clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

//===--- SemaTemplateInstantiateDecl.cpp - C++ Template Decl Instantiation ===/
//
// 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 C++ template instantiation for declarations.
//
//===----------------------------------------------------------------------===/

#include "TreeTransform.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTMutationListener.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclVisitor.h"
#include "clang/AST/DependentDiagnostic.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/PrettyDeclStackTrace.h"
#include "clang/AST/TypeLoc.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Sema/Initialization.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/ScopeInfo.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Sema/Template.h"
#include "clang/Sema/TemplateInstCallback.h"
#include "llvm/Support/TimeProfiler.h"

using namespace clang;

static bool isDeclWithinFunction(const Decl *D) {
  const DeclContext *DC = D->getDeclContext();
  if (DC->isFunctionOrMethod())
    return true;

  if (DC->isRecord())
    return cast<CXXRecordDecl>(DC)->isLocalClass();

  return false;
}

template<typename DeclT>
static bool SubstQualifier(Sema &SemaRef, const DeclT *OldDecl, DeclT *NewDecl,
                           const MultiLevelTemplateArgumentList &TemplateArgs) {
  if (!OldDecl->getQualifierLoc())
    return false;

  assert((NewDecl->getFriendObjectKind() ||
          !OldDecl->getLexicalDeclContext()->isDependentContext()) &&
         "non-friend with qualified name defined in dependent context");
  Sema::ContextRAII SavedContext(
      SemaRef,
      const_cast<DeclContext *>(NewDecl->getFriendObjectKind()
                                    ? NewDecl->getLexicalDeclContext()
                                    : OldDecl->getLexicalDeclContext()));

  NestedNameSpecifierLoc NewQualifierLoc
      = SemaRef.SubstNestedNameSpecifierLoc(OldDecl->getQualifierLoc(),
                                            TemplateArgs);

  if (!NewQualifierLoc)
    return true;

  NewDecl->setQualifierInfo(NewQualifierLoc);
  return false;
}

bool TemplateDeclInstantiator::SubstQualifier(const DeclaratorDecl *OldDecl,
                                              DeclaratorDecl *NewDecl) {
  return ::SubstQualifier(SemaRef, OldDecl, NewDecl, TemplateArgs);
}

bool TemplateDeclInstantiator::SubstQualifier(const TagDecl *OldDecl,
                                              TagDecl *NewDecl) {
  return ::SubstQualifier(SemaRef, OldDecl, NewDecl, TemplateArgs);
}

// Include attribute instantiation code.
#include "clang/Sema/AttrTemplateInstantiate.inc"

static void instantiateDependentAlignedAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AlignedAttr *Aligned, Decl *New, bool IsPackExpansion) {
  if (Aligned->isAlignmentExpr()) {
    // The alignment expression is a constant expression.
    EnterExpressionEvaluationContext Unevaluated(
        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
    ExprResult Result = S.SubstExpr(Aligned->getAlignmentExpr(), TemplateArgs);
    if (!Result.isInvalid())
      S.AddAlignedAttr(New, *Aligned, Result.getAs<Expr>(), IsPackExpansion);
  } else {
    TypeSourceInfo *Result = S.SubstType(Aligned->getAlignmentType(),
                                         TemplateArgs, Aligned->getLocation(),
                                         DeclarationName());
    if (Result)
      S.AddAlignedAttr(New, *Aligned, Result, IsPackExpansion);
  }
}

static void instantiateDependentAlignedAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AlignedAttr *Aligned, Decl *New) {
  if (!Aligned->isPackExpansion()) {
    instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, false);
    return;
  }

  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
  if (Aligned->isAlignmentExpr())
    S.collectUnexpandedParameterPacks(Aligned->getAlignmentExpr(),
                                      Unexpanded);
  else
    S.collectUnexpandedParameterPacks(Aligned->getAlignmentType()->getTypeLoc(),
                                      Unexpanded);
  assert(!Unexpanded.empty() && "Pack expansion without parameter packs?");

  // Determine whether we can expand this attribute pack yet.
  bool Expand = true, RetainExpansion = false;
  Optional<unsigned> NumExpansions;
  // FIXME: Use the actual location of the ellipsis.
  SourceLocation EllipsisLoc = Aligned->getLocation();
  if (S.CheckParameterPacksForExpansion(EllipsisLoc, Aligned->getRange(),
                                        Unexpanded, TemplateArgs, Expand,
                                        RetainExpansion, NumExpansions))
    return;

  if (!Expand) {
    Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, -1);
    instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, true);
  } else {
    for (unsigned I = 0; I != *NumExpansions; ++I) {
      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, I);
      instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, false);
    }
  }
}

static void instantiateDependentAssumeAlignedAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AssumeAlignedAttr *Aligned, Decl *New) {
  // The alignment expression is a constant expression.
  EnterExpressionEvaluationContext Unevaluated(
      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);

  Expr *E, *OE = nullptr;
  ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
  if (Result.isInvalid())
    return;
  E = Result.getAs<Expr>();

  if (Aligned->getOffset()) {
    Result = S.SubstExpr(Aligned->getOffset(), TemplateArgs);
    if (Result.isInvalid())
      return;
    OE = Result.getAs<Expr>();
  }

  S.AddAssumeAlignedAttr(New, *Aligned, E, OE);
}

static void instantiateDependentAlignValueAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AlignValueAttr *Aligned, Decl *New) {
  // The alignment expression is a constant expression.
  EnterExpressionEvaluationContext Unevaluated(
      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
  ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
  if (!Result.isInvalid())
    S.AddAlignValueAttr(New, *Aligned, Result.getAs<Expr>());
}

static void instantiateDependentAllocAlignAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AllocAlignAttr *Align, Decl *New) {
  Expr *Param = IntegerLiteral::Create(
      S.getASTContext(),
      llvm::APInt(64, Align->getParamIndex().getSourceIndex()),
      S.getASTContext().UnsignedLongLongTy, Align->getLocation());
  S.AddAllocAlignAttr(New, *Align, Param);
}

static void instantiateDependentAnnotationAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AnnotateAttr *Attr, Decl *New) {
  EnterExpressionEvaluationContext Unevaluated(
      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
  SmallVector<Expr *, 4> Args;
  Args.reserve(Attr->args_size());
  for (auto *E : Attr->args()) {
    ExprResult Result = S.SubstExpr(E, TemplateArgs);
    if (!Result.isUsable())
      return;
    Args.push_back(Result.get());
  }
  S.AddAnnotationAttr(New, *Attr, Attr->getAnnotation(), Args);
}

static Expr *instantiateDependentFunctionAttrCondition(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const Attr *A, Expr *OldCond, const Decl *Tmpl, FunctionDecl *New) {
  Expr *Cond = nullptr;
  {
    Sema::ContextRAII SwitchContext(S, New);
    EnterExpressionEvaluationContext Unevaluated(
        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
    ExprResult Result = S.SubstExpr(OldCond, TemplateArgs);
    if (Result.isInvalid())
      return nullptr;
    Cond = Result.getAs<Expr>();
  }
  if (!Cond->isTypeDependent()) {
    ExprResult Converted = S.PerformContextuallyConvertToBool(Cond);
    if (Converted.isInvalid())
      return nullptr;
    Cond = Converted.get();
  }

  SmallVector<PartialDiagnosticAt, 8> Diags;
  if (OldCond->isValueDependent() && !Cond->isValueDependent() &&
      !Expr::isPotentialConstantExprUnevaluated(Cond, New, Diags)) {
    S.Diag(A->getLocation(), diag::err_attr_cond_never_constant_expr) << A;
    for (const auto &P : Diags)
      S.Diag(P.first, P.second);
    return nullptr;
  }
  return Cond;
}

static void instantiateDependentEnableIfAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const EnableIfAttr *EIA, const Decl *Tmpl, FunctionDecl *New) {
  Expr *Cond = instantiateDependentFunctionAttrCondition(
      S, TemplateArgs, EIA, EIA->getCond(), Tmpl, New);

  if (Cond)
    New->addAttr(new (S.getASTContext()) EnableIfAttr(S.getASTContext(), *EIA,
                                                      Cond, EIA->getMessage()));
}

static void instantiateDependentDiagnoseIfAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const DiagnoseIfAttr *DIA, const Decl *Tmpl, FunctionDecl *New) {
  Expr *Cond = instantiateDependentFunctionAttrCondition(
      S, TemplateArgs, DIA, DIA->getCond(), Tmpl, New);

  if (Cond)
    New->addAttr(new (S.getASTContext()) DiagnoseIfAttr(
        S.getASTContext(), *DIA, Cond, DIA->getMessage(),
        DIA->getDiagnosticType(), DIA->getArgDependent(), New));
}

// Constructs and adds to New a new instance of CUDALaunchBoundsAttr using
// template A as the base and arguments from TemplateArgs.
static void instantiateDependentCUDALaunchBoundsAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const CUDALaunchBoundsAttr &Attr, Decl *New) {
  // The alignment expression is a constant expression.
  EnterExpressionEvaluationContext Unevaluated(
      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);

  ExprResult Result = S.SubstExpr(Attr.getMaxThreads(), TemplateArgs);
  if (Result.isInvalid())
    return;
  Expr *MaxThreads = Result.getAs<Expr>();

  Expr *MinBlocks = nullptr;
  if (Attr.getMinBlocks()) {
    Result = S.SubstExpr(Attr.getMinBlocks(), TemplateArgs);
    if (Result.isInvalid())
      return;
    MinBlocks = Result.getAs<Expr>();
  }

  S.AddLaunchBoundsAttr(New, Attr, MaxThreads, MinBlocks);
}

static void
instantiateDependentModeAttr(Sema &S,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             const ModeAttr &Attr, Decl *New) {
  S.AddModeAttr(New, Attr, Attr.getMode(),
                /*InInstantiation=*/true);
}

/// Instantiation of 'declare simd' attribute and its arguments.
static void instantiateOMPDeclareSimdDeclAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const OMPDeclareSimdDeclAttr &Attr, Decl *New) {
  // Allow 'this' in clauses with varlists.
  if (auto *FTD = dyn_cast<FunctionTemplateDecl>(New))
    New = FTD->getTemplatedDecl();
  auto *FD = cast<FunctionDecl>(New);
  auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(FD->getDeclContext());
  SmallVector<Expr *, 4> Uniforms, Aligneds, Alignments, Linears, Steps;
  SmallVector<unsigned, 4> LinModifiers;

  auto SubstExpr = [&](Expr *E) -> ExprResult {
    if (auto *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts()))
      if (auto *PVD = dyn_cast<ParmVarDecl>(DRE->getDecl())) {
        Sema::ContextRAII SavedContext(S, FD);
        LocalInstantiationScope Local(S);
        if (FD->getNumParams() > PVD->getFunctionScopeIndex())
          Local.InstantiatedLocal(
              PVD, FD->getParamDecl(PVD->getFunctionScopeIndex()));
        return S.SubstExpr(E, TemplateArgs);
      }
    Sema::CXXThisScopeRAII ThisScope(S, ThisContext, Qualifiers(),
                                     FD->isCXXInstanceMember());
    return S.SubstExpr(E, TemplateArgs);
  };

  // Substitute a single OpenMP clause, which is a potentially-evaluated
  // full-expression.
  auto Subst = [&](Expr *E) -> ExprResult {
    EnterExpressionEvaluationContext Evaluated(
        S, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
    ExprResult Res = SubstExpr(E);
    if (Res.isInvalid())
      return Res;
    return S.ActOnFinishFullExpr(Res.get(), false);
  };

  ExprResult Simdlen;
  if (auto *E = Attr.getSimdlen())
    Simdlen = Subst(E);

  if (Attr.uniforms_size() > 0) {
    for(auto *E : Attr.uniforms()) {
      ExprResult Inst = Subst(E);
      if (Inst.isInvalid())
        continue;
      Uniforms.push_back(Inst.get());
    }
  }

  auto AI = Attr.alignments_begin();
  for (auto *E : Attr.aligneds()) {
    ExprResult Inst = Subst(E);
    if (Inst.isInvalid())
      continue;
    Aligneds.push_back(Inst.get());
    Inst = ExprEmpty();
    if (*AI)
      Inst = S.SubstExpr(*AI, TemplateArgs);
    Alignments.push_back(Inst.get());
    ++AI;
  }

  auto SI = Attr.steps_begin();
  for (auto *E : Attr.linears()) {
    ExprResult Inst = Subst(E);
    if (Inst.isInvalid())
      continue;
    Linears.push_back(Inst.get());
    Inst = ExprEmpty();
    if (*SI)
      Inst = S.SubstExpr(*SI, TemplateArgs);
    Steps.push_back(Inst.get());
    ++SI;
  }
  LinModifiers.append(Attr.modifiers_begin(), Attr.modifiers_end());
  (void)S.ActOnOpenMPDeclareSimdDirective(
      S.ConvertDeclToDeclGroup(New), Attr.getBranchState(), Simdlen.get(),
      Uniforms, Aligneds, Alignments, Linears, LinModifiers, Steps,
      Attr.getRange());
}

