValueType().getUnqualifiedType();
    Res = ImplicitCastExpr::Create(Context, T, CK_AtomicToNonAtomic, Res.get(),
                                   nullptr, VK_RValue);
  }

  return Res;
}

ExprResult Sema::DefaultFunctionArrayLvalueConversion(Expr *E, bool Diagnose) {
  ExprResult Res = DefaultFunctionArrayConversion(E, Diagnose);
  if (Res.isInvalid())
    return ExprError();
  Res = DefaultLvalueConversion(Res.get());
  if (Res.isInvalid())
    return ExprError();
  return Res;
}

/// CallExprUnaryConversions - a special case of an unary conversion
/// performed on a function designator of a call expression.
ExprResult Sema::CallExprUnaryConversions(Expr *E) {
  QualType Ty = E->getType();
  ExprResult Res = E;
  // Only do implicit cast for a function type, but not for a pointer
  // to function type.
  if (Ty->isFunctionType()) {
    Res = ImpCastExprToType(E, Context.getPointerType(Ty),
                            CK_FunctionToPointerDecay).get();
    if (Res.isInvalid())
      return ExprError();
  }
  Res = DefaultLvalueConversion(Res.get());
  if (Res.isInvalid())
    return ExprError();
  return Res.get();
}

/// UsualUnaryConversions - Performs various conversions that are common to most
/// operators (C99 6.3). The conversions of array and function types are
/// sometimes suppressed. For example, the array->pointer conversion doesn't
/// apply if the array is an argument to the sizeof or address (&) operators.
/// In these instances, this routine should *not* be called.
ExprResult Sema::UsualUnaryConversions(Expr *E) {
  // First, convert to an r-value.
  ExprResult Res = DefaultFunctionArrayLvalueConversion(E);
  if (Res.isInvalid())
    return ExprError();
  E = Res.get();

  QualType Ty = E->getType();
  assert(!Ty.isNull() && "UsualUnaryConversions - missing type");

  // Half FP have to be promoted to float unless it is natively supported
  if (Ty->isHalfType() && !getLangOpts().NativeHalfType)
    return ImpCastExprToType(Res.get(), Context.FloatTy, CK_FloatingCast);

  // Try to perform integral promotions if the object has a theoretically
  // promotable type.
  if (Ty->isIntegralOrUnscopedEnumerationType()) {
    // C99 6.3.1.1p2:
    //
    //   The following may be used in an expression wherever an int or
    //   unsigned int may be used:
    //     - an object or expression with an integer type whose integer
    //       conversion rank is less than or equal to the rank of int
    //       and unsigned int.
    //     - A bit-field of type _Bool, int, signed int, or unsigned int.
    //
    //   If an int can represent all values of the original type, the
    //   value is converted to an int; otherwise, it is converted to an
    //   unsigned int. These are called the integer promotions. All
    //   other types are unchanged by the integer promotions.

    QualType PTy = Context.isPromotableBitField(E);
    if (!PTy.isNull()) {
      E = ImpCastExprToType(E, PTy, CK_IntegralCast).get();
      return E;
    }
    if (Ty->isPromotableIntegerType()) {
      QualType PT = Context.getPromotedIntegerType(Ty);
      E = ImpCastExprToType(E, PT, CK_IntegralCast).get();
      return E;
    }
  }
  return E;
}

/// DefaultArgumentPromotion (C99 6.5.2.2p6). Used for function calls that
/// do not have a prototype. Arguments that have type float or __fp16
/// are promoted to double. All other argument types are converted by
/// UsualUnaryConversions().
ExprResult Sema::DefaultArgumentPromotion(Expr *E) {
  QualType Ty = E->getType();
  assert(!Ty.isNull() && "DefaultArgumentPromotion - missing type");

  ExprResult Res = UsualUnaryConversions(E);
  if (Res.isInvalid())
    return ExprError();
  E = Res.get();

  // If this is a 'float'  or '__fp16' (CVR qualified or typedef)
  // promote to double.
  // Note that default argument promotion applies only to float (and
  // half/fp16); it does not apply to _Float16.
  const BuiltinType *BTy = Ty->getAs<BuiltinType>();
  if (BTy && (BTy->getKind() == BuiltinType::Half ||
              BTy->getKind() == BuiltinType::Float)) {
    if (getLangOpts().OpenCL &&
        !getOpenCLOptions().isEnabled("cl_khr_fp64")) {
        if (BTy->getKind() == BuiltinType::Half) {
            E = ImpCastExprToType(E, Context.FloatTy, CK_FloatingCast).get();
        }
    } else {
      E = ImpCastExprToType(E, Context.DoubleTy, CK_FloatingCast).get();
    }
  }

  // C++ performs lvalue-to-rvalue conversion as a default argument
  // promotion, even on class types, but note:
  //   C++11 [conv.lval]p2:
  //     When an lvalue-to-rvalue conversion occurs in an unevaluated
  //     operand or a subexpression thereof the value contained in the
  //     referenced object is not accessed. Otherwise, if the glvalue
  //     has a class type, the conversion copy-initializes a temporary
  //     of type T from the glvalue and the result of the conversion
  //     is a prvalue for the temporary.
  // FIXME: add some way to gate this entire thing for correctness in
  // potentially potentially evaluated contexts.
  if (getLangOpts().CPlusPlus && E->isGLValue() && !isUnevaluatedContext()) {
    ExprResult Temp = PerformCopyInitialization(
                       InitializedEntity::InitializeTemporary(E->getType()),
                                                E->getExprLoc(), E);
    if (Temp.isInvalid())
      return ExprError();
    E = Temp.get();
  }

  return E;
}

/// Determine the degree of POD-ness for an expression.
/// Incomplete types are considered POD, since this check can be performed
/// when we're in an unevaluated context.
Sema::VarArgKind Sema::isValidVarArgType(const QualType &Ty) {
  if (Ty->isIncompleteType()) {
    // C++11 [expr.call]p7:
    //   After these conversions, if the argument does not have arithmetic,
    //   enumeration, pointer, pointer to member, or class type, the program
    //   is ill-formed.
    //
    // Since we've already performed array-to-pointer and function-to-pointer
    // decay, the only such type in C++ is cv void. This also handles
    // initializer lists as variadic arguments.
    if (Ty->isVoidType())
      return VAK_Invalid;

    if (Ty->isObjCObjectType())
      return VAK_Invalid;
    return VAK_Valid;
  }

  if (Ty.isDestructedType() == QualType::DK_nontrivial_c_struct)
    return VAK_Invalid;

  if (Ty.isCXX98PODType(Context))
    return VAK_Valid;

  // C++11 [expr.call]p7:
  //   Passing a potentially-evaluated argument of class type (Clause 9)
  //   having a non-trivial copy constructor, a non-trivial move constructor,
  //   or a non-trivial destructor, with no corresponding parameter,
  //   is conditionally-supported with implementation-defined semantics.
  if (getLangOpts().CPlusPlus11 && !Ty->isDependentType())
    if (CXXRecordDecl *Record = Ty->getAsCXXRecordDecl())
      if (!Record->hasNonTrivialCopyConstructor() &&
          !Record->hasNonTrivialMoveConstructor() &&
          !Record->hasNonTrivialDestructor())
        return VAK_ValidInCXX11;

  if (getLangOpts().ObjCAutoRefCount && Ty->isObjCLifetimeType())
    return VAK_Valid;

  if (Ty->isObjCObjectType())
    return VAK_Invalid;

  if (getLangOpts().MSVCCompat)
    return VAK_MSVCUndefined;

  // FIXME: In C++11, these cases are conditionally-supported, meaning we're
  // permitted to reject them. We should consider doing so.
  return VAK_Undefined;
}

void Sema::checkVariadicArgument(const Expr *E, VariadicCallType CT) {
  // Don't allow one to pass an Objective-C interface to a vararg.
  const QualType &Ty = E->getType();
  VarArgKind VAK = isValidVarArgType(Ty);

  // Complain about passing non-POD types through varargs.
  switch (VAK) {
  case VAK_ValidInCXX11:
    DiagRuntimeBehavior(
        E->getBeginLoc(), nullptr,
        PDiag(diag::warn_cxx98_compat_pass_non_pod_arg_to_vararg) << Ty << CT);
    LLVM_FALLTHROUGH;
  case VAK_Valid:
    if (Ty->isRecordType()) {
      // This is unlikely to be what the user intended. If the class has a
      // 'c_str' member function, the user probably meant to call that.
      DiagRuntimeBehavior(E->getBeginLoc(), nullptr,
                          PDiag(diag::warn_pass_class_arg_to_vararg)
                              << Ty << CT << hasCStrMethod(E) << ".c_str()");
    }
    break;

  case VAK_Undefined:
  case VAK_MSVCUndefined:
    DiagRuntimeBehavior(E->getBeginLoc(), nullptr,
                        PDiag(diag::warn_cannot_pass_non_pod_arg_to_vararg)
                            << getLangOpts().CPlusPlus11 << Ty << CT);
    break;

  case VAK_Invalid:
    if (Ty.isDestructedType() == QualType::DK_nontrivial_c_struct)
      Diag(E->getBeginLoc(),
           diag::err_cannot_pass_non_trivial_c_struct_to_vararg)
          << Ty << CT;
    else if (Ty->isObjCObjectType())
      DiagRuntimeBehavior(E->getBeginLoc(), nullptr,
                          PDiag(diag::err_cannot_pass_objc_interface_to_vararg)
                              << Ty << CT);
    else
      Diag(E->getBeginLoc(), diag::err_cannot_pass_to_vararg)
          << isa<InitListExpr>(E) << Ty << CT;
    break;
  }
}

/// DefaultVariadicArgumentPromotion - Like DefaultArgumentPromotion, but
/// will create a trap if the resulting type is not a POD type.
ExprResult Sema::DefaultVariadicArgumentPromotion(Expr *E, VariadicCallType CT,
                                                  FunctionDecl *FDecl) {
  if (const BuiltinType *PlaceholderTy = E->getType()->getAsPlaceholderType()) {
    // Strip the unbridged-cast placeholder expression off, if applicable.
    if (PlaceholderTy->getKind() == BuiltinType::ARCUnbridgedCast &&
        (CT == VariadicMethod ||
         (FDecl && FDecl->hasAttr<CFAuditedTransferAttr>()))) {
      E = stripARCUnbridgedCast(E);

    // Otherwise, do normal placeholder checking.
    } else {
      ExprResult ExprRes = CheckPlaceholderExpr(E);
      if (ExprRes.isInvalid())
        return ExprError();
      E = ExprRes.get();
    }
  }

  ExprResult ExprRes = DefaultArgumentPromotion(E);
  if (ExprRes.isInvalid())
    return ExprError();
  E = ExprRes.get();

  // Diagnostics regarding non-POD argument types are
  // emitted along with format string checking in Sema::CheckFunctionCall().
  if (isValidVarArgType(E->getType()) == VAK_Undefined) {
    // Turn this into a trap.
    CXXScopeSpec SS;
    SourceLocation TemplateKWLoc;
    UnqualifiedId Name;
    Name.setIdentifier(PP.getIdentifierInfo("__builtin_trap"),
                       E->getBeginLoc());
    ExprResult TrapFn = ActOnIdExpression(TUScope, SS, TemplateKWLoc, Name,
                                          /*HasTrailingLParen=*/true,
                                          /*IsAddressOfOperand=*/false);
    if (TrapFn.isInvalid())
      return ExprError();

    ExprResult Call = BuildCallExpr(TUScope, TrapFn.get(), E->getBeginLoc(),
                                    None, E->getEndLoc());
    if (Call.isInvalid())
      return ExprError();

    ExprResult Comma =
        ActOnBinOp(TUScope, E->getBeginLoc(), tok::comma, Call.get(), E);
    if (Comma.isInvalid())
      return ExprError();
    return Comma.get();
  }

  if (!getLangOpts().CPlusPlus &&
      RequireCompleteType(E->getExprLoc(), E->getType(),
                          diag::err_call_incomplete_argument))
    return ExprError();

  return E;
}

/// Converts an integer to complex float type.  Helper function of
/// UsualArithmeticConversions()
///
/// \return false if the integer expression is an integer type and is
/// successfully converted to the complex type.
static bool handleIntegerToComplexFloatConversion(Sema &S, ExprResult &IntExpr,
                                                  ExprResult &ComplexExpr,
                                                  QualType IntTy,
                                                  QualType ComplexTy,
                                                  bool SkipCast) {
  if (IntTy->isComplexType() || IntTy->isRealFloatingType()) return true;
  if (SkipCast) return false;
  if (IntTy->isIntegerType()) {
    QualType fpTy = cast<ComplexType>(ComplexTy)->getElementType();
    IntExpr = S.ImpCastExprToType(IntExpr.get(), fpTy, CK_IntegralToFloating);
    IntExpr = S.ImpCastExprToType(IntExpr.get(), ComplexTy,
                                  CK_FloatingRealToComplex);
  } else {
    assert(IntTy->isComplexIntegerType());
    IntExpr = S.ImpCastExprToType(IntExpr.get(), ComplexTy,
                                  CK_IntegralComplexToFloatingComplex);
  }
  return false;
}

/// Handle arithmetic conversion with complex types.  Helper function of
/// UsualArithmeticConversions()
static QualType handleComplexFloatConversion(Sema &S, ExprResult &LHS,
                                             ExprResult &RHS, QualType LHSType,
                                             QualType RHSType,
                                             bool IsCompAssign) {
  // if we have an integer operand, the result is the complex type.
  if (!handleIntegerToComplexFloatConversion(S, RHS, LHS, RHSType, LHSType,
                                             /*skipCast*/false))
    return LHSType;
  if (!handleIntegerToComplexFloatConversion(S, LHS, RHS, LHSType, RHSType,
                                             /*skipCast*/IsCompAssign))
    return RHSType;

  // This handles complex/complex, complex/float, or float/complex.
  // When both operands are complex, the shorter operand is converted to the
  // type of the longer, and that is the type of the result. This corresponds
  // to what is done when combining two real floating-point operands.
  // The fun begins when size promotion occur across type domains.
  // From H&S 6.3.4: When one operand is complex and the other is a real
  // floating-point type, the less precise type is converted, within it's
  // real or complex domain, to the precision of the other type. For example,
  // when combining a "long double" with a "double _Complex", the
  // "double _Complex" is promoted to "long double _Complex".

  // Compute the rank of the two types, regardless of whether they are complex.
  int Order = S.Context.getFloatingTypeOrder(LHSType, RHSType);

  auto *LHSComplexType = dyn_cast<ComplexType>(LHSType);
  auto *RHSComplexType = dyn_cast<ComplexType>(RHSType);
  QualType LHSElementType =
      LHSComplexType ? LHSComplexType->getElementType() : LHSType;
  QualType RHSElementType =
      RHSComplexType ? RHSComplexType->getElementType() : RHSType;

  QualType ResultType = S.Context.getComplexType(LHSElementType);
  if (Order < 0) {
    // Promote the precision of the LHS if not an assignment.
    ResultType = S.Context.getComplexType(RHSElementType);
    if (!IsCompAssign) {
      if (LHSComplexType)
        LHS =
            S.ImpCastExprToType(LHS.get(), ResultType, CK_FloatingComplexCast);
      else
        LHS = S.ImpCastExprToType(LHS.get(), RHSElementType, CK_FloatingCast);
    }
  } else if (Order > 0) {
    // Promote the precision of the RHS.
    if (RHSComplexType)
      RHS = S.ImpCastExprToType(RHS.get(), ResultType, CK_FloatingComplexCast);
    else
      RHS = S.ImpCastExprToType(RHS.get(), LHSElementType, CK_FloatingCast);
  }
  return ResultType;
}

/// Handle arithmetic conversion from integer to float.  Helper function
/// of UsualArithmeticConversions()
static QualType handleIntToFloatConversion(Sema &S, ExprResult &FloatExpr,
                                           ExprResult &IntExpr,
                                           QualType FloatTy, QualType IntTy,
                                           bool ConvertFloat, bool ConvertInt) {
  if (IntTy->isIntegerType()) {
    if (ConvertInt)
      // Convert intExpr to the lhs floating point type.
      IntExpr = S.ImpCastExprToType(IntExpr.get(), FloatTy,
                                    CK_IntegralToFloating);
    return FloatTy;
  }

  // Convert both sides to the appropriate complex float.
  assert(IntTy->isComplexIntegerType());
  QualType result = S.Context.getComplexType(FloatTy);

  // _Complex int -> _Complex float
  if (ConvertInt)
    IntExpr = S.ImpCastExprToType(IntExpr.get(), result,
                                  CK_IntegralComplexToFloatingComplex);

  // float -> _Complex float
  if (ConvertFloat)
    FloatExpr = S.ImpCastExprToType(FloatExpr.get(), result,
                                    CK_FloatingRealToComplex);

  return result;
}

/// Handle arithmethic conversion with floating point types.  Helper
/// function of UsualArithmeticConversions()
static QualType handleFloatConversion(Sema &S, ExprResult &LHS,
                                      ExprResult &RHS, QualType LHSType,
                                      QualType RHSType, bool IsCompAssign) {
  bool LHSFloat = LHSType->isRealFloatingType();
  bool RHSFloat = RHSType->isRealFloatingType();

  // If we have two real floating types, convert the smaller operand
  // to the bigger result.
  if (LHSFloat && RHSFloat) {
    int order = S.Context.getFloatingTypeOrder(LHSType, RHSType);
    if (order > 0) {
      RHS = S.ImpCastExprToType(RHS.get(), LHSType, CK_FloatingCast);
      return LHSType;
    }

    assert(order < 0 && "illegal float comparison");
    if (!IsCompAssign)
      LHS = S.ImpCastExprToType(LHS.get(), RHSType, CK_FloatingCast);
    return RHSType;
  }

  if (LHSFloat) {
    // Half FP has to be promoted to float unless it is natively supported
    if (LHSType->isHalfType() && !S.getLangOpts().NativeHalfType)
      LHSType = S.Context.FloatTy;

    return handleIntToFloatConversion(S, LHS, RHS, LHSType, RHSType,
                                      /*ConvertFloat=*/!IsCompAssign,
                                      /*ConvertInt=*/ true);
  }
  assert(RHSFloat);
  return handleIntToFloatConversion(S, RHS, LHS, RHSType, LHSType,
                                    /*convertInt=*/ true,
                                    /*convertFloat=*/!IsCompAssign);
}

/// Diagnose attempts to convert between __float128 and long double if
/// there is no support for such conversion. Helper function of
/// UsualArithmeticConversions().
static bool unsupportedTypeConversion(const Sema &S, QualType LHSType,
                                      QualType RHSType) {
  /*  No issue converting if at least one of the types is not a floating point
      type or the two types have the same rank.
  */
  if (!LHSType->isFloatingType() || !RHSType->isFloatingType() ||
      S.Context.getFloatingTypeOrder(LHSType, RHSType) == 0)
    return false;

  assert(LHSType->isFloatingType() && RHSType->isFloatingType() &&
         "The remaining types must be floating point types.");

  auto *LHSComplex = LHSType->getAs<ComplexType>();
  auto *RHSComplex = RHSType->getAs<ComplexType>();

  QualType LHSElemType = LHSComplex ?
    LHSComplex->getElementType() : LHSType;
  QualType RHSElemType = RHSComplex ?
    RHSComplex->getElementType() : RHSType;

  // No issue if the two types have the same representation
  if (&S.Context.getFloatTypeSemantics(LHSElemType) ==
      &S.Context.getFloatTypeSemantics(RHSElemType))
    return false;

  bool Float128AndLongDouble = (LHSElemType == S.Context.Float128Ty &&
                                RHSElemType == S.Context.LongDoubleTy);
  Float128AndLongDouble |= (LHSElemType == S.Context.LongDoubleTy &&
                            RHSElemType == S.Context.Float128Ty);

  // We've handled the situation where __float128 and long double have the same
  // representation. We allow all conversions for all possible long double types
  // except PPC's double double.
  return Float128AndLongDouble &&
    (&S.Context.getFloatTypeSemantics(S.Context.LongDoubleTy) ==
     &llvm::APFloat::PPCDoubleDouble());
}

typedef ExprResult PerformCastFn(Sema &S, Expr *operand, QualType toType);

namespace {
/// These helper callbacks are placed in an anonymous namespace to
/// permit their use as function template parameters.
ExprResult doIntegralCast(Sema &S, Expr *op, QualType toType) {
  return S.ImpCastExprToType(op, toType, CK_IntegralCast);
}

ExprResult doComplexIntegralCast(Sema &S, Expr *op, QualType toType) {
  return S.ImpCastExprToType(op, S.Context.getComplexType(toType),
                             CK_IntegralComplexCast);
}
}

/// Handle integer arithmetic conversions.  Helper function of
/// UsualArithmeticConversions()
template <PerformCastFn doLHSCast, PerformCastFn doRHSCast>
static QualType handleIntegerConversion(Sema &S, ExprResult &LHS,
                                        ExprResult &RHS, QualType LHSType,
                                        QualType RHSType, bool IsCompAssign) {
  // The rules for this case are in C99 6.3.1.8
  int order = S.Context.getIntegerTypeOrder(LHSType, RHSType);
  bool LHSSigned = LHSType->hasSignedIntegerRepresentation();
  bool RHSSigned = RHSType->hasSignedIntegerRepresentation();
  if (LHSSigned == RHSSigned) {
    // Same signedness; use the higher-ranked type
    if (order >= 0) {
      RHS = (*doRHSCast)(S, RHS.get(), LHSType);
      return LHSType;
    } else if (!IsCompAssign)
      LHS = (*doLHSCast)(S, LHS.get(), RHSType);
    return RHSType;
  } else if (order != (LHSSigned ? 1 : -1)) {
    // The unsigned type has greater than or equal rank to the
    // signed type, so use the unsigned type
    if (RHSSigned) {
      RHS = (*doRHSCast)(S, RHS.get(), LHSType);
      return LHSType;
    } else if (!IsCompAssign)
      LHS = (*doLHSCast)(S, LHS.get(), RHSType);
    return RHSType;
  } else if (S.Context.getIntWidth(LHSType) != S.Context.getIntWidth(RHSType)) {
    // The two types are different widths; if we are here, that
    // means the signed type is larger than the unsigned type, so
    // use the signed type.
    if (LHSSigned) {
      RHS = (*doRHSCast)(S, RHS.get(), LHSType);
      return LHSType;
    } else if (!IsCompAssign)
      LHS = (*doLHSCast)(S, LHS.get(), RHSType);
    return RHSType;
  } else {
    // The signed type is higher-ranked than the unsigned type,
    // but isn't actually any bigger (like unsigned int and long
    // on most 32-bit systems).  Use the unsigned type corresponding
    // to the signed type.
    QualType result =
      S.Context.getCorrespondingUnsignedType(LHSSigned ? LHSType : RHSType);
    RHS = (*doRHSCast)(S, RHS.get(), result);
    if (!IsCompAssign)
      LHS = (*doLHSCast)(S, LHS.get(), result);
    return result;
  }
}

/// Handle conversions with GCC complex int extension.  Helper function
/// of UsualArithmeticConversions()
static QualType handleComplexIntConversion(Sema &S, ExprResult &LHS,
                                           ExprResult &RHS, QualType LHSType,
                                           QualType RHSType,
                                           bool IsCompAssign) {
  const ComplexType *LHSComplexInt = LHSType->getAsComplexIntegerType();
  const ComplexType *RHSComplexInt = RHSType->getAsComplexIntegerType();

  if (LHSComplexInt && RHSComplexInt) {
    QualType LHSEltType = LHSComplexInt->getElementType();
    QualType RHSEltType = RHSComplexInt->getElementType();
    QualType ScalarType =
      handleIntegerConversion<doComplexIntegralCast, doComplexIntegralCast>
        (S, LHS, RHS, LHSEltType, RHSEltType, IsCompAssign);

    return S.Context.getComplexType(ScalarType);
  }

  if (LHSComplexInt) {
    QualType LHSEltType = LHSComplexInt->getElementType();
    QualType ScalarType =
      handleIntegerConversion<doComplexIntegralCast, doIntegralCast>
        (S, LHS, RHS, LHSEltType, RHSType, IsCompAssign);
    QualType ComplexType = S.Context.getComplexType(ScalarType);
    RHS = S.ImpCastExprToType(RHS.get(), ComplexType,
                              CK_IntegralRealToComplex);

    return ComplexType;
  }

  assert(RHSComplexInt);

  QualType RHSEltType = RHSComplexInt->getElementType();
  QualType ScalarType =
    handleIntegerConversion<doIntegralCast, doComplexIntegralCast>
      (S, LHS, RHS, LHSType, RHSEltType, IsCompAssign);
  QualType ComplexType = S.Context.getComplexType(ScalarType);

  if (!IsCompAssign)
    LHS = S.ImpCastExprToType(LHS.get(), ComplexType,
                              CK_IntegralRealToComplex);
  return ComplexType;
}

