//===--- JumpDiagnostics.cpp - Protected scope jump analysis ------*- C++ -*-=//

//

// 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 the JumpScopeChecker class, which is used to diagnose

// jumps that enter a protected scope in an invalid way.

//

//===----------------------------------------------------------------------===//

#include "clang/AST/DeclCXX.h"

#include "clang/AST/Expr.h"

#include "clang/AST/ExprCXX.h"

#include "clang/AST/StmtCXX.h"

#include "clang/AST/StmtObjC.h"

#include "clang/AST/StmtOpenMP.h"

#include "clang/Basic/SourceLocation.h"

#include "clang/Sema/SemaInternal.h"

#include "llvm/ADT/BitVector.h"

using namespace clang;

namespace {

/// JumpScopeChecker - This object is used by Sema to diagnose invalid jumps

/// into VLA and other protected scopes.  For example, this rejects:

///    goto L;

///    int a[n];

///  L:

///

/// We also detect jumps out of protected scopes when it's not possible to do

/// cleanups properly. Indirect jumps and ASM jumps can't do cleanups because

/// the target is unknown. Return statements with \c [[clang::musttail]] cannot

/// handle any cleanups due to the nature of a tail call.

class JumpScopeChecker {

  Sema &S;

  /// Permissive - True when recovering from errors, in which case precautions

  /// are taken to handle incomplete scope information.

  const bool Permissive;

  /// GotoScope - This is a record that we use to keep track of all of the

  /// scopes that are introduced by VLAs and other things that scope jumps like

  /// gotos.  This scope tree has nothing to do with the source scope tree,

  /// because you can have multiple VLA scopes per compound statement, and most

  /// compound statements don't introduce any scopes.

  struct GotoScope {

    /// ParentScope - The index in ScopeMap of the parent scope.  This is 0 for

    /// the parent scope is the function body.

    unsigned ParentScope;

    /// InDiag - The note to emit if there is a jump into this scope.

    unsigned InDiag;

    /// OutDiag - The note to emit if there is an indirect jump out

    /// of this scope.  Direct jumps always clean up their current scope

    /// in an orderly way.

    unsigned OutDiag;

    /// Loc - Location to emit the diagnostic.

    SourceLocation Loc;

    GotoScope(unsigned parentScope, unsigned InDiag, unsigned OutDiag,

              SourceLocation L)

      : ParentScope(parentScope), InDiag(InDiag), OutDiag(OutDiag), Loc(L) {}

  };

  SmallVector<GotoScope, 48> Scopes;

  llvm::DenseMap<Stmt*, unsigned> LabelAndGotoScopes;

  SmallVector<Stmt*, 16> Jumps;

  SmallVector<Stmt*, 4> IndirectJumps;

  SmallVector<LabelDecl *, 4> IndirectJumpTargets;

  SmallVector<AttributedStmt *, 4> MustTailStmts;

public:

  JumpScopeChecker(Stmt *Body, Sema &S);

private:

  void BuildScopeInformation(Decl *D, unsigned &ParentScope);

  void BuildScopeInformation(VarDecl *D, const BlockDecl *BDecl,

                             unsigned &ParentScope);

  void BuildScopeInformation(CompoundLiteralExpr *CLE, unsigned &ParentScope);

  void BuildScopeInformation(Stmt *S, unsigned &origParentScope);

  void VerifyJumps();

  void VerifyIndirectJumps();

  void VerifyMustTailStmts();

  void NoteJumpIntoScopes(ArrayRef<unsigned> ToScopes);

  void DiagnoseIndirectOrAsmJump(Stmt *IG, unsigned IGScope, LabelDecl *Target,

                                 unsigned TargetScope);

  void CheckJump(Stmt *From, Stmt *To, SourceLocation DiagLoc,

                 unsigned JumpDiag, unsigned JumpDiagWarning,

                 unsigned JumpDiagCXX98Compat);

  void CheckGotoStmt(GotoStmt *GS);

  const Attr *GetMustTailAttr(AttributedStmt *AS);

  unsigned GetDeepestCommonScope(unsigned A, unsigned B);

};

} // end anonymous namespace

#define CHECK_PERMISSIVE(x) (assert(Permissive || !(x)), (Permissive && (x)))

JumpScopeChecker::JumpScopeChecker(Stmt *Body, Sema &s)

    : S(s), Permissive(s.hasAnyUnrecoverableErrorsInThisFunction()) {

  // Add a scope entry for function scope.