/// Instantiation of 'declare variant' attribute and its arguments.
static void instantiateOMPDeclareVariantAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const OMPDeclareVariantAttr &Attr, Decl *New) {
  // Allow 'this' in clauses with varlists.
  if (auto *FTD = dyn_cast<FunctionTemplateDecl>(New))
    New = FTD->getTemplatedDecl();
  auto *FD = cast<FunctionDecl>(New);
  auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(FD->getDeclContext());

  auto &&SubstExpr = [FD, ThisContext, &S, &TemplateArgs](Expr *E) {
    if (auto *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts()))
      if (auto *PVD = dyn_cast<ParmVarDecl>(DRE->getDecl())) {
        Sema::ContextRAII SavedContext(S, FD);
        LocalInstantiationScope Local(S);
        if (FD->getNumParams() > PVD->getFunctionScopeIndex())
          Local.InstantiatedLocal(
              PVD, FD->getParamDecl(PVD->getFunctionScopeIndex()));
        return S.SubstExpr(E, TemplateArgs);
      }
    Sema::CXXThisScopeRAII ThisScope(S, ThisContext, Qualifiers(),
                                     FD->isCXXInstanceMember());
    return S.SubstExpr(E, TemplateArgs);
  };

  // Substitute a single OpenMP clause, which is a potentially-evaluated
  // full-expression.
  auto &&Subst = [&SubstExpr, &S](Expr *E) {
    EnterExpressionEvaluationContext Evaluated(
        S, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
    ExprResult Res = SubstExpr(E);
    if (Res.isInvalid())
      return Res;
    return S.ActOnFinishFullExpr(Res.get(), false);
  };

  ExprResult VariantFuncRef;
  if (Expr *E = Attr.getVariantFuncRef()) {
    // Do not mark function as is used to prevent its emission if this is the
    // only place where it is used.
    EnterExpressionEvaluationContext Unevaluated(
        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
    VariantFuncRef = Subst(E);
  }

  // Copy the template version of the OMPTraitInfo and run substitute on all
  // score and condition expressiosn.
  OMPTraitInfo &TI = S.getASTContext().getNewOMPTraitInfo();
  TI = *Attr.getTraitInfos();

  // Try to substitute template parameters in score and condition expressions.
  auto SubstScoreOrConditionExpr = [&S, Subst](Expr *&E, bool) {
    if (E) {
      EnterExpressionEvaluationContext Unevaluated(
          S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
      ExprResult ER = Subst(E);
      if (ER.isUsable())
        E = ER.get();
      else
        return true;
    }
    return false;
  };
  if (TI.anyScoreOrCondition(SubstScoreOrConditionExpr))
    return;

  Expr *E = VariantFuncRef.get();

  // Check function/variant ref for `omp declare variant` but not for `omp
  // begin declare variant` (which use implicit attributes).
  Optional<std::pair<FunctionDecl *, Expr *>> DeclVarData =
      S.checkOpenMPDeclareVariantFunction(S.ConvertDeclToDeclGroup(New), E, TI,
                                          Attr.appendArgs_size(),
                                          Attr.getRange());

  if (!DeclVarData)
    return;

  E = DeclVarData.getValue().second;
  FD = DeclVarData.getValue().first;

  if (auto *VariantDRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts())) {
    if (auto *VariantFD = dyn_cast<FunctionDecl>(VariantDRE->getDecl())) {
      if (auto *VariantFTD = VariantFD->getDescribedFunctionTemplate()) {
        if (!VariantFTD->isThisDeclarationADefinition())
          return;
        Sema::TentativeAnalysisScope Trap(S);
        const TemplateArgumentList *TAL = TemplateArgumentList::CreateCopy(
            S.Context, TemplateArgs.getInnermost());

        auto *SubstFD = S.InstantiateFunctionDeclaration(VariantFTD, TAL,
                                                         New->getLocation());
        if (!SubstFD)
          return;
        QualType NewType = S.Context.mergeFunctionTypes(
            SubstFD->getType(), FD->getType(),
            /* OfBlockPointer */ false,
            /* Unqualified */ false, /* AllowCXX */ true);
        if (NewType.isNull())
          return;
        S.InstantiateFunctionDefinition(
            New->getLocation(), SubstFD, /* Recursive */ true,
            /* DefinitionRequired */ false, /* AtEndOfTU */ false);
        SubstFD->setInstantiationIsPending(!SubstFD->isDefined());
        E = DeclRefExpr::Create(S.Context, NestedNameSpecifierLoc(),
                                SourceLocation(), SubstFD,
                                /* RefersToEnclosingVariableOrCapture */ false,
                                /* NameLoc */ SubstFD->getLocation(),
                                SubstFD->getType(), ExprValueKind::VK_PRValue);
      }
    }
  }

  SmallVector<Expr *, 8> NothingExprs;
  SmallVector<Expr *, 8> NeedDevicePtrExprs;
  SmallVector<OMPDeclareVariantAttr::InteropType, 8> AppendArgs;

  for (Expr *E : Attr.adjustArgsNothing()) {
    ExprResult ER = Subst(E);
    if (ER.isInvalid())
      continue;
    NothingExprs.push_back(ER.get());
  }
  for (Expr *E : Attr.adjustArgsNeedDevicePtr()) {
    ExprResult ER = Subst(E);
    if (ER.isInvalid())
      continue;
    NeedDevicePtrExprs.push_back(ER.get());
  }
  for (auto A : Attr.appendArgs())
    AppendArgs.push_back(A);

  S.ActOnOpenMPDeclareVariantDirective(
      FD, E, TI, NothingExprs, NeedDevicePtrExprs, AppendArgs, SourceLocation(),
      SourceLocation(), Attr.getRange());
}

static void instantiateDependentAMDGPUFlatWorkGroupSizeAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AMDGPUFlatWorkGroupSizeAttr &Attr, Decl *New) {
  // Both min and max expression are constant expressions.
  EnterExpressionEvaluationContext Unevaluated(
      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);

  ExprResult Result = S.SubstExpr(Attr.getMin(), TemplateArgs);
  if (Result.isInvalid())
    return;
  Expr *MinExpr = Result.getAs<Expr>();

  Result = S.SubstExpr(Attr.getMax(), TemplateArgs);
  if (Result.isInvalid())
    return;
  Expr *MaxExpr = Result.getAs<Expr>();

  S.addAMDGPUFlatWorkGroupSizeAttr(New, Attr, MinExpr, MaxExpr);
}

static ExplicitSpecifier
instantiateExplicitSpecifier(Sema &S,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             ExplicitSpecifier ES, FunctionDecl *New) {
  if (!ES.getExpr())
    return ES;
  Expr *OldCond = ES.getExpr();
  Expr *Cond = nullptr;
  {
    EnterExpressionEvaluationContext Unevaluated(
        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
    ExprResult SubstResult = S.SubstExpr(OldCond, TemplateArgs);
    if (SubstResult.isInvalid()) {
      return ExplicitSpecifier::Invalid();
    }
    Cond = SubstResult.get();
  }
  ExplicitSpecifier Result(Cond, ES.getKind());
  if (!Cond->isTypeDependent())
    S.tryResolveExplicitSpecifier(Result);
  return Result;
}

static void instantiateDependentAMDGPUWavesPerEUAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const AMDGPUWavesPerEUAttr &Attr, Decl *New) {
  // Both min and max expression are constant expressions.
  EnterExpressionEvaluationContext Unevaluated(
      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);

  ExprResult Result = S.SubstExpr(Attr.getMin(), TemplateArgs);
  if (Result.isInvalid())
    return;
  Expr *MinExpr = Result.getAs<Expr>();

  Expr *MaxExpr = nullptr;
  if (auto Max = Attr.getMax()) {
    Result = S.SubstExpr(Max, TemplateArgs);
    if (Result.isInvalid())
      return;
    MaxExpr = Result.getAs<Expr>();
  }

  S.addAMDGPUWavesPerEUAttr(New, Attr, MinExpr, MaxExpr);
}

// This doesn't take any template parameters, but we have a custom action that
// needs to happen when the kernel itself is instantiated. We need to run the
// ItaniumMangler to mark the names required to name this kernel.
static void instantiateDependentSYCLKernelAttr(
    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
    const SYCLKernelAttr &Attr, Decl *New) {
  New->addAttr(Attr.clone(S.getASTContext()));
}

/// Determine whether the attribute A might be relevant to the declaration D.
/// If not, we can skip instantiating it. The attribute may or may not have
/// been instantiated yet.
static bool isRelevantAttr(Sema &S, const Decl *D, const Attr *A) {
  // 'preferred_name' is only relevant to the matching specialization of the
  // template.
  if (const auto *PNA = dyn_cast<PreferredNameAttr>(A)) {
    QualType T = PNA->getTypedefType();
    const auto *RD = cast<CXXRecordDecl>(D);
    if (!T->isDependentType() && !RD->isDependentContext() &&
        !declaresSameEntity(T->getAsCXXRecordDecl(), RD))
      return false;
    for (const auto *ExistingPNA : D->specific_attrs<PreferredNameAttr>())
      if (S.Context.hasSameType(ExistingPNA->getTypedefType(),
                                PNA->getTypedefType()))
        return false;
    return true;
  }

  return true;
}

void Sema::InstantiateAttrsForDecl(
    const MultiLevelTemplateArgumentList &TemplateArgs, const Decl *Tmpl,
    Decl *New, LateInstantiatedAttrVec *LateAttrs,
    LocalInstantiationScope *OuterMostScope) {
  if (NamedDecl *ND = dyn_cast<NamedDecl>(New)) {
    // FIXME: This function is called multiple times for the same template
    // specialization. We should only instantiate attributes that were added
    // since the previous instantiation.
    for (const auto *TmplAttr : Tmpl->attrs()) {
      if (!isRelevantAttr(*this, New, TmplAttr))
        continue;

      // FIXME: If any of the special case versions from InstantiateAttrs become
      // applicable to template declaration, we'll need to add them here.
      CXXThisScopeRAII ThisScope(
          *this, dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext()),
          Qualifiers(), ND->isCXXInstanceMember());

      Attr *NewAttr = sema::instantiateTemplateAttributeForDecl(
          TmplAttr, Context, *this, TemplateArgs);
      if (NewAttr && isRelevantAttr(*this, New, NewAttr))
        New->addAttr(NewAttr);
    }
  }
}

static Sema::RetainOwnershipKind
attrToRetainOwnershipKind(const Attr *A) {
  switch (A->getKind()) {
  case clang::attr::CFConsumed:
    return Sema::RetainOwnershipKind::CF;
  case clang::attr::OSConsumed:
    return Sema::RetainOwnershipKind::OS;
  case clang::attr::NSConsumed:
    return Sema::RetainOwnershipKind::NS;
  default:
    llvm_unreachable("Wrong argument supplied");
  }
}

void Sema::InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
                            const Decl *Tmpl, Decl *New,
                            LateInstantiatedAttrVec *LateAttrs,
                            LocalInstantiationScope *OuterMostScope) {
  for (const auto *TmplAttr : Tmpl->attrs()) {
    if (!isRelevantAttr(*this, New, TmplAttr))
      continue;

    // FIXME: This should be generalized to more than just the AlignedAttr.
    const AlignedAttr *Aligned = dyn_cast<AlignedAttr>(TmplAttr);
    if (Aligned && Aligned->isAlignmentDependent()) {
      instantiateDependentAlignedAttr(*this, TemplateArgs, Aligned, New);
      continue;
    }

    if (const auto *AssumeAligned = dyn_cast<AssumeAlignedAttr>(TmplAttr)) {
      instantiateDependentAssumeAlignedAttr(*this, TemplateArgs, AssumeAligned, New);
      continue;
    }

    if (const auto *AlignValue = dyn_cast<AlignValueAttr>(TmplAttr)) {
      instantiateDependentAlignValueAttr(*this, TemplateArgs, AlignValue, New);
      continue;
    }

    if (const auto *AllocAlign = dyn_cast<AllocAlignAttr>(TmplAttr)) {
      instantiateDependentAllocAlignAttr(*this, TemplateArgs, AllocAlign, New);
      continue;
    }

    if (const auto *Annotate = dyn_cast<AnnotateAttr>(TmplAttr)) {
      instantiateDependentAnnotationAttr(*this, TemplateArgs, Annotate, New);
      continue;
    }

    if (const auto *EnableIf = dyn_cast<EnableIfAttr>(TmplAttr)) {
      instantiateDependentEnableIfAttr(*this, TemplateArgs, EnableIf, Tmpl,
                                       cast<FunctionDecl>(New));
      continue;
    }

    if (const auto *DiagnoseIf = dyn_cast<DiagnoseIfAttr>(TmplAttr)) {
      instantiateDependentDiagnoseIfAttr(*this, TemplateArgs, DiagnoseIf, Tmpl,
                                         cast<FunctionDecl>(New));
      continue;
    }

    if (const auto *CUDALaunchBounds =
            dyn_cast<CUDALaunchBoundsAttr>(TmplAttr)) {
      instantiateDependentCUDALaunchBoundsAttr(*this, TemplateArgs,
                                               *CUDALaunchBounds, New);
      continue;
    }

    if (const auto *Mode = dyn_cast<ModeAttr>(TmplAttr)) {
      instantiateDependentModeAttr(*this, TemplateArgs, *Mode, New);
      continue;
    }

    if (const auto *OMPAttr = dyn_cast<OMPDeclareSimdDeclAttr>(TmplAttr)) {
      instantiateOMPDeclareSimdDeclAttr(*this, TemplateArgs, *OMPAttr, New);
      continue;
    }

    if (const auto *OMPAttr = dyn_cast<OMPDeclareVariantAttr>(TmplAttr)) {
      instantiateOMPDeclareVariantAttr(*this, TemplateArgs, *OMPAttr, New);
      continue;
    }

    if (const auto *AMDGPUFlatWorkGroupSize =
            dyn_cast<AMDGPUFlatWorkGroupSizeAttr>(TmplAttr)) {
      instantiateDependentAMDGPUFlatWorkGroupSizeAttr(
          *this, TemplateArgs, *AMDGPUFlatWorkGroupSize, New);
    }

    if (const auto *AMDGPUFlatWorkGroupSize =
            dyn_cast<AMDGPUWavesPerEUAttr>(TmplAttr)) {
      instantiateDependentAMDGPUWavesPerEUAttr(*this, TemplateArgs,
                                               *AMDGPUFlatWorkGroupSize, New);
    }