/// Return the rank of a given fixed point or integer type. The value itself
/// doesn't matter, but the values must be increasing with proper increasing
/// rank as described in N1169 4.1.1.
static unsigned GetFixedPointRank(QualType Ty) {
  const auto *BTy = Ty->getAs<BuiltinType>();
  assert(BTy && "Expected a builtin type.");

  switch (BTy->getKind()) {
  case BuiltinType::ShortFract:
  case BuiltinType::UShortFract:
  case BuiltinType::SatShortFract:
  case BuiltinType::SatUShortFract:
    return 1;
  case BuiltinType::Fract:
  case BuiltinType::UFract:
  case BuiltinType::SatFract:
  case BuiltinType::SatUFract:
    return 2;
  case BuiltinType::LongFract:
  case BuiltinType::ULongFract:
  case BuiltinType::SatLongFract:
  case BuiltinType::SatULongFract:
    return 3;
  case BuiltinType::ShortAccum:
  case BuiltinType::UShortAccum:
  case BuiltinType::SatShortAccum:
  case BuiltinType::SatUShortAccum:
    return 4;
  case BuiltinType::Accum:
  case BuiltinType::UAccum:
  case BuiltinType::SatAccum:
  case BuiltinType::SatUAccum:
    return 5;
  case BuiltinType::LongAccum:
  case BuiltinType::ULongAccum:
  case BuiltinType::SatLongAccum:
  case BuiltinType::SatULongAccum:
    return 6;
  default:
    if (BTy->isInteger())
      return 0;
    llvm_unreachable("Unexpected fixed point or integer type");
  }
}

/// handleFixedPointConversion - Fixed point operations between fixed
/// point types and integers or other fixed point types do not fall under
/// usual arithmetic conversion since these conversions could result in loss
/// of precsision (N1169 4.1.4). These operations should be calculated with
/// the full precision of their result type (N1169 4.1.6.2.1).
static QualType handleFixedPointConversion(Sema &S, QualType LHSTy,
                                           QualType RHSTy) {
  assert((LHSTy->isFixedPointType() || RHSTy->isFixedPointType()) &&
         "Expected at least one of the operands to be a fixed point type");
  assert((LHSTy->isFixedPointOrIntegerType() ||
          RHSTy->isFixedPointOrIntegerType()) &&
         "Special fixed point arithmetic operation conversions are only "
         "applied to ints or other fixed point types");

  // If one operand has signed fixed-point type and the other operand has
  // unsigned fixed-point type, then the unsigned fixed-point operand is
  // converted to its corresponding signed fixed-point type and the resulting
  // type is the type of the converted operand.
  if (RHSTy->isSignedFixedPointType() && LHSTy->isUnsignedFixedPointType())
    LHSTy = S.Context.getCorrespondingSignedFixedPointType(LHSTy);
  else if (RHSTy->isUnsignedFixedPointType() && LHSTy->isSignedFixedPointType())
    RHSTy = S.Context.getCorrespondingSignedFixedPointType(RHSTy);

  // The result type is the type with the highest rank, whereby a fixed-point
  // conversion rank is always greater than an integer conversion rank; if the
  // type of either of the operands is a saturating fixedpoint type, the result
  // type shall be the saturating fixed-point type corresponding to the type
  // with the highest rank; the resulting value is converted (taking into
  // account rounding and overflow) to the precision of the resulting type.
  // Same ranks between signed and unsigned types are resolved earlier, so both
  // types are either signed or both unsigned at this point.
  unsigned LHSTyRank = GetFixedPointRank(LHSTy);
  unsigned RHSTyRank = GetFixedPointRank(RHSTy);

  QualType ResultTy = LHSTyRank > RHSTyRank ? LHSTy : RHSTy;

  if (LHSTy->isSaturatedFixedPointType() || RHSTy->isSaturatedFixedPointType())
    ResultTy = S.Context.getCorrespondingSaturatedType(ResultTy);

  return ResultTy;
}

/// UsualArithmeticConversions - Performs various conversions that are common to
/// binary operators (C99 6.3.1.8). If both operands aren't arithmetic, this
/// routine returns the first non-arithmetic type found. The client is
/// responsible for emitting appropriate error diagnostics.
QualType Sema::UsualArithmeticConversions(ExprResult &LHS, ExprResult &RHS,
                                          bool IsCompAssign) {
  if (!IsCompAssign) {
    LHS = UsualUnaryConversions(LHS.get());
    if (LHS.isInvalid())
      return QualType();
  }

  RHS = UsualUnaryConversions(RHS.get());
  if (RHS.isInvalid())
    return QualType();

  // For conversion purposes, we ignore any qualifiers.
  // For example, "const float" and "float" are equivalent.
  QualType LHSType =
    Context.getCanonicalType(LHS.get()->getType()).getUnqualifiedType();
  QualType RHSType =
    Context.getCanonicalType(RHS.get()->getType()).getUnqualifiedType();

  // For conversion purposes, we ignore any atomic qualifier on the LHS.
  if (const AtomicType *AtomicLHS = LHSType->getAs<AtomicType>())
    LHSType = AtomicLHS->getValueType();

  // If both types are identical, no conversion is needed.
  if (LHSType == RHSType)
    return LHSType;

  // If either side is a non-arithmetic type (e.g. a pointer), we are done.
  // The caller can deal with this (e.g. pointer + int).
  if (!LHSType->isArithmeticType() || !RHSType->isArithmeticType())
    return QualType();

  // Apply unary and bitfield promotions to the LHS's type.
  QualType LHSUnpromotedType = LHSType;
  if (LHSType->isPromotableIntegerType())
    LHSType = Context.getPromotedIntegerType(LHSType);
  QualType LHSBitfieldPromoteTy = Context.isPromotableBitField(LHS.get());
  if (!LHSBitfieldPromoteTy.isNull())
    LHSType = LHSBitfieldPromoteTy;
  if (LHSType != LHSUnpromotedType && !IsCompAssign)
    LHS = ImpCastExprToType(LHS.get(), LHSType, CK_IntegralCast);

  // If both types are identical, no conversion is needed.
  if (LHSType == RHSType)
    return LHSType;

  // At this point, we have two different arithmetic types.

  // Diagnose attempts to convert between __float128 and long double where
  // such conversions currently can't be handled.
  if (unsupportedTypeConversion(*this, LHSType, RHSType))
    return QualType();

  // Handle complex types first (C99 6.3.1.8p1).
  if (LHSType->isComplexType() || RHSType->isComplexType())
    return handleComplexFloatConversion(*this, LHS, RHS, LHSType, RHSType,
                                        IsCompAssign);

  // Now handle "real" floating types (i.e. float, double, long double).
  if (LHSType->isRealFloatingType() || RHSType->isRealFloatingType())
    return handleFloatConversion(*this, LHS, RHS, LHSType, RHSType,
                                 IsCompAssign);

  // Handle GCC complex int extension.
  if (LHSType->isComplexIntegerType() || RHSType->isComplexIntegerType())
    return handleComplexIntConversion(*this, LHS, RHS, LHSType, RHSType,
                                      IsCompAssign);

  if (LHSType->isFixedPointType() || RHSType->isFixedPointType())
    return handleFixedPointConversion(*this, LHSType, RHSType);

  // Finally, we have two differing integer types.
  return handleIntegerConversion<doIntegralCast, doIntegralCast>
           (*this, LHS, RHS, LHSType, RHSType, IsCompAssign);
}

//===----------------------------------------------------------------------===//
//  Semantic Analysis for various Expression Types
//===----------------------------------------------------------------------===//


ExprResult
Sema::ActOnGenericSelectionExpr(SourceLocation KeyLoc,
                                SourceLocation DefaultLoc,
                                SourceLocation RParenLoc,
                                Expr *ControllingExpr,
                                ArrayRef<ParsedType> ArgTypes,
                                ArrayRef<Expr *> ArgExprs) {
  unsigned NumAssocs = ArgTypes.size();
  assert(NumAssocs == ArgExprs.size());

  TypeSourceInfo **Types = new TypeSourceInfo*[NumAssocs];
  for (unsigned i = 0; i < NumAssocs; ++i) {
    if (ArgTypes[i])
      (void) GetTypeFromParser(ArgTypes[i], &Types[i]);
    else
      Types[i] = nullptr;
  }

  ExprResult ER = CreateGenericSelectionExpr(KeyLoc, DefaultLoc, RParenLoc,
                                             ControllingExpr,
                                             llvm::makeArrayRef(Types, NumAssocs),
                                             ArgExprs);
  delete [] Types;
  return ER;
}

ExprResult
Sema::CreateGenericSelectionExpr(SourceLocation KeyLoc,
                                 SourceLocation DefaultLoc,
                                 SourceLocation RParenLoc,
                                 Expr *ControllingExpr,
                                 ArrayRef<TypeSourceInfo *> Types,
                                 ArrayRef<Expr *> Exprs) {
  unsigned NumAssocs = Types.size();
  assert(NumAssocs == Exprs.size());

  // Decay and strip qualifiers for the controlling expression type, and handle
  // placeholder type replacement. See committee discussion from WG14 DR423.
  {
    EnterExpressionEvaluationContext Unevaluated(
        *this, Sema::ExpressionEvaluationContext::Unevaluated);
    ExprResult R = DefaultFunctionArrayLvalueConversion(ControllingExpr);
    if (R.isInvalid())
      return ExprError();
    ControllingExpr = R.get();
  }

  // The controlling expression is an unevaluated operand, so side effects are
  // likely unintended.
  if (!inTemplateInstantiation() &&
      ControllingExpr->HasSideEffects(Context, false))
    Diag(ControllingExpr->getExprLoc(),
         diag::warn_side_effects_unevaluated_context);

  bool TypeErrorFound = false,
       IsResultDependent = ControllingExpr->isTypeDependent(),
       ContainsUnexpandedParameterPack
         = ControllingExpr->containsUnexpandedParameterPack();

  for (unsigned i = 0; i < NumAssocs; ++i) {
    if (Exprs[i]->containsUnexpandedParameterPack())
      ContainsUnexpandedParameterPack = true;

    if (Types[i]) {
      if (Types[i]->getType()->containsUnexpandedParameterPack())
        ContainsUnexpandedParameterPack = true;

      if (Types[i]->getType()->isDependentType()) {
        IsResultDependent = true;
      } else {
        // C11 6.5.1.1p2 "The type name in a generic association shall specify a
        // complete object type other than a variably modified type."
        unsigned D = 0;
        if (Types[i]->getType()->isIncompleteType())
          D = diag::err_assoc_type_incomplete;
        else if (!Types[i]->getType()->isObjectType())
          D = diag::err_assoc_type_nonobject;
        else if (Types[i]->getType()->isVariablyModifiedType())
          D = diag::err_assoc_type_variably_modified;

        if (D != 0) {
          Diag(Types[i]->getTypeLoc().getBeginLoc(), D)
            << Types[i]->getTypeLoc().getSourceRange()
            << Types[i]->getType();
          TypeErrorFound = true;
        }

        // C11 6.5.1.1p2 "No two generic associations in the same generic
        // selection shall specify compatible types."
        for (unsigned j = i+1; j < NumAssocs; ++j)
          if (Types[j] && !Types[j]->getType()->isDependentType() &&
              Context.typesAreCompatible(Types[i]->getType(),
                                         Types[j]->getType())) {
            Diag(Types[j]->getTypeLoc().getBeginLoc(),
                 diag::err_assoc_compatible_types)
              << Types[j]->getTypeLoc().getSourceRange()
              << Types[j]->getType()
              << Types[i]->getType();
            Diag(Types[i]->getTypeLoc().getBeginLoc(),
                 diag::note_compat_assoc)
              << Types[i]->getTypeLoc().getSourceRange()
              << Types[i]->getType();
            TypeErrorFound = true;
          }
      }
    }
  }
  if (TypeErrorFound)
    return ExprError();

  // If we determined that the generic selection is result-dependent, don't
  // try to compute the result expression.
  if (IsResultDependent)
    return GenericSelectionExpr::Create(Context, KeyLoc, ControllingExpr, Types,
                                        Exprs, DefaultLoc, RParenLoc,
                                        ContainsUnexpandedParameterPack);

  SmallVector<unsigned, 1> CompatIndices;
  unsigned DefaultIndex = -1U;
  for (unsigned i = 0; i < NumAssocs; ++i) {
    if (!Types[i])
      DefaultIndex = i;
    else if (Context.typesAreCompatible(ControllingExpr->getType(),
                                        Types[i]->getType()))
      CompatIndices.push_back(i);
  }

  // C11 6.5.1.1p2 "The controlling expression of a generic selection shall have
  // type compatible with at most one of the types named in its generic
  // association list."
  if (CompatIndices.size() > 1) {
    // We strip parens here because the controlling expression is typically
    // parenthesized in macro definitions.
    ControllingExpr = ControllingExpr->IgnoreParens();
    Diag(ControllingExpr->getBeginLoc(), diag::err_generic_sel_multi_match)
        << ControllingExpr->getSourceRange() << ControllingExpr->getType()
        << (unsigned)CompatIndices.size();
    for (unsigned I : CompatIndices) {
      Diag(Types[I]->getTypeLoc().getBeginLoc(),
           diag::note_compat_assoc)
        << Types[I]->getTypeLoc().getSourceRange()
        << Types[I]->getType();
    }
    return ExprError();
  }

  // C11 6.5.1.1p2 "If a generic selection has no default generic association,
  // its controlling expression shall have type compatible with exactly one of
  // the types named in its generic association list."
  if (DefaultIndex == -1U && CompatIndices.size() == 0) {
    // We strip parens here because the controlling expression is typically
    // parenthesized in macro definitions.
    ControllingExpr = ControllingExpr->IgnoreParens();
    Diag(ControllingExpr->getBeginLoc(), diag::err_generic_sel_no_match)
        << ControllingExpr->getSourceRange() << ControllingExpr->getType();
    return ExprError();
  }

  // C11 6.5.1.1p3 "If a generic selection has a generic association with a
  // type name that is compatible with the type of the controlling expression,
  // then the result expression of the generic selection is the expression
  // in that generic association. Otherwise, the result expression of the
  // generic selection is the expression in the default generic association."
  unsigned ResultIndex =
    CompatIndices.size() ? CompatIndices[0] : DefaultIndex;

  return GenericSelectionExpr::Create(
      Context, KeyLoc, ControllingExpr, Types, Exprs, DefaultLoc, RParenLoc,
      ContainsUnexpandedParameterPack, ResultIndex);
}

/// getUDSuffixLoc - Create a SourceLocation for a ud-suffix, given the
/// location of the token and the offset of the ud-suffix within it.
static SourceLocation getUDSuffixLoc(Sema &S, SourceLocation TokLoc,
                                     unsigned Offset) {
  return Lexer::AdvanceToTokenCharacter(TokLoc, Offset, S.getSourceManager(),
                                        S.getLangOpts());
}

/// BuildCookedLiteralOperatorCall - A user-defined literal was found. Look up
/// the corresponding cooked (non-raw) literal operator, and build a call to it.
static ExprResult BuildCookedLiteralOperatorCall(Sema &S, Scope *Scope,
                                                 IdentifierInfo *UDSuffix,
                                                 SourceLocation UDSuffixLoc,
                                                 ArrayRef<Expr*> Args,
                                                 SourceLocation LitEndLoc) {
  assert(Args.size() <= 2 && "too many arguments for literal operator");

  QualType ArgTy[2];
  for (unsigned ArgIdx = 0; ArgIdx != Args.size(); ++ArgIdx) {
    ArgTy[ArgIdx] = Args[ArgIdx]->getType();
    if (ArgTy[ArgIdx]->isArrayType())
      ArgTy[ArgIdx] = S.Context.getArrayDecayedType(ArgTy[ArgIdx]);
  }

  DeclarationName OpName =
    S.Context.DeclarationNames.getCXXLiteralOperatorName(UDSuffix);
  DeclarationNameInfo OpNameInfo(OpName, UDSuffixLoc);
  OpNameInfo.setCXXLiteralOperatorNameLoc(UDSuffixLoc);

  LookupResult R(S, OpName, UDSuffixLoc, Sema::LookupOrdinaryName);
  if (S.LookupLiteralOperator(Scope, R, llvm::makeArrayRef(ArgTy, Args.size()),
                              /*AllowRaw*/ false, /*AllowTemplate*/ false,
                              /*AllowStringTemplate*/ false,
                              /*DiagnoseMissing*/ true) == Sema::LOLR_Error)
    return ExprError();

  return S.BuildLiteralOperatorCall(R, OpNameInfo, Args, LitEndLoc);
}

/// ActOnStringLiteral - The specified tokens were lexed as pasted string
/// fragments (e.g. "foo" "bar" L"baz").  The result string has to handle string
/// concatenation ([C99 5.1.1.2, translation phase #6]), so it may come from
/// multiple tokens.  However, the common case is that StringToks points to one
/// string.
///
ExprResult
Sema::ActOnStringLiteral(ArrayRef<Token> StringToks, Scope *UDLScope) {
  assert(!StringToks.empty() && "Must have at least one string!");

  StringLiteralParser Literal(StringToks, PP);
  if (Literal.hadError)
    return ExprError();

  SmallVector<SourceLocation, 4> StringTokLocs;
  for (const Token &Tok : StringToks)
    StringTokLocs.push_back(Tok.getLocation());

  QualType CharTy = Context.CharTy;
  StringLiteral::StringKind Kind = StringLiteral::Ascii;
  if (Literal.isWide()) {
    CharTy = Context.getWideCharType();
    Kind = StringLiteral::Wide;
  } else if (Literal.isUTF8()) {
    if (getLangOpts().Char8)
      CharTy = Context.Char8Ty;
    Kind = StringLiteral::UTF8;
  } else if (Literal.isUTF16()) {
    CharTy = Context.Char16Ty;
    Kind = StringLiteral::UTF16;
  } else if (Literal.isUTF32()) {
    CharTy = Context.Char32Ty;
    Kind = StringLiteral::UTF32;
  } else if (Literal.isPascal()) {
    CharTy = Context.UnsignedCharTy;
  }

  // Warn on initializing an array of char from a u8 string literal; this
  // becomes ill-formed in C++2a.
  if (getLangOpts().CPlusPlus && !getLangOpts().CPlusPlus2a &&
      !getLangOpts().Char8 && Kind == StringLiteral::UTF8) {
    Diag(StringTokLocs.front(), diag::warn_cxx2a_compat_utf8_string);

    // Create removals for all 'u8' prefixes in the string literal(s). This
    // ensures C++2a compatibility (but may change the program behavior when
    // built by non-Clang compilers for which the execution character set is
    // not always UTF-8).
    auto RemovalDiag = PDiag(diag::note_cxx2a_compat_utf8_string_remove_u8);
    SourceLocation RemovalDiagLoc;
    for (const Token &Tok : StringToks) {
      if (Tok.getKind() == tok::utf8_string_literal) {
        if (RemovalDiagLoc.isInvalid())
          RemovalDiagLoc = Tok.getLocation();
        RemovalDiag << FixItHint::CreateRemoval(CharSourceRange::getCharRange(
            Tok.getLocation(),
            Lexer::AdvanceToTokenCharacter(Tok.getLocation(), 2,
                                           getSourceManager(), getLangOpts())));
      }
    }
    Diag(RemovalDiagLoc, RemovalDiag);
  }

  QualType StrTy =
      Context.getStringLiteralArrayType(CharTy, Literal.GetNumStringChars());

  // Pass &StringTokLocs[0], StringTokLocs.size() to factory!
  StringLiteral *Lit = StringLiteral::Create(Context, Literal.GetString(),
                                             Kind, Literal.Pascal, StrTy,
                                             &StringTokLocs[0],
                                             StringTokLocs.size());
  if (Literal.getUDSuffix().empty())
    return Lit;

  // We're building a user-defined literal.
  IdentifierInfo *UDSuffix = &Context.Idents.get(Literal.getUDSuffix());
  SourceLocation UDSuffixLoc =
    getUDSuffixLoc(*this, StringTokLocs[Literal.getUDSuffixToken()],
                   Literal.getUDSuffixOffset());

  // Make sure we're allowed user-defined literals here.
  if (!UDLScope)
    return ExprError(Diag(UDSuffixLoc, diag::err_invalid_string_udl));

  // C++11 [lex.ext]p5: The literal L is treated as a call of the form
  //   operator "" X (str, len)
  QualType SizeType = Context.getSizeType();

  DeclarationName OpName =
    Context.DeclarationNames.getCXXLiteralOperatorName(UDSuffix);
  DeclarationNameInfo OpNameInfo(OpName, UDSuffixLoc);
  OpNameInfo.setCXXLiteralOperatorNameLoc(UDSuffixLoc);

  QualType ArgTy[] = {
    Context.getArrayDecayedType(StrTy), SizeType
  };

  LookupResult R(*this, OpName, UDSuffixLoc, LookupOrdinaryName);
  switch (LookupLiteralOperator(UDLScope, R, ArgTy,
                                /*AllowRaw*/ false, /*AllowTemplate*/ false,
                                /*AllowStringTemplate*/ true,
                                /*DiagnoseMissing*/ true)) {

  case LOLR_Cooked: {
    llvm::APInt Len(Context.getIntWidth(SizeType), Literal.GetNumStringChars());
    IntegerLiteral *LenArg = IntegerLiteral::Create(Context, Len, SizeType,
                                                    StringTokLocs[0]);
    Expr *Args[] = { Lit, LenArg };

    return BuildLiteralOperatorCall(R, OpNameInfo, Args, StringTokLocs.back());
  }

  case LOLR_StringTemplate: {
    TemplateArgumentListInfo ExplicitArgs;

    unsigned CharBits = Context.getIntWidth(CharTy);
    bool CharIsUnsigned = CharTy->isUnsignedIntegerType();
    llvm::APSInt Value(CharBits, CharIsUnsigned);

    TemplateArgument TypeArg(CharTy);
    TemplateArgumentLocInfo TypeArgInfo(Context.getTrivialTypeSourceInfo(CharTy));
    ExplicitArgs.addArgument(TemplateArgumentLoc(TypeArg, TypeArgInfo));

    for (unsigned I = 0, N = Lit->getLength(); I != N; ++I) {
      Value = Lit->getCodeUnit(I);
      TemplateArgument Arg(Context, Value, CharTy);
      TemplateArgumentLocInfo ArgInfo;
      ExplicitArgs.addArgument(TemplateArgumentLoc(Arg, ArgInfo));
    }
    return BuildLiteralOperatorCall(R, OpNameInfo, None, StringTokLocs.back(),
                                    &ExplicitArgs);
  }
  case LOLR_Raw:
  case LOLR_Template:
  case LOLR_ErrorNoDiagnostic:
    llvm_unreachable("unexpected literal operator lookup result");
  case LOLR_Error:
    return ExprError();
  }
  llvm_unreachable("unexpected literal operator lookup result");
}

DeclRefExpr *
Sema::BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                       SourceLocation Loc,
                       const CXXScopeSpec *SS) {
  DeclarationNameInfo NameInfo(D->getDeclName(), Loc);
  return BuildDeclRefExpr(D, Ty, VK, NameInfo, SS);
}

DeclRefExpr *
Sema::BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                       const DeclarationNameInfo &NameInfo,
                       const CXXScopeSpec *SS, NamedDecl *FoundD,
                       SourceLocation TemplateKWLoc,
                       const TemplateArgumentListInfo *TemplateArgs) {
  NestedNameSpecifierLoc NNS =
      SS ? SS->getWithLocInContext(Context) : NestedNameSpecifierLoc();
  return BuildDeclRefExpr(D, Ty, VK, NameInfo, NNS, FoundD, TemplateKWLoc,
                          TemplateArgs);
}

NonOdrUseReason Sema::getNonOdrUseReasonInCurrentContext(ValueDecl *D) {
  // A declaration named in an unevaluated operand never constitutes an odr-use.
  if (isUnevaluatedContext())
    return NOUR_Unevaluated;

  // C++2a [basic.def.odr]p4:
  //   A variable x whose name appears as a potentially-evaluated expression e
  //   is odr-used by e unless [...] x is a reference that is usable in
  //   constant expressions.
  if (VarDecl *VD = dyn_cast<VarDecl>(D)) {
    if (VD->getType()->isReferenceType() &&
        !(getLangOpts().OpenMP && isOpenMPCapturedDecl(D)) &&
        VD->isUsableInConstantExpressions(Context))
      return NOUR_Constant;
  }

  // All remaining non-variable cases constitute an odr-use. For variables, we
  // need to wait and see how the expression is used.
  return NOUR_None;
}

/// BuildDeclRefExpr - Build an expression that references a
/// declaration that does not require a closure capture.
DeclRefExpr *
Sema::BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                       const DeclarationNameInfo &NameInfo,
                       NestedNameSpecifierLoc NNS, NamedDecl *FoundD,
                       SourceLocation TemplateKWLoc,
                       const TemplateArgumentListInfo *TemplateArgs) {
  bool RefersToCapturedVariable =
      isa<VarDecl>(D) &&
      NeedToCaptureVariable(cast<VarDecl>(D), NameInfo.getLoc());