  Scopes.push_back(GotoScope(~0U, ~0U, ~0U, SourceLocation()));

  // Build information for the top level compound statement, so that we have a

  // defined scope record for every "goto" and label.

  unsigned BodyParentScope = 0;

  BuildScopeInformation(Body, BodyParentScope);

  // Check that all jumps we saw are kosher.

  VerifyJumps();

  VerifyIndirectJumps();

  VerifyMustTailStmts();

}

/// GetDeepestCommonScope - Finds the innermost scope enclosing the

/// two scopes.

unsigned JumpScopeChecker::GetDeepestCommonScope(unsigned A, unsigned B) {

  while (A != B) {

    // Inner scopes are created after outer scopes and therefore have

    // higher indices.

    if (A < B) {

      assert(Scopes[B].ParentScope < B);

      B = Scopes[B].ParentScope;

    } else {

      assert(Scopes[A].ParentScope < A);

      A = Scopes[A].ParentScope;

    }

  }

  return A;

}

typedef std::pair<unsigned,unsigned> ScopePair;

/// GetDiagForGotoScopeDecl - If this decl induces a new goto scope, return a

/// diagnostic that should be emitted if control goes over it. If not, return 0.

static ScopePair GetDiagForGotoScopeDecl(Sema &S, const Decl *D) {

  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {

    unsigned InDiag = 0;

    unsigned OutDiag = 0;

    if (VD->getType()->isVariablyModifiedType())

      InDiag = diag::note_protected_by_vla;

    if (VD->hasAttr<BlocksAttr>())

      return ScopePair(diag::note_protected_by___block,

                       diag::note_exits___block);

    if (VD->hasAttr<CleanupAttr>())

      return ScopePair(diag::note_protected_by_cleanup,

                       diag::note_exits_cleanup);

    if (VD->hasLocalStorage()) {

      switch (VD->getType().isDestructedType()) {

      case QualType::DK_objc_strong_lifetime:

        return ScopePair(diag::note_protected_by_objc_strong_init,

                         diag::note_exits_objc_strong);

      case QualType::DK_objc_weak_lifetime:

        return ScopePair(diag::note_protected_by_objc_weak_init,

                         diag::note_exits_objc_weak);

      case QualType::DK_nontrivial_c_struct:

        return ScopePair(diag::note_protected_by_non_trivial_c_struct_init,

                         diag::note_exits_dtor);

      case QualType::DK_cxx_destructor:

        OutDiag = diag::note_exits_dtor;

        break;

      case QualType::DK_none:

        break;

      }

    }

    const Expr *Init = VD->getInit();

    if (S.Context.getLangOpts().CPlusPlus && VD->hasLocalStorage() && Init) {

      // C++11 [stmt.dcl]p3:

      //   A program that jumps from a point where a variable with automatic

      //   storage duration is not in scope to a point where it is in scope

      //   is ill-formed unless the variable has scalar type, class type with

      //   a trivial default constructor and a trivial destructor, a

      //   cv-qualified version of one of these types, or an array of one of

      //   the preceding types and is declared without an initializer.

      // C++03 [stmt.dcl.p3:

      //   A program that jumps from a point where a local variable

      //   with automatic storage duration is not in scope to a point

      //   where it is in scope is ill-formed unless the variable has

      //   POD type and is declared without an initializer.

      InDiag = diag::note_protected_by_variable_init;

      // For a variable of (array of) class type declared without an

      // initializer, we will have call-style initialization and the initializer

      // will be the CXXConstructExpr with no intervening nodes.

      if (const CXXConstructExpr *CCE = dyn_cast<CXXConstructExpr>(Init)) {

        const CXXConstructorDecl *Ctor = CCE->getConstructor();

        if (Ctor->isTrivial() && Ctor->isDefaultConstructor() &&

            VD->getInitStyle() == VarDecl::CallInit) {

          if (OutDiag)

            InDiag = diag::note_protected_by_variable_nontriv_destructor;

          else if (!Ctor->getParent()->isPOD())

            InDiag = diag::note_protected_by_variable_non_pod;

          else

            InDiag = 0;