    // Existing DLL attribute on the instantiation takes precedence.
    if (TmplAttr->getKind() == attr::DLLExport ||
        TmplAttr->getKind() == attr::DLLImport) {
      if (New->hasAttr<DLLExportAttr>() || New->hasAttr<DLLImportAttr>()) {
        continue;
      }
    }

    if (const auto *ABIAttr = dyn_cast<ParameterABIAttr>(TmplAttr)) {
      AddParameterABIAttr(New, *ABIAttr, ABIAttr->getABI());
      continue;
    }

    if (isa<NSConsumedAttr>(TmplAttr) || isa<OSConsumedAttr>(TmplAttr) ||
        isa<CFConsumedAttr>(TmplAttr)) {
      AddXConsumedAttr(New, *TmplAttr, attrToRetainOwnershipKind(TmplAttr),
                       /*template instantiation=*/true);
      continue;
    }

    if (auto *A = dyn_cast<PointerAttr>(TmplAttr)) {
      if (!New->hasAttr<PointerAttr>())
        New->addAttr(A->clone(Context));
      continue;
    }

    if (auto *A = dyn_cast<OwnerAttr>(TmplAttr)) {
      if (!New->hasAttr<OwnerAttr>())
        New->addAttr(A->clone(Context));
      continue;
    }

    if (auto *A = dyn_cast<SYCLKernelAttr>(TmplAttr)) {
      instantiateDependentSYCLKernelAttr(*this, TemplateArgs, *A, New);
      continue;
    }

    assert(!TmplAttr->isPackExpansion());
    if (TmplAttr->isLateParsed() && LateAttrs) {
      // Late parsed attributes must be instantiated and attached after the
      // enclosing class has been instantiated.  See Sema::InstantiateClass.
      LocalInstantiationScope *Saved = nullptr;
      if (CurrentInstantiationScope)
        Saved = CurrentInstantiationScope->cloneScopes(OuterMostScope);
      LateAttrs->push_back(LateInstantiatedAttribute(TmplAttr, Saved, New));
    } else {
      // Allow 'this' within late-parsed attributes.
      auto *ND = cast<NamedDecl>(New);
      auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext());
      CXXThisScopeRAII ThisScope(*this, ThisContext, Qualifiers(),
                                 ND->isCXXInstanceMember());

      Attr *NewAttr = sema::instantiateTemplateAttribute(TmplAttr, Context,
                                                         *this, TemplateArgs);
      if (NewAttr && isRelevantAttr(*this, New, TmplAttr))
        New->addAttr(NewAttr);
    }
  }
}

/// In the MS ABI, we need to instantiate default arguments of dllexported
/// default constructors along with the constructor definition. This allows IR
/// gen to emit a constructor closure which calls the default constructor with
/// its default arguments.
void Sema::InstantiateDefaultCtorDefaultArgs(CXXConstructorDecl *Ctor) {
  assert(Context.getTargetInfo().getCXXABI().isMicrosoft() &&
         Ctor->isDefaultConstructor());
  unsigned NumParams = Ctor->getNumParams();
  if (NumParams == 0)
    return;
  DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>();
  if (!Attr)
    return;
  for (unsigned I = 0; I != NumParams; ++I) {
    (void)CheckCXXDefaultArgExpr(Attr->getLocation(), Ctor,
                                   Ctor->getParamDecl(I));
    DiscardCleanupsInEvaluationContext();
  }
}

/// Get the previous declaration of a declaration for the purposes of template
/// instantiation. If this finds a previous declaration, then the previous
/// declaration of the instantiation of D should be an instantiation of the
/// result of this function.
template<typename DeclT>
static DeclT *getPreviousDeclForInstantiation(DeclT *D) {
  DeclT *Result = D->getPreviousDecl();

  // If the declaration is within a class, and the previous declaration was
  // merged from a different definition of that class, then we don't have a
  // previous declaration for the purpose of template instantiation.
  if (Result && isa<CXXRecordDecl>(D->getDeclContext()) &&
      D->getLexicalDeclContext() != Result->getLexicalDeclContext())
    return nullptr;

  return Result;
}

Decl *
TemplateDeclInstantiator::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
  llvm_unreachable("Translation units cannot be instantiated");
}

Decl *
TemplateDeclInstantiator::VisitPragmaCommentDecl(PragmaCommentDecl *D) {
  llvm_unreachable("pragma comment cannot be instantiated");
}

Decl *TemplateDeclInstantiator::VisitPragmaDetectMismatchDecl(
    PragmaDetectMismatchDecl *D) {
  llvm_unreachable("pragma comment cannot be instantiated");
}

Decl *
TemplateDeclInstantiator::VisitExternCContextDecl(ExternCContextDecl *D) {
  llvm_unreachable("extern \"C\" context cannot be instantiated");
}

Decl *TemplateDeclInstantiator::VisitMSGuidDecl(MSGuidDecl *D) {
  llvm_unreachable("GUID declaration cannot be instantiated");
}

Decl *TemplateDeclInstantiator::VisitTemplateParamObjectDecl(
    TemplateParamObjectDecl *D) {
  llvm_unreachable("template parameter objects cannot be instantiated");
}

Decl *
TemplateDeclInstantiator::VisitLabelDecl(LabelDecl *D) {
  LabelDecl *Inst = LabelDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                      D->getIdentifier());
  Owner->addDecl(Inst);
  return Inst;
}

Decl *
TemplateDeclInstantiator::VisitNamespaceDecl(NamespaceDecl *D) {
  llvm_unreachable("Namespaces cannot be instantiated");
}

Decl *
TemplateDeclInstantiator::VisitNamespaceAliasDecl(NamespaceAliasDecl *D) {
  NamespaceAliasDecl *Inst
    = NamespaceAliasDecl::Create(SemaRef.Context, Owner,
                                 D->getNamespaceLoc(),
                                 D->getAliasLoc(),
                                 D->getIdentifier(),
                                 D->getQualifierLoc(),
                                 D->getTargetNameLoc(),
                                 D->getNamespace());
  Owner->addDecl(Inst);
  return Inst;
}

Decl *TemplateDeclInstantiator::InstantiateTypedefNameDecl(TypedefNameDecl *D,
                                                           bool IsTypeAlias) {
  bool Invalid = false;
  TypeSourceInfo *DI = D->getTypeSourceInfo();
  if (DI->getType()->isInstantiationDependentType() ||
      DI->getType()->isVariablyModifiedType()) {
    DI = SemaRef.SubstType(DI, TemplateArgs,
                           D->getLocation(), D->getDeclName());
    if (!DI) {
      Invalid = true;
      DI = SemaRef.Context.getTrivialTypeSourceInfo(SemaRef.Context.IntTy);
    }
  } else {
    SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
  }

  // HACK: 2012-10-23 g++ has a bug where it gets the value kind of ?: wrong.
  // libstdc++ relies upon this bug in its implementation of common_type.  If we
  // happen to be processing that implementation, fake up the g++ ?:
  // semantics. See LWG issue 2141 for more information on the bug.  The bugs
  // are fixed in g++ and libstdc++ 4.9.0 (2014-04-22).
  const DecltypeType *DT = DI->getType()->getAs<DecltypeType>();
  CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D->getDeclContext());
  if (DT && RD && isa<ConditionalOperator>(DT->getUnderlyingExpr()) &&
      DT->isReferenceType() &&
      RD->getEnclosingNamespaceContext() == SemaRef.getStdNamespace() &&
      RD->getIdentifier() && RD->getIdentifier()->isStr("common_type") &&
      D->getIdentifier() && D->getIdentifier()->isStr("type") &&
      SemaRef.getSourceManager().isInSystemHeader(D->getBeginLoc()))
    // Fold it to the (non-reference) type which g++ would have produced.
    DI = SemaRef.Context.getTrivialTypeSourceInfo(
      DI->getType().getNonReferenceType());

  // Create the new typedef
  TypedefNameDecl *Typedef;
  if (IsTypeAlias)
    Typedef = TypeAliasDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
                                    D->getLocation(), D->getIdentifier(), DI);
  else
    Typedef = TypedefDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
                                  D->getLocation(), D->getIdentifier(), DI);
  if (Invalid)
    Typedef->setInvalidDecl();

  // If the old typedef was the name for linkage purposes of an anonymous
  // tag decl, re-establish that relationship for the new typedef.
  if (const TagType *oldTagType = D->getUnderlyingType()->getAs<TagType>()) {
    TagDecl *oldTag = oldTagType->getDecl();
    if (oldTag->getTypedefNameForAnonDecl() == D && !Invalid) {
      TagDecl *newTag = DI->getType()->castAs<TagType>()->getDecl();
      assert(!newTag->hasNameForLinkage());
      newTag->setTypedefNameForAnonDecl(Typedef);
    }
  }

  if (TypedefNameDecl *Prev = getPreviousDeclForInstantiation(D)) {
    NamedDecl *InstPrev = SemaRef.FindInstantiatedDecl(D->getLocation(), Prev,
                                                       TemplateArgs);
    if (!InstPrev)
      return nullptr;

    TypedefNameDecl *InstPrevTypedef = cast<TypedefNameDecl>(InstPrev);

    // If the typedef types are not identical, reject them.
    SemaRef.isIncompatibleTypedef(InstPrevTypedef, Typedef);

    Typedef->setPreviousDecl(InstPrevTypedef);
  }

  SemaRef.InstantiateAttrs(TemplateArgs, D, Typedef);

  if (D->getUnderlyingType()->getAs<DependentNameType>())
    SemaRef.inferGslPointerAttribute(Typedef);

  Typedef->setAccess(D->getAccess());

  return Typedef;
}

Decl *TemplateDeclInstantiator::VisitTypedefDecl(TypedefDecl *D) {
  Decl *Typedef = InstantiateTypedefNameDecl(D, /*IsTypeAlias=*/false);
  if (Typedef)
    Owner->addDecl(Typedef);
  return Typedef;
}

Decl *TemplateDeclInstantiator::VisitTypeAliasDecl(TypeAliasDecl *D) {
  Decl *Typedef = InstantiateTypedefNameDecl(D, /*IsTypeAlias=*/true);
  if (Typedef)
    Owner->addDecl(Typedef);
  return Typedef;
}

Decl *
TemplateDeclInstantiator::VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D) {
  // Create a local instantiation scope for this type alias template, which
  // will contain the instantiations of the template parameters.
  LocalInstantiationScope Scope(SemaRef);

  TemplateParameterList *TempParams = D->getTemplateParameters();
  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
  if (!InstParams)
    return nullptr;

  TypeAliasDecl *Pattern = D->getTemplatedDecl();

  TypeAliasTemplateDecl *PrevAliasTemplate = nullptr;
  if (getPreviousDeclForInstantiation<TypedefNameDecl>(Pattern)) {
    DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
    if (!Found.empty()) {
      PrevAliasTemplate = dyn_cast<TypeAliasTemplateDecl>(Found.front());
    }
  }

  TypeAliasDecl *AliasInst = cast_or_null<TypeAliasDecl>(
    InstantiateTypedefNameDecl(Pattern, /*IsTypeAlias=*/true));
  if (!AliasInst)
    return nullptr;

  TypeAliasTemplateDecl *Inst
    = TypeAliasTemplateDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                    D->getDeclName(), InstParams, AliasInst);
  AliasInst->setDescribedAliasTemplate(Inst);
  if (PrevAliasTemplate)
    Inst->setPreviousDecl(PrevAliasTemplate);