  DeclRefExpr *E = DeclRefExpr::Create(
      Context, NNS, TemplateKWLoc, D, RefersToCapturedVariable, NameInfo, Ty,
      VK, FoundD, TemplateArgs, getNonOdrUseReasonInCurrentContext(D));
  MarkDeclRefReferenced(E);

  if (getLangOpts().ObjCWeak && isa<VarDecl>(D) &&
      Ty.getObjCLifetime() == Qualifiers::OCL_Weak && !isUnevaluatedContext() &&
      !Diags.isIgnored(diag::warn_arc_repeated_use_of_weak, E->getBeginLoc()))
    getCurFunction()->recordUseOfWeak(E);

  FieldDecl *FD = dyn_cast<FieldDecl>(D);
  if (IndirectFieldDecl *IFD = dyn_cast<IndirectFieldDecl>(D))
    FD = IFD->getAnonField();
  if (FD) {
    UnusedPrivateFields.remove(FD);
    // Just in case we're building an illegal pointer-to-member.
    if (FD->isBitField())
      E->setObjectKind(OK_BitField);
  }

  // C++ [expr.prim]/8: The expression [...] is a bit-field if the identifier
  // designates a bit-field.
  if (auto *BD = dyn_cast<BindingDecl>(D))
    if (auto *BE = BD->getBinding())
      E->setObjectKind(BE->getObjectKind());

  return E;
}

/// Decomposes the given name into a DeclarationNameInfo, its location, and
/// possibly a list of template arguments.
///
/// If this produces template arguments, it is permitted to call
/// DecomposeTemplateName.
///
/// This actually loses a lot of source location information for
/// non-standard name kinds; we should consider preserving that in
/// some way.
void
Sema::DecomposeUnqualifiedId(const UnqualifiedId &Id,
                             TemplateArgumentListInfo &Buffer,
                             DeclarationNameInfo &NameInfo,
                             const TemplateArgumentListInfo *&TemplateArgs) {
  if (Id.getKind() == UnqualifiedIdKind::IK_TemplateId) {
    Buffer.setLAngleLoc(Id.TemplateId->LAngleLoc);
    Buffer.setRAngleLoc(Id.TemplateId->RAngleLoc);

    ASTTemplateArgsPtr TemplateArgsPtr(Id.TemplateId->getTemplateArgs(),
                                       Id.TemplateId->NumArgs);
    translateTemplateArguments(TemplateArgsPtr, Buffer);

    TemplateName TName = Id.TemplateId->Template.get();
    SourceLocation TNameLoc = Id.TemplateId->TemplateNameLoc;
    NameInfo = Context.getNameForTemplate(TName, TNameLoc);
    TemplateArgs = &Buffer;
  } else {
    NameInfo = GetNameFromUnqualifiedId(Id);
    TemplateArgs = nullptr;
  }
}

static void emitEmptyLookupTypoDiagnostic(
    const TypoCorrection &TC, Sema &SemaRef, const CXXScopeSpec &SS,
    DeclarationName Typo, SourceLocation TypoLoc, ArrayRef<Expr *> Args,
    unsigned DiagnosticID, unsigned DiagnosticSuggestID) {
  DeclContext *Ctx =
      SS.isEmpty() ? nullptr : SemaRef.computeDeclContext(SS, false);
  if (!TC) {
    // Emit a special diagnostic for failed member lookups.
    // FIXME: computing the declaration context might fail here (?)
    if (Ctx)
      SemaRef.Diag(TypoLoc, diag::err_no_member) << Typo << Ctx
                                                 << SS.getRange();
    else
      SemaRef.Diag(TypoLoc, DiagnosticID) << Typo;
    return;
  }

  std::string CorrectedStr = TC.getAsString(SemaRef.getLangOpts());
  bool DroppedSpecifier =
      TC.WillReplaceSpecifier() && Typo.getAsString() == CorrectedStr;
  unsigned NoteID = TC.getCorrectionDeclAs<ImplicitParamDecl>()
                        ? diag::note_implicit_param_decl
                        : diag::note_previous_decl;
  if (!Ctx)
    SemaRef.diagnoseTypo(TC, SemaRef.PDiag(DiagnosticSuggestID) << Typo,
                         SemaRef.PDiag(NoteID));
  else
    SemaRef.diagnoseTypo(TC, SemaRef.PDiag(diag::err_no_member_suggest)
                                 << Typo << Ctx << DroppedSpecifier
                                 << SS.getRange(),
                         SemaRef.PDiag(NoteID));
}

/// Diagnose an empty lookup.
///
/// \return false if new lookup candidates were found
bool Sema::DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
                               CorrectionCandidateCallback &CCC,
                               TemplateArgumentListInfo *ExplicitTemplateArgs,
                               ArrayRef<Expr *> Args, TypoExpr **Out) {
  DeclarationName Name = R.getLookupName();

  unsigned diagnostic = diag::err_undeclared_var_use;
  unsigned diagnostic_suggest = diag::err_undeclared_var_use_suggest;
  if (Name.getNameKind() == DeclarationName::CXXOperatorName ||
      Name.getNameKind() == DeclarationName::CXXLiteralOperatorName ||
      Name.getNameKind() == DeclarationName::CXXConversionFunctionName) {
    diagnostic = diag::err_undeclared_use;
    diagnostic_suggest = diag::err_undeclared_use_suggest;
  }

  // If the original lookup was an unqualified lookup, fake an
  // unqualified lookup.  This is useful when (for example) the
  // original lookup would not have found something because it was a
  // dependent name.
  DeclContext *DC = SS.isEmpty() ? CurContext : nullptr;
  while (DC) {
    if (isa<CXXRecordDecl>(DC)) {
      LookupQualifiedName(R, DC);

      if (!R.empty()) {
        // Don't give errors about ambiguities in this lookup.
        R.suppressDiagnostics();

        // During a default argument instantiation the CurContext points
        // to a CXXMethodDecl; but we can't apply a this-> fixit inside a
        // function parameter list, hence add an explicit check.
        bool isDefaultArgument =
            !CodeSynthesisContexts.empty() &&
            CodeSynthesisContexts.back().Kind ==
                CodeSynthesisContext::DefaultFunctionArgumentInstantiation;
        CXXMethodDecl *CurMethod = dyn_cast<CXXMethodDecl>(CurContext);
        bool isInstance = CurMethod &&
                          CurMethod->isInstance() &&
                          DC == CurMethod->getParent() && !isDefaultArgument;

        // Give a code modification hint to insert 'this->'.
        // TODO: fixit for inserting 'Base<T>::' in the other cases.
        // Actually quite difficult!
        if (getLangOpts().MSVCCompat)
          diagnostic = diag::ext_found_via_dependent_bases_lookup;
        if (isInstance) {
          Diag(R.getNameLoc(), diagnostic) << Name
            << FixItHint::CreateInsertion(R.getNameLoc(), "this->");
          CheckCXXThisCapture(R.getNameLoc());
        } else {
          Diag(R.getNameLoc(), diagnostic) << Name;
        }

        // Do we really want to note all of these?
        for (NamedDecl *D : R)
          Diag(D->getLocation(), diag::note_dependent_var_use);

        // Return true if we are inside a default argument instantiation
        // and the found name refers to an instance member function, otherwise
        // the function calling DiagnoseEmptyLookup will try to create an
        // implicit member call and this is wrong for default argument.
        if (isDefaultArgument && ((*R.begin())->isCXXInstanceMember())) {
          Diag(R.getNameLoc(), diag::err_member_call_without_object);
          return true;
        }

        // Tell the callee to try to recover.
        return false;
      }

      R.clear();
    }

    // In Microsoft mode, if we are performing lookup from within a friend
    // function definition declared at class scope then we must set
    // DC to the lexical parent to be able to search into the parent
    // class.
    if (getLangOpts().MSVCCompat && isa<FunctionDecl>(DC) &&
        cast<FunctionDecl>(DC)->getFriendObjectKind() &&
        DC->getLexicalParent()->isRecord())
      DC = DC->getLexicalParent();
    else
      DC = DC->getParent();
  }

  // We didn't find anything, so try to correct for a typo.
  TypoCorrection Corrected;
  if (S && Out) {
    SourceLocation TypoLoc = R.getNameLoc();
    assert(!ExplicitTemplateArgs &&
           "Diagnosing an empty lookup with explicit template args!");
    *Out = CorrectTypoDelayed(
        R.getLookupNameInfo(), R.getLookupKind(), S, &SS, CCC,
        [=](const TypoCorrection &TC) {
          emitEmptyLookupTypoDiagnostic(TC, *this, SS, Name, TypoLoc, Args,
                                        diagnostic, diagnostic_suggest);
        },
        nullptr, CTK_ErrorRecovery);
    if (*Out)
      return true;
  } else if (S &&
             (Corrected = CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(),
                                      S, &SS, CCC, CTK_ErrorRecovery))) {
    std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
    bool DroppedSpecifier =
        Corrected.WillReplaceSpecifier() && Name.getAsString() == CorrectedStr;
    R.setLookupName(Corrected.getCorrection());

    bool AcceptableWithRecovery = false;
    bool AcceptableWithoutRecovery = false;
    NamedDecl *ND = Corrected.getFoundDecl();
    if (ND) {
      if (Corrected.isOverloaded()) {
        OverloadCandidateSet OCS(R.getNameLoc(),
                                 OverloadCandidateSet::CSK_Normal);
        OverloadCandidateSet::iterator Best;
        for (NamedDecl *CD : Corrected) {
          if (FunctionTemplateDecl *FTD =
                   dyn_cast<FunctionTemplateDecl>(CD))
            AddTemplateOverloadCandidate(
                FTD, DeclAccessPair::make(FTD, AS_none), ExplicitTemplateArgs,
                Args, OCS);
          else if (FunctionDecl *FD = dyn_cast<FunctionDecl>(CD))
            if (!ExplicitTemplateArgs || ExplicitTemplateArgs->size() == 0)
              AddOverloadCandidate(FD, DeclAccessPair::make(FD, AS_none),
                                   Args, OCS);
        }
        switch (OCS.BestViableFunction(*this, R.getNameLoc(), Best)) {
        case OR_Success:
          ND = Best->FoundDecl;
          Corrected.setCorrectionDecl(ND);
          break;
        default:
          // FIXME: Arbitrarily pick the first declaration for the note.
          Corrected.setCorrectionDecl(ND);
          break;
        }
      }
      R.addDecl(ND);
      if (getLangOpts().CPlusPlus && ND->isCXXClassMember()) {
        CXXRecordDecl *Record = nullptr;
        if (Corrected.getCorrectionSpecifier()) {
          const Type *Ty = Corrected.getCorrectionSpecifier()->getAsType();
          Record = Ty->getAsCXXRecordDecl();
        }
        if (!Record)
          Record = cast<CXXRecordDecl>(
              ND->getDeclContext()->getRedeclContext());
        R.setNamingClass(Record);
      }

      auto *UnderlyingND = ND->getUnderlyingDecl();
      AcceptableWithRecovery = isa<ValueDecl>(UnderlyingND) ||
                               isa<FunctionTemplateDecl>(UnderlyingND);
      // FIXME: If we ended up with a typo for a type name or
      // Objective-C class name, we're in trouble because the parser
      // is in the wrong place to recover. Suggest the typo
      // correction, but don't make it a fix-it since we're not going
      // to recover well anyway.
      AcceptableWithoutRecovery = isa<TypeDecl>(UnderlyingND) ||
                                  getAsTypeTemplateDecl(UnderlyingND) ||
                                  isa<ObjCInterfaceDecl>(UnderlyingND);
    } else {
      // FIXME: We found a keyword. Suggest it, but don't provide a fix-it
      // because we aren't able to recover.
      AcceptableWithoutRecovery = true;
    }

    if (AcceptableWithRecovery || AcceptableWithoutRecovery) {
      unsigned NoteID = Corrected.getCorrectionDeclAs<ImplicitParamDecl>()
                            ? diag::note_implicit_param_decl
                            : diag::note_previous_decl;
      if (SS.isEmpty())
        diagnoseTypo(Corrected, PDiag(diagnostic_suggest) << Name,
                     PDiag(NoteID), AcceptableWithRecovery);
      else
        diagnoseTypo(Corrected, PDiag(diag::err_no_member_suggest)
                                  << Name << computeDeclContext(SS, false)
                                  << DroppedSpecifier << SS.getRange(),
                     PDiag(NoteID), AcceptableWithRecovery);

      // Tell the callee whether to try to recover.
      return !AcceptableWithRecovery;
    }
  }
  R.clear();

  // Emit a special diagnostic for failed member lookups.
  // FIXME: computing the declaration context might fail here (?)
  if (!SS.isEmpty()) {
    Diag(R.getNameLoc(), diag::err_no_member)
      << Name << computeDeclContext(SS, false)
      << SS.getRange();
    return true;
  }

  // Give up, we can't recover.
  Diag(R.getNameLoc(), diagnostic) << Name;
  return true;
}

/// In Microsoft mode, if we are inside a template class whose parent class has
/// dependent base classes, and we can't resolve an unqualified identifier, then
/// assume the identifier is a member of a dependent base class.  We can only
/// recover successfully in static methods, instance methods, and other contexts
/// where 'this' is available.  This doesn't precisely match MSVC's
/// instantiation model, but it's close enough.
static Expr *
recoverFromMSUnqualifiedLookup(Sema &S, ASTContext &Context,
                               DeclarationNameInfo &NameInfo,
                               SourceLocation TemplateKWLoc,
                               const TemplateArgumentListInfo *TemplateArgs) {
  // Only try to recover from lookup into dependent bases in static methods or
  // contexts where 'this' is available.
  QualType ThisType = S.getCurrentThisType();
  const CXXRecordDecl *RD = nullptr;
  if (!ThisType.isNull())
    RD = ThisType->getPointeeType()->getAsCXXRecordDecl();
  else if (auto *MD = dyn_cast<CXXMethodDecl>(S.CurContext))
    RD = MD->getParent();
  if (!RD || !RD->hasAnyDependentBases())
    return nullptr;

  // Diagnose this as unqualified lookup into a dependent base class.  If 'this'
  // is available, suggest inserting 'this->' as a fixit.
  SourceLocation Loc = NameInfo.getLoc();
  auto DB = S.Diag(Loc, diag::ext_undeclared_unqual_id_with_dependent_base);
  DB << NameInfo.getName() << RD;

  if (!ThisType.isNull()) {
    DB << FixItHint::CreateInsertion(Loc, "this->");
    return CXXDependentScopeMemberExpr::Create(
        Context, /*This=*/nullptr, ThisType, /*IsArrow=*/true,
        /*Op=*/SourceLocation(), NestedNameSpecifierLoc(), TemplateKWLoc,
        /*FirstQualifierFoundInScope=*/nullptr, NameInfo, TemplateArgs);
  }

  // Synthesize a fake NNS that points to the derived class.  This will
  // perform name lookup during template instantiation.
  CXXScopeSpec SS;
  auto *NNS =
      NestedNameSpecifier::Create(Context, nullptr, true, RD->getTypeForDecl());
  SS.MakeTrivial(Context, NNS, SourceRange(Loc, Loc));
  return DependentScopeDeclRefExpr::Create(
      Context, SS.getWithLocInContext(Context), TemplateKWLoc, NameInfo,
      TemplateArgs);
}

ExprResult
Sema::ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
                        SourceLocation TemplateKWLoc, UnqualifiedId &Id,
                        bool HasTrailingLParen, bool IsAddressOfOperand,
                        CorrectionCandidateCallback *CCC,
                        bool IsInlineAsmIdentifier, Token *KeywordReplacement) {
  assert(!(IsAddressOfOperand && HasTrailingLParen) &&
         "cannot be direct & operand and have a trailing lparen");
  if (SS.isInvalid())
    return ExprError();

  TemplateArgumentListInfo TemplateArgsBuffer;

  // Decompose the UnqualifiedId into the following data.
  DeclarationNameInfo NameInfo;
  const TemplateArgumentListInfo *TemplateArgs;
  DecomposeUnqualifiedId(Id, TemplateArgsBuffer, NameInfo, TemplateArgs);

  DeclarationName Name = NameInfo.getName();
  IdentifierInfo *II = Name.getAsIdentifierInfo();
  SourceLocation NameLoc = NameInfo.getLoc();

  if (II && II->isEditorPlaceholder()) {
    // FIXME: When typed placeholders are supported we can create a typed
    // placeholder expression node.
    return ExprError();
  }

  // C++ [temp.dep.expr]p3:
  //   An id-expression is type-dependent if it contains:
  //     -- an identifier that was declared with a dependent type,
  //        (note: handled after lookup)
  //     -- a template-id that is dependent,
  //        (note: handled in BuildTemplateIdExpr)
  //     -- a conversion-function-id that specifies a dependent type,
  //     -- a nested-name-specifier that contains a class-name that
  //        names a dependent type.
  // Determine whether this is a member of an unknown specialization;
  // we need to handle these differently.
  bool DependentID = false;
  if (Name.getNameKind() == DeclarationName::CXXConversionFunctionName &&
      Name.getCXXNameType()->isDependentType()) {
    DependentID = true;
  } else if (SS.isSet()) {
    if (DeclContext *DC = computeDeclContext(SS, false)) {
      if (RequireCompleteDeclContext(SS, DC))
        return ExprError();
    } else {
      DependentID = true;
    }
  }

  if (DependentID)
    return ActOnDependentIdExpression(SS, TemplateKWLoc, NameInfo,
                                      IsAddressOfOperand, TemplateArgs);

  // Perform the required lookup.
  LookupResult R(*this, NameInfo,
                 (Id.getKind() == UnqualifiedIdKind::IK_ImplicitSelfParam)
                     ? LookupObjCImplicitSelfParam
                     : LookupOrdinaryName);
  if (TemplateKWLoc.isValid() || TemplateArgs) {
    // Lookup the template name again to correctly establish the context in
    // which it was found. This is really unfortunate as we already did the
    // lookup to determine that it was a template name in the first place. If
    // this becomes a performance hit, we can work harder to preserve those
    // results until we get here but it's likely not worth it.
    bool MemberOfUnknownSpecialization;
    AssumedTemplateKind AssumedTemplate;
    if (LookupTemplateName(R, S, SS, QualType(), /*EnteringContext=*/false,
                           MemberOfUnknownSpecialization, TemplateKWLoc,
                           &AssumedTemplate))
      return ExprError();

    if (MemberOfUnknownSpecialization ||
        (R.getResultKind() == LookupResult::NotFoundInCurrentInstantiation))
      return ActOnDependentIdExpression(SS, TemplateKWLoc, NameInfo,
                                        IsAddressOfOperand, TemplateArgs);
  } else {
    bool IvarLookupFollowUp = II && !SS.isSet() && getCurMethodDecl();
    LookupParsedName(R, S, &SS, !IvarLookupFollowUp);

    // If the result might be in a dependent base class, this is a dependent
    // id-expression.
    if (R.getResultKind() == LookupResult::NotFoundInCurrentInstantiation)
      return ActOnDependentIdExpression(SS, TemplateKWLoc, NameInfo,
                                        IsAddressOfOperand, TemplateArgs);

    // If this reference is in an Objective-C method, then we need to do
    // some special Objective-C lookup, too.
    if (IvarLookupFollowUp) {
      ExprResult E(LookupInObjCMethod(R, S, II, true));
      if (E.isInvalid())
        return ExprError();

      if (Expr *Ex = E.getAs<Expr>())
        return Ex;
    }
  }

  if (R.isAmbiguous())
    return ExprError();

  // This could be an implicitly declared function reference (legal in C90,
  // extension in C99, forbidden in C++).
  if (R.empty() && HasTrailingLParen && II && !getLangOpts().CPlusPlus) {
    NamedDecl *D = ImplicitlyDefineFunction(NameLoc, *II, S);
    if (D) R.addDecl(D);
  }

  // Determine whether this name might be a candidate for
  // argument-dependent lookup.
  bool ADL = UseArgumentDependentLookup(SS, R, HasTrailingLParen);

  if (R.empty() && !ADL) {
    if (SS.isEmpty() && getLangOpts().MSVCCompat) {
      if (Expr *E = recoverFromMSUnqualifiedLookup(*this, Context, NameInfo,
                                                   TemplateKWLoc, TemplateArgs))
        return E;
    }

    // Don't diagnose an empty lookup for inline assembly.
    if (IsInlineAsmIdentifier)
      return ExprError();

    // If this name wasn't predeclared and if this is not a function
    // call, diagnose the problem.
    TypoExpr *TE = nullptr;
    DefaultFilterCCC DefaultValidator(II, SS.isValid() ? SS.getScopeRep()
                                                       : nullptr);
    DefaultValidator.IsAddressOfOperand = IsAddressOfOperand;
    assert((!CCC || CCC->IsAddressOfOperand == IsAddressOfOperand) &&
           "Typo correction callback misconfigured");
    if (CCC) {
      // Make sure the callback knows what the typo being diagnosed is.
      CCC->setTypoName(II);
      if (SS.isValid())
        CCC->setTypoNNS(SS.getScopeRep());
    }
    // FIXME: DiagnoseEmptyLookup produces bad diagnostics if we're looking for
    // a template name, but we happen to have always already looked up the name
    // before we get here if it must be a template name.
    if (DiagnoseEmptyLookup(S, SS, R, CCC ? *CCC : DefaultValidator, nullptr,
                            None, &TE)) {
      if (TE && KeywordReplacement) {
        auto &State = getTypoExprState(TE);
        auto BestTC = State.Consumer->getNextCorrection();
        if (BestTC.isKeyword()) {
          auto *II = BestTC.getCorrectionAsIdentifierInfo();
          if (State.DiagHandler)
            State.DiagHandler(BestTC);
          KeywordReplacement->startToken();
          KeywordReplacement->setKind(II->getTokenID());
          KeywordReplacement->setIdentifierInfo(II);
          KeywordReplacement->setLocation(BestTC.getCorrectionRange().getBegin());
          // Clean up the state associated with the TypoExpr, since it has
          // now been diagnosed (without a call to CorrectDelayedTyposInExpr).
          clearDelayedTypo(TE);
          // Signal that a correction to a keyword was performed by returning a
          // valid-but-null ExprResult.
          return (Expr*)nullptr;
        }
        State.Consumer->resetCorrectionStream();
      }
      return TE ? TE : ExprError();
    }

    assert(!R.empty() &&
           "DiagnoseEmptyLookup returned false but added no results");

    // If we found an Objective-C instance variable, let
    // LookupInObjCMethod build the appropriate expression to
    // reference the ivar.
    if (ObjCIvarDecl *Ivar = R.getAsSingle<ObjCIvarDecl>()) {
      R.clear();
      ExprResult E(LookupInObjCMethod(R, S, Ivar->getIdentifier()));
      // In a hopelessly buggy code, Objective-C instance variable
      // lookup fails and no expression will be built to reference it.
      if (!E.isInvalid() && !E.get())
        return ExprError();
      return E;
    }
  }

  // This is guaranteed from this point on.
  assert(!R.empty() || ADL);

  // Check whether this might be a C++ implicit instance member access.
  // C++ [class.mfct.non-static]p3:
  //   When an id-expression that is not part of a class member access
  //   syntax and not used to form a pointer to member is used in the
  //   body of a non-static member function of class X, if name lookup
  //   resolves the name in the id-expression to a non-static non-type
  //   member of some class C, the id-expression is transformed into a
  //   class member access expression using (*this) as the
  //   postfix-expression to the left of the . operator.
  //
  // But we don't actually need to do this for '&' operands if R
  // resolved to a function or overloaded function set, because the
  // expression is ill-formed if it actually works out to be a
  // non-static member function:
  //
  // C++ [expr.ref]p4:
  //   Otherwise, if E1.E2 refers to a non-static member function. . .
  //   [t]he expression can be used only as the left-hand operand of a
  //   member function call.
  //
  // There are other safeguards against such uses, but it's important
  // to get this right here so that we don't end up making a
  // spuriously dependent expression if we're inside a dependent
  // instance method.
  if (!R.empty() && (*R.begin())->isCXXClassMember()) {
    bool MightBeImplicitMember;
    if (!IsAddressOfOperand)
      MightBeImplicitMember = true;
    else if (!SS.isEmpty())
      MightBeImplicitMember = false;
    else if (R.isOverloadedResult())
      MightBeImplicitMember = false;
    else if (R.isUnresolvableResult())
      MightBeImplicitMember = true;
    else
      MightBeImplicitMember = isa<FieldDecl>(R.getFoundDecl()) ||
                              isa<IndirectFieldDecl>(R.getFoundDecl()) ||
                              isa<MSPropertyDecl>(R.getFoundDecl());

    if (MightBeImplicitMember)
      return BuildPossibleImplicitMemberExpr(SS, TemplateKWLoc,
                                             R, TemplateArgs, S);
  }

  if (TemplateArgs || TemplateKWLoc.isValid()) {

    // In C++1y, if this is a variable template id, then check it
    // in BuildTemplateIdExpr().
    // The single lookup result must be a variable template declaration.
    if (Id.getKind() == UnqualifiedIdKind::IK_TemplateId && Id.TemplateId &&
        Id.TemplateId->Kind == TNK_Var_template) {
      assert(R.getAsSingle<VarTemplateDecl>() &&
             "There should only be one declaration found.");
    }

    return BuildTemplateIdExpr(SS, TemplateKWLoc, R, ADL, TemplateArgs);
  }

  return BuildDeclarationNameExpr(SS, R, ADL);
}

/// BuildQualifiedDeclarationNameExpr - Build a C++ qualified
/// declaration name, generally during template instantiation.
/// There's a large number of things which don't need to be done along
/// this path.
ExprResult Sema::BuildQualifiedDeclarationNameExpr(
    CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo,
    bool IsAddressOfOperand, const Scope *S, TypeSourceInfo **RecoveryTSI) {
  DeclContext *DC = computeDeclContext(SS, false);
  if (!DC)
    return BuildDependentDeclRefExpr(SS, /*TemplateKWLoc=*/SourceLocation(),
                                     NameInfo, /*TemplateArgs=*/nullptr);

  if (RequireCompleteDeclContext(SS, DC))
    return ExprError();