        }

      }

    }

    return ScopePair(InDiag, OutDiag);

  }

  if (const TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D)) {

    if (TD->getUnderlyingType()->isVariablyModifiedType())

      return ScopePair(isa<TypedefDecl>(TD)

                           ? diag::note_protected_by_vla_typedef

                           : diag::note_protected_by_vla_type_alias,

                       0);

  }

  return ScopePair(0U, 0U);

}

/// Build scope information for a declaration that is part of a DeclStmt.

void JumpScopeChecker::BuildScopeInformation(Decl *D, unsigned &ParentScope) {

  // If this decl causes a new scope, push and switch to it.

  std::pair<unsigned,unsigned> Diags = GetDiagForGotoScopeDecl(S, D);

  if (Diags.first || Diags.second) {

    Scopes.push_back(GotoScope(ParentScope, Diags.first, Diags.second,

                               D->getLocation()));

    ParentScope = Scopes.size()-1;

  }

  // If the decl has an initializer, walk it with the potentially new

  // scope we just installed.

  if (VarDecl *VD = dyn_cast<VarDecl>(D))

    if (Expr *Init = VD->getInit())

      BuildScopeInformation(Init, ParentScope);

}

/// Build scope information for a captured block literal variables.

void JumpScopeChecker::BuildScopeInformation(VarDecl *D,

                                             const BlockDecl *BDecl,

                                             unsigned &ParentScope) {

  // exclude captured __block variables; there's no destructor

  // associated with the block literal for them.

  if (D->hasAttr<BlocksAttr>())

    return;

  QualType T = D->getType();

  QualType::DestructionKind destructKind = T.isDestructedType();

  if (destructKind != QualType::DK_none) {

    std::pair<unsigned,unsigned> Diags;

    switch (destructKind) {

      case QualType::DK_cxx_destructor:

        Diags = ScopePair(diag::note_enters_block_captures_cxx_obj,

                          diag::note_exits_block_captures_cxx_obj);

        break;

      case QualType::DK_objc_strong_lifetime:

        Diags = ScopePair(diag::note_enters_block_captures_strong,

                          diag::note_exits_block_captures_strong);

        break;

      case QualType::DK_objc_weak_lifetime:

        Diags = ScopePair(diag::note_enters_block_captures_weak,

                          diag::note_exits_block_captures_weak);

        break;

      case QualType::DK_nontrivial_c_struct:

        Diags = ScopePair(diag::note_enters_block_captures_non_trivial_c_struct,

                          diag::note_exits_block_captures_non_trivial_c_struct);

        break;

      case QualType::DK_none:

        llvm_unreachable("non-lifetime captured variable");

    }

    SourceLocation Loc = D->getLocation();

    if (Loc.isInvalid())

      Loc = BDecl->getLocation();

    Scopes.push_back(GotoScope(ParentScope,

                               Diags.first, Diags.second, Loc));

    ParentScope = Scopes.size()-1;

  }

}

/// Build scope information for compound literals of C struct types that are

/// non-trivial to destruct.

void JumpScopeChecker::BuildScopeInformation(CompoundLiteralExpr *CLE,

                                             unsigned &ParentScope) {

  unsigned InDiag = diag::note_enters_compound_literal_scope;

  unsigned OutDiag = diag::note_exits_compound_literal_scope;

  Scopes.push_back(GotoScope(ParentScope, InDiag, OutDiag, CLE->getExprLoc()));

  ParentScope = Scopes.size() - 1;

}

/// BuildScopeInformation - The statements from CI to CE are known to form a

/// coherent VLA scope with a specified parent node.  Walk through the

/// statements, adding any labels or gotos to LabelAndGotoScopes and recursively

/// walking the AST as needed.

void JumpScopeChecker::BuildScopeInformation(Stmt *S,

                                             unsigned &origParentScope) {

  // If this is a statement, rather than an expression, scopes within it don't

  // propagate out into the enclosing scope.  Otherwise we have to worry

  // about block literals, which have the lifetime of their enclosing statement.

  unsigned independentParentScope = origParentScope;

  unsigned &ParentScope = ((isa<Expr>(S) && !isa<StmtExpr>(S))

                            ? origParentScope : independentParentScope);

  unsigned StmtsToSkip = 0u;

  // If we found a label, remember that it is in ParentScope scope.