  Inst->setAccess(D->getAccess());

  if (!PrevAliasTemplate)
    Inst->setInstantiatedFromMemberTemplate(D);

  Owner->addDecl(Inst);

  return Inst;
}

Decl *TemplateDeclInstantiator::VisitBindingDecl(BindingDecl *D) {
  auto *NewBD = BindingDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                    D->getIdentifier());
  NewBD->setReferenced(D->isReferenced());
  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewBD);
  return NewBD;
}

Decl *TemplateDeclInstantiator::VisitDecompositionDecl(DecompositionDecl *D) {
  // Transform the bindings first.
  SmallVector<BindingDecl*, 16> NewBindings;
  for (auto *OldBD : D->bindings())
    NewBindings.push_back(cast<BindingDecl>(VisitBindingDecl(OldBD)));
  ArrayRef<BindingDecl*> NewBindingArray = NewBindings;

  auto *NewDD = cast_or_null<DecompositionDecl>(
      VisitVarDecl(D, /*InstantiatingVarTemplate=*/false, &NewBindingArray));

  if (!NewDD || NewDD->isInvalidDecl())
    for (auto *NewBD : NewBindings)
      NewBD->setInvalidDecl();

  return NewDD;
}

Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D) {
  return VisitVarDecl(D, /*InstantiatingVarTemplate=*/false);
}

Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D,
                                             bool InstantiatingVarTemplate,
                                             ArrayRef<BindingDecl*> *Bindings) {

  // Do substitution on the type of the declaration
  TypeSourceInfo *DI = SemaRef.SubstType(
      D->getTypeSourceInfo(), TemplateArgs, D->getTypeSpecStartLoc(),
      D->getDeclName(), /*AllowDeducedTST*/true);
  if (!DI)
    return nullptr;

  if (DI->getType()->isFunctionType()) {
    SemaRef.Diag(D->getLocation(), diag::err_variable_instantiates_to_function)
      << D->isStaticDataMember() << DI->getType();
    return nullptr;
  }

  DeclContext *DC = Owner;
  if (D->isLocalExternDecl())
    SemaRef.adjustContextForLocalExternDecl(DC);

  // Build the instantiated declaration.
  VarDecl *Var;
  if (Bindings)
    Var = DecompositionDecl::Create(SemaRef.Context, DC, D->getInnerLocStart(),
                                    D->getLocation(), DI->getType(), DI,
                                    D->getStorageClass(), *Bindings);
  else
    Var = VarDecl::Create(SemaRef.Context, DC, D->getInnerLocStart(),
                          D->getLocation(), D->getIdentifier(), DI->getType(),
                          DI, D->getStorageClass());

  // In ARC, infer 'retaining' for variables of retainable type.
  if (SemaRef.getLangOpts().ObjCAutoRefCount &&
      SemaRef.inferObjCARCLifetime(Var))
    Var->setInvalidDecl();

  if (SemaRef.getLangOpts().OpenCL)
    SemaRef.deduceOpenCLAddressSpace(Var);

  // Substitute the nested name specifier, if any.
  if (SubstQualifier(D, Var))
    return nullptr;

  SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs, Owner,
                                     StartingScope, InstantiatingVarTemplate);
  if (D->isNRVOVariable() && !Var->isInvalidDecl()) {
    QualType RT;
    if (auto *F = dyn_cast<FunctionDecl>(DC))
      RT = F->getReturnType();
    else if (isa<BlockDecl>(DC))
      RT = cast<FunctionType>(SemaRef.getCurBlock()->FunctionType)
               ->getReturnType();
    else
      llvm_unreachable("Unknown context type");

    // This is the last chance we have of checking copy elision eligibility
    // for functions in dependent contexts. The sema actions for building
    // the return statement during template instantiation will have no effect
    // regarding copy elision, since NRVO propagation runs on the scope exit
    // actions, and these are not run on instantiation.
    // This might run through some VarDecls which were returned from non-taken
    // 'if constexpr' branches, and these will end up being constructed on the
    // return slot even if they will never be returned, as a sort of accidental
    // 'optimization'. Notably, functions with 'auto' return types won't have it
    // deduced by this point. Coupled with the limitation described
    // previously, this makes it very hard to support copy elision for these.
    Sema::NamedReturnInfo Info = SemaRef.getNamedReturnInfo(Var);
    bool NRVO = SemaRef.getCopyElisionCandidate(Info, RT) != nullptr;
    Var->setNRVOVariable(NRVO);
  }

  Var->setImplicit(D->isImplicit());

  if (Var->isStaticLocal())
    SemaRef.CheckStaticLocalForDllExport(Var);

  return Var;
}

Decl *TemplateDeclInstantiator::VisitAccessSpecDecl(AccessSpecDecl *D) {
  AccessSpecDecl* AD
    = AccessSpecDecl::Create(SemaRef.Context, D->getAccess(), Owner,
                             D->getAccessSpecifierLoc(), D->getColonLoc());
  Owner->addHiddenDecl(AD);
  return AD;
}

Decl *TemplateDeclInstantiator::VisitFieldDecl(FieldDecl *D) {
  bool Invalid = false;
  TypeSourceInfo *DI = D->getTypeSourceInfo();
  if (DI->getType()->isInstantiationDependentType() ||
      DI->getType()->isVariablyModifiedType())  {
    DI = SemaRef.SubstType(DI, TemplateArgs,
                           D->getLocation(), D->getDeclName());
    if (!DI) {
      DI = D->getTypeSourceInfo();
      Invalid = true;
    } else if (DI->getType()->isFunctionType()) {
      // C++ [temp.arg.type]p3:
      //   If a declaration acquires a function type through a type
      //   dependent on a template-parameter and this causes a
      //   declaration that does not use the syntactic form of a
      //   function declarator to have function type, the program is
      //   ill-formed.
      SemaRef.Diag(D->getLocation(), diag::err_field_instantiates_to_function)
        << DI->getType();
      Invalid = true;
    }
  } else {
    SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
  }

  Expr *BitWidth = D->getBitWidth();
  if (Invalid)
    BitWidth = nullptr;
  else if (BitWidth) {
    // The bit-width expression is a constant expression.
    EnterExpressionEvaluationContext Unevaluated(
        SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);

    ExprResult InstantiatedBitWidth
      = SemaRef.SubstExpr(BitWidth, TemplateArgs);
    if (InstantiatedBitWidth.isInvalid()) {
      Invalid = true;
      BitWidth = nullptr;
    } else
      BitWidth = InstantiatedBitWidth.getAs<Expr>();
  }

  FieldDecl *Field = SemaRef.CheckFieldDecl(D->getDeclName(),
                                            DI->getType(), DI,
                                            cast<RecordDecl>(Owner),
                                            D->getLocation(),
                                            D->isMutable(),
                                            BitWidth,
                                            D->getInClassInitStyle(),
                                            D->getInnerLocStart(),
                                            D->getAccess(),
                                            nullptr);
  if (!Field) {
    cast<Decl>(Owner)->setInvalidDecl();
    return nullptr;
  }

  SemaRef.InstantiateAttrs(TemplateArgs, D, Field, LateAttrs, StartingScope);

  if (Field->hasAttrs())
    SemaRef.CheckAlignasUnderalignment(Field);

  if (Invalid)
    Field->setInvalidDecl();

  if (!Field->getDeclName()) {
    // Keep track of where this decl came from.
    SemaRef.Context.setInstantiatedFromUnnamedFieldDecl(Field, D);
  }
  if (CXXRecordDecl *Parent= dyn_cast<CXXRecordDecl>(Field->getDeclContext())) {
    if (Parent->isAnonymousStructOrUnion() &&
        Parent->getRedeclContext()->isFunctionOrMethod())
      SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Field);
  }

  Field->setImplicit(D->isImplicit());
  Field->setAccess(D->getAccess());
  Owner->addDecl(Field);

  return Field;
}

Decl *TemplateDeclInstantiator::VisitMSPropertyDecl(MSPropertyDecl *D) {
  bool Invalid = false;
  TypeSourceInfo *DI = D->getTypeSourceInfo();

  if (DI->getType()->isVariablyModifiedType()) {
    SemaRef.Diag(D->getLocation(), diag::err_property_is_variably_modified)
      << D;
    Invalid = true;
  } else if (DI->getType()->isInstantiationDependentType())  {
    DI = SemaRef.SubstType(DI, TemplateArgs,
                           D->getLocation(), D->getDeclName());
    if (!DI) {
      DI = D->getTypeSourceInfo();
      Invalid = true;
    } else if (DI->getType()->isFunctionType()) {
      // C++ [temp.arg.type]p3:
      //   If a declaration acquires a function type through a type
      //   dependent on a template-parameter and this causes a
      //   declaration that does not use the syntactic form of a
      //   function declarator to have function type, the program is
      //   ill-formed.
      SemaRef.Diag(D->getLocation(), diag::err_field_instantiates_to_function)
      << DI->getType();
      Invalid = true;
    }
  } else {
    SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
  }

  MSPropertyDecl *Property = MSPropertyDecl::Create(
      SemaRef.Context, Owner, D->getLocation(), D->getDeclName(), DI->getType(),
      DI, D->getBeginLoc(), D->getGetterId(), D->getSetterId());

  SemaRef.InstantiateAttrs(TemplateArgs, D, Property, LateAttrs,
                           StartingScope);

  if (Invalid)
    Property->setInvalidDecl();

  Property->setAccess(D->getAccess());
  Owner->addDecl(Property);

  return Property;
}

Decl *TemplateDeclInstantiator::VisitIndirectFieldDecl(IndirectFieldDecl *D) {
  NamedDecl **NamedChain =
    new (SemaRef.Context)NamedDecl*[D->getChainingSize()];

  int i = 0;
  for (auto *PI : D->chain()) {
    NamedDecl *Next = SemaRef.FindInstantiatedDecl(D->getLocation(), PI,
                                              TemplateArgs);
    if (!Next)
      return nullptr;

    NamedChain[i++] = Next;
  }

  QualType T = cast<FieldDecl>(NamedChain[i-1])->getType();
  IndirectFieldDecl *IndirectField = IndirectFieldDecl::Create(
      SemaRef.Context, Owner, D->getLocation(), D->getIdentifier(), T,
      {NamedChain, D->getChainingSize()});

  for (const auto *Attr : D->attrs())
    IndirectField->addAttr(Attr->clone(SemaRef.Context));

  IndirectField->setImplicit(D->isImplicit());
  IndirectField->setAccess(D->getAccess());
  Owner->addDecl(IndirectField);
  return IndirectField;
}

Decl *TemplateDeclInstantiator::VisitFriendDecl(FriendDecl *D) {
  // Handle friend type expressions by simply substituting template
  // parameters into the pattern type and checking the result.
  if (TypeSourceInfo *Ty = D->getFriendType()) {
    TypeSourceInfo *InstTy;
    // If this is an unsupported friend, don't bother substituting template
    // arguments into it. The actual type referred to won't be used by any
    // parts of Clang, and may not be valid for instantiating. Just use the
    // same info for the instantiated friend.
    if (D->isUnsupportedFriend()) {
      InstTy = Ty;
    } else {
      InstTy = SemaRef.SubstType(Ty, TemplateArgs,
                                 D->getLocation(), DeclarationName());
    }
    if (!InstTy)
      return nullptr;

    FriendDecl *FD = SemaRef.CheckFriendTypeDecl(D->getBeginLoc(),
                                                 D->getFriendLoc(), InstTy);
    if (!FD)
      return nullptr;

    FD->setAccess(AS_public);
    FD->setUnsupportedFriend(D->isUnsupportedFriend());
    Owner->addDecl(FD);
    return FD;
  }

  NamedDecl *ND = D->getFriendDecl();
  assert(ND && "friend decl must be a decl or a type!");

  // All of the Visit implementations for the various potential friend
  // declarations have to be carefully written to work for friend
  // objects, with the most important detail being that the target
  // decl should almost certainly not be placed in Owner.
  Decl *NewND = Visit(ND);
  if (!NewND) return nullptr;

  FriendDecl *FD =
    FriendDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                       cast<NamedDecl>(NewND), D->getFriendLoc());
  FD->setAccess(AS_public);
  FD->setUnsupportedFriend(D->isUnsupportedFriend());
  Owner->addDecl(FD);
  return FD;
}

Decl *TemplateDeclInstantiator::VisitStaticAssertDecl(StaticAssertDecl *D) {
  Expr *AssertExpr = D->getAssertExpr();

  // The expression in a static assertion is a constant expression.
  EnterExpressionEvaluationContext Unevaluated(
      SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);

  ExprResult InstantiatedAssertExpr
    = SemaRef.SubstExpr(AssertExpr, TemplateArgs);
  if (InstantiatedAssertExpr.isInvalid())
    return nullptr;

  return SemaRef.BuildStaticAssertDeclaration(D->getLocation(),
                                              InstantiatedAssertExpr.get(),
                                              D->getMessage(),
                                              D->getRParenLoc(),
                                              D->isFailed());
}