  LookupResult R(*this, NameInfo, LookupOrdinaryName);
  LookupQualifiedName(R, DC);

  if (R.isAmbiguous())
    return ExprError();

  if (R.getResultKind() == LookupResult::NotFoundInCurrentInstantiation)
    return BuildDependentDeclRefExpr(SS, /*TemplateKWLoc=*/SourceLocation(),
                                     NameInfo, /*TemplateArgs=*/nullptr);

  if (R.empty()) {
    Diag(NameInfo.getLoc(), diag::err_no_member)
      << NameInfo.getName() << DC << SS.getRange();
    return ExprError();
  }

  if (const TypeDecl *TD = R.getAsSingle<TypeDecl>()) {
    // Diagnose a missing typename if this resolved unambiguously to a type in
    // a dependent context.  If we can recover with a type, downgrade this to
    // a warning in Microsoft compatibility mode.
    unsigned DiagID = diag::err_typename_missing;
    if (RecoveryTSI && getLangOpts().MSVCCompat)
      DiagID = diag::ext_typename_missing;
    SourceLocation Loc = SS.getBeginLoc();
    auto D = Diag(Loc, DiagID);
    D << SS.getScopeRep() << NameInfo.getName().getAsString()
      << SourceRange(Loc, NameInfo.getEndLoc());

    // Don't recover if the caller isn't expecting us to or if we're in a SFINAE
    // context.
    if (!RecoveryTSI)
      return ExprError();

    // Only issue the fixit if we're prepared to recover.
    D << FixItHint::CreateInsertion(Loc, "typename ");

    // Recover by pretending this was an elaborated type.
    QualType Ty = Context.getTypeDeclType(TD);
    TypeLocBuilder TLB;
    TLB.pushTypeSpec(Ty).setNameLoc(NameInfo.getLoc());

    QualType ET = getElaboratedType(ETK_None, SS, Ty);
    ElaboratedTypeLoc QTL = TLB.push<ElaboratedTypeLoc>(ET);
    QTL.setElaboratedKeywordLoc(SourceLocation());
    QTL.setQualifierLoc(SS.getWithLocInContext(Context));

    *RecoveryTSI = TLB.getTypeSourceInfo(Context, ET);

    return ExprEmpty();
  }

  // Defend against this resolving to an implicit member access. We usually
  // won't get here if this might be a legitimate a class member (we end up in
  // BuildMemberReferenceExpr instead), but this can be valid if we're forming
  // a pointer-to-member or in an unevaluated context in C++11.
  if (!R.empty() && (*R.begin())->isCXXClassMember() && !IsAddressOfOperand)
    return BuildPossibleImplicitMemberExpr(SS,
                                           /*TemplateKWLoc=*/SourceLocation(),
                                           R, /*TemplateArgs=*/nullptr, S);

  return BuildDeclarationNameExpr(SS, R, /* ADL */ false);
}

/// LookupInObjCMethod - The parser has read a name in, and Sema has
/// detected that we're currently inside an ObjC method.  Perform some
/// additional lookup.
///
/// Ideally, most of this would be done by lookup, but there's
/// actually quite a lot of extra work involved.
///
/// Returns a null sentinel to indicate trivial success.
ExprResult
Sema::LookupInObjCMethod(LookupResult &Lookup, Scope *S,
                         IdentifierInfo *II, bool AllowBuiltinCreation) {
  SourceLocation Loc = Lookup.getNameLoc();
  ObjCMethodDecl *CurMethod = getCurMethodDecl();

  // Check for error condition which is already reported.
  if (!CurMethod)
    return ExprError();

  // There are two cases to handle here.  1) scoped lookup could have failed,
  // in which case we should look for an ivar.  2) scoped lookup could have
  // found a decl, but that decl is outside the current instance method (i.e.
  // a global variable).  In these two cases, we do a lookup for an ivar with
  // this name, if the lookup sucedes, we replace it our current decl.

  // If we're in a class method, we don't normally want to look for
  // ivars.  But if we don't find anything else, and there's an
  // ivar, that's an error.
  bool IsClassMethod = CurMethod->isClassMethod();

  bool LookForIvars;
  if (Lookup.empty())
    LookForIvars = true;
  else if (IsClassMethod)
    LookForIvars = false;
  else
    LookForIvars = (Lookup.isSingleResult() &&
                    Lookup.getFoundDecl()->isDefinedOutsideFunctionOrMethod());
  ObjCInterfaceDecl *IFace = nullptr;
  if (LookForIvars) {
    IFace = CurMethod->getClassInterface();
    ObjCInterfaceDecl *ClassDeclared;
    ObjCIvarDecl *IV = nullptr;
    if (IFace && (IV = IFace->lookupInstanceVariable(II, ClassDeclared))) {
      // Diagnose using an ivar in a class method.
      if (IsClassMethod)
        return ExprError(Diag(Loc, diag::err_ivar_use_in_class_method)
                         << IV->getDeclName());

      // If we're referencing an invalid decl, just return this as a silent
      // error node.  The error diagnostic was already emitted on the decl.
      if (IV->isInvalidDecl())
        return ExprError();

      // Check if referencing a field with __attribute__((deprecated)).
      if (DiagnoseUseOfDecl(IV, Loc))
        return ExprError();

      // Diagnose the use of an ivar outside of the declaring class.
      if (IV->getAccessControl() == ObjCIvarDecl::Private &&
          !declaresSameEntity(ClassDeclared, IFace) &&
          !getLangOpts().DebuggerSupport)
        Diag(Loc, diag::err_private_ivar_access) << IV->getDeclName();

      // FIXME: This should use a new expr for a direct reference, don't
      // turn this into Self->ivar, just return a BareIVarExpr or something.
      IdentifierInfo &II = Context.Idents.get("self");
      UnqualifiedId SelfName;
      SelfName.setIdentifier(&II, SourceLocation());
      SelfName.setKind(UnqualifiedIdKind::IK_ImplicitSelfParam);
      CXXScopeSpec SelfScopeSpec;
      SourceLocation TemplateKWLoc;
      ExprResult SelfExpr =
          ActOnIdExpression(S, SelfScopeSpec, TemplateKWLoc, SelfName,
                            /*HasTrailingLParen=*/false,
                            /*IsAddressOfOperand=*/false);
      if (SelfExpr.isInvalid())
        return ExprError();

      SelfExpr = DefaultLvalueConversion(SelfExpr.get());
      if (SelfExpr.isInvalid())
        return ExprError();

      MarkAnyDeclReferenced(Loc, IV, true);

      ObjCMethodFamily MF = CurMethod->getMethodFamily();
      if (MF != OMF_init && MF != OMF_dealloc && MF != OMF_finalize &&
          !IvarBacksCurrentMethodAccessor(IFace, CurMethod, IV))
        Diag(Loc, diag::warn_direct_ivar_access) << IV->getDeclName();

      ObjCIvarRefExpr *Result = new (Context)
          ObjCIvarRefExpr(IV, IV->getUsageType(SelfExpr.get()->getType()), Loc,
                          IV->getLocation(), SelfExpr.get(), true, true);

      if (IV->getType().getObjCLifetime() == Qualifiers::OCL_Weak) {
        if (!isUnevaluatedContext() &&
            !Diags.isIgnored(diag::warn_arc_repeated_use_of_weak, Loc))
          getCurFunction()->recordUseOfWeak(Result);
      }
      if (getLangOpts().ObjCAutoRefCount)
        if (const BlockDecl *BD = CurContext->getInnermostBlockDecl())
          ImplicitlyRetainedSelfLocs.push_back({Loc, BD});

      return Result;
    }
  } else if (CurMethod->isInstanceMethod()) {
    // We should warn if a local variable hides an ivar.
    if (ObjCInterfaceDecl *IFace = CurMethod->getClassInterface()) {
      ObjCInterfaceDecl *ClassDeclared;
      if (ObjCIvarDecl *IV = IFace->lookupInstanceVariable(II, ClassDeclared)) {
        if (IV->getAccessControl() != ObjCIvarDecl::Private ||
            declaresSameEntity(IFace, ClassDeclared))
          Diag(Loc, diag::warn_ivar_use_hidden) << IV->getDeclName();
      }
    }
  } else if (Lookup.isSingleResult() &&
             Lookup.getFoundDecl()->isDefinedOutsideFunctionOrMethod()) {
    // If accessing a stand-alone ivar in a class method, this is an error.
    if (const ObjCIvarDecl *IV = dyn_cast<ObjCIvarDecl>(Lookup.getFoundDecl()))
      return ExprError(Diag(Loc, diag::err_ivar_use_in_class_method)
                       << IV->getDeclName());
  }

  if (Lookup.empty() && II && AllowBuiltinCreation) {
    // FIXME. Consolidate this with similar code in LookupName.
    if (unsigned BuiltinID = II->getBuiltinID()) {
      if (!(getLangOpts().CPlusPlus &&
            Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID))) {
        NamedDecl *D = LazilyCreateBuiltin((IdentifierInfo *)II, BuiltinID,
                                           S, Lookup.isForRedeclaration(),
                                           Lookup.getNameLoc());
        if (D) Lookup.addDecl(D);
      }
    }
  }
  // Sentinel value saying that we didn't do anything special.
  return ExprResult((Expr *)nullptr);
}

/// Cast a base object to a member's actual type.
///
/// Logically this happens in three phases:
///
/// * First we cast from the base type to the naming class.
///   The naming class is the class into which we were looking
///   when we found the member;  it's the qualifier type if a
///   qualifier was provided, and otherwise it's the base type.
///
/// * Next we cast from the naming class to the declaring class.
///   If the member we found was brought into a class's scope by
///   a using declaration, this is that class;  otherwise it's
///   the class declaring the member.
///
/// * Finally we cast from the declaring class to the "true"
///   declaring class of the member.  This conversion does not
///   obey access control.
ExprResult
Sema::PerformObjectMemberConversion(Expr *From,
                                    NestedNameSpecifier *Qualifier,
                                    NamedDecl *FoundDecl,
                                    NamedDecl *Member) {
  CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Member->getDeclContext());
  if (!RD)
    return From;

  QualType DestRecordType;
  QualType DestType;
  QualType FromRecordType;
  QualType FromType = From->getType();
  bool PointerConversions = false;
  if (isa<FieldDecl>(Member)) {
    DestRecordType = Context.getCanonicalType(Context.getTypeDeclType(RD));
    auto FromPtrType = FromType->getAs<PointerType>();
    DestRecordType = Context.getAddrSpaceQualType(
        DestRecordType, FromPtrType
                            ? FromType->getPointeeType().getAddressSpace()
                            : FromType.getAddressSpace());

    if (FromPtrType) {
      DestType = Context.getPointerType(DestRecordType);
      FromRecordType = FromPtrType->getPointeeType();
      PointerConversions = true;
    } else {
      DestType = DestRecordType;
      FromRecordType = FromType;
    }
  } else if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member)) {
    if (Method->isStatic())
      return From;

    DestType = Method->getThisType();
    DestRecordType = DestType->getPointeeType();

    if (FromType->getAs<PointerType>()) {
      FromRecordType = FromType->getPointeeType();
      PointerConversions = true;
    } else {
      FromRecordType = FromType;
      DestType = DestRecordType;
    }
  } else {
    // No conversion necessary.
    return From;
  }

  if (DestType->isDependentType() || FromType->isDependentType())
    return From;

  // If the unqualified types are the same, no conversion is necessary.
  if (Context.hasSameUnqualifiedType(FromRecordType, DestRecordType))
    return From;

  SourceRange FromRange = From->getSourceRange();
  SourceLocation FromLoc = FromRange.getBegin();

  ExprValueKind VK = From->getValueKind();

  // C++ [class.member.lookup]p8:
  //   [...] Ambiguities can often be resolved by qualifying a name with its
  //   class name.
  //
  // If the member was a qualified name and the qualified referred to a
  // specific base subobject type, we'll cast to that intermediate type
  // first and then to the object in which the member is declared. That allows
  // one to resolve ambiguities in, e.g., a diamond-shaped hierarchy such as:
  //
  //   class Base { public: int x; };
  //   class Derived1 : public Base { };
  //   class Derived2 : public Base { };
  //   class VeryDerived : public Derived1, public Derived2 { void f(); };
  //
  //   void VeryDerived::f() {
  //     x = 17; // error: ambiguous base subobjects
  //     Derived1::x = 17; // okay, pick the Base subobject of Derived1
  //   }
  if (Qualifier && Qualifier->getAsType()) {
    QualType QType = QualType(Qualifier->getAsType(), 0);
    assert(QType->isRecordType() && "lookup done with non-record type");

    QualType QRecordType = QualType(QType->getAs<RecordType>(), 0);

    // In C++98, the qualifier type doesn't actually have to be a base
    // type of the object type, in which case we just ignore it.
    // Otherwise build the appropriate casts.
    if (IsDerivedFrom(FromLoc, FromRecordType, QRecordType)) {
      CXXCastPath BasePath;
      if (CheckDerivedToBaseConversion(FromRecordType, QRecordType,
                                       FromLoc, FromRange, &BasePath))
        return ExprError();

      if (PointerConversions)
        QType = Context.getPointerType(QType);
      From = ImpCastExprToType(From, QType, CK_UncheckedDerivedToBase,
                               VK, &BasePath).get();

      FromType = QType;
      FromRecordType = QRecordType;

      // If the qualifier type was the same as the destination type,
      // we're done.
      if (Context.hasSameUnqualifiedType(FromRecordType, DestRecordType))
        return From;
    }
  }

  bool IgnoreAccess = false;

  // If we actually found the member through a using declaration, cast
  // down to the using declaration's type.
  //
  // Pointer equality is fine here because only one declaration of a
  // class ever has member declarations.
  if (FoundDecl->getDeclContext() != Member->getDeclContext()) {
    assert(isa<UsingShadowDecl>(FoundDecl));
    QualType URecordType = Context.getTypeDeclType(
                           cast<CXXRecordDecl>(FoundDecl->getDeclContext()));

    // We only need to do this if the naming-class to declaring-class
    // conversion is non-trivial.
    if (!Context.hasSameUnqualifiedType(FromRecordType, URecordType)) {
      assert(IsDerivedFrom(FromLoc, FromRecordType, URecordType));
      CXXCastPath BasePath;
      if (CheckDerivedToBaseConversion(FromRecordType, URecordType,
                                       FromLoc, FromRange, &BasePath))
        return ExprError();

      QualType UType = URecordType;
      if (PointerConversions)
        UType = Context.getPointerType(UType);
      From = ImpCastExprToType(From, UType, CK_UncheckedDerivedToBase,
                               VK, &BasePath).get();
      FromType = UType;
      FromRecordType = URecordType;
    }

    // We don't do access control for the conversion from the
    // declaring class to the true declaring class.
    IgnoreAccess = true;
  }

  CXXCastPath BasePath;
  if (CheckDerivedToBaseConversion(FromRecordType, DestRecordType,
                                   FromLoc, FromRange, &BasePath,
                                   IgnoreAccess))
    return ExprError();

  return ImpCastExprToType(From, DestType, CK_UncheckedDerivedToBase,
                           VK, &BasePath);
}

bool Sema::UseArgumentDependentLookup(const CXXScopeSpec &SS,
                                      const LookupResult &R,
                                      bool HasTrailingLParen) {
  // Only when used directly as the postfix-expression of a call.
  if (!HasTrailingLParen)
    return false;

  // Never if a scope specifier was provided.
  if (SS.isSet())
    return false;

  // Only in C++ or ObjC++.
  if (!getLangOpts().CPlusPlus)
    return false;

  // Turn off ADL when we find certain kinds of declarations during
  // normal lookup:
  for (NamedDecl *D : R) {
    // C++0x [basic.lookup.argdep]p3:
    //     -- a declaration of a class member
    // Since using decls preserve this property, we check this on the
    // original decl.
    if (D->isCXXClassMember())
      return false;

    // C++0x [basic.lookup.argdep]p3:
    //     -- a block-scope function declaration that is not a
    //        using-declaration
    // NOTE: we also trigger this for function templates (in fact, we
    // don't check the decl type at all, since all other decl types
    // turn off ADL anyway).
    if (isa<UsingShadowDecl>(D))
      D = cast<UsingShadowDecl>(D)->getTargetDecl();
    else if (D->getLexicalDeclContext()->isFunctionOrMethod())
      return false;

    // C++0x [basic.lookup.argdep]p3:
    //     -- a declaration that is neither a function or a function
    //        template
    // And also for builtin functions.
    if (isa<FunctionDecl>(D)) {
      FunctionDecl *FDecl = cast<FunctionDecl>(D);

      // But also builtin functions.
      if (FDecl->getBuiltinID() && FDecl->isImplicit())
        return false;
    } else if (!isa<FunctionTemplateDecl>(D))
      return false;
  }

  return true;
}


/// Diagnoses obvious problems with the use of the given declaration
/// as an expression.  This is only actually called for lookups that
/// were not overloaded, and it doesn't promise that the declaration
/// will in fact be used.
static bool CheckDeclInExpr(Sema &S, SourceLocation Loc, NamedDecl *D) {
  if (D->isInvalidDecl())
    return true;

  if (isa<TypedefNameDecl>(D)) {
    S.Diag(Loc, diag::err_unexpected_typedef) << D->getDeclName();
    return true;
  }

  if (isa<ObjCInterfaceDecl>(D)) {
    S.Diag(Loc, diag::err_unexpected_interface) << D->getDeclName();
    return true;
  }

  if (isa<NamespaceDecl>(D)) {
    S.Diag(Loc, diag::err_unexpected_namespace) << D->getDeclName();
    return true;
  }

  return false;
}

// Certain multiversion types should be treated as overloaded even when there is
// only one result.
static bool ShouldLookupResultBeMultiVersionOverload(const LookupResult &R) {
  assert(R.isSingleResult() && "Expected only a single result");
  const auto *FD = dyn_cast<FunctionDecl>(R.getFoundDecl());
  return FD &&
         (FD->isCPUDispatchMultiVersion() || FD->isCPUSpecificMultiVersion());
}

ExprResult Sema::BuildDeclarationNameExpr(const CXXScopeSpec &SS,
                                          LookupResult &R, bool NeedsADL,
                                          bool AcceptInvalidDecl) {
  // If this is a single, fully-resolved result and we don't need ADL,
  // just build an ordinary singleton decl ref.
  if (!NeedsADL && R.isSingleResult() &&
      !R.getAsSingle<FunctionTemplateDecl>() &&
      !ShouldLookupResultBeMultiVersionOverload(R))
    return BuildDeclarationNameExpr(SS, R.getLookupNameInfo(), R.getFoundDecl(),
                                    R.getRepresentativeDecl(), nullptr,
                                    AcceptInvalidDecl);

  // We only need to check the declaration if there's exactly one
  // result, because in the overloaded case the results can only be
  // functions and function templates.
  if (R.isSingleResult() && !ShouldLookupResultBeMultiVersionOverload(R) &&
      CheckDeclInExpr(*this, R.getNameLoc(), R.getFoundDecl()))
    return ExprError();

  // Otherwise, just build an unresolved lookup expression.  Suppress
  // any lookup-related diagnostics; we'll hash these out later, when
  // we've picked a target.
  R.suppressDiagnostics();

  UnresolvedLookupExpr *ULE
    = UnresolvedLookupExpr::Create(Context, R.getNamingClass(),
                                   SS.getWithLocInContext(Context),
                                   R.getLookupNameInfo(),
                                   NeedsADL, R.isOverloadedResult(),
                                   R.begin(), R.end());

  return ULE;
}

static void
diagnoseUncapturableValueReference(Sema &S, SourceLocation loc,
                                   ValueDecl *var, DeclContext *DC);

/// Complete semantic analysis for a reference to the given declaration.
ExprResult Sema::BuildDeclarationNameExpr(
    const CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo, NamedDecl *D,
    NamedDecl *FoundD, const TemplateArgumentListInfo *TemplateArgs,
    bool AcceptInvalidDecl) {
  assert(D && "Cannot refer to a NULL declaration");
  assert(!isa<FunctionTemplateDecl>(D) &&
         "Cannot refer unambiguously to a function template");

  SourceLocation Loc = NameInfo.getLoc();
  if (CheckDeclInExpr(*this, Loc, D))
    return ExprError();

  if (TemplateDecl *Template = dyn_cast<TemplateDecl>(D)) {
    // Specifically diagnose references to class templates that are missing
    // a template argument list.
    diagnoseMissingTemplateArguments(TemplateName(Template), Loc);
    return ExprError();
  }

  // Make sure that we're referring to a value.
  ValueDecl *VD = dyn_cast<ValueDecl>(D);
  if (!VD) {
    Diag(Loc, diag::err_ref_non_value)
      << D << SS.getRange();
    Diag(D->getLocation(), diag::note_declared_at);
    return ExprError();
  }

  // Check whether this declaration can be used. Note that we suppress
  // this check when we're going to perform argument-dependent lookup
  // on this function name, because this might not be the function
  // that overload resolution actually selects.
  if (DiagnoseUseOfDecl(VD, Loc))
    return ExprError();

  // Only create DeclRefExpr's for valid Decl's.
  if (VD->isInvalidDecl() && !AcceptInvalidDecl)
    return ExprError();

  // Handle members of anonymous structs and unions.  If we got here,
  // and the reference is to a class member indirect field, then this
  // must be the subject of a pointer-to-member expression.
  if (IndirectFieldDecl *indirectField = dyn_cast<IndirectFieldDecl>(VD))
    if (!indirectField->isCXXClassMember())
      return BuildAnonymousStructUnionMemberReference(SS, NameInfo.getLoc(),
                                                      indirectField);

  {
    QualType type = VD->getType();
    if (type.isNull())
      return ExprError();
    if (auto *FPT = type->getAs<FunctionProtoType>()) {
      // C++ [except.spec]p17:
      //   An exception-specification is considered to be needed when:
      //   - in an expression, the function is the unique lookup result or
      //     the selected member of a set of overloaded functions.
      ResolveExceptionSpec(Loc, FPT);
      type = VD->getType();
    }
    ExprValueKind valueKind = VK_RValue;

    switch (D->getKind()) {
    // Ignore all the non-ValueDecl kinds.
#define ABSTRACT_DECL(kind)
#define VALUE(type, base)
#define DECL(type, base) \
    case Decl::type:
#include "clang/AST/DeclNodes.inc"
      llvm_unreachable("invalid value decl kind");

    // These shouldn't make it here.
    case Decl::ObjCAtDefsField:
      llvm_unreachable("forming non-member reference to ivar?");

    // Enum constants are always r-values and never references.
    // Unresolved using declarations are dependent.
    case Decl::EnumConstant:
    case Decl::UnresolvedUsingValue:
    case Decl::OMPDeclareReduction:
    case Decl::OMPDeclareMapper:
      valueKind = VK_RValue;
      break;

    // Fields and indirect fields that got here must be for
    // pointer-to-member expressions; we just call them l-values for
    // internal consistency, because this subexpression doesn't really
    // exist in the high-level semantics.
    case Decl::Field:
    case Decl::IndirectField:
    case Decl::ObjCIvar:
      assert(getLangOpts().CPlusPlus &&
             "building reference to field in C?");

      // These can't have reference type in well-formed programs, but
      // for internal consistency we do this anyway.
      type = type.getNonReferenceType();
      valueKind = VK_LValue;
      break;

    // Non-type template parameters are either l-values or r-values
    // depending on the type.
    case Decl::NonTypeTemplateParm: {
      if (const ReferenceType *reftype = type->getAs<ReferenceType>()) {
        type = reftype->getPointeeType();
        valueKind = VK_LValue; // even if the parameter is an r-value reference
        break;
      }

      // For non-references, we need to strip qualifiers just in case
      // the template parameter was declared as 'const int' or whatever.
      valueKind = VK_RValue;
      type = type.getUnqualifiedType();
      break;
    }

    case Decl::Var:
    case Decl::VarTemplateSpecialization:
    case Decl::VarTemplatePartialSpecialization:
    case Decl::Decomposition:
    case Decl::OMPCapturedExpr:
      // In C, "extern void blah;" is valid and is an r-value.
      if (!getLangOpts().CPlusPlus &&
          !type.hasQualifiers() &&
          type->isVoidType()) {
        valueKind = VK_RValue;
        break;
      }
      LLVM_FALLTHROUGH;

    case Decl::ImplicitParam:
    case Decl::ParmVar: {
      // These are always l-values.
      valueKind = VK_LValue;
      type = type.getNonReferenceType();

      // FIXME: Does the addition of const really only apply in
      // potentially-evaluated contexts? Since the variable isn't actually
      // captured in an unevaluated context, it seems that the answer is no.
      if (!isUnevaluatedContext()) {
        QualType CapturedType = getCapturedDeclRefType(cast<VarDecl>(VD), Loc);
        if (!CapturedType.isNull())
          type = CapturedType;
      }

      break;
    }

    case Decl::Binding: {
      // These are always lvalues.
      valueKind = VK_LValue;
      type = type.getNonReferenceType();
      // FIXME: Support lambda-capture of BindingDecls, once CWG actually
      // decides how that's supposed to work.
      auto *BD = cast<BindingDecl>(VD);
      if (BD->getDeclContext() != CurContext) {
        auto *DD = dyn_cast_or_null<VarDecl>(BD->getDecomposedDecl());
        if (DD && DD->hasLocalStorage())
          diagnoseUncapturableValueReference(*this, Loc, BD, CurContext);
      }
      break;
    }

    case Decl::Function: {
      if (unsigned BID = cast<FunctionDecl>(VD)->getBuiltinID()) {
        if (!Context.BuiltinInfo.isPredefinedLibFunction(BID)) {
          type = Context.BuiltinFnTy;
          valueKind = VK_RValue;
          break;
        }
      }

      const FunctionType *fty = type->castAs<FunctionType>();

      // If we're referring to a function with an __unknown_anytype
      // result type, make the entire expression __unknown_anytype.
      if (fty->getReturnType() == Context.UnknownAnyTy) {
        type = Context.UnknownAnyTy;
        valueKind = VK_RValue;
        break;
      }

      // Functions are l-values in C++.
      if (getLangOpts().CPlusPlus) {
        valueKind = VK_LValue;
        break;
      }

      // C99 DR 316 says that, if a function type comes from a
      // function definition (without a prototype), that type is only
      // used for checking compatibility. Therefore, when referencing
      // the function, we pretend that we don't have the full function
      // type.
      if (!cast<FunctionDecl>(VD)->hasPrototype() &&
          isa<FunctionProtoType>(fty))
        type = Context.getFunctionNoProtoType(fty->getReturnType(),
                                              fty->getExtInfo());

      // Functions are r-values in C.
      valueKind = VK_RValue;
      break;
    }

    case Decl::CXXDeductionGuide:
      llvm_unreachable("building reference to deduction guide");

    case Decl::MSProperty:
      valueKind = VK_LValue;
      break;

    case Decl::CXXMethod:
      // If we're referring to a method with an __unknown_anytype
      // result type, make the entire expression __unknown_anytype.
      // This should only be possible with a type written directly.
      if (const FunctionProtoType *proto
            = dyn_cast<FunctionProtoType>(VD->getType()))
        if (proto->getReturnType() == Context.UnknownAnyTy) {
          type = Context.UnknownAnyTy;
          valueKind = VK_RValue;
          break;
        }

      // C++ methods are l-values if static, r-values if non-static.
      if (cast<CXXMethodDecl>(VD)->isStatic()) {
        valueKind = VK_LValue;
        break;
      }
      LLVM_FALLTHROUGH;

    case Decl::CXXConversion:
    case Decl::CXXDestructor:
    case Decl::CXXConstructor:
      valueKind = VK_RValue;
      break;
    }

    return BuildDeclRefExpr(VD, type, valueKind, NameInfo, &SS, FoundD,
                            /*FIXME: TemplateKWLoc*/ SourceLocation(),
                            TemplateArgs);
  }
}

static void ConvertUTF8ToWideString(unsigned CharByteWidth, StringRef Source,
                                    SmallString<32> &Target) {
  Target.resize(CharByteWidth * (Source.size() + 1));
  char *ResultPtr = &Target[0];
  const llvm::UTF8 *ErrorPtr;
  bool success =
      llvm::ConvertUTF8toWide(CharByteWidth, Source, ResultPtr, ErrorPtr);
  (void)success;
  assert(success);
  Target.resize(ResultPtr - &Target[0]);
}

ExprResult Sema::BuildPredefinedExpr(SourceLocation Loc,
                                     PredefinedExpr::IdentKind IK) {
  // Pick the current block, lambda, captured statement or function.
  Decl *currentDecl = nullptr;
  if (const BlockScopeInfo *BSI = getCurBlock())
    currentDecl = BSI->TheDecl;
  else if (const LambdaScopeInfo *LSI = getCurLambda())
    currentDecl = LSI->CallOperator;
  else if (const CapturedRegionScopeInfo *CSI = getCurCapturedRegion())
    currentDecl = CSI->TheCapturedDecl;
  else
    currentDecl = getCurFunctionOrMethodDecl();

  if (!currentDecl) {
    Diag(Loc, diag::ext_predef_outside_function);
    currentDecl = Context.getTranslationUnitDecl();
  }

  QualType ResTy;
  StringLiteral *SL = nullptr;
  if (cast<DeclContext>(currentDecl)->isDependentContext())
    ResTy = Context.DependentTy;
  else {
    // Pre-defined identifiers are of type char[x], where x is the length of
    // the string.
    auto Str = PredefinedExpr::ComputeName(IK, currentDecl);
    unsigned Length = Str.length();

    llvm::APInt LengthI(32, Length + 1);
    if (IK == PredefinedExpr::LFunction || IK == PredefinedExpr::LFuncSig) {
      ResTy =
          Context.adjustStringLiteralBaseType(Context.WideCharTy.withConst());
      SmallString<32> RawChars;
      ConvertUTF8ToWideString(Context.getTypeSizeInChars(ResTy).getQuantity(),
                              Str, RawChars);
      ResTy = Context.getConstantArrayType(ResTy, LengthI, ArrayType::Normal,
                                           /*IndexTypeQuals*/ 0);
      SL = StringLiteral::Create(Context, RawChars, StringLiteral::Wide,
                                 /*Pascal*/ false, ResTy, Loc);
    } else {
      ResTy = Context.adjustStringLiteralBaseType(Context.CharTy.withConst());
      ResTy = Context.getConstantArrayType(ResTy, LengthI, ArrayType::Normal,
                                           /*IndexTypeQuals*/ 0);
      SL = StringLiteral::Create(Context, Str, StringLiteral::Ascii,
                                 /*Pascal*/ false, ResTy, Loc);
    }
  }

  return PredefinedExpr::Create(Context, Loc, ResTy, IK, SL);
}

ExprResult Sema::ActOnPredefinedExpr(SourceLocation Loc, tok::TokenKind Kind) {
  PredefinedExpr::IdentKind IK;

  switch (Kind) {
  default: llvm_unreachable("Unknown simple primary expr!");
  case tok::kw___func__: IK = PredefinedExpr::Func; break; // [C99 6.4.2.2]
  case tok::kw___FUNCTION__: IK = PredefinedExpr::Function; break;
  case tok::kw___FUNCDNAME__: IK = PredefinedExpr::FuncDName; break; // [MS]
  case tok::kw___FUNCSIG__: IK = PredefinedExpr::FuncSig; break; // [MS]
  case tok::kw_L__FUNCTION__: IK = PredefinedExpr::LFunction; break; // [MS]
  case tok::kw_L__FUNCSIG__: IK = PredefinedExpr::LFuncSig; break; // [MS]
  case tok::kw___PRETTY_FUNCTION__: IK = PredefinedExpr::PrettyFunction; break;
  }

  return BuildPredefinedExpr(Loc, IK);
}

ExprResult Sema::ActOnCharacterConstant(const Token &Tok, Scope *UDLScope) {
  SmallString<16> CharBuffer;
  bool Invalid = false;
  StringRef ThisTok = PP.getSpelling(Tok, CharBuffer, &Invalid);
  if (Invalid)
    return ExprError();

  CharLiteralParser Literal(ThisTok.begin(), ThisTok.end(), Tok.getLocation(),
                            PP, Tok.getKind());
  if (Literal.hadError())
    return ExprError();

  QualType Ty;
  if (Literal.isWide())
    Ty = Context.WideCharTy; // L'x' -> wchar_t in C and C++.
  else if (Literal.isUTF8() && getLangOpts().Char8)
    Ty = Context.Char8Ty; // u8'x' -> char8_t when it exists.
  else if (Literal.isUTF16())
    Ty = Context.Char16Ty; // u'x' -> char16_t in C11 and C++11.
  else if (Literal.isUTF32())
    Ty = Context.Char32Ty; // U'x' -> char32_t in C11 and C++11.
  else if (!getLangOpts().CPlusPlus || Literal.isMultiChar())
    Ty = Context.IntTy;   // 'x' -> int in C, 'wxyz' -> int in C++.
  else
    Ty = Context.CharTy;  // 'x' -> char in C++

  CharacterLiteral::CharacterKind Kind = CharacterLiteral::Ascii;
  if (Literal.isWide())
    Kind = CharacterLiteral::Wide;
  else if (Literal.isUTF16())
    Kind = CharacterLiteral::UTF16;
  else if (Literal.isUTF32())
    Kind = CharacterLiteral::UTF32;
  else if (Literal.isUTF8())
    Kind = CharacterLiteral::UTF8;

  Expr *Lit = new (Context) CharacterLiteral(Literal.getValue(), Kind, Ty,
                                             Tok.getLocation());

  if (Literal.getUDSuffix().empty())
    return Lit;

  // We're building a user-defined literal.
  IdentifierInfo *UDSuffix = &Context.Idents.get(Literal.getUDSuffix());
  SourceLocation UDSuffixLoc =
    getUDSuffixLoc(*this, Tok.getLocation(), Literal.getUDSuffixOffset());

  // Make sure we're allowed user-defined literals here.
  if (!UDLScope)
    return ExprError(Diag(UDSuffixLoc, diag::err_invalid_character_udl));

  // C++11 [lex.ext]p6: The literal L is treated as a call of the form
  //   operator "" X (ch)
  return BuildCookedLiteralOperatorCall(*this, UDLScope, UDSuffix, UDSuffixLoc,
                                        Lit, Tok.getLocation());
}

ExprResult Sema::ActOnIntegerConstant(SourceLocation Loc, uint64_t Val) {
  unsigned IntSize = Context.getTargetInfo().getIntWidth();
  return IntegerLiteral::Create(Context, llvm::APInt(IntSize, Val),
                                Context.IntTy, Loc);
}

static Expr *BuildFloatingLiteral(Sema &S, NumericLiteralParser &Literal,
                                  QualType Ty, SourceLocation Loc) {
  const llvm::fltSemantics &Format = S.Context.getFloatTypeSemantics(Ty);

  using llvm::APFloat;
  APFloat Val(Format);

  APFloat::opStatus result = Literal.GetFloatValue(Val);

  // Overflow is always an error, but underflow is only an error if
  // we underflowed to zero (APFloat reports denormals as underflow).
  if ((result & APFloat::opOverflow) ||
      ((result & APFloat::opUnderflow) && Val.isZero())) {
    unsigned diagnostic;
    SmallString<20> buffer;
    if (result & APFloat::opOverflow) {
      diagnostic = diag::warn_float_overflow;
      APFloat::getLargest(Format).toString(buffer);
    } else {
      diagnostic = diag::warn_float_underflow;
      APFloat::getSmallest(Format).toString(buffer);
    }

    S.Diag(Loc, diagnostic)
      << Ty
      << StringRef(buffer.data(), buffer.size());
  }

  bool isExact = (result == APFloat::opOK);
  return FloatingLiteral::Create(S.Context, Val, isExact, Ty, Loc);
}

bool Sema::CheckLoopHintExpr(Expr *E, SourceLocation Loc) {
  assert(E && "Invalid expression");

  if (E->isValueDependent())
    return false;

  QualType QT = E->getType();
  if (!QT->isIntegerType() || QT->isBooleanType() || QT->isCharType()) {
    Diag(E->getExprLoc(), diag::err_pragma_loop_invalid_argument_type) << QT;
    return true;
  }

  llvm::APSInt ValueAPS;
  ExprResult R = VerifyIntegerConstantExpression(E, &ValueAPS);

  if (R.isInvalid())
    return true;

  bool ValueIsPositive = ValueAPS.isStrictlyPositive();
  if (!ValueIsPositive || ValueAPS.getActiveBits() > 31) {
    Diag(E->getExprLoc(), diag::err_pragma_loop_invalid_argument_value)
        << ValueAPS.toString(10) << ValueIsPositive;
    return true;
  }

  return false;
}

ExprResult Sema::ActOnNumericConstant(const Token &Tok, Scope *UDLScope) {
  // Fast path for a single digit (which is quite common).  A single digit
  // cannot have a trigraph, escaped newline, radix prefix, or suffix.
  if (Tok.getLength() == 1) {
    const char Val = PP.getSpellingOfSingleCharacterNumericConstant(Tok);
    return ActOnIntegerConstant(Tok.getLocation(), Val-'0');
  }

  SmallString<128> SpellingBuffer;
  // NumericLiteralParser wants to overread by one character.  Add padding to
  // the buffer in case the token is copied to the buffer.  If getSpelling()
  // returns a StringRef to the memory buffer, it should have a null char at
  // the EOF, so it is also safe.
  SpellingBuffer.resize(Tok.getLength() + 1);

  // Get the spelling of the token, which eliminates trigraphs, etc.
  bool Invalid = false;
  StringRef TokSpelling = PP.getSpelling(Tok, SpellingBuffer, &Invalid);
  if (Invalid)
    return ExprError();

  NumericLiteralParser Literal(TokSpelling, Tok.getLocation(), PP);
  if (Literal.hadError)
    return ExprError();

  if (Literal.hasUDSuffix()) {
    // We're building a user-defined literal.
    IdentifierInfo *UDSuffix = &Context.Idents.get(Literal.getUDSuffix());
    SourceLocation UDSuffixLoc =
      getUDSuffixLoc(*this, Tok.getLocation(), Literal.getUDSuffixOffset());

    // Make sure we're allowed user-defined literals here.
    if (!UDLScope)
      return ExprError(Diag(UDSuffixLoc, diag::err_invalid_numeric_udl));

    QualType CookedTy;
    if (Literal.isFloatingLiteral()) {
      // C++11 [lex.ext]p4: If S contains a literal operator with parameter type
      // long double, the literal is treated as a call of the form
      //   operator "" X (f L)
      CookedTy = Context.LongDoubleTy;
    } else {
      // C++11 [lex.ext]p3: If S contains a literal operator with parameter type
      // unsigned long long, the literal is treated as a call of the form
      //   operator "" X (n ULL)
      CookedTy = Context.UnsignedLongLongTy;
    }

    DeclarationName OpName =
      Context.DeclarationNames.getCXXLiteralOperatorName(UDSuffix);
    DeclarationNameInfo OpNameInfo(OpName, UDSuffixLoc);
    OpNameInfo.setCXXLiteralOperatorNameLoc(UDSuffixLoc);

    SourceLocation TokLoc = Tok.getLocation();

    // Perform literal operator lookup to determine if we're building a raw
    // literal or a cooked one.
    LookupResult R(*this, OpName, UDSuffixLoc, LookupOrdinaryName);
    switch (LookupLiteralOperator(UDLScope, R, CookedTy,
                                  /*AllowRaw*/ true, /*AllowTemplate*/ true,
                                  /*AllowStringTemplate*/ false,
                                  /*DiagnoseMissing*/ !Literal.isImaginary)) {
    case LOLR_ErrorNoDiagnostic:
      // Lookup failure for imaginary constants isn't fatal, there's still the
      // GNU extension producing _Complex types.
      break;
    case LOLR_Error:
      return ExprError();
    case LOLR_Cooked: {
      Expr *Lit;
      if (Literal.isFloatingLiteral()) {
        Lit = BuildFloatingLiteral(*this, Literal, CookedTy, Tok.getLocation());
      } else {
        llvm::APInt ResultVal(Context.getTargetInfo().getLongLongWidth(), 0);
        if (Literal.GetIntegerValue(ResultVal))
          Diag(Tok.getLocation(), diag::err_integer_literal_too_large)
              << /* Unsigned */ 1;
        Lit = IntegerLiteral::Create(Context, ResultVal, CookedTy,
                                     Tok.getLocation());
      }
      return BuildLiteralOperatorCall(R, OpNameInfo, Lit, TokLoc);
    }

    case LOLR_Raw: {
      // C++11 [lit.ext]p3, p4: If S contains a raw literal operator, the
      // literal is treated as a call of the form
      //   operator "" X ("n")
      unsigned Length = Literal.getUDSuffixOffset();
      QualType StrTy = Context.getConstantArrayType(
          Context.adjustStringLiteralBaseType(Context.CharTy.withConst()),
          llvm::APInt(32, Length + 1), ArrayType::Normal, 0);
      Expr *Lit = StringLiteral::Create(
          Context, StringRef(TokSpelling.data(), Length), StringLiteral::Ascii,
          /*Pascal*/false, StrTy, &TokLoc, 1);
      return BuildLiteralOperatorCall(R, OpNameInfo, Lit, TokLoc);
    }

    case LOLR_Template: {
      // C++11 [lit.ext]p3, p4: Otherwise (S contains a literal operator
      // template), L is treated as a call fo the form
      //   operator "" X <'c1', 'c2', ... 'ck'>()
      // where n is the source character sequence c1 c2 ... ck.
      TemplateArgumentListInfo ExplicitArgs;
      unsigned CharBits = Context.getIntWidth(Context.CharTy);
      bool CharIsUnsigned = Context.CharTy->isUnsignedIntegerType();
      llvm::APSInt Value(CharBits, CharIsUnsigned);
      for (unsigned I = 0, N = Literal.getUDSuffixOffset(); I != N; ++I) {
        Value = TokSpelling[I];
        TemplateArgument Arg(Context, Value, Context.CharTy);
        TemplateArgumentLocInfo ArgInfo;
        ExplicitArgs.addArgument(TemplateArgumentLoc(Arg, ArgInfo));
      }
      return BuildLiteralOperatorCall(R, OpNameInfo, None, TokLoc,
                                      &ExplicitArgs);
    }
    case LOLR_StringTemplate:
      llvm_unreachable("unexpected literal operator lookup result");
    }
  }

  Expr *Res;

  if (Literal.isFixedPointLiteral()) {
    QualType Ty;

    if (Literal.isAccum) {
      if (Literal.isHalf) {
        Ty = Context.ShortAccumTy;
      } else if (Literal.isLong) {
        Ty = Context.LongAccumTy;
      } else {
        Ty = Context.AccumTy;
      }
    } else if (Literal.isFract) {
      if (Literal.isHalf) {
        Ty = Context.ShortFractTy;
      } else if (Literal.isLong) {
        Ty = Context.LongFractTy;
      } else {
        Ty = Context.FractTy;
      }
    }

    if (Literal.isUnsigned) Ty = Context.getCorrespondingUnsignedType(Ty);

    bool isSigned = !Literal.isUnsigned;
    unsigned scale = Context.getFixedPointScale(Ty);
    unsigned bit_width = Context.getTypeInfo(Ty).Width;

    llvm::APInt Val(bit_width, 0, isSigned);
    bool Overflowed = Literal.GetFixedPointValue(Val, scale);
    bool ValIsZero = Val.isNullValue() && !Overflowed;

    auto MaxVal = Context.getFixedPointMax(Ty).getValue();
    if (Literal.isFract && Val == MaxVal + 1 && !ValIsZero)
      // Clause 6.4.4 - The value of a constant shall be in the range of
      // representable values for its type, with exception for constants of a
      // fract type with a value of exactly 1; such a constant shall denote
      // the maximal value for the type.
      --Val;
    else if (Val.ugt(MaxVal) || Overflowed)
      Diag(Tok.getLocation(), diag::err_too_large_for_fixed_point);

    Res = FixedPointLiteral::CreateFromRawInt(Context, Val, Ty,
                                              Tok.getLocation(), scale);
  } else if (Literal.isFloatingLiteral()) {
    QualType Ty;
    if (Literal.isHalf){
      if (getOpenCLOptions().isEnabled("cl_khr_fp16"))
        Ty = Context.HalfTy;
      else {
        Diag(Tok.getLocation(), diag::err_half_const_requires_fp16);
        return ExprError();
      }
    } else if (Literal.isFloat)
      Ty = Context.FloatTy;
    else if (Literal.isLong)
      Ty = Context.LongDoubleTy;
    else if (Literal.isFloat16)
      Ty = Context.Float16Ty;
    else if (Literal.isFloat128)
      Ty = Context.Float128Ty;
    else
      Ty = Context.DoubleTy;

    Res = BuildFloatingLiteral(*this, Literal, Ty, Tok.getLocation());

    if (Ty == Context.DoubleTy) {
      if (getLangOpts().SinglePrecisionConstants) {
        const BuiltinType *BTy = Ty->getAs<BuiltinType>();
        if (BTy->getKind() != BuiltinType::Float) {
          Res = ImpCastExprToType(Res, Context.FloatTy, CK_FloatingCast).get();
        }
      } else if (getLangOpts().OpenCL &&
                 !getOpenCLOptions().isEnabled("cl_khr_fp64")) {
        // Impose single-precision float type when cl_khr_fp64 is not enabled.
        Diag(Tok.getLocation(), diag::warn_double_const_requires_fp64);
        Res = ImpCastExprToType(Res, Context.FloatTy, CK_FloatingCast).get();
      }
    }
  } else if (!Literal.isIntegerLiteral()) {
    return ExprError();
  } else {
    QualType Ty;

    // 'long long' is a C99 or C++11 feature.
    if (!getLangOpts().C99 && Literal.isLongLong) {
      if (getLangOpts().CPlusPlus)
        Diag(Tok.getLocation(),
             getLangOpts().CPlusPlus11 ?
             diag::warn_cxx98_compat_longlong : diag::ext_cxx11_longlong);
      else
        Diag(Tok.getLocation(), diag::ext_c99_longlong);
    }

    // Get the value in the widest-possible width.
    unsigned MaxWidth = Context.getTargetInfo().getIntMaxTWidth();
    llvm::APInt ResultVal(MaxWidth, 0);

    if (Literal.GetIntegerValue(ResultVal)) {
      // If this value didn't fit into uintmax_t, error and force to ull.
      Diag(Tok.getLocation(), diag::err_integer_literal_too_large)
          << /* Unsigned */ 1;
      Ty = Context.UnsignedLongLongTy;
      assert(Context.getTypeSize(Ty) == ResultVal.getBitWidth() &&
             "long long is not intmax_t?");
    } else {
      // If this value fits into a ULL, try to figure out what else it fits into
      // according to the rules of C99 6.4.4.1p5.