Decl *TemplateDeclInstantiator::VisitEnumDecl(EnumDecl *D) {
  EnumDecl *PrevDecl = nullptr;
  if (EnumDecl *PatternPrev = getPreviousDeclForInstantiation(D)) {
    NamedDecl *Prev = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                   PatternPrev,
                                                   TemplateArgs);
    if (!Prev) return nullptr;
    PrevDecl = cast<EnumDecl>(Prev);
  }

  EnumDecl *Enum =
      EnumDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
                       D->getLocation(), D->getIdentifier(), PrevDecl,
                       D->isScoped(), D->isScopedUsingClassTag(), D->isFixed());
  if (D->isFixed()) {
    if (TypeSourceInfo *TI = D->getIntegerTypeSourceInfo()) {
      // If we have type source information for the underlying type, it means it
      // has been explicitly set by the user. Perform substitution on it before
      // moving on.
      SourceLocation UnderlyingLoc = TI->getTypeLoc().getBeginLoc();
      TypeSourceInfo *NewTI = SemaRef.SubstType(TI, TemplateArgs, UnderlyingLoc,
                                                DeclarationName());
      if (!NewTI || SemaRef.CheckEnumUnderlyingType(NewTI))
        Enum->setIntegerType(SemaRef.Context.IntTy);
      else
        Enum->setIntegerTypeSourceInfo(NewTI);
    } else {
      assert(!D->getIntegerType()->isDependentType()
             && "Dependent type without type source info");
      Enum->setIntegerType(D->getIntegerType());
    }
  }

  SemaRef.InstantiateAttrs(TemplateArgs, D, Enum);

  Enum->setInstantiationOfMemberEnum(D, TSK_ImplicitInstantiation);
  Enum->setAccess(D->getAccess());
  // Forward the mangling number from the template to the instantiated decl.
  SemaRef.Context.setManglingNumber(Enum, SemaRef.Context.getManglingNumber(D));
  // See if the old tag was defined along with a declarator.
  // If it did, mark the new tag as being associated with that declarator.
  if (DeclaratorDecl *DD = SemaRef.Context.getDeclaratorForUnnamedTagDecl(D))
    SemaRef.Context.addDeclaratorForUnnamedTagDecl(Enum, DD);
  // See if the old tag was defined along with a typedef.
  // If it did, mark the new tag as being associated with that typedef.
  if (TypedefNameDecl *TND = SemaRef.Context.getTypedefNameForUnnamedTagDecl(D))
    SemaRef.Context.addTypedefNameForUnnamedTagDecl(Enum, TND);
  if (SubstQualifier(D, Enum)) return nullptr;
  Owner->addDecl(Enum);

  EnumDecl *Def = D->getDefinition();
  if (Def && Def != D) {
    // If this is an out-of-line definition of an enum member template, check
    // that the underlying types match in the instantiation of both
    // declarations.
    if (TypeSourceInfo *TI = Def->getIntegerTypeSourceInfo()) {
      SourceLocation UnderlyingLoc = TI->getTypeLoc().getBeginLoc();
      QualType DefnUnderlying =
        SemaRef.SubstType(TI->getType(), TemplateArgs,
                          UnderlyingLoc, DeclarationName());
      SemaRef.CheckEnumRedeclaration(Def->getLocation(), Def->isScoped(),
                                     DefnUnderlying, /*IsFixed=*/true, Enum);
    }
  }

  // C++11 [temp.inst]p1: The implicit instantiation of a class template
  // specialization causes the implicit instantiation of the declarations, but
  // not the definitions of scoped member enumerations.
  //
  // DR1484 clarifies that enumeration definitions inside of a template
  // declaration aren't considered entities that can be separately instantiated
  // from the rest of the entity they are declared inside of.
  if (isDeclWithinFunction(D) ? D == Def : Def && !Enum->isScoped()) {
    SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Enum);
    InstantiateEnumDefinition(Enum, Def);
  }

  return Enum;
}

void TemplateDeclInstantiator::InstantiateEnumDefinition(
    EnumDecl *Enum, EnumDecl *Pattern) {
  Enum->startDefinition();

  // Update the location to refer to the definition.
  Enum->setLocation(Pattern->getLocation());

  SmallVector<Decl*, 4> Enumerators;

  EnumConstantDecl *LastEnumConst = nullptr;
  for (auto *EC : Pattern->enumerators()) {
    // The specified value for the enumerator.
    ExprResult Value((Expr *)nullptr);
    if (Expr *UninstValue = EC->getInitExpr()) {
      // The enumerator's value expression is a constant expression.
      EnterExpressionEvaluationContext Unevaluated(
          SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);

      Value = SemaRef.SubstExpr(UninstValue, TemplateArgs);
    }

    // Drop the initial value and continue.
    bool isInvalid = false;
    if (Value.isInvalid()) {
      Value = nullptr;
      isInvalid = true;
    }

    EnumConstantDecl *EnumConst
      = SemaRef.CheckEnumConstant(Enum, LastEnumConst,
                                  EC->getLocation(), EC->getIdentifier(),
                                  Value.get());

    if (isInvalid) {
      if (EnumConst)
        EnumConst->setInvalidDecl();
      Enum->setInvalidDecl();
    }

    if (EnumConst) {
      SemaRef.InstantiateAttrs(TemplateArgs, EC, EnumConst);

      EnumConst->setAccess(Enum->getAccess());
      Enum->addDecl(EnumConst);
      Enumerators.push_back(EnumConst);
      LastEnumConst = EnumConst;

      if (Pattern->getDeclContext()->isFunctionOrMethod() &&
          !Enum->isScoped()) {
        // If the enumeration is within a function or method, record the enum
        // constant as a local.
        SemaRef.CurrentInstantiationScope->InstantiatedLocal(EC, EnumConst);
      }
    }
  }

  SemaRef.ActOnEnumBody(Enum->getLocation(), Enum->getBraceRange(), Enum,
                        Enumerators, nullptr, ParsedAttributesView());
}

Decl *TemplateDeclInstantiator::VisitEnumConstantDecl(EnumConstantDecl *D) {
  llvm_unreachable("EnumConstantDecls can only occur within EnumDecls.");
}

Decl *
TemplateDeclInstantiator::VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D) {
  llvm_unreachable("BuiltinTemplateDecls cannot be instantiated.");
}

Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
  bool isFriend = (D->getFriendObjectKind() != Decl::FOK_None);

  // Create a local instantiation scope for this class template, which
  // will contain the instantiations of the template parameters.
  LocalInstantiationScope Scope(SemaRef);
  TemplateParameterList *TempParams = D->getTemplateParameters();
  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
  if (!InstParams)
    return nullptr;

  CXXRecordDecl *Pattern = D->getTemplatedDecl();

  // Instantiate the qualifier.  We have to do this first in case
  // we're a friend declaration, because if we are then we need to put
  // the new declaration in the appropriate context.
  NestedNameSpecifierLoc QualifierLoc = Pattern->getQualifierLoc();
  if (QualifierLoc) {
    QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
                                                       TemplateArgs);
    if (!QualifierLoc)
      return nullptr;
  }

  CXXRecordDecl *PrevDecl = nullptr;
  ClassTemplateDecl *PrevClassTemplate = nullptr;

  if (!isFriend && getPreviousDeclForInstantiation(Pattern)) {
    DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
    if (!Found.empty()) {
      PrevClassTemplate = dyn_cast<ClassTemplateDecl>(Found.front());
      if (PrevClassTemplate)
        PrevDecl = PrevClassTemplate->getTemplatedDecl();
    }
  }

  // If this isn't a friend, then it's a member template, in which
  // case we just want to build the instantiation in the
  // specialization.  If it is a friend, we want to build it in
  // the appropriate context.
  DeclContext *DC = Owner;
  if (isFriend) {
    if (QualifierLoc) {
      CXXScopeSpec SS;
      SS.Adopt(QualifierLoc);
      DC = SemaRef.computeDeclContext(SS);
      if (!DC) return nullptr;
    } else {
      DC = SemaRef.FindInstantiatedContext(Pattern->getLocation(),
                                           Pattern->getDeclContext(),
                                           TemplateArgs);
    }

    // Look for a previous declaration of the template in the owning
    // context.
    LookupResult R(SemaRef, Pattern->getDeclName(), Pattern->getLocation(),
                   Sema::LookupOrdinaryName,
                   SemaRef.forRedeclarationInCurContext());
    SemaRef.LookupQualifiedName(R, DC);

    if (R.isSingleResult()) {
      PrevClassTemplate = R.getAsSingle<ClassTemplateDecl>();
      if (PrevClassTemplate)
        PrevDecl = PrevClassTemplate->getTemplatedDecl();
    }

    if (!PrevClassTemplate && QualifierLoc) {
      SemaRef.Diag(Pattern->getLocation(), diag::err_not_tag_in_scope)
        << D->getTemplatedDecl()->getTagKind() << Pattern->getDeclName() << DC
        << QualifierLoc.getSourceRange();
      return nullptr;
    }

    if (PrevClassTemplate) {
      TemplateParameterList *PrevParams
        = PrevClassTemplate->getMostRecentDecl()->getTemplateParameters();

      // Make sure the parameter lists match.
      if (!SemaRef.TemplateParameterListsAreEqual(InstParams, PrevParams, true,
                                                  Sema::TPL_TemplateMatch))
        return nullptr;

      // Do some additional validation, then merge default arguments
      // from the existing declarations.
      if (SemaRef.CheckTemplateParameterList(InstParams, PrevParams,
                                             Sema::TPC_ClassTemplate))
        return nullptr;
    }
  }

  CXXRecordDecl *RecordInst = CXXRecordDecl::Create(
      SemaRef.Context, Pattern->getTagKind(), DC, Pattern->getBeginLoc(),
      Pattern->getLocation(), Pattern->getIdentifier(), PrevDecl,
      /*DelayTypeCreation=*/true);

  if (QualifierLoc)
    RecordInst->setQualifierInfo(QualifierLoc);

  SemaRef.InstantiateAttrsForDecl(TemplateArgs, Pattern, RecordInst, LateAttrs,
                                                              StartingScope);

  ClassTemplateDecl *Inst
    = ClassTemplateDecl::Create(SemaRef.Context, DC, D->getLocation(),
                                D->getIdentifier(), InstParams, RecordInst);
  assert(!(isFriend && Owner->isDependentContext()));
  Inst->setPreviousDecl(PrevClassTemplate);

  RecordInst->setDescribedClassTemplate(Inst);

  if (isFriend) {
    if (PrevClassTemplate)
      Inst->setAccess(PrevClassTemplate->getAccess());
    else
      Inst->setAccess(D->getAccess());

    Inst->setObjectOfFriendDecl();
    // TODO: do we want to track the instantiation progeny of this
    // friend target decl?
  } else {
    Inst->setAccess(D->getAccess());
    if (!PrevClassTemplate)
      Inst->setInstantiatedFromMemberTemplate(D);
  }

  // Trigger creation of the type for the instantiation.
  SemaRef.Context.getInjectedClassNameType(RecordInst,
                                    Inst->getInjectedClassNameSpecialization());

  // Finish handling of friends.
  if (isFriend) {
    DC->makeDeclVisibleInContext(Inst);
    Inst->setLexicalDeclContext(Owner);
    RecordInst->setLexicalDeclContext(Owner);
    return Inst;
  }

  if (D->isOutOfLine()) {
    Inst->setLexicalDeclContext(D->getLexicalDeclContext());
    RecordInst->setLexicalDeclContext(D->getLexicalDeclContext());
  }

  Owner->addDecl(Inst);

  if (!PrevClassTemplate) {
    // Queue up any out-of-line partial specializations of this member
    // class template; the client will force their instantiation once
    // the enclosing class has been instantiated.
    SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
    D->getPartialSpecializations(PartialSpecs);
    for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I)
      if (PartialSpecs[I]->getFirstDecl()->isOutOfLine())
        OutOfLinePartialSpecs.push_back(std::make_pair(Inst, PartialSpecs[I]));
  }

  return Inst;
}

Decl *
TemplateDeclInstantiator::VisitClassTemplatePartialSpecializationDecl(
                                   ClassTemplatePartialSpecializationDecl *D) {
  ClassTemplateDecl *ClassTemplate = D->getSpecializedTemplate();

  // Lookup the already-instantiated declaration in the instantiation
  // of the class template and return that.
  DeclContext::lookup_result Found
    = Owner->lookup(ClassTemplate->getDeclName());
  if (Found.empty())
    return nullptr;

  ClassTemplateDecl *InstClassTemplate
    = dyn_cast<ClassTemplateDecl>(Found.front());
  if (!InstClassTemplate)
    return nullptr;

  if (ClassTemplatePartialSpecializationDecl *Result
        = InstClassTemplate->findPartialSpecInstantiatedFromMember(D))
    return Result;

  return InstantiateClassTemplatePartialSpecialization(InstClassTemplate, D);
}

Decl *TemplateDeclInstantiator::VisitVarTemplateDecl(VarTemplateDecl *D) {
  assert(D->getTemplatedDecl()->isStaticDataMember() &&
         "Only static data member templates are allowed.");