      // Octal, Hexadecimal, and integers with a U suffix are allowed to
      // be an unsigned int.
      bool AllowUnsigned = Literal.isUnsigned || Literal.getRadix() != 10;

      // Check from smallest to largest, picking the smallest type we can.
      unsigned Width = 0;

      // Microsoft specific integer suffixes are explicitly sized.
      if (Literal.MicrosoftInteger) {
        if (Literal.MicrosoftInteger == 8 && !Literal.isUnsigned) {
          Width = 8;
          Ty = Context.CharTy;
        } else {
          Width = Literal.MicrosoftInteger;
          Ty = Context.getIntTypeForBitwidth(Width,
                                             /*Signed=*/!Literal.isUnsigned);
        }
      }

      if (Ty.isNull() && !Literal.isLong && !Literal.isLongLong) {
        // Are int/unsigned possibilities?
        unsigned IntSize = Context.getTargetInfo().getIntWidth();

        // Does it fit in a unsigned int?
        if (ResultVal.isIntN(IntSize)) {
          // Does it fit in a signed int?
          if (!Literal.isUnsigned && ResultVal[IntSize-1] == 0)
            Ty = Context.IntTy;
          else if (AllowUnsigned)
            Ty = Context.UnsignedIntTy;
          Width = IntSize;
        }
      }

      // Are long/unsigned long possibilities?
      if (Ty.isNull() && !Literal.isLongLong) {
        unsigned LongSize = Context.getTargetInfo().getLongWidth();

        // Does it fit in a unsigned long?
        if (ResultVal.isIntN(LongSize)) {
          // Does it fit in a signed long?
          if (!Literal.isUnsigned && ResultVal[LongSize-1] == 0)
            Ty = Context.LongTy;
          else if (AllowUnsigned)
            Ty = Context.UnsignedLongTy;
          // Check according to the rules of C90 6.1.3.2p5. C++03 [lex.icon]p2
          // is compatible.
          else if (!getLangOpts().C99 && !getLangOpts().CPlusPlus11) {
            const unsigned LongLongSize =
                Context.getTargetInfo().getLongLongWidth();
            Diag(Tok.getLocation(),
                 getLangOpts().CPlusPlus
                     ? Literal.isLong
                           ? diag::warn_old_implicitly_unsigned_long_cxx
                           : /*C++98 UB*/ diag::
                                 ext_old_implicitly_unsigned_long_cxx
                     : diag::warn_old_implicitly_unsigned_long)
                << (LongLongSize > LongSize ? /*will have type 'long long'*/ 0
                                            : /*will be ill-formed*/ 1);
            Ty = Context.UnsignedLongTy;
          }
          Width = LongSize;
        }
      }

      // Check long long if needed.
      if (Ty.isNull()) {
        unsigned LongLongSize = Context.getTargetInfo().getLongLongWidth();

        // Does it fit in a unsigned long long?
        if (ResultVal.isIntN(LongLongSize)) {
          // Does it fit in a signed long long?
          // To be compatible with MSVC, hex integer literals ending with the
          // LL or i64 suffix are always signed in Microsoft mode.
          if (!Literal.isUnsigned && (ResultVal[LongLongSize-1] == 0 ||
              (getLangOpts().MSVCCompat && Literal.isLongLong)))
            Ty = Context.LongLongTy;
          else if (AllowUnsigned)
            Ty = Context.UnsignedLongLongTy;
          Width = LongLongSize;
        }
      }

      // If we still couldn't decide a type, we probably have something that
      // does not fit in a signed long long, but has no U suffix.
      if (Ty.isNull()) {
        Diag(Tok.getLocation(), diag::ext_integer_literal_too_large_for_signed);
        Ty = Context.UnsignedLongLongTy;
        Width = Context.getTargetInfo().getLongLongWidth();
      }

      if (ResultVal.getBitWidth() != Width)
        ResultVal = ResultVal.trunc(Width);
    }
    Res = IntegerLiteral::Create(Context, ResultVal, Ty, Tok.getLocation());
  }

  // If this is an imaginary literal, create the ImaginaryLiteral wrapper.
  if (Literal.isImaginary) {
    Res = new (Context) ImaginaryLiteral(Res,
                                        Context.getComplexType(Res->getType()));

    Diag(Tok.getLocation(), diag::ext_imaginary_constant);
  }
  return Res;
}

ExprResult Sema::ActOnParenExpr(SourceLocation L, SourceLocation R, Expr *E) {
  assert(E && "ActOnParenExpr() missing expr");
  return new (Context) ParenExpr(L, R, E);
}

static bool CheckVecStepTraitOperandType(Sema &S, QualType T,
                                         SourceLocation Loc,
                                         SourceRange ArgRange) {
  // [OpenCL 1.1 6.11.12] "The vec_step built-in function takes a built-in
  // scalar or vector data type argument..."
  // Every built-in scalar type (OpenCL 1.1 6.1.1) is either an arithmetic
  // type (C99 6.2.5p18) or void.
  if (!(T->isArithmeticType() || T->isVoidType() || T->isVectorType())) {
    S.Diag(Loc, diag::err_vecstep_non_scalar_vector_type)
      << T << ArgRange;
    return true;
  }

  assert((T->isVoidType() || !T->isIncompleteType()) &&
         "Scalar types should always be complete");
  return false;
}

static bool CheckExtensionTraitOperandType(Sema &S, QualType T,
                                           SourceLocation Loc,
                                           SourceRange ArgRange,
                                           UnaryExprOrTypeTrait TraitKind) {
  // Invalid types must be hard errors for SFINAE in C++.
  if (S.LangOpts.CPlusPlus)
    return true;

  // C99 6.5.3.4p1:
  if (T->isFunctionType() &&
      (TraitKind == UETT_SizeOf || TraitKind == UETT_AlignOf ||
       TraitKind == UETT_PreferredAlignOf)) {
    // sizeof(function)/alignof(function) is allowed as an extension.
    S.Diag(Loc, diag::ext_sizeof_alignof_function_type)
      << TraitKind << ArgRange;
    return false;
  }

  // Allow sizeof(void)/alignof(void) as an extension, unless in OpenCL where
  // this is an error (OpenCL v1.1 s6.3.k)
  if (T->isVoidType()) {
    unsigned DiagID = S.LangOpts.OpenCL ? diag::err_opencl_sizeof_alignof_type
                                        : diag::ext_sizeof_alignof_void_type;
    S.Diag(Loc, DiagID) << TraitKind << ArgRange;
    return false;
  }

  return true;
}

static bool CheckObjCTraitOperandConstraints(Sema &S, QualType T,
                                             SourceLocation Loc,
                                             SourceRange ArgRange,
                                             UnaryExprOrTypeTrait TraitKind) {
  // Reject sizeof(interface) and sizeof(interface<proto>) if the
  // runtime doesn't allow it.
  if (!S.LangOpts.ObjCRuntime.allowsSizeofAlignof() && T->isObjCObjectType()) {
    S.Diag(Loc, diag::err_sizeof_nonfragile_interface)
      << T << (TraitKind == UETT_SizeOf)
      << ArgRange;
    return true;
  }

  return false;
}

/// Check whether E is a pointer from a decayed array type (the decayed
/// pointer type is equal to T) and emit a warning if it is.
static void warnOnSizeofOnArrayDecay(Sema &S, SourceLocation Loc, QualType T,
                                     Expr *E) {
  // Don't warn if the operation changed the type.
  if (T != E->getType())
    return;

  // Now look for array decays.
  ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E);
  if (!ICE || ICE->getCastKind() != CK_ArrayToPointerDecay)
    return;

  S.Diag(Loc, diag::warn_sizeof_array_decay) << ICE->getSourceRange()
                                             << ICE->getType()
                                             << ICE->getSubExpr()->getType();
}

/// Check the constraints on expression operands to unary type expression
/// and type traits.
///
/// Completes any types necessary and validates the constraints on the operand
/// expression. The logic mostly mirrors the type-based overload, but may modify
/// the expression as it completes the type for that expression through template
/// instantiation, etc.
bool Sema::CheckUnaryExprOrTypeTraitOperand(Expr *E,
                                            UnaryExprOrTypeTrait ExprKind) {
  QualType ExprTy = E->getType();
  assert(!ExprTy->isReferenceType());

  if (ExprKind == UETT_VecStep)
    return CheckVecStepTraitOperandType(*this, ExprTy, E->getExprLoc(),
                                        E->getSourceRange());

  // Whitelist some types as extensions
  if (!CheckExtensionTraitOperandType(*this, ExprTy, E->getExprLoc(),
                                      E->getSourceRange(), ExprKind))
    return false;

  // 'alignof' applied to an expression only requires the base element type of
  // the expression to be complete. 'sizeof' requires the expression's type to
  // be complete (and will attempt to complete it if it's an array of unknown
  // bound).
  if (ExprKind == UETT_AlignOf || ExprKind == UETT_PreferredAlignOf) {
    if (RequireCompleteType(E->getExprLoc(),
                            Context.getBaseElementType(E->getType()),
                            diag::err_sizeof_alignof_incomplete_type, ExprKind,
                            E->getSourceRange()))
      return true;
  } else {
    if (RequireCompleteExprType(E, diag::err_sizeof_alignof_incomplete_type,
                                ExprKind, E->getSourceRange()))
      return true;
  }

  // Completing the expression's type may have changed it.
  ExprTy = E->getType();
  assert(!ExprTy->isReferenceType());

  if (ExprTy->isFunctionType()) {
    Diag(E->getExprLoc(), diag::err_sizeof_alignof_function_type)
      << ExprKind << E->getSourceRange();
    return true;
  }

  // The operand for sizeof and alignof is in an unevaluated expression context,
  // so side effects could result in unintended consequences.
  if ((ExprKind == UETT_SizeOf || ExprKind == UETT_AlignOf ||
       ExprKind == UETT_PreferredAlignOf) &&
      !inTemplateInstantiation() && E->HasSideEffects(Context, false))
    Diag(E->getExprLoc(), diag::warn_side_effects_unevaluated_context);

  if (CheckObjCTraitOperandConstraints(*this, ExprTy, E->getExprLoc(),
                                       E->getSourceRange(), ExprKind))
    return true;

  if (ExprKind == UETT_SizeOf) {
    if (DeclRefExpr *DeclRef = dyn_cast<DeclRefExpr>(E->IgnoreParens())) {
      if (ParmVarDecl *PVD = dyn_cast<ParmVarDecl>(DeclRef->getFoundDecl())) {
        QualType OType = PVD->getOriginalType();
        QualType Type = PVD->getType();
        if (Type->isPointerType() && OType->isArrayType()) {
          Diag(E->getExprLoc(), diag::warn_sizeof_array_param)
            << Type << OType;
          Diag(PVD->getLocation(), diag::note_declared_at);
        }
      }
    }

    // Warn on "sizeof(array op x)" and "sizeof(x op array)", where the array
    // decays into a pointer and returns an unintended result. This is most
    // likely a typo for "sizeof(array) op x".
    if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E->IgnoreParens())) {
      warnOnSizeofOnArrayDecay(*this, BO->getOperatorLoc(), BO->getType(),
                               BO->getLHS());
      warnOnSizeofOnArrayDecay(*this, BO->getOperatorLoc(), BO->getType(),
                               BO->getRHS());
    }
  }

  return false;
}

/// Check the constraints on operands to unary expression and type
/// traits.
///
/// This will complete any types necessary, and validate the various constraints
/// on those operands.
///
/// The UsualUnaryConversions() function is *not* called by this routine.
/// C99 6.3.2.1p[2-4] all state:
///   Except when it is the operand of the sizeof operator ...
///
/// C++ [expr.sizeof]p4
///   The lvalue-to-rvalue, array-to-pointer, and function-to-pointer
///   standard conversions are not applied to the operand of sizeof.
///
/// This policy is followed for all of the unary trait expressions.
bool Sema::CheckUnaryExprOrTypeTraitOperand(QualType ExprType,
                                            SourceLocation OpLoc,
                                            SourceRange ExprRange,
                                            UnaryExprOrTypeTrait ExprKind) {
  if (ExprType->isDependentType())
    return false;

  // C++ [expr.sizeof]p2:
  //     When applied to a reference or a reference type, the result
  //     is the size of the referenced type.
  // C++11 [expr.alignof]p3:
  //     When alignof is applied to a reference type, the result
  //     shall be the alignment of the referenced type.
  if (const ReferenceType *Ref = ExprType->getAs<ReferenceType>())
    ExprType = Ref->getPointeeType();

  // C11 6.5.3.4/3, C++11 [expr.alignof]p3:
  //   When alignof or _Alignof is applied to an array type, the result
  //   is the alignment of the element type.
  if (ExprKind == UETT_AlignOf || ExprKind == UETT_PreferredAlignOf ||
      ExprKind == UETT_OpenMPRequiredSimdAlign)
    ExprType = Context.getBaseElementType(ExprType);

  if (ExprKind == UETT_VecStep)
    return CheckVecStepTraitOperandType(*this, ExprType, OpLoc, ExprRange);

  // Whitelist some types as extensions
  if (!CheckExtensionTraitOperandType(*this, ExprType, OpLoc, ExprRange,
                                      ExprKind))
    return false;

  if (RequireCompleteType(OpLoc, ExprType,
                          diag::err_sizeof_alignof_incomplete_type,
                          ExprKind, ExprRange))
    return true;

  if (ExprType->isFunctionType()) {
    Diag(OpLoc, diag::err_sizeof_alignof_function_type)
      << ExprKind << ExprRange;
    return true;
  }

  if (CheckObjCTraitOperandConstraints(*this, ExprType, OpLoc, ExprRange,
                                       ExprKind))
    return true;

  return false;
}

static bool CheckAlignOfExpr(Sema &S, Expr *E, UnaryExprOrTypeTrait ExprKind) {
  E = E->IgnoreParens();

  // Cannot know anything else if the expression is dependent.
  if (E->isTypeDependent())
    return false;

  if (E->getObjectKind() == OK_BitField) {
    S.Diag(E->getExprLoc(), diag::err_sizeof_alignof_typeof_bitfield)
       << 1 << E->getSourceRange();
    return true;
  }

  ValueDecl *D = nullptr;
  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
    D = DRE->getDecl();
  } else if (MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
    D = ME->getMemberDecl();
  }

  // If it's a field, require the containing struct to have a
  // complete definition so that we can compute the layout.
  //
  // This can happen in C++11 onwards, either by naming the member
  // in a way that is not transformed into a member access expression
  // (in an unevaluated operand, for instance), or by naming the member
  // in a trailing-return-type.
  //
  // For the record, since __alignof__ on expressions is a GCC
  // extension, GCC seems to permit this but always gives the
  // nonsensical answer 0.
  //
  // We don't really need the layout here --- we could instead just
  // directly check for all the appropriate alignment-lowing
  // attributes --- but that would require duplicating a lot of
  // logic that just isn't worth duplicating for such a marginal
  // use-case.
  if (FieldDecl *FD = dyn_cast_or_null<FieldDecl>(D)) {
    // Fast path this check, since we at least know the record has a
    // definition if we can find a member of it.
    if (!FD->getParent()->isCompleteDefinition()) {
      S.Diag(E->getExprLoc(), diag::err_alignof_member_of_incomplete_type)
        << E->getSourceRange();
      return true;
    }

    // Otherwise, if it's a field, and the field doesn't have
    // reference type, then it must have a complete type (or be a
    // flexible array member, which we explicitly want to
    // white-list anyway), which makes the following checks trivial.
    if (!FD->getType()->isReferenceType())
      return false;
  }

  return S.CheckUnaryExprOrTypeTraitOperand(E, ExprKind);
}

bool Sema::CheckVecStepExpr(Expr *E) {
  E = E->IgnoreParens();

  // Cannot know anything else if the expression is dependent.
  if (E->isTypeDependent())
    return false;

  return CheckUnaryExprOrTypeTraitOperand(E, UETT_VecStep);
}

static void captureVariablyModifiedType(ASTContext &Context, QualType T,
                                        CapturingScopeInfo *CSI) {
  assert(T->isVariablyModifiedType());
  assert(CSI != nullptr);

  // We're going to walk down into the type and look for VLA expressions.
  do {
    const Type *Ty = T.getTypePtr();
    switch (Ty->getTypeClass()) {
#define TYPE(Class, Base)
#define ABSTRACT_TYPE(Class, Base)
#define NON_CANONICAL_TYPE(Class, Base)
#define DEPENDENT_TYPE(Class, Base) case Type::Class:
#define NON_CANONICAL_UNLESS_DEPENDENT_TYPE(Class, Base)
#include "clang/AST/TypeNodes.def"
      T = QualType();
      break;
    // These types are never variably-modified.
    case Type::Builtin:
    case Type::Complex:
    case Type::Vector:
    case Type::ExtVector:
    case Type::Record:
    case Type::Enum:
    case Type::Elaborated:
    case Type::TemplateSpecialization:
    case Type::ObjCObject:
    case Type::ObjCInterface:
    case Type::ObjCObjectPointer:
    case Type::ObjCTypeParam:
    case Type::Pipe:
      llvm_unreachable("type class is never variably-modified!");
    case Type::Adjusted:
      T = cast<AdjustedType>(Ty)->getOriginalType();
      break;
    case Type::Decayed:
      T = cast<DecayedType>(Ty)->getPointeeType();
      break;
    case Type::Pointer:
      T = cast<PointerType>(Ty)->getPointeeType();
      break;
    case Type::BlockPointer:
      T = cast<BlockPointerType>(Ty)->getPointeeType();
      break;
    case Type::LValueReference:
    case Type::RValueReference:
      T = cast<ReferenceType>(Ty)->getPointeeType();
      break;
    case Type::MemberPointer:
      T = cast<MemberPointerType>(Ty)->getPointeeType();
      break;
    case Type::ConstantArray:
    case Type::IncompleteArray:
      // Losing element qualification here is fine.
      T = cast<ArrayType>(Ty)->getElementType();
      break;
    case Type::VariableArray: {
      // Losing element qualification here is fine.
      const VariableArrayType *VAT = cast<VariableArrayType>(Ty);

      // Unknown size indication requires no size computation.
      // Otherwise, evaluate and record it.
      auto Size = VAT->getSizeExpr();
      if (Size && !CSI->isVLATypeCaptured(VAT) &&
          (isa<CapturedRegionScopeInfo>(CSI) || isa<LambdaScopeInfo>(CSI)))
        CSI->addVLATypeCapture(Size->getExprLoc(), VAT, Context.getSizeType());

      T = VAT->getElementType();
      break;
    }
    case Type::FunctionProto:
    case Type::FunctionNoProto:
      T = cast<FunctionType>(Ty)->getReturnType();
      break;
    case Type::Paren:
    case Type::TypeOf:
    case Type::UnaryTransform:
    case Type::Attributed:
    case Type::SubstTemplateTypeParm:
    case Type::PackExpansion:
    case Type::MacroQualified:
      // Keep walking after single level desugaring.
      T = T.getSingleStepDesugaredType(Context);
      break;
    case Type::Typedef:
      T = cast<TypedefType>(Ty)->desugar();
      break;
    case Type::Decltype:
      T = cast<DecltypeType>(Ty)->desugar();
      break;
    case Type::Auto:
    case Type::DeducedTemplateSpecialization:
      T = cast<DeducedType>(Ty)->getDeducedType();
      break;
    case Type::TypeOfExpr:
      T = cast<TypeOfExprType>(Ty)->getUnderlyingExpr()->getType();
      break;
    case Type::Atomic:
      T = cast<AtomicType>(Ty)->getValueType();
      break;
    }
  } while (!T.isNull() && T->isVariablyModifiedType());
}

/// Build a sizeof or alignof expression given a type operand.
ExprResult
Sema::CreateUnaryExprOrTypeTraitExpr(TypeSourceInfo *TInfo,
                                     SourceLocation OpLoc,
                                     UnaryExprOrTypeTrait ExprKind,
                                     SourceRange R) {
  if (!TInfo)
    return ExprError();

  QualType T = TInfo->getType();

  if (!T->isDependentType() &&
      CheckUnaryExprOrTypeTraitOperand(T, OpLoc, R, ExprKind))
    return ExprError();

  if (T->isVariablyModifiedType() && FunctionScopes.size() > 1) {
    if (auto *TT = T->getAs<TypedefType>()) {
      for (auto I = FunctionScopes.rbegin(),
                E = std::prev(FunctionScopes.rend());
           I != E; ++I) {
        auto *CSI = dyn_cast<CapturingScopeInfo>(*I);
        if (CSI == nullptr)
          break;
        DeclContext *DC = nullptr;
        if (auto *LSI = dyn_cast<LambdaScopeInfo>(CSI))
          DC = LSI->CallOperator;
        else if (auto *CRSI = dyn_cast<CapturedRegionScopeInfo>(CSI))
          DC = CRSI->TheCapturedDecl;
        else if (auto *BSI = dyn_cast<BlockScopeInfo>(CSI))
          DC = BSI->TheDecl;
        if (DC) {
          if (DC->containsDecl(TT->getDecl()))
            break;
          captureVariablyModifiedType(Context, T, CSI);
        }
      }
    }
  }

  // C99 6.5.3.4p4: the type (an unsigned integer type) is size_t.
  return new (Context) UnaryExprOrTypeTraitExpr(
      ExprKind, TInfo, Context.getSizeType(), OpLoc, R.getEnd());
}

/// Build a sizeof or alignof expression given an expression
/// operand.
ExprResult
Sema::CreateUnaryExprOrTypeTraitExpr(Expr *E, SourceLocation OpLoc,
                                     UnaryExprOrTypeTrait ExprKind) {
  ExprResult PE = CheckPlaceholderExpr(E);
  if (PE.isInvalid())
    return ExprError();

  E = PE.get();

  // Verify that the operand is valid.
  bool isInvalid = false;
  if (E->isTypeDependent()) {
    // Delay type-checking for type-dependent expressions.
  } else if (ExprKind == UETT_AlignOf || ExprKind == UETT_PreferredAlignOf) {
    isInvalid = CheckAlignOfExpr(*this, E, ExprKind);
  } else if (ExprKind == UETT_VecStep) {
    isInvalid = CheckVecStepExpr(E);
  } else if (ExprKind == UETT_OpenMPRequiredSimdAlign) {
      Diag(E->getExprLoc(), diag::err_openmp_default_simd_align_expr);
      isInvalid = true;
  } else if (E->refersToBitField()) {  // C99 6.5.3.4p1.
    Diag(E->getExprLoc(), diag::err_sizeof_alignof_typeof_bitfield) << 0;
    isInvalid = true;
  } else {
    isInvalid = CheckUnaryExprOrTypeTraitOperand(E, UETT_SizeOf);
  }

  if (isInvalid)
    return ExprError();

  if (ExprKind == UETT_SizeOf && E->getType()->isVariableArrayType()) {
    PE = TransformToPotentiallyEvaluated(E);
    if (PE.isInvalid()) return ExprError();
    E = PE.get();
  }

  // C99 6.5.3.4p4: the type (an unsigned integer type) is size_t.
  return new (Context) UnaryExprOrTypeTraitExpr(
      ExprKind, E, Context.getSizeType(), OpLoc, E->getSourceRange().getEnd());
}

/// ActOnUnaryExprOrTypeTraitExpr - Handle @c sizeof(type) and @c sizeof @c
/// expr and the same for @c alignof and @c __alignof
/// Note that the ArgRange is invalid if isType is false.
ExprResult
Sema::ActOnUnaryExprOrTypeTraitExpr(SourceLocation OpLoc,
                                    UnaryExprOrTypeTrait ExprKind, bool IsType,
                                    void *TyOrEx, SourceRange ArgRange) {
  // If error parsing type, ignore.
  if (!TyOrEx) return ExprError();

  if (IsType) {
    TypeSourceInfo *TInfo;
    (void) GetTypeFromParser(ParsedType::getFromOpaquePtr(TyOrEx), &TInfo);
    return CreateUnaryExprOrTypeTraitExpr(TInfo, OpLoc, ExprKind, ArgRange);
  }

  Expr *ArgEx = (Expr *)TyOrEx;
  ExprResult Result = CreateUnaryExprOrTypeTraitExpr(ArgEx, OpLoc, ExprKind);
  return Result;
}

static QualType CheckRealImagOperand(Sema &S, ExprResult &V, SourceLocation Loc,
                                     bool IsReal) {
  if (V.get()->isTypeDependent())
    return S.Context.DependentTy;

  // _Real and _Imag are only l-values for normal l-values.
  if (V.get()->getObjectKind() != OK_Ordinary) {
    V = S.DefaultLvalueConversion(V.get());
    if (V.isInvalid())
      return QualType();
  }

  // These operators return the element type of a complex type.
  if (const ComplexType *CT = V.get()->getType()->getAs<ComplexType>())
    return CT->getElementType();

  // Otherwise they pass through real integer and floating point types here.
  if (V.get()->getType()->isArithmeticType())
    return V.get()->getType();

  // Test for placeholders.
  ExprResult PR = S.CheckPlaceholderExpr(V.get());
  if (PR.isInvalid()) return QualType();
  if (PR.get() != V.get()) {
    V = PR;
    return CheckRealImagOperand(S, V, Loc, IsReal);
  }

  // Reject anything else.
  S.Diag(Loc, diag::err_realimag_invalid_type) << V.get()->getType()
    << (IsReal ? "__real" : "__imag");
  return QualType();
}



ExprResult
Sema::ActOnPostfixUnaryOp(Scope *S, SourceLocation OpLoc,
                          tok::TokenKind Kind, Expr *Input) {
  UnaryOperatorKind Opc;
  switch (Kind) {
  default: llvm_unreachable("Unknown unary op!");
  case tok::plusplus:   Opc = UO_PostInc; break;
  case tok::minusminus: Opc = UO_PostDec; break;
  }

  // Since this might is a postfix expression, get rid of ParenListExprs.
  ExprResult Result = MaybeConvertParenListExprToParenExpr(S, Input);
  if (Result.isInvalid()) return ExprError();
  Input = Result.get();

  return BuildUnaryOp(S, OpLoc, Opc, Input);
}

/// Diagnose if arithmetic on the given ObjC pointer is illegal.
///
/// \return true on error
static bool checkArithmeticOnObjCPointer(Sema &S,
                                         SourceLocation opLoc,
                                         Expr *op) {
  assert(op->getType()->isObjCObjectPointerType());
  if (S.LangOpts.ObjCRuntime.allowsPointerArithmetic() &&
      !S.LangOpts.ObjCSubscriptingLegacyRuntime)
    return false;

  S.Diag(opLoc, diag::err_arithmetic_nonfragile_interface)
    << op->getType()->castAs<ObjCObjectPointerType>()->getPointeeType()
    << op->getSourceRange();
  return true;
}

static bool isMSPropertySubscriptExpr(Sema &S, Expr *Base) {
  auto *BaseNoParens = Base->IgnoreParens();
  if (auto *MSProp = dyn_cast<MSPropertyRefExpr>(BaseNoParens))
    return MSProp->getPropertyDecl()->getType()->isArrayType();
  return isa<MSPropertySubscriptExpr>(BaseNoParens);
}

ExprResult
Sema::ActOnArraySubscriptExpr(Scope *S, Expr *base, SourceLocation lbLoc,
                              Expr *idx, SourceLocation rbLoc) {
  if (base && !base->getType().isNull() &&
      base->getType()->isSpecificPlaceholderType(BuiltinType::OMPArraySection))
    return ActOnOMPArraySectionExpr(base, lbLoc, idx, SourceLocation(),
                                    /*Length=*/nullptr, rbLoc);

  // Since this might be a postfix expression, get rid of ParenListExprs.
  if (isa<ParenListExpr>(base)) {
    ExprResult result = MaybeConvertParenListExprToParenExpr(S, base);
    if (result.isInvalid()) return ExprError();
    base = result.get();
  }

  // Handle any non-overload placeholder types in the base and index
  // expressions.  We can't handle overloads here because the other
  // operand might be an overloadable type, in which case the overload
  // resolution for the operator overload should get the first crack
  // at the overload.
  bool IsMSPropertySubscript = false;
  if (base->getType()->isNonOverloadPlaceholderType()) {
    IsMSPropertySubscript = isMSPropertySubscriptExpr(*this, base);
    if (!IsMSPropertySubscript) {
      ExprResult result = CheckPlaceholderExpr(base);
      if (result.isInvalid())
        return ExprError();
      base = result.get();
    }
  }
  if (idx->getType()->isNonOverloadPlaceholderType()) {
    ExprResult result = CheckPlaceholderExpr(idx);
    if (result.isInvalid()) return ExprError();
    idx = result.get();
  }

  // Build an unanalyzed expression if either operand is type-dependent.
  if (getLangOpts().CPlusPlus &&
      (base->isTypeDependent() || idx->isTypeDependent())) {
    return new (Context) ArraySubscriptExpr(base, idx, Context.DependentTy,
                                            VK_LValue, OK_Ordinary, rbLoc);
  }

  // MSDN, property (C++)
  // https://msdn.microsoft.com/en-us/library/yhfk0thd(v=vs.120).aspx
  // This attribute can also be used in the declaration of an empty array in a
  // class or structure definition. For example:
  // __declspec(property(get=GetX, put=PutX)) int x[];
  // The above statement indicates that x[] can be used with one or more array
  // indices. In this case, i=p->x[a][b] will be turned into i=p->GetX(a, b),
  // and p->x[a][b] = i will be turned into p->PutX(a, b, i);
  if (IsMSPropertySubscript) {
    // Build MS property subscript expression if base is MS property reference
    // or MS property subscript.
    return new (Context) MSPropertySubscriptExpr(
        base, idx, Context.PseudoObjectTy, VK_LValue, OK_Ordinary, rbLoc);
  }

  // Use C++ overloaded-operator rules if either operand has record
  // type.  The spec says to do this if either type is *overloadable*,
  // but enum types can't declare subscript operators or conversion
  // operators, so there's nothing interesting for overload resolution
  // to do if there aren't any record types involved.
  //
  // ObjC pointers have their own subscripting logic that is not tied
  // to overload resolution and so should not take this path.
  if (getLangOpts().CPlusPlus &&
      (base->getType()->isRecordType() ||
       (!base->getType()->isObjCObjectPointerType() &&
        idx->getType()->isRecordType()))) {
    return CreateOverloadedArraySubscriptExpr(lbLoc, rbLoc, base, idx);
  }

  ExprResult Res = CreateBuiltinArraySubscriptExpr(base, lbLoc, idx, rbLoc);

  if (!Res.isInvalid() && isa<ArraySubscriptExpr>(Res.get()))
    CheckSubscriptAccessOfNoDeref(cast<ArraySubscriptExpr>(Res.get()));

  return Res;
}

void Sema::CheckAddressOfNoDeref(const Expr *E) {
  ExpressionEvaluationContextRecord &LastRecord = ExprEvalContexts.back();
  const Expr *StrippedExpr = E->IgnoreParenImpCasts();

  // For expressions like `&(*s).b`, the base is recorded and what should be
  // checked.
  const MemberExpr *Member = nullptr;
  while ((Member = dyn_cast<MemberExpr>(StrippedExpr)) && !Member->isArrow())
    StrippedExpr = Member->getBase()->IgnoreParenImpCasts();

  LastRecord.PossibleDerefs.erase(StrippedExpr);
}

void Sema::CheckSubscriptAccessOfNoDeref(const ArraySubscriptExpr *E) {
  QualType ResultTy = E->getType();
  ExpressionEvaluationContextRecord &LastRecord = ExprEvalContexts.back();

  // Bail if the element is an array since it is not memory access.
  if (isa<ArrayType>(ResultTy))
    return;

  if (ResultTy->hasAttr(attr::NoDeref)) {
    LastRecord.PossibleDerefs.insert(E);
    return;
  }

  // Check if the base type is a pointer to a member access of a struct
  // marked with noderef.
  const Expr *Base = E->getBase();
  QualType BaseTy = Base->getType();
  if (!(isa<ArrayType>(BaseTy) || isa<PointerType>(BaseTy)))
    // Not a pointer access
    return;

  const MemberExpr *Member = nullptr;
  while ((Member = dyn_cast<MemberExpr>(Base->IgnoreParenCasts())) &&
         Member->isArrow())
    Base = Member->getBase();

  if (const auto *Ptr = dyn_cast<PointerType>(Base->getType())) {
    if (Ptr->getPointeeType()->hasAttr(attr::NoDeref))
      LastRecord.PossibleDerefs.insert(E);
  }
}

ExprResult Sema::ActOnOMPArraySectionExpr(Expr *Base, SourceLocation LBLoc,
                                          Expr *LowerBound,
                                          SourceLocation ColonLoc, Expr *Length,
                                          SourceLocation RBLoc) {
  if (Base->getType()->isPlaceholderType() &&
      !Base->getType()->isSpecificPlaceholderType(
          BuiltinType::OMPArraySection)) {
    ExprResult Result = CheckPlaceholderExpr(Base);
    if (Result.isInvalid())
      return ExprError();
    Base = Result.get();
  }
  if (LowerBound && LowerBound->getType()->isNonOverloadPlaceholderType()) {
    ExprResult Result = CheckPlaceholderExpr(LowerBound);
    if (Result.isInvalid())
      return ExprError();
    Result = DefaultLvalueConversion(Result.get());
    if (Result.isInvalid())
      return ExprError();
    LowerBound = Result.get();
  }
  if (Length && Length->getType()->isNonOverloadPlaceholderType()) {
    ExprResult Result = CheckPlaceholderExpr(Length);
    if (Result.isInvalid())
      return ExprError();
    Result = DefaultLvalueConversion(Result.get());
    if (Result.isInvalid())
      return ExprError();
    Length = Result.get();
  }

  // Build an unanalyzed expression if either operand is type-dependent.
  if (Base->isTypeDependent() ||
      (LowerBound &&
       (LowerBound->isTypeDependent() || LowerBound->isValueDependent())) ||
      (Length && (Length->isTypeDependent() || Length->isValueDependent()))) {
    return new (Context)
        OMPArraySectionExpr(Base, LowerBound, Length, Context.DependentTy,
                            VK_LValue, OK_Ordinary, ColonLoc, RBLoc);
  }

  // Perform default conversions.
  QualType OriginalTy = OMPArraySectionExpr::getBaseOriginalType(Base);
  QualType ResultTy;
  if (OriginalTy->isAnyPointerType()) {
    ResultTy = OriginalTy->getPointeeType();
  } else if (OriginalTy->isArrayType()) {
    ResultTy = OriginalTy->getAsArrayTypeUnsafe()->getElementType();
  } else {
    return ExprError(
        Diag(Base->getExprLoc(), diag::err_omp_typecheck_section_value)
        << Base->getSourceRange());
  }
  // C99 6.5.2.1p1
  if (LowerBound) {
    auto Res = PerformOpenMPImplicitIntegerConversion(LowerBound->getExprLoc(),
                                                      LowerBound);
    if (Res.isInvalid())
      return ExprError(Diag(LowerBound->getExprLoc(),
                            diag::err_omp_typecheck_section_not_integer)
                       << 0 << LowerBound->getSourceRange());
    LowerBound = Res.get();

    if (LowerBound->getType()->isSpecificBuiltinType(BuiltinType::Char_S) ||
        LowerBound->getType()->isSpecificBuiltinType(BuiltinType::Char_U))
      Diag(LowerBound->getExprLoc(), diag::warn_omp_section_is_char)
          << 0 << LowerBound->getSourceRange();
  }
  if (Length) {
    auto Res =
        PerformOpenMPImplicitIntegerConversion(Length->getExprLoc(), Length);
    if (Res.isInvalid())
      return ExprError(Diag(Length->getExprLoc(),
                            diag::err_omp_typecheck_section_not_integer)
                       << 1 << Length->getSourceRange());
    Length = Res.get();

    if (Length->getType()->isSpecificBuiltinType(BuiltinType::Char_S) ||
        Length->getType()->isSpecificBuiltinType(BuiltinType::Char_U))
      Diag(Length->getExprLoc(), diag::warn_omp_section_is_char)
          << 1 << Length->getSourceRange();
  }

  // C99 6.5.2.1p1: "shall have type "pointer to *object* type". Similarly,
  // C++ [expr.sub]p1: The type "T" shall be a completely-defined object
  // type. Note that functions are not objects, and that (in C99 parlance)
  // incomplete types are not object types.
  if (ResultTy->isFunctionType()) {
    Diag(Base->getExprLoc(), diag::err_omp_section_function_type)
        << ResultTy << Base->getSourceRange();
    return ExprError();
  }

  if (RequireCompleteType(Base->getExprLoc(), ResultTy,
                          diag::err_omp_section_incomplete_type, Base))
    return ExprError();

  if (LowerBound && !OriginalTy->isAnyPointerType()) {
    Expr::EvalResult Result;
    if (LowerBound->EvaluateAsInt(Result, Context)) {
      // OpenMP 4.5, [2.4 Array Sections]
      // The array section must be a subset of the original array.
      llvm::APSInt LowerBoundValue = Result.Val.getInt();
      if (LowerBoundValue.isNegative()) {
        Diag(LowerBound->getExprLoc(), diag::err_omp_section_not_subset_of_array)
            << LowerBound->getSourceRange();
        return ExprError();
      }
    }
  }

  if (Length) {
    Expr::EvalResult Result;
    if (Length->EvaluateAsInt(Result, Context)) {
      // OpenMP 4.5, [2.4 Array Sections]
      // The length must evaluate to non-negative integers.
      llvm::APSInt LengthValue = Result.Val.getInt();
      if (LengthValue.isNegative()) {
        Diag(Length->getExprLoc(), diag::err_omp_section_length_negative)
            << LengthValue.toString(/*Radix=*/10, /*Signed=*/true)
            << Length->getSourceRange();
        return ExprError();
      }
    }
  } else if (ColonLoc.isValid() &&
             (OriginalTy.isNull() || (!OriginalTy->isConstantArrayType() &&
                                      !OriginalTy->isVariableArrayType()))) {
    // OpenMP 4.5, [2.4 Array Sections]
    // When the size of the array dimension is not known, the length must be
    // specified explicitly.
    Diag(ColonLoc, diag::err_omp_section_length_undefined)
        << (!OriginalTy.isNull() && OriginalTy->isArrayType());
    return ExprError();
  }

  if (!Base->getType()->isSpecificPlaceholderType(
          BuiltinType::OMPArraySection)) {
    ExprResult Result = DefaultFunctionArrayLvalueConversion(Base);
    if (Result.isInvalid())
      return ExprError();
    Base = Result.get();
  }
  return new (Context)
      OMPArraySectionExpr(Base, LowerBound, Length, Context.OMPArraySectionTy,
                          VK_LValue, OK_Ordinary, ColonLoc, RBLoc);
}

ExprResult
Sema::CreateBuiltinArraySubscriptExpr(Expr *Base, SourceLocation LLoc,
                                      Expr *Idx, SourceLocation RLoc) {
  Expr *LHSExp = Base;
  Expr *RHSExp = Idx;

  ExprValueKind VK = VK_LValue;
  ExprObjectKind OK = OK_Ordinary;

  // Per C++ core issue 1213, the result is an xvalue if either operand is
  // a non-lvalue array, and an lvalue otherwise.
  if (getLangOpts().CPlusPlus11) {
    for (auto *Op : {LHSExp, RHSExp}) {
      Op = Op->IgnoreImplicit();
      if (Op->getType()->isArrayType() && !Op->isLValue())
        VK = VK_XValue;
    }
  }

  // Perform default conversions.
  if (!LHSExp->getType()->getAs<VectorType>()) {
    ExprResult Result = DefaultFunctionArrayLvalueConversion(LHSExp);
    if (Result.isInvalid())
      return ExprError();
    LHSExp = Result.get();
  }
  ExprResult Result = DefaultFunctionArrayLvalueConversion(RHSExp);
  if (Result.isInvalid())
    return ExprError();
  RHSExp = Result.get();

  QualType LHSTy = LHSExp->getType(), RHSTy = RHSExp->getType();

  // C99 6.5.2.1p2: the expression e1[e2] is by definition precisely equivalent
  // to the expression *((e1)+(e2)). This means the array "Base" may actually be
  // in the subscript position. As a result, we need to derive the array base
  // and index from the expression types.
  Expr *BaseExpr, *IndexExpr;
  QualType ResultType;
  if (LHSTy->isDependentType() || RHSTy->isDependentType()) {
    BaseExpr = LHSExp;
    IndexExpr = RHSExp;
    ResultType = Context.DependentTy;
  } else if (const PointerType *PTy = LHSTy->getAs<PointerType>()) {
    BaseExpr = LHSExp;
    IndexExpr = RHSExp;
    ResultType = PTy->getPointeeType();
  } else if (const ObjCObjectPointerType *PTy =
               LHSTy->getAs<ObjCObjectPointerType>()) {
    BaseExpr = LHSExp;
    IndexExpr = RHSExp;

    // Use custom logic if this should be the pseudo-object subscript
    // expression.
    if (!LangOpts.isSubscriptPointerArithmetic())
      return BuildObjCSubscriptExpression(RLoc, BaseExpr, IndexExpr, nullptr,
                                          nullptr);

    ResultType = PTy->getPointeeType();
  } else if (const PointerType *PTy = RHSTy->getAs<PointerType>()) {
     // Handle the uncommon case of "123[Ptr]".
    BaseExpr = RHSExp;
    IndexExpr = LHSExp;
    ResultType = PTy->getPointeeType();
  } else if (const ObjCObjectPointerType *PTy =
               RHSTy->getAs<ObjCObjectPointerType>()) {
     // Handle the uncommon case of "123[Ptr]".
    BaseExpr = RHSExp;
    IndexExpr = LHSExp;
    ResultType = PTy->getPointeeType();
    if (!LangOpts.isSubscriptPointerArithmetic()) {
      Diag(LLoc, diag::err_subscript_nonfragile_interface)
        << ResultType << BaseExpr->getSourceRange();
      return ExprError();
    }
  } else if (const VectorType *VTy = LHSTy->getAs<VectorType>()) {
    BaseExpr = LHSExp;    // vectors: V[123]
    IndexExpr = RHSExp;
    // We apply C++ DR1213 to vector subscripting too.
    if (getLangOpts().CPlusPlus11 && LHSExp->getValueKind() == VK_RValue) {
      ExprResult Materialized = TemporaryMaterializationConversion(LHSExp);
      if (Materialized.isInvalid())
        return ExprError();
      LHSExp = Materialized.get();
    }
    VK = LHSExp->getValueKind();
    if (VK != VK_RValue)
      OK = OK_VectorComponent;

    ResultType = VTy->getElementType();
    QualType BaseType = BaseExpr->getType();
    Qualifiers BaseQuals = BaseType.getQualifiers();
    Qualifiers MemberQuals = ResultType.getQualifiers();
    Qualifiers Combined = BaseQuals + MemberQuals;
    if (Combined != MemberQuals)
      ResultType = Context.getQualifiedType(ResultType, Combined);
  } else if (LHSTy->isArrayType()) {
    // If we see an array that wasn't promoted by
    // DefaultFunctionArrayLvalueConversion, it must be an array that
    // wasn't promoted because of the C90 rule that doesn't
    // allow promoting non-lvalue arrays.  Warn, then
    // force the promotion here.
    Diag(LHSExp->getBeginLoc(), diag::ext_subscript_non_lvalue)
        << LHSExp->getSourceRange();
    LHSExp = ImpCastExprToType(LHSExp, Context.getArrayDecayedType(LHSTy),
                               CK_ArrayToPointerDecay).get();
    LHSTy = LHSExp->getType();

    BaseExpr = LHSExp;
    IndexExpr = RHSExp;
    ResultType = LHSTy->getAs<PointerType>()->getPointeeType();
  } else if (RHSTy->isArrayType()) {
    // Same as previous, except for 123[f().a] case
    Diag(RHSExp->getBeginLoc(), diag::ext_subscript_non_lvalue)
        << RHSExp->getSourceRange();
    RHSExp = ImpCastExprToType(RHSExp, Context.getArrayDecayedType(RHSTy),
                               CK_ArrayToPointerDecay).get();
    RHSTy = RHSExp->getType();

    BaseExpr = RHSExp;
    IndexExpr = LHSExp;
    ResultType = RHSTy->getAs<PointerType>()->getPointeeType();
  } else {
    return ExprError(Diag(LLoc, diag::err_typecheck_subscript_value)
       << LHSExp->getSourceRange() << RHSExp->getSourceRange());
  }
  // C99 6.5.2.1p1
  if (!IndexExpr->getType()->isIntegerType() && !IndexExpr->isTypeDependent())
    return ExprError(Diag(LLoc, diag::err_typecheck_subscript_not_integer)
                     << IndexExpr->getSourceRange());

  if ((IndexExpr->getType()->isSpecificBuiltinType(BuiltinType::Char_S) ||
       IndexExpr->getType()->isSpecificBuiltinType(BuiltinType::Char_U))
         && !IndexExpr->isTypeDependent())
    Diag(LLoc, diag::warn_subscript_is_char) << IndexExpr->getSourceRange();

  // C99 6.5.2.1p1: "shall have type "pointer to *object* type". Similarly,
  // C++ [expr.sub]p1: The type "T" shall be a completely-defined object
  // type. Note that Functions are not objects, and that (in C99 parlance)
  // incomplete types are not object types.
  if (ResultType->isFunctionType()) {
    Diag(BaseExpr->getBeginLoc(), diag::err_subscript_function_type)
        << ResultType << BaseExpr->getSourceRange();
    return ExprError();
  }

  if (ResultType->isVoidType() && !getLangOpts().CPlusPlus) {
    // GNU extension: subscripting on pointer to void
    Diag(LLoc, diag::ext_gnu_subscript_void_type)
      << BaseExpr->getSourceRange();

    // C forbids expressions of unqualified void type from being l-values.
    // See IsCForbiddenLValueType.
    if (!ResultType.hasQualifiers()) VK = VK_RValue;
  } else if (!ResultType->isDependentType() &&
      RequireCompleteType(LLoc, ResultType,
                          diag::err_subscript_incomplete_type, BaseExpr))
    return ExprError();

  assert(VK == VK_RValue || LangOpts.CPlusPlus ||
         !ResultType.isCForbiddenLValueType());

  if (LHSExp->IgnoreParenImpCasts()->getType()->isVariablyModifiedType() &&
      FunctionScopes.size() > 1) {
    if (auto *TT =
            LHSExp->IgnoreParenImpCasts()->getType()->getAs<TypedefType>()) {
      for (auto I = FunctionScopes.rbegin(),
                E = std::prev(FunctionScopes.rend());
           I != E; ++I) {
        auto *CSI = dyn_cast<CapturingScopeInfo>(*I);
        if (CSI == nullptr)
          break;
        DeclContext *DC = nullptr;
        if (auto *LSI = dyn_cast<LambdaScopeInfo>(CSI))
          DC = LSI->CallOperator;
        else if (auto *CRSI = dyn_cast<CapturedRegionScopeInfo>(CSI))
          DC = CRSI->TheCapturedDecl;
        else if (auto *BSI = dyn_cast<BlockScopeInfo>(CSI))
          DC = BSI->TheDecl;
        if (DC) {
          if (DC->containsDecl(TT->getDecl()))
            break;
          captureVariablyModifiedType(
              Context, LHSExp->IgnoreParenImpCasts()->getType(), CSI);
        }
      }
    }
  }

  return new (Context)
      ArraySubscriptExpr(LHSExp, RHSExp, ResultType, VK, OK, RLoc);
}

bool Sema::CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
                                  ParmVarDecl *Param) {
  if (Param->hasUnparsedDefaultArg()) {
    Diag(CallLoc,
         diag::err_use_of_default_argument_to_function_declared_later) <<
      FD << cast<CXXRecordDecl>(FD->getDeclContext())->getDeclName();
    Diag(UnparsedDefaultArgLocs[Param],
         diag::note_default_argument_declared_here);
    return true;
  }

  if (Param->hasUninstantiatedDefaultArg()) {
    Expr *UninstExpr = Param->getUninstantiatedDefaultArg();

    EnterExpressionEvaluationContext EvalContext(
        *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);

    // Instantiate the expression.
    //
    // FIXME: Pass in a correct Pattern argument, otherwise
    // getTemplateInstantiationArgs uses the lexical context of FD, e.g.
    //
    // template<typename T>
    // struct A {
    //   static int FooImpl();
    //
    //   template<typename Tp>
    //   // bug: default argument A<T>::FooImpl() is evaluated with 2-level
    //   // template argument list [[T], [Tp]], should be [[Tp]].
    //   friend A<Tp> Foo(int a);
    // };
    //
    // template<typename T>
    // A<T> Foo(int a = A<T>::FooImpl());
    MultiLevelTemplateArgumentList MutiLevelArgList
      = getTemplateInstantiationArgs(FD, nullptr, /*RelativeToPrimary=*/true);

    InstantiatingTemplate Inst(*this, CallLoc, Param,
                               MutiLevelArgList.getInnermost());
    if (Inst.isInvalid())
      return true;
    if (Inst.isAlreadyInstantiating()) {
      Diag(Param->getBeginLoc(), diag::err_recursive_default_argument) << FD;
      Param->setInvalidDecl();
      return true;
    }

    ExprResult Result;
    {
      // C++ [dcl.fct.default]p5:
      //   The names in the [default argument] expression are bound, and
      //   the semantic constraints are checked, at the point where the
      //   default argument expression appears.
      ContextRAII SavedContext(*this, FD);
      LocalInstantiationScope Local(*this);
      Result = SubstInitializer(UninstExpr, MutiLevelArgList,
                                /*DirectInit*/false);
    }
    if (Result.isInvalid())
      return true;

    // Check the expression as an initializer for the parameter.
    InitializedEntity Entity
      = InitializedEntity::InitializeParameter(Context, Param);
    InitializationKind Kind = InitializationKind::CreateCopy(
        Param->getLocation(),
        /*FIXME:EqualLoc*/ UninstExpr->getBeginLoc());
    Expr *ResultE = Result.getAs<Expr>();

    InitializationSequence InitSeq(*this, Entity, Kind, ResultE);
    Result = InitSeq.Perform(*this, Entity, Kind, ResultE);
    if (Result.isInvalid())
      return true;

    Result =
        ActOnFinishFullExpr(Result.getAs<Expr>(), Param->getOuterLocStart(),
                            /*DiscardedValue*/ false);
    if (Result.isInvalid())
      return true;

    // Remember the instantiated default argument.
    Param->setDefaultArg(Result.getAs<Expr>());
    if (ASTMutationListener *L = getASTMutationListener()) {
      L->DefaultArgumentInstantiated(Param);
    }
  }

  // If the default argument expression is not set yet, we are building it now.
  if (!Param->hasInit()) {
    Diag(Param->getBeginLoc(), diag::err_recursive_default_argument) << FD;
    Param->setInvalidDecl();
    return true;
  }

  // If the default expression creates temporaries, we need to
  // push them to the current stack of expression temporaries so they'll
  // be properly destroyed.
  // FIXME: We should really be rebuilding the default argument with new
  // bound temporaries; see the comment in PR5810.
  // We don't need to do that with block decls, though, because
  // blocks in default argument expression can never capture anything.
  if (auto Init = dyn_cast<ExprWithCleanups>(Param->getInit())) {
    // Set the "needs cleanups" bit regardless of whether there are
    // any explicit objects.
    Cleanup.setExprNeedsCleanups(Init->cleanupsHaveSideEffects());

    // Append all the objects to the cleanup list.  Right now, this
    // should always be a no-op, because blocks in default argument
    // expressions should never be able to capture anything.
    assert(!Init->getNumObjects() &&
           "default argument expression has capturing blocks?");
  }