  // Create a local instantiation scope for this variable template, which
  // will contain the instantiations of the template parameters.
  LocalInstantiationScope Scope(SemaRef);
  TemplateParameterList *TempParams = D->getTemplateParameters();
  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
  if (!InstParams)
    return nullptr;

  VarDecl *Pattern = D->getTemplatedDecl();
  VarTemplateDecl *PrevVarTemplate = nullptr;

  if (getPreviousDeclForInstantiation(Pattern)) {
    DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
    if (!Found.empty())
      PrevVarTemplate = dyn_cast<VarTemplateDecl>(Found.front());
  }

  VarDecl *VarInst =
      cast_or_null<VarDecl>(VisitVarDecl(Pattern,
                                         /*InstantiatingVarTemplate=*/true));
  if (!VarInst) return nullptr;

  DeclContext *DC = Owner;

  VarTemplateDecl *Inst = VarTemplateDecl::Create(
      SemaRef.Context, DC, D->getLocation(), D->getIdentifier(), InstParams,
      VarInst);
  VarInst->setDescribedVarTemplate(Inst);
  Inst->setPreviousDecl(PrevVarTemplate);

  Inst->setAccess(D->getAccess());
  if (!PrevVarTemplate)
    Inst->setInstantiatedFromMemberTemplate(D);

  if (D->isOutOfLine()) {
    Inst->setLexicalDeclContext(D->getLexicalDeclContext());
    VarInst->setLexicalDeclContext(D->getLexicalDeclContext());
  }

  Owner->addDecl(Inst);

  if (!PrevVarTemplate) {
    // Queue up any out-of-line partial specializations of this member
    // variable template; the client will force their instantiation once
    // the enclosing class has been instantiated.
    SmallVector<VarTemplatePartialSpecializationDecl *, 4> PartialSpecs;
    D->getPartialSpecializations(PartialSpecs);
    for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I)
      if (PartialSpecs[I]->getFirstDecl()->isOutOfLine())
        OutOfLineVarPartialSpecs.push_back(
            std::make_pair(Inst, PartialSpecs[I]));
  }

  return Inst;
}

Decl *TemplateDeclInstantiator::VisitVarTemplatePartialSpecializationDecl(
    VarTemplatePartialSpecializationDecl *D) {
  assert(D->isStaticDataMember() &&
         "Only static data member templates are allowed.");

  VarTemplateDecl *VarTemplate = D->getSpecializedTemplate();

  // Lookup the already-instantiated declaration and return that.
  DeclContext::lookup_result Found = Owner->lookup(VarTemplate->getDeclName());
  assert(!Found.empty() && "Instantiation found nothing?");

  VarTemplateDecl *InstVarTemplate = dyn_cast<VarTemplateDecl>(Found.front());
  assert(InstVarTemplate && "Instantiation did not find a variable template?");

  if (VarTemplatePartialSpecializationDecl *Result =
          InstVarTemplate->findPartialSpecInstantiatedFromMember(D))
    return Result;

  return InstantiateVarTemplatePartialSpecialization(InstVarTemplate, D);
}

Decl *
TemplateDeclInstantiator::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
  // Create a local instantiation scope for this function template, which
  // will contain the instantiations of the template parameters and then get
  // merged with the local instantiation scope for the function template
  // itself.
  LocalInstantiationScope Scope(SemaRef);

  TemplateParameterList *TempParams = D->getTemplateParameters();
  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
  if (!InstParams)
    return nullptr;

  FunctionDecl *Instantiated = nullptr;
  if (CXXMethodDecl *DMethod = dyn_cast<CXXMethodDecl>(D->getTemplatedDecl()))
    Instantiated = cast_or_null<FunctionDecl>(VisitCXXMethodDecl(DMethod,
                                                                 InstParams));
  else
    Instantiated = cast_or_null<FunctionDecl>(VisitFunctionDecl(
                                                          D->getTemplatedDecl(),
                                                                InstParams));

  if (!Instantiated)
    return nullptr;

  // Link the instantiated function template declaration to the function
  // template from which it was instantiated.
  FunctionTemplateDecl *InstTemplate
    = Instantiated->getDescribedFunctionTemplate();
  InstTemplate->setAccess(D->getAccess());
  assert(InstTemplate &&
         "VisitFunctionDecl/CXXMethodDecl didn't create a template!");

  bool isFriend = (InstTemplate->getFriendObjectKind() != Decl::FOK_None);

  // Link the instantiation back to the pattern *unless* this is a
  // non-definition friend declaration.
  if (!InstTemplate->getInstantiatedFromMemberTemplate() &&
      !(isFriend && !D->getTemplatedDecl()->isThisDeclarationADefinition()))
    InstTemplate->setInstantiatedFromMemberTemplate(D);

  // Make declarations visible in the appropriate context.
  if (!isFriend) {
    Owner->addDecl(InstTemplate);
  } else if (InstTemplate->getDeclContext()->isRecord() &&
             !getPreviousDeclForInstantiation(D)) {
    SemaRef.CheckFriendAccess(InstTemplate);
  }

  return InstTemplate;
}

Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
  CXXRecordDecl *PrevDecl = nullptr;
  if (CXXRecordDecl *PatternPrev = getPreviousDeclForInstantiation(D)) {
    NamedDecl *Prev = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                   PatternPrev,
                                                   TemplateArgs);
    if (!Prev) return nullptr;
    PrevDecl = cast<CXXRecordDecl>(Prev);
  }

  CXXRecordDecl *Record = nullptr;
  bool IsInjectedClassName = D->isInjectedClassName();
  if (D->isLambda())
    Record = CXXRecordDecl::CreateLambda(
        SemaRef.Context, Owner, D->getLambdaTypeInfo(), D->getLocation(),
        D->isDependentLambda(), D->isGenericLambda(),
        D->getLambdaCaptureDefault());
  else
    Record = CXXRecordDecl::Create(SemaRef.Context, D->getTagKind(), Owner,
                                   D->getBeginLoc(), D->getLocation(),
                                   D->getIdentifier(), PrevDecl,
                                   /*DelayTypeCreation=*/IsInjectedClassName);
  // Link the type of the injected-class-name to that of the outer class.
  if (IsInjectedClassName)
    (void)SemaRef.Context.getTypeDeclType(Record, cast<CXXRecordDecl>(Owner));

  // Substitute the nested name specifier, if any.
  if (SubstQualifier(D, Record))
    return nullptr;

  SemaRef.InstantiateAttrsForDecl(TemplateArgs, D, Record, LateAttrs,
                                                              StartingScope);

  Record->setImplicit(D->isImplicit());
  // FIXME: Check against AS_none is an ugly hack to work around the issue that
  // the tag decls introduced by friend class declarations don't have an access
  // specifier. Remove once this area of the code gets sorted out.
  if (D->getAccess() != AS_none)
    Record->setAccess(D->getAccess());
  if (!IsInjectedClassName)
    Record->setInstantiationOfMemberClass(D, TSK_ImplicitInstantiation);

  // If the original function was part of a friend declaration,
  // inherit its namespace state.
  if (D->getFriendObjectKind())
    Record->setObjectOfFriendDecl();

  // Make sure that anonymous structs and unions are recorded.
  if (D->isAnonymousStructOrUnion())
    Record->setAnonymousStructOrUnion(true);

  if (D->isLocalClass())
    SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Record);

  // Forward the mangling number from the template to the instantiated decl.
  SemaRef.Context.setManglingNumber(Record,
                                    SemaRef.Context.getManglingNumber(D));

  // See if the old tag was defined along with a declarator.
  // If it did, mark the new tag as being associated with that declarator.
  if (DeclaratorDecl *DD = SemaRef.Context.getDeclaratorForUnnamedTagDecl(D))
    SemaRef.Context.addDeclaratorForUnnamedTagDecl(Record, DD);

  // See if the old tag was defined along with a typedef.
  // If it did, mark the new tag as being associated with that typedef.
  if (TypedefNameDecl *TND = SemaRef.Context.getTypedefNameForUnnamedTagDecl(D))
    SemaRef.Context.addTypedefNameForUnnamedTagDecl(Record, TND);

  Owner->addDecl(Record);

  // DR1484 clarifies that the members of a local class are instantiated as part
  // of the instantiation of their enclosing entity.
  if (D->isCompleteDefinition() && D->isLocalClass()) {
    Sema::LocalEagerInstantiationScope LocalInstantiations(SemaRef);

    SemaRef.InstantiateClass(D->getLocation(), Record, D, TemplateArgs,
                             TSK_ImplicitInstantiation,
                             /*Complain=*/true);

    // For nested local classes, we will instantiate the members when we
    // reach the end of the outermost (non-nested) local class.
    if (!D->isCXXClassMember())
      SemaRef.InstantiateClassMembers(D->getLocation(), Record, TemplateArgs,
                                      TSK_ImplicitInstantiation);

    // This class may have local implicit instantiations that need to be
    // performed within this scope.
    LocalInstantiations.perform();
  }

  SemaRef.DiagnoseUnusedNestedTypedefs(Record);

  if (IsInjectedClassName)
    assert(Record->isInjectedClassName() && "Broken injected-class-name");

  return Record;
}

/// Adjust the given function type for an instantiation of the
/// given declaration, to cope with modifications to the function's type that
/// aren't reflected in the type-source information.
///
/// \param D The declaration we're instantiating.
/// \param TInfo The already-instantiated type.
static QualType adjustFunctionTypeForInstantiation(ASTContext &Context,
                                                   FunctionDecl *D,
                                                   TypeSourceInfo *TInfo) {
  const FunctionProtoType *OrigFunc
    = D->getType()->castAs<FunctionProtoType>();
  const FunctionProtoType *NewFunc
    = TInfo->getType()->castAs<FunctionProtoType>();
  if (OrigFunc->getExtInfo() == NewFunc->getExtInfo())
    return TInfo->getType();

  FunctionProtoType::ExtProtoInfo NewEPI = NewFunc->getExtProtoInfo();
  NewEPI.ExtInfo = OrigFunc->getExtInfo();
  return Context.getFunctionType(NewFunc->getReturnType(),
                                 NewFunc->getParamTypes(), NewEPI);
}

/// Normal class members are of more specific types and therefore
/// don't make it here.  This function serves three purposes:
///   1) instantiating function templates
///   2) substituting friend declarations
///   3) substituting deduction guide declarations for nested class templates
Decl *TemplateDeclInstantiator::VisitFunctionDecl(
    FunctionDecl *D, TemplateParameterList *TemplateParams,
    RewriteKind FunctionRewriteKind) {
  // Check whether there is already a function template specialization for
  // this declaration.
  FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
  if (FunctionTemplate && !TemplateParams) {
    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();

    void *InsertPos = nullptr;
    FunctionDecl *SpecFunc
      = FunctionTemplate->findSpecialization(Innermost, InsertPos);

    // If we already have a function template specialization, return it.
    if (SpecFunc)
      return SpecFunc;
  }

  bool isFriend;
  if (FunctionTemplate)
    isFriend = (FunctionTemplate->getFriendObjectKind() != Decl::FOK_None);
  else
    isFriend = (D->getFriendObjectKind() != Decl::FOK_None);

  bool MergeWithParentScope = (TemplateParams != nullptr) ||
    Owner->isFunctionOrMethod() ||
    !(isa<Decl>(Owner) &&
      cast<Decl>(Owner)->isDefinedOutsideFunctionOrMethod());
  LocalInstantiationScope Scope(SemaRef, MergeWithParentScope);

  ExplicitSpecifier InstantiatedExplicitSpecifier;
  if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
    InstantiatedExplicitSpecifier = instantiateExplicitSpecifier(
        SemaRef, TemplateArgs, DGuide->getExplicitSpecifier(), DGuide);
    if (InstantiatedExplicitSpecifier.isInvalid())
      return nullptr;
  }

  SmallVector<ParmVarDecl *, 4> Params;
  TypeSourceInfo *TInfo = SubstFunctionType(D, Params);
  if (!TInfo)
    return nullptr;
  QualType T = adjustFunctionTypeForInstantiation(SemaRef.Context, D, TInfo);

  if (TemplateParams && TemplateParams->size()) {
    auto *LastParam =
        dyn_cast<TemplateTypeParmDecl>(TemplateParams->asArray().back());
    if (LastParam && LastParam->isImplicit() &&
        LastParam->hasTypeConstraint()) {
      // In abbreviated templates, the type-constraints of invented template
      // type parameters are instantiated with the function type, invalidating
      // the TemplateParameterList which relied on the template type parameter
      // not having a type constraint. Recreate the TemplateParameterList with
      // the updated parameter list.
      TemplateParams = TemplateParameterList::Create(
          SemaRef.Context, TemplateParams->getTemplateLoc(),
          TemplateParams->getLAngleLoc(), TemplateParams->asArray(),
          TemplateParams->getRAngleLoc(), TemplateParams->getRequiresClause());
    }
  }

  NestedNameSpecifierLoc QualifierLoc = D->getQualifierLoc();
  if (QualifierLoc) {
    QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
                                                       TemplateArgs);
    if (!QualifierLoc)
      return nullptr;
  }

  // FIXME: Concepts: Do not substitute into constraint expressions
  Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
  if (TrailingRequiresClause) {
    EnterExpressionEvaluationContext ConstantEvaluated(
        SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
    ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
                                           TemplateArgs);
    if (SubstRC.isInvalid())
      return nullptr;
    TrailingRequiresClause = SubstRC.get();
    if (!SemaRef.CheckConstraintExpression(TrailingRequiresClause))
      return nullptr;
  }

  // If we're instantiating a local function declaration, put the result
  // in the enclosing namespace; otherwise we need to find the instantiated
  // context.
  DeclContext *DC;
  if (D->isLocalExternDecl()) {
    DC = Owner;
    SemaRef.adjustContextForLocalExternDecl(DC);
  } else if (isFriend && QualifierLoc) {
    CXXScopeSpec SS;
    SS.Adopt(QualifierLoc);
    DC = SemaRef.computeDeclContext(SS);
    if (!DC) return nullptr;
  } else {
    DC = SemaRef.FindInstantiatedContext(D->getLocation(), D->getDeclContext(),
                                         TemplateArgs);
  }

  DeclarationNameInfo NameInfo
    = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);

  if (FunctionRewriteKind != RewriteKind::None)
    adjustForRewrite(FunctionRewriteKind, D, T, TInfo, NameInfo);

  FunctionDecl *Function;
  if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
    Function = CXXDeductionGuideDecl::Create(
        SemaRef.Context, DC, D->getInnerLocStart(),
        InstantiatedExplicitSpecifier, NameInfo, T, TInfo,
        D->getSourceRange().getEnd());
    if (DGuide->isCopyDeductionCandidate())
      cast<CXXDeductionGuideDecl>(Function)->setIsCopyDeductionCandidate();
    Function->setAccess(D->getAccess());
  } else {
    Function = FunctionDecl::Create(
        SemaRef.Context, DC, D->getInnerLocStart(), NameInfo, T, TInfo,
        D->getCanonicalDecl()->getStorageClass(), D->UsesFPIntrin(),
        D->isInlineSpecified(), D->hasWrittenPrototype(), D->getConstexprKind(),
        TrailingRequiresClause);
    Function->setRangeEnd(D->getSourceRange().getEnd());
  }

  if (D->isInlined())
    Function->setImplicitlyInline();

  if (QualifierLoc)
    Function->setQualifierInfo(QualifierLoc);

  if (D->isLocalExternDecl())
    Function->setLocalExternDecl();

  DeclContext *LexicalDC = Owner;
  if (!isFriend && D->isOutOfLine() && !D->isLocalExternDecl()) {
    assert(D->getDeclContext()->isFileContext());
    LexicalDC = D->getDeclContext();
  }

  Function->setLexicalDeclContext(LexicalDC);

  // Attach the parameters
  for (unsigned P = 0; P < Params.size(); ++P)
    if (Params[P])
      Params[P]->setOwningFunction(Function);
  Function->setParams(Params);

  if (TrailingRequiresClause)
    Function->setTrailingRequiresClause(TrailingRequiresClause);

  if (TemplateParams) {
    // Our resulting instantiation is actually a function template, since we
    // are substituting only the outer template parameters. For example, given
    //
    //   template<typename T>
    //   struct X {
    //     template<typename U> friend void f(T, U);
    //   };
    //
    //   X<int> x;
    //
    // We are instantiating the friend function template "f" within X<int>,
    // which means substituting int for T, but leaving "f" as a friend function
    // template.
    // Build the function template itself.
    FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, DC,
                                                    Function->getLocation(),
                                                    Function->getDeclName(),
                                                    TemplateParams, Function);
    Function->setDescribedFunctionTemplate(FunctionTemplate);

    FunctionTemplate->setLexicalDeclContext(LexicalDC);

    if (isFriend && D->isThisDeclarationADefinition()) {
      FunctionTemplate->setInstantiatedFromMemberTemplate(
                                           D->getDescribedFunctionTemplate());
    }
  } else if (FunctionTemplate) {
    // Record this function template specialization.
    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
    Function->setFunctionTemplateSpecialization(FunctionTemplate,
                            TemplateArgumentList::CreateCopy(SemaRef.Context,
                                                             Innermost),
                                                /*InsertPos=*/nullptr);
  } else if (isFriend && D->isThisDeclarationADefinition()) {
    // Do not connect the friend to the template unless it's actually a
    // definition. We don't want non-template functions to be marked as being
    // template instantiations.
    Function->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
  }

  if (isFriend) {
    Function->setObjectOfFriendDecl();
    if (FunctionTemplateDecl *FT = Function->getDescribedFunctionTemplate())
      FT->setObjectOfFriendDecl();
  }

  if (InitFunctionInstantiation(Function, D))
    Function->setInvalidDecl();

  bool IsExplicitSpecialization = false;

  LookupResult Previous(
      SemaRef, Function->getDeclName(), SourceLocation(),
      D->isLocalExternDecl() ? Sema::LookupRedeclarationWithLinkage
                             : Sema::LookupOrdinaryName,
      D->isLocalExternDecl() ? Sema::ForExternalRedeclaration
                             : SemaRef.forRedeclarationInCurContext());

  if (DependentFunctionTemplateSpecializationInfo *Info
        = D->getDependentSpecializationInfo()) {
    assert(isFriend && "non-friend has dependent specialization info?");

    // Instantiate the explicit template arguments.
    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                          Info->getRAngleLoc());
    if (SemaRef.SubstTemplateArguments(Info->arguments(), TemplateArgs,
                                       ExplicitArgs))
      return nullptr;

    // Map the candidate templates to their instantiations.
    for (unsigned I = 0, E = Info->getNumTemplates(); I != E; ++I) {
      Decl *Temp = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                Info->getTemplate(I),
                                                TemplateArgs);
      if (!Temp) return nullptr;

      Previous.addDecl(cast<FunctionTemplateDecl>(Temp));
    }

    if (SemaRef.CheckFunctionTemplateSpecialization(Function,
                                                    &ExplicitArgs,
                                                    Previous))
      Function->setInvalidDecl();

    IsExplicitSpecialization = true;
  } else if (const ASTTemplateArgumentListInfo *Info =
                 D->getTemplateSpecializationArgsAsWritten()) {
    // The name of this function was written as a template-id.
    SemaRef.LookupQualifiedName(Previous, DC);

    // Instantiate the explicit template arguments.
    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                          Info->getRAngleLoc());
    if (SemaRef.SubstTemplateArguments(Info->arguments(), TemplateArgs,
                                       ExplicitArgs))
      return nullptr;

    if (SemaRef.CheckFunctionTemplateSpecialization(Function,
                                                    &ExplicitArgs,
                                                    Previous))
      Function->setInvalidDecl();

    IsExplicitSpecialization = true;
  } else if (TemplateParams || !FunctionTemplate) {
    // Look only into the namespace where the friend would be declared to
    // find a previous declaration. This is the innermost enclosing namespace,
    // as described in ActOnFriendFunctionDecl.
    SemaRef.LookupQualifiedName(Previous, DC->getRedeclContext());

    // In C++, the previous declaration we find might be a tag type
    // (class or enum). In this case, the new declaration will hide the
    // tag type. Note that this does does not apply if we're declaring a
    // typedef (C++ [dcl.typedef]p4).
    if (Previous.isSingleTagDecl())
      Previous.clear();

    // Filter out previous declarations that don't match the scope. The only
    // effect this has is to remove declarations found in inline namespaces
    // for friend declarations with unqualified names.
    SemaRef.FilterLookupForScope(Previous, DC, /*Scope*/ nullptr,
                                 /*ConsiderLinkage*/ true,
                                 QualifierLoc.hasQualifier());
  }

  SemaRef.CheckFunctionDeclaration(/*Scope*/ nullptr, Function, Previous,
                                   IsExplicitSpecialization);

  // Check the template parameter list against the previous declaration. The
  // goal here is to pick up default arguments added since the friend was
  // declared; we know the template parameter lists match, since otherwise
  // we would not have picked this template as the previous declaration.
  if (isFriend && TemplateParams && FunctionTemplate->getPreviousDecl()) {
    SemaRef.CheckTemplateParameterList(
        TemplateParams,
        FunctionTemplate->getPreviousDecl()->getTemplateParameters(),
        Function->isThisDeclarationADefinition()
            ? Sema::TPC_FriendFunctionTemplateDefinition
            : Sema::TPC_FriendFunctionTemplate);
  }

  // If we're introducing a friend definition after the first use, trigger
  // instantiation.
  // FIXME: If this is a friend function template definition, we should check
  // to see if any specializations have been used.
  if (isFriend && D->isThisDeclarationADefinition() && Function->isUsed(false)) {
    if (MemberSpecializationInfo *MSInfo =
            Function->getMemberSpecializationInfo()) {
      if (MSInfo->getPointOfInstantiation().isInvalid()) {
        SourceLocation Loc = D->getLocation(); // FIXME
        MSInfo->setPointOfInstantiation(Loc);
        SemaRef.PendingLocalImplicitInstantiations.push_back(
            std::make_pair(Function, Loc));
      }
    }
  }

  if (D->isExplicitlyDefaulted()) {
    if (SubstDefaultedFunction(Function, D))
      return nullptr;
  }
  if (D->isDeleted())
    SemaRef.SetDeclDeleted(Function, D->getLocation());

  NamedDecl *PrincipalDecl =
      (TemplateParams ? cast<NamedDecl>(FunctionTemplate) : Function);

  // If this declaration lives in a different context from its lexical context,
  // add it to the corresponding lookup table.
  if (isFriend ||
      (Function->isLocalExternDecl() && !Function->getPreviousDecl()))
    DC->makeDeclVisibleInContext(PrincipalDecl);

  if (Function->isOverloadedOperator() && !DC->isRecord() &&
      PrincipalDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary))
    PrincipalDecl->setNonMemberOperator();

  return Function;
}

Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
    CXXMethodDecl *D, TemplateParameterList *TemplateParams,
    Optional<const ASTTemplateArgumentListInfo *> ClassScopeSpecializationArgs,
    RewriteKind FunctionRewriteKind) {
  FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
  if (FunctionTemplate && !TemplateParams) {
    // We are creating a function template specialization from a function
    // template. Check whether there is already a function template
    // specialization for this particular set of template arguments.
    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();

    void *InsertPos = nullptr;
    FunctionDecl *SpecFunc
      = FunctionTemplate->findSpecialization(Innermost, InsertPos);

    // If we already have a function template specialization, return it.
    if (SpecFunc)
      return SpecFunc;
  }

  bool isFriend;
  if (FunctionTemplate)
    isFriend = (FunctionTemplate->getFriendObjectKind() != Decl::FOK_None);
  else
    isFriend = (D->getFriendObjectKind() != Decl::FOK_None);

  bool MergeWithParentScope = (TemplateParams != nullptr) ||
    !(isa<Decl>(Owner) &&
      cast<Decl>(Owner)->isDefinedOutsideFunctionOrMethod());
  LocalInstantiationScope Scope(SemaRef, MergeWithParentScope);

  // Instantiate enclosing template arguments for friends.
  SmallVector<TemplateParameterList *, 4> TempParamLists;
  unsigned NumTempParamLists = 0;
  if (isFriend && (NumTempParamLists = D->getNumTemplateParameterLists())) {
    TempParamLists.resize(NumTempParamLists);
    for (unsigned I = 0; I != NumTempParamLists; ++I) {
      TemplateParameterList *TempParams = D->getTemplateParameterList(I);
      TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
      if (!InstParams)
        return nullptr;
      TempParamLists[I] = InstParams;
    }
  }

  ExplicitSpecifier InstantiatedExplicitSpecifier =
      instantiateExplicitSpecifier(SemaRef, TemplateArgs,
                                   ExplicitSpecifier::getFromDecl(D), D);
  if (InstantiatedExplicitSpecifier.isInvalid())
    return nullptr;

  // Implicit destructors/constructors created for local classes in
  // DeclareImplicit* (see SemaDeclCXX.cpp) might not have an associated TSI.
  // Unfortunately there isn't enough context in those functions to
  // conditionally populate the TSI without breaking non-template related use
  // cases. Populate TSIs prior to calling SubstFunctionType to make sure we get
  // a proper transformation.
  if (cast<CXXRecordDecl>(D->getParent())->isLambda() &&
      !D->getTypeSourceInfo() &&
      isa<CXXConstructorDecl, CXXDestructorDecl>(D)) {
    TypeSourceInfo *TSI =
        SemaRef.Context.getTrivialTypeSourceInfo(D->getType());
    D->setTypeSourceInfo(TSI);
  }