  // We already type-checked the argument, so we know it works.
  // Just mark all of the declarations in this potentially-evaluated expression
  // as being "referenced".
  EnterExpressionEvaluationContext EvalContext(
      *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
  MarkDeclarationsReferencedInExpr(Param->getDefaultArg(),
                                   /*SkipLocalVariables=*/true);
  return false;
}

ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
                                        FunctionDecl *FD, ParmVarDecl *Param) {
  if (CheckCXXDefaultArgExpr(CallLoc, FD, Param))
    return ExprError();
  return CXXDefaultArgExpr::Create(Context, CallLoc, Param, CurContext);
}

Sema::VariadicCallType
Sema::getVariadicCallType(FunctionDecl *FDecl, const FunctionProtoType *Proto,
                          Expr *Fn) {
  if (Proto && Proto->isVariadic()) {
    if (dyn_cast_or_null<CXXConstructorDecl>(FDecl))
      return VariadicConstructor;
    else if (Fn && Fn->getType()->isBlockPointerType())
      return VariadicBlock;
    else if (FDecl) {
      if (CXXMethodDecl *Method = dyn_cast_or_null<CXXMethodDecl>(FDecl))
        if (Method->isInstance())
          return VariadicMethod;
    } else if (Fn && Fn->getType() == Context.BoundMemberTy)
      return VariadicMethod;
    return VariadicFunction;
  }
  return VariadicDoesNotApply;
}

namespace {
class FunctionCallCCC final : public FunctionCallFilterCCC {
public:
  FunctionCallCCC(Sema &SemaRef, const IdentifierInfo *FuncName,
                  unsigned NumArgs, MemberExpr *ME)
      : FunctionCallFilterCCC(SemaRef, NumArgs, false, ME),
        FunctionName(FuncName) {}

  bool ValidateCandidate(const TypoCorrection &candidate) override {
    if (!candidate.getCorrectionSpecifier() ||
        candidate.getCorrectionAsIdentifierInfo() != FunctionName) {
      return false;
    }

    return FunctionCallFilterCCC::ValidateCandidate(candidate);
  }

  std::unique_ptr<CorrectionCandidateCallback> clone() override {
    return llvm::make_unique<FunctionCallCCC>(*this);
  }

private:
  const IdentifierInfo *const FunctionName;
};
}

static TypoCorrection TryTypoCorrectionForCall(Sema &S, Expr *Fn,
                                               FunctionDecl *FDecl,
                                               ArrayRef<Expr *> Args) {
  MemberExpr *ME = dyn_cast<MemberExpr>(Fn);
  DeclarationName FuncName = FDecl->getDeclName();
  SourceLocation NameLoc = ME ? ME->getMemberLoc() : Fn->getBeginLoc();

  FunctionCallCCC CCC(S, FuncName.getAsIdentifierInfo(), Args.size(), ME);
  if (TypoCorrection Corrected = S.CorrectTypo(
          DeclarationNameInfo(FuncName, NameLoc), Sema::LookupOrdinaryName,
          S.getScopeForContext(S.CurContext), nullptr, CCC,
          Sema::CTK_ErrorRecovery)) {
    if (NamedDecl *ND = Corrected.getFoundDecl()) {
      if (Corrected.isOverloaded()) {
        OverloadCandidateSet OCS(NameLoc, OverloadCandidateSet::CSK_Normal);
        OverloadCandidateSet::iterator Best;
        for (NamedDecl *CD : Corrected) {
          if (FunctionDecl *FD = dyn_cast<FunctionDecl>(CD))
            S.AddOverloadCandidate(FD, DeclAccessPair::make(FD, AS_none), Args,
                                   OCS);
        }
        switch (OCS.BestViableFunction(S, NameLoc, Best)) {
        case OR_Success:
          ND = Best->FoundDecl;
          Corrected.setCorrectionDecl(ND);
          break;
        default:
          break;
        }
      }
      ND = ND->getUnderlyingDecl();
      if (isa<ValueDecl>(ND) || isa<FunctionTemplateDecl>(ND))
        return Corrected;
    }
  }
  return TypoCorrection();
}

/// ConvertArgumentsForCall - Converts the arguments specified in
/// Args/NumArgs to the parameter types of the function FDecl with
/// function prototype Proto. Call is the call expression itself, and
/// Fn is the function expression. For a C++ member function, this
/// routine does not attempt to convert the object argument. Returns
/// true if the call is ill-formed.
bool
Sema::ConvertArgumentsForCall(CallExpr *Call, Expr *Fn,
                              FunctionDecl *FDecl,
                              const FunctionProtoType *Proto,
                              ArrayRef<Expr *> Args,
                              SourceLocation RParenLoc,
                              bool IsExecConfig) {
  // Bail out early if calling a builtin with custom typechecking.
  if (FDecl)
    if (unsigned ID = FDecl->getBuiltinID())
      if (Context.BuiltinInfo.hasCustomTypechecking(ID))
        return false;

  // C99 6.5.2.2p7 - the arguments are implicitly converted, as if by
  // assignment, to the types of the corresponding parameter, ...
  unsigned NumParams = Proto->getNumParams();
  bool Invalid = false;
  unsigned MinArgs = FDecl ? FDecl->getMinRequiredArguments() : NumParams;
  unsigned FnKind = Fn->getType()->isBlockPointerType()
                       ? 1 /* block */
                       : (IsExecConfig ? 3 /* kernel function (exec config) */
                                       : 0 /* function */);

  // If too few arguments are available (and we don't have default
  // arguments for the remaining parameters), don't make the call.
  if (Args.size() < NumParams) {
    if (Args.size() < MinArgs) {
      TypoCorrection TC;
      if (FDecl && (TC = TryTypoCorrectionForCall(*this, Fn, FDecl, Args))) {
        unsigned diag_id =
            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())
        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();
      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();

      // Emit the location of the prototype.
      if (!TC && FDecl && !FDecl->getBuiltinID() && !IsExecConfig)
        Diag(FDecl->getBeginLoc(), diag::note_callee_decl) << FDecl;

      return true;
    }
    // We reserve space for the default arguments when we create
    // the call expression, before calling ConvertArgumentsForCall.
    assert((Call->getNumArgs() == NumParams) &&
           "We should have reserved space for the default arguments before!");
  }

  // If too many are passed and not variadic, error on the extras and drop
  // them.
  if (Args.size() > NumParams) {
    if (!Proto->isVariadic()) {
      TypoCorrection TC;
      if (FDecl && (TC = TryTypoCorrectionForCall(*this, Fn, FDecl, Args))) {
        unsigned diag_id =
            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())
        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()
            << 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()
            << SourceRange(Args[NumParams]->getBeginLoc(),
                           Args.back()->getEndLoc());

      // Emit the location of the prototype.
      if (!TC && FDecl && !FDecl->getBuiltinID() && !IsExecConfig)
        Diag(FDecl->getBeginLoc(), diag::note_callee_decl) << FDecl;

      // This deletes the extra arguments.
      Call->shrinkNumArgs(NumParams);
      return true;
    }
  }
  SmallVector<Expr *, 8> AllArgs;
  VariadicCallType CallType = getVariadicCallType(FDecl, Proto, Fn);

  Invalid = GatherArgumentsForCall(Call->getBeginLoc(), FDecl, Proto, 0, Args,
                                   AllArgs, CallType);
  if (Invalid)
    return true;
  unsigned TotalNumArgs = AllArgs.size();
  for (unsigned i = 0; i < TotalNumArgs; ++i)
    Call->setArg(i, AllArgs[i]);

  return false;
}

bool Sema::GatherArgumentsForCall(SourceLocation CallLoc, FunctionDecl *FDecl,
                                  const FunctionProtoType *Proto,
                                  unsigned FirstParam, ArrayRef<Expr *> Args,
                                  SmallVectorImpl<Expr *> &AllArgs,
                                  VariadicCallType CallType, bool AllowExplicit,
                                  bool IsListInitialization) {
  unsigned NumParams = Proto->getNumParams();
  bool Invalid = false;
  size_t ArgIx = 0;
  // Continue to check argument types (even if we have too few/many args).
  for (unsigned i = FirstParam; i < NumParams; i++) {
    QualType ProtoArgType = Proto->getParamType(i);

    Expr *Arg;
    ParmVarDecl *Param = FDecl ? FDecl->getParamDecl(i) : nullptr;
    if (ArgIx < Args.size()) {
      Arg = Args[ArgIx++];

      if (RequireCompleteType(Arg->getBeginLoc(), ProtoArgType,
                              diag::err_call_incomplete_argument, Arg))
        return true;

      // Strip the unbridged-cast placeholder expression off, if applicable.
      bool CFAudited = false;
      if (Arg->getType() == Context.ARCUnbridgedCastTy &&
          FDecl && FDecl->hasAttr<CFAuditedTransferAttr>() &&
          (!Param || !Param->hasAttr<CFConsumedAttr>()))
        Arg = stripARCUnbridgedCast(Arg);
      else if (getLangOpts().ObjCAutoRefCount &&
               FDecl && FDecl->hasAttr<CFAuditedTransferAttr>() &&
               (!Param || !Param->hasAttr<CFConsumedAttr>()))
        CFAudited = true;

      if (Proto->getExtParameterInfo(i).isNoEscape())
        if (auto *BE = dyn_cast<BlockExpr>(Arg->IgnoreParenNoopCasts(Context)))
          BE->getBlockDecl()->setDoesNotEscape();

      InitializedEntity Entity =
          Param ? InitializedEntity::InitializeParameter(Context, Param,
                                                         ProtoArgType)
                : InitializedEntity::InitializeParameter(
                      Context, ProtoArgType, Proto->isParamConsumed(i));

      // Remember that parameter belongs to a CF audited API.
      if (CFAudited)
        Entity.setParameterCFAudited();

      ExprResult ArgE = PerformCopyInitialization(
          Entity, SourceLocation(), Arg, IsListInitialization, AllowExplicit);
      if (ArgE.isInvalid())
        return true;

      Arg = ArgE.getAs<Expr>();
    } else {
      assert(Param && "can't use default arguments without a known callee");

      ExprResult ArgExpr = BuildCXXDefaultArgExpr(CallLoc, FDecl, Param);
      if (ArgExpr.isInvalid())
        return true;

      Arg = ArgExpr.getAs<Expr>();
    }

    // Check for array bounds violations for each argument to the call. This
    // check only triggers warnings when the argument isn't a more complex Expr
    // with its own checking, such as a BinaryOperator.
    CheckArrayAccess(Arg);

    // Check for violations of C99 static array rules (C99 6.7.5.3p7).
    CheckStaticArrayArgument(CallLoc, Param, Arg);

    AllArgs.push_back(Arg);
  }

  // If this is a variadic call, handle args passed through "...".
  if (CallType != VariadicDoesNotApply) {
    // Assume that extern "C" functions with variadic arguments that
    // return __unknown_anytype aren't *really* variadic.
    if (Proto->getReturnType() == Context.UnknownAnyTy && FDecl &&
        FDecl->isExternC()) {
      for (Expr *A : Args.slice(ArgIx)) {
        QualType paramType; // ignored
        ExprResult arg = checkUnknownAnyArg(CallLoc, A, paramType);
        Invalid |= arg.isInvalid();
        AllArgs.push_back(arg.get());
      }

    // Otherwise do argument promotion, (C99 6.5.2.2p7).
    } else {
      for (Expr *A : Args.slice(ArgIx)) {
        ExprResult Arg = DefaultVariadicArgumentPromotion(A, CallType, FDecl);
        Invalid |= Arg.isInvalid();
        AllArgs.push_back(Arg.get());
      }
    }

    // Check for array bounds violations.
    for (Expr *A : Args.slice(ArgIx))
      CheckArrayAccess(A);
  }
  return Invalid;
}

static void DiagnoseCalleeStaticArrayParam(Sema &S, ParmVarDecl *PVD) {
  TypeLoc TL = PVD->getTypeSourceInfo()->getTypeLoc();
  if (DecayedTypeLoc DTL = TL.getAs<DecayedTypeLoc>())
    TL = DTL.getOriginalLoc();
  if (ArrayTypeLoc ATL = TL.getAs<ArrayTypeLoc>())
    S.Diag(PVD->getLocation(), diag::note_callee_static_array)
      << ATL.getLocalSourceRange();
}

/// CheckStaticArrayArgument - If the given argument corresponds to a static
/// array parameter, check that it is non-null, and that if it is formed by
/// array-to-pointer decay, the underlying array is sufficiently large.
///
/// C99 6.7.5.3p7: If the keyword static also appears within the [ and ] of the
/// array type derivation, then for each call to the function, the value of the
/// corresponding actual argument shall provide access to the first element of
/// an array with at least as many elements as specified by the size expression.
void
Sema::CheckStaticArrayArgument(SourceLocation CallLoc,
                               ParmVarDecl *Param,
                               const Expr *ArgExpr) {
  // Static array parameters are not supported in C++.
  if (!Param || getLangOpts().CPlusPlus)
    return;

  QualType OrigTy = Param->getOriginalType();

  const ArrayType *AT = Context.getAsArrayType(OrigTy);
  if (!AT || AT->getSizeModifier() != ArrayType::Static)
    return;

  if (ArgExpr->isNullPointerConstant(Context,
                                     Expr::NPC_NeverValueDependent)) {
    Diag(CallLoc, diag::warn_null_arg) << ArgExpr->getSourceRange();
    DiagnoseCalleeStaticArrayParam(*this, Param);
    return;
  }

  const ConstantArrayType *CAT = dyn_cast<ConstantArrayType>(AT);
  if (!CAT)
    return;

  const ConstantArrayType *ArgCAT =
    Context.getAsConstantArrayType(ArgExpr->IgnoreParenCasts()->getType());
  if (!ArgCAT)
    return;

  if (getASTContext().hasSameUnqualifiedType(CAT->getElementType(),
                                             ArgCAT->getElementType())) {
    if (ArgCAT->getSize().ult(CAT->getSize())) {
      Diag(CallLoc, diag::warn_static_array_too_small)
          << ArgExpr->getSourceRange()
          << (unsigned)ArgCAT->getSize().getZExtValue()
          << (unsigned)CAT->getSize().getZExtValue() << 0;
      DiagnoseCalleeStaticArrayParam(*this, Param);
    }
    return;
  }

  Optional<CharUnits> ArgSize =
      getASTContext().getTypeSizeInCharsIfKnown(ArgCAT);
  Optional<CharUnits> ParmSize = getASTContext().getTypeSizeInCharsIfKnown(CAT);
  if (ArgSize && ParmSize && *ArgSize < *ParmSize) {
    Diag(CallLoc, diag::warn_static_array_too_small)
        << ArgExpr->getSourceRange() << (unsigned)ArgSize->getQuantity()
        << (unsigned)ParmSize->getQuantity() << 1;
    DiagnoseCalleeStaticArrayParam(*this, Param);
  }
}

/// Given a function expression of unknown-any type, try to rebuild it
/// to have a function type.
static ExprResult rebuildUnknownAnyFunction(Sema &S, Expr *fn);

/// Is the given type a placeholder that we need to lower out
/// immediately during argument processing?
static bool isPlaceholderToRemoveAsArg(QualType type) {
  // Placeholders are never sugared.
  const BuiltinType *placeholder = dyn_cast<BuiltinType>(type);
  if (!placeholder) return false;

  switch (placeholder->getKind()) {
  // Ignore all the non-placeholder types.
#define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix) \
  case BuiltinType::Id:
#include "clang/Basic/OpenCLImageTypes.def"
#define EXT_OPAQUE_TYPE(ExtType, Id, Ext) \
  case BuiltinType::Id:
#include "clang/Basic/OpenCLExtensionTypes.def"
#define PLACEHOLDER_TYPE(ID, SINGLETON_ID)
#define BUILTIN_TYPE(ID, SINGLETON_ID) case BuiltinType::ID:
#include "clang/AST/BuiltinTypes.def"
    return false;

  // We cannot lower out overload sets; they might validly be resolved
  // by the call machinery.
  case BuiltinType::Overload:
    return false;

  // Unbridged casts in ARC can be handled in some call positions and
  // should be left in place.
  case BuiltinType::ARCUnbridgedCast:
    return false;

  // Pseudo-objects should be converted as soon as possible.
  case BuiltinType::PseudoObject:
    return true;

  // The debugger mode could theoretically but currently does not try
  // to resolve unknown-typed arguments based on known parameter types.
  case BuiltinType::UnknownAny:
    return true;

  // These are always invalid as call arguments and should be reported.
  case BuiltinType::BoundMember:
  case BuiltinType::BuiltinFn:
  case BuiltinType::OMPArraySection:
    return true;

  }
  llvm_unreachable("bad builtin type kind");
}

/// Check an argument list for placeholders that we won't try to
/// handle later.
static bool checkArgsForPlaceholders(Sema &S, MultiExprArg args) {
  // Apply this processing to all the arguments at once instead of
  // dying at the first failure.
  bool hasInvalid = false;
  for (size_t i = 0, e = args.size(); i != e; i++) {
    if (isPlaceholderToRemoveAsArg(args[i]->getType())) {
      ExprResult result = S.CheckPlaceholderExpr(args[i]);
      if (result.isInvalid()) hasInvalid = true;
      else args[i] = result.get();
    } else if (hasInvalid) {
      (void)S.CorrectDelayedTyposInExpr(args[i]);
    }
  }
  return hasInvalid;
}

/// If a builtin function has a pointer argument with no explicit address
/// space, then it should be able to accept a pointer to any address
/// space as input.  In order to do this, we need to replace the
/// standard builtin declaration with one that uses the same address space
/// as the call.
///
/// \returns nullptr If this builtin is not a candidate for a rewrite i.e.
///                  it does not contain any pointer arguments without
///                  an address space qualifer.  Otherwise the rewritten
///                  FunctionDecl is returned.
/// TODO: Handle pointer return types.
static FunctionDecl *rewriteBuiltinFunctionDecl(Sema *Sema, ASTContext &Context,
                                                FunctionDecl *FDecl,
                                                MultiExprArg ArgExprs) {

  QualType DeclType = FDecl->getType();
  const FunctionProtoType *FT = dyn_cast<FunctionProtoType>(DeclType);

  if (!Context.BuiltinInfo.hasPtrArgsOrResult(FDecl->getBuiltinID()) ||
      !FT || FT->isVariadic() || ArgExprs.size() != FT->getNumParams())
    return nullptr;

  bool NeedsNewDecl = false;
  unsigned i = 0;
  SmallVector<QualType, 8> OverloadParams;

  for (QualType ParamType : FT->param_types()) {

    // Convert array arguments to pointer to simplify type lookup.
    ExprResult ArgRes =
        Sema->DefaultFunctionArrayLvalueConversion(ArgExprs[i++]);
    if (ArgRes.isInvalid())
      return nullptr;
    Expr *Arg = ArgRes.get();
    QualType ArgType = Arg->getType();
    if (!ParamType->isPointerType() ||
        ParamType.getQualifiers().hasAddressSpace() ||
        !ArgType->isPointerType() ||
        !ArgType->getPointeeType().getQualifiers().hasAddressSpace()) {
      OverloadParams.push_back(ParamType);
      continue;
    }

    QualType PointeeType = ParamType->getPointeeType();
    if (PointeeType.getQualifiers().hasAddressSpace())
      continue;

    NeedsNewDecl = true;
    LangAS AS = ArgType->getPointeeType().getAddressSpace();

    PointeeType = Context.getAddrSpaceQualType(PointeeType, AS);
    OverloadParams.push_back(Context.getPointerType(PointeeType));
  }

  if (!NeedsNewDecl)
    return nullptr;

  FunctionProtoType::ExtProtoInfo EPI;
  QualType OverloadTy = Context.getFunctionType(FT->getReturnType(),
                                                OverloadParams, EPI);
  DeclContext *Parent = FDecl->getParent();
  FunctionDecl *OverloadDecl = FunctionDecl::Create(Context, Parent,
                                                    FDecl->getLocation(),
                                                    FDecl->getLocation(),
                                                    FDecl->getIdentifier(),
                                                    OverloadTy,
                                                    /*TInfo=*/nullptr,
                                                    SC_Extern, false,
                                                    /*hasPrototype=*/true);
  SmallVector<ParmVarDecl*, 16> Params;
  FT = cast<FunctionProtoType>(OverloadTy);
  for (unsigned i = 0, e = FT->getNumParams(); i != e; ++i) {
    QualType ParamType = FT->getParamType(i);
    ParmVarDecl *Parm =
        ParmVarDecl::Create(Context, OverloadDecl, SourceLocation(),
                                SourceLocation(), nullptr, ParamType,
                                /*TInfo=*/nullptr, SC_None, nullptr);
    Parm->setScopeInfo(0, i);
    Params.push_back(Parm);
  }
  OverloadDecl->setParams(Params);
  return OverloadDecl;
}

static void checkDirectCallValidity(Sema &S, const Expr *Fn,
                                    FunctionDecl *Callee,
                                    MultiExprArg ArgExprs) {
  // `Callee` (when called with ArgExprs) may be ill-formed. enable_if (and
  // similar attributes) really don't like it when functions are called with an
  // invalid number of args.
  if (S.TooManyArguments(Callee->getNumParams(), ArgExprs.size(),
                         /*PartialOverloading=*/false) &&
      !Callee->isVariadic())
    return;
  if (Callee->getMinRequiredArguments() > ArgExprs.size())
    return;

  if (const EnableIfAttr *Attr = S.CheckEnableIf(Callee, ArgExprs, true)) {
    S.Diag(Fn->getBeginLoc(),
           isa<CXXMethodDecl>(Callee)
               ? diag::err_ovl_no_viable_member_function_in_call
               : diag::err_ovl_no_viable_function_in_call)
        << Callee << Callee->getSourceRange();
    S.Diag(Callee->getLocation(),
           diag::note_ovl_candidate_disabled_by_function_cond_attr)
        << Attr->getCond()->getSourceRange() << Attr->getMessage();
    return;
  }
}

static bool enclosingClassIsRelatedToClassInWhichMembersWereFound(
    const UnresolvedMemberExpr *const UME, Sema &S) {

  const auto GetFunctionLevelDCIfCXXClass =
      [](Sema &S) -> const CXXRecordDecl * {
    const DeclContext *const DC = S.getFunctionLevelDeclContext();
    if (!DC || !DC->getParent())
      return nullptr;

    // If the call to some member function was made from within a member
    // function body 'M' return return 'M's parent.
    if (const auto *MD = dyn_cast<CXXMethodDecl>(DC))
      return MD->getParent()->getCanonicalDecl();
    // else the call was made from within a default member initializer of a
    // class, so return the class.
    if (const auto *RD = dyn_cast<CXXRecordDecl>(DC))
      return RD->getCanonicalDecl();
    return nullptr;
  };
  // If our DeclContext is neither a member function nor a class (in the
  // case of a lambda in a default member initializer), we can't have an
  // enclosing 'this'.

  const CXXRecordDecl *const CurParentClass = GetFunctionLevelDCIfCXXClass(S);
  if (!CurParentClass)
    return false;

  // The naming class for implicit member functions call is the class in which
  // name lookup starts.
  const CXXRecordDecl *const NamingClass =
      UME->getNamingClass()->getCanonicalDecl();
  assert(NamingClass && "Must have naming class even for implicit access");

  // If the unresolved member functions were found in a 'naming class' that is
  // related (either the same or derived from) to the class that contains the
  // member function that itself contained the implicit member access.

  return CurParentClass == NamingClass ||
         CurParentClass->isDerivedFrom(NamingClass);
}

static void
tryImplicitlyCaptureThisIfImplicitMemberFunctionAccessWithDependentArgs(
    Sema &S, const UnresolvedMemberExpr *const UME, SourceLocation CallLoc) {

  if (!UME)
    return;

  LambdaScopeInfo *const CurLSI = S.getCurLambda();
  // Only try and implicitly capture 'this' within a C++ Lambda if it hasn't
  // already been captured, or if this is an implicit member function call (if
  // it isn't, an attempt to capture 'this' should already have been made).
  if (!CurLSI || CurLSI->ImpCaptureStyle == CurLSI->ImpCap_None ||
      !UME->isImplicitAccess() || CurLSI->isCXXThisCaptured())
    return;

  // Check if the naming class in which the unresolved members were found is
  // related (same as or is a base of) to the enclosing class.

  if (!enclosingClassIsRelatedToClassInWhichMembersWereFound(UME, S))
    return;


  DeclContext *EnclosingFunctionCtx = S.CurContext->getParent()->getParent();
  // If the enclosing function is not dependent, then this lambda is
  // capture ready, so if we can capture this, do so.
  if (!EnclosingFunctionCtx->isDependentContext()) {
    // If the current lambda and all enclosing lambdas can capture 'this' -
    // then go ahead and capture 'this' (since our unresolved overload set
    // contains at least one non-static member function).
    if (!S.CheckCXXThisCapture(CallLoc, /*Explcit*/ false, /*Diagnose*/ false))
      S.CheckCXXThisCapture(CallLoc);
  } else if (S.CurContext->isDependentContext()) {
    // ... since this is an implicit member reference, that might potentially
    // involve a 'this' capture, mark '