  SmallVector<ParmVarDecl *, 4> Params;
  TypeSourceInfo *TInfo = SubstFunctionType(D, Params);
  if (!TInfo)
    return nullptr;
  QualType T = adjustFunctionTypeForInstantiation(SemaRef.Context, D, TInfo);

  if (TemplateParams && TemplateParams->size()) {
    auto *LastParam =
        dyn_cast<TemplateTypeParmDecl>(TemplateParams->asArray().back());
    if (LastParam && LastParam->isImplicit() &&
        LastParam->hasTypeConstraint()) {
      // In abbreviated templates, the type-constraints of invented template
      // type parameters are instantiated with the function type, invalidating
      // the TemplateParameterList which relied on the template type parameter
      // not having a type constraint. Recreate the TemplateParameterList with
      // the updated parameter list.
      TemplateParams = TemplateParameterList::Create(
          SemaRef.Context, TemplateParams->getTemplateLoc(),
          TemplateParams->getLAngleLoc(), TemplateParams->asArray(),
          TemplateParams->getRAngleLoc(), TemplateParams->getRequiresClause());
    }
  }

  NestedNameSpecifierLoc QualifierLoc = D->getQualifierLoc();
  if (QualifierLoc) {
    QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
                                                 TemplateArgs);
    if (!QualifierLoc)
      return nullptr;
  }

  // FIXME: Concepts: Do not substitute into constraint expressions
  Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
  if (TrailingRequiresClause) {
    EnterExpressionEvaluationContext ConstantEvaluated(
        SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
    auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(Owner);
    Sema::CXXThisScopeRAII ThisScope(SemaRef, ThisContext,
                                     D->getMethodQualifiers(), ThisContext);
    ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
                                           TemplateArgs);
    if (SubstRC.isInvalid())
      return nullptr;
    TrailingRequiresClause = SubstRC.get();
    if (!SemaRef.CheckConstraintExpression(TrailingRequiresClause))
      return nullptr;
  }

  DeclContext *DC = Owner;
  if (isFriend) {
    if (QualifierLoc) {
      CXXScopeSpec SS;
      SS.Adopt(QualifierLoc);
      DC = SemaRef.computeDeclContext(SS);

      if (DC && SemaRef.RequireCompleteDeclContext(SS, DC))
        return nullptr;
    } else {
      DC = SemaRef.FindInstantiatedContext(D->getLocation(),
                                           D->getDeclContext(),
                                           TemplateArgs);
    }
    if (!DC) return nullptr;
  }

  DeclarationNameInfo NameInfo
    = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);

  if (FunctionRewriteKind != RewriteKind::None)
    adjustForRewrite(FunctionRewriteKind, D, T, TInfo, NameInfo);

  // Build the instantiated method declaration.
  CXXRecordDecl *Record = cast<CXXRecordDecl>(DC);
  CXXMethodDecl *Method = nullptr;

  SourceLocation StartLoc = D->getInnerLocStart();
  if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(D)) {
    Method = CXXConstructorDecl::Create(
        SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
        InstantiatedExplicitSpecifier, Constructor->UsesFPIntrin(),
        Constructor->isInlineSpecified(), false,
        Constructor->getConstexprKind(), InheritedConstructor(),
        TrailingRequiresClause);
    Method->setRangeEnd(Constructor->getEndLoc());
  } else if (CXXDestructorDecl *Destructor = dyn_cast<CXXDestructorDecl>(D)) {
    Method = CXXDestructorDecl::Create(
        SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
        Destructor->UsesFPIntrin(), Destructor->isInlineSpecified(), false,
        Destructor->getConstexprKind(), TrailingRequiresClause);
    Method->setRangeEnd(Destructor->getEndLoc());
    Method->setDeclName(SemaRef.Context.DeclarationNames.getCXXDestructorName(
        SemaRef.Context.getCanonicalType(
            SemaRef.Context.getTypeDeclType(Record))));
  } else if (CXXConversionDecl *Conversion = dyn_cast<CXXConversionDecl>(D)) {
    Method = CXXConversionDecl::Create(
        SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
        Conversion->UsesFPIntrin(), Conversion->isInlineSpecified(),
        InstantiatedExplicitSpecifier, Conversion->getConstexprKind(),
        Conversion->getEndLoc(), TrailingRequiresClause);
  } else {
    StorageClass SC = D->isStatic() ? SC_Static : SC_None;
    Method = CXXMethodDecl::Create(
        SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo, SC,
        D->UsesFPIntrin(), D->isInlineSpecified(), D->getConstexprKind(),
        D->getEndLoc(), TrailingRequiresClause);
  }

  if (D->isInlined())
    Method->setImplicitlyInline();

  if (QualifierLoc)
    Method->setQualifierInfo(QualifierLoc);

  if (TemplateParams) {
    // Our resulting instantiation is actually a function template, since we
    // are substituting only the outer template parameters. For example, given
    //
    //   template<typename T>
    //   struct X {
    //     template<typename U> void f(T, U);
    //   };
    //
    //   X<int> x;
    //
    // We are instantiating the member template "f" within X<int>, which means
    // substituting int for T, but leaving "f" as a member function template.
    // Build the function template itself.
    FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, Record,
                                                    Method->getLocation(),
                                                    Method->getDeclName(),
                                                    TemplateParams, Method);
    if (isFriend) {
      FunctionTemplate->setLexicalDeclContext(Owner);
      FunctionTemplate->setObjectOfFriendDecl();
    } else if (D->isOutOfLine())
      FunctionTemplate->setLexicalDeclContext(D->getLexicalDeclContext());
    Method->setDescribedFunctionTemplate(FunctionTemplate);
  } else if (FunctionTemplate) {
    // Record this function template specialization.
    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
    Method->setFunctionTemplateSpecialization(FunctionTemplate,
                         TemplateArgumentList::CreateCopy(SemaRef.Context,
                                                          Innermost),
                                              /*InsertPos=*/nullptr);
  } else if (!isFriend) {
    // Record that this is an instantiation of a member function.
    Method->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
  }

  // If we are instantiating a member function defined
  // out-of-line, the instantiation will have the same lexical
  // context (which will be a namespace scope) as the template.
  if (isFriend) {
    if (NumTempParamLists)
      Method->setTemplateParameterListsInfo(
          SemaRef.Context,
          llvm::makeArrayRef(TempParamLists.data(), NumTempParamLists));

    Method->setLexicalDeclContext(Owner);
    Method->setObjectOfFriendDecl();
  } else if (D->isOutOfLine())
    Method->setLexicalDeclContext(D->getLexicalDeclContext());

  // Attach the parameters
  for (unsigned P = 0; P < Params.size(); ++P)
    Params[P]->setOwningFunction(Method);
  Method->setParams(Params);

  if (InitMethodInstantiation(Method, D))
    Method->setInvalidDecl();

  LookupResult Previous(SemaRef, NameInfo, Sema::LookupOrdinaryName,
                        Sema::ForExternalRedeclaration);

  bool IsExplicitSpecialization = false;

  // If the name of this function was written as a template-id, instantiate
  // the explicit template arguments.
  if (DependentFunctionTemplateSpecializationInfo *Info
        = D->getDependentSpecializationInfo()) {
    assert(isFriend && "non-friend has dependent specialization info?");

    // Instantiate the explicit template arguments.
    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                          Info->getRAngleLoc());
    if (SemaRef.SubstTemplateArguments(Info->arguments(), TemplateArgs,
                                       ExplicitArgs))
      return nullptr;

    // Map the candidate templates to their instantiations.
    for (unsigned I = 0, E = Info->getNumTemplates(); I != E; ++I) {
      Decl *Temp = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                Info->getTemplate(I),
                                                TemplateArgs);
      if (!Temp) return nullptr;

      Previous.addDecl(cast<FunctionTemplateDecl>(Temp));
    }

    if (SemaRef.CheckFunctionTemplateSpecialization(Method,
                                                    &ExplicitArgs,
                                                    Previous))
      Method->setInvalidDecl();

    IsExplicitSpecialization = true;
  } else if (const ASTTemplateArgumentListInfo *Info =
                 ClassScopeSpecializationArgs.getValueOr(
                     D->getTemplateSpecializationArgsAsWritten())) {
    SemaRef.LookupQualifiedName(Previous, DC);

    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                          Info->getRAngleLoc());
    if (SemaRef.SubstTemplateArguments(Info->arguments(), TemplateArgs,
                                       ExplicitArgs))
      return nullptr;

    if (SemaRef.CheckFunctionTemplateSpecialization(Method,
                                                    &ExplicitArgs,
                                                    Previous))
      Method->setInvalidDecl();

    IsExplicitSpecialization = true;
  } else if (ClassScopeSpecializationArgs) {
    // Class-scope explicit specialization written without explicit template
    // arguments.
    SemaRef.LookupQualifiedName(Previous, DC);
    if (SemaRef.CheckFunctionTemplateSpecialization(Method, nullptr, Previous))
      Method->setInvalidDecl();

    IsExplicitSpecialization = true;
  } else if (!FunctionTemplate || TemplateParams || isFriend) {
    SemaRef.LookupQualifiedName(Previous, Record);

    // In C++, the previous declaration we find might be a tag type
    // (class or enum). In this case, the new declaration will hide the
    // tag type. Note that this does does not apply if we're declaring a
    // typedef (C++ [dcl.typedef]p4).
    if (Previous.isSingleTagDecl())
      Previous.clear();
  }

  SemaRef.CheckFunctionDeclaration(nullptr, Method, Previous,
                                   IsExplicitSpecialization);

  if (D->isPure())
    SemaRef.CheckPureMethod(Method, SourceRange());

  // Propagate access.  For a non-friend declaration, the access is
  // whatever we're propagating from.  For a friend, it should be the
  // previous declaration we just found.
  if (isFriend && Method->getPreviousDecl())
    Method->setAccess(Method->getPreviousDecl()->getAccess());
  else
    Method->setAccess(D->getAccess());
  if (FunctionTemplate)
    FunctionTemplate->setAccess(Method->getAccess());

  SemaRef.CheckOverrideControl(Method);

  // If a function is defined as defaulted or deleted, mark it as such now.
  if (D->isExplicitlyDefaulted()) {
    if (SubstDefaultedFunction(Method, D))
      return nullptr;
  }
  if (D->isDeletedAsWritten())
    SemaRef.SetDeclDeleted(Method, Method->getLocation());

  // If this is an explicit specialization, mark the implicitly-instantiated
  // template specialization as being an explicit specialization too.
  // FIXME: Is this necessary?
  if (IsExplicitSpecialization && !isFriend)
    SemaRef.CompleteMemberSpecialization(Method, Previous);

  // If there's a function template, let our caller handle it.
  if (FunctionTemplate) {
    // do nothing

  // Don't hide a (potentially) valid declaration with an invalid one.
  } else if (Method->isInvalidDecl() && !Previous.empty()) {
    // do nothing

  // Otherwise, check access to friends and make them visible.
  } else if (isFriend) {
    // We only need to re-check access for methods which we didn't
    // manage to match during parsing.
    if (!D->getPreviousDecl())
      SemaRef.CheckFriendAccess(Method);

    Record->makeDeclVisibleInContext(Method);

  // Otherwise, add the declaration.  We don't need to do this for
  // class-scope specializations because we'll have matched them with
  // the appropriate template.
  } else {
    Owner->addDecl(Method);
  }

  // PR17480: Honor the used attribute to instantiate member function
  // definitions
  if (Method->hasAttr<UsedAttr>()) {
    if (const auto *A = dyn_cast<CXXRecordDecl>(Owner)) {
      SourceLocation Loc;
      if (const MemberSpecializationInfo *MSInfo =
              A->getMemberSpecializationInfo())
        Loc = MSInfo->getPointOfInstantiation();
      else if (const auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(A))
        Loc = Spec->getPointOfInstantiation();
      SemaRef.MarkFunctionReferenced(Loc, Method);
    }
  }

  return Method;
}

Decl *TemplateDeclInstantiator::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
  return VisitCXXMethodDecl(D);
}

Decl *TemplateDeclInstantiator::VisitCXXDestructorDecl(CXXDestructorDecl *D) {
  return VisitCXXMethodDecl(D);
}

Decl *TemplateDeclInstantiator::VisitCXXConversionDecl(CXXConversionDecl *D) {
  return VisitCXXMethodDecl(D);
}

Decl *TemplateDeclInstantiator::VisitParmVarDecl(ParmVarDecl *D) {
  return SemaRef.SubstParmVarDecl(D, TemplateArgs, /*indexAdjustment*/ 0, None,
                                  /*ExpectParameterPack=*/ false);
}

Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
                                                    TemplateTypeParmDecl *D) {
  assert(D->getTypeForDecl()->isTemplateTypeParmType());

  Optional<unsigned> NumExpanded;

  if (const TypeConstraint *TC = D->getTypeConstraint()) {
    if (D->isPackExpansion() && !D->isExpandedParameterPack()) {
      assert(TC->getTemplateArgsAsWritten() &&
             "type parameter can only be an expansion when explicit arguments "
             "are specified");
      // The template type parameter pack's type is a pack expansion of types.
      // Determine whether we need to expand this parameter pack into separate
      // types.
      SmallVector<UnexpandedParameterPack, 2> Unexpanded;