  switch (S->getStmtClass()) {

  case Stmt::AddrLabelExprClass:

    IndirectJumpTargets.push_back(cast<AddrLabelExpr>(S)->getLabel());

    break;

  case Stmt::ObjCForCollectionStmtClass: {

    auto *CS = cast<ObjCForCollectionStmt>(S);

    unsigned Diag = diag::note_protected_by_objc_fast_enumeration;

    unsigned NewParentScope = Scopes.size();

    Scopes.push_back(GotoScope(ParentScope, Diag, 0, S->getBeginLoc()));

    BuildScopeInformation(CS->getBody(), NewParentScope);

    return;

  }

  case Stmt::IndirectGotoStmtClass:

    // "goto *&&lbl;" is a special case which we treat as equivalent

    // to a normal goto.  In addition, we don't calculate scope in the

    // operand (to avoid recording the address-of-label use), which

    // works only because of the restricted set of expressions which

    // we detect as constant targets.

    if (cast<IndirectGotoStmt>(S)->getConstantTarget())

      goto RecordJumpScope;

    LabelAndGotoScopes[S] = ParentScope;

    IndirectJumps.push_back(S);

    break;

  case Stmt::SwitchStmtClass:

    // Evaluate the C++17 init stmt and condition variable

    // before entering the scope of the switch statement.

    if (Stmt *Init = cast<SwitchStmt>(S)->getInit()) {

      BuildScopeInformation(Init, ParentScope);

      ++StmtsToSkip;

    }

    if (VarDecl *Var = cast<SwitchStmt>(S)->getConditionVariable()) {

      BuildScopeInformation(Var, ParentScope);

      ++StmtsToSkip;

    }

    goto RecordJumpScope;

  case Stmt::GCCAsmStmtClass:

    if (!cast<GCCAsmStmt>(S)->isAsmGoto())

      break;

    [[fallthrough]];

  case Stmt::GotoStmtClass:

  RecordJumpScope:

    // Remember both what scope a goto is in as well as the fact that we have

    // it.  This makes the second scan not have to walk the AST again.

    LabelAndGotoScopes[S] = ParentScope;

    Jumps.push_back(S);

    break;

  case Stmt::IfStmtClass: {

    IfStmt *IS = cast<IfStmt>(S);

    if (!(IS->isConstexpr() || IS->isConsteval() ||

          IS->isObjCAvailabilityCheck()))

      break;

    unsigned Diag = diag::note_protected_by_if_available;

    if (IS->isConstexpr())

      Diag = diag::note_protected_by_constexpr_if;

    else if (IS->isConsteval())

      Diag = diag::note_protected_by_consteval_if;

    if (VarDecl *Var = IS->getConditionVariable())

      BuildScopeInformation(Var, ParentScope);

    // Cannot jump into the middle of the condition.

    unsigned NewParentScope = Scopes.size();

    Scopes.push_back(GotoScope(ParentScope, Diag, 0, IS->getBeginLoc()));

    if (!IS->isConsteval())

      BuildScopeInformation(IS->getCond(), NewParentScope);

    // Jumps into either arm of an 'if constexpr' are not allowed.

    NewParentScope = Scopes.size();

    Scopes.push_back(GotoScope(ParentScope, Diag, 0, IS->getBeginLoc()));

    BuildScopeInformation(IS->getThen(), NewParentScope);

    if (Stmt *Else = IS->getElse()) {

      NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope, Diag, 0, IS->getBeginLoc()));

      BuildScopeInformation(Else, NewParentScope);

    }

    return;

  }

  case Stmt::CXXTryStmtClass: {

    CXXTryStmt *TS = cast<CXXTryStmt>(S);

    {

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_cxx_try,

                                 diag::note_exits_cxx_try,

                                 TS->getSourceRange().getBegin()));

      if (Stmt *TryBlock = TS->getTryBlock())

        BuildScopeInformation(TryBlock, NewParentScope);

    }

    // Jump from the catch into the try is not allowed either.

    for (unsigned I = 0, E = TS->getNumHandlers(); I != E; ++I) {

      CXXCatchStmt *CS = TS->getHandler(I);

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_cxx_catch,

                                 diag::note_exits_cxx_catch,

                                 CS->getSourceRange().getBegin()));

      BuildScopeInformation(CS->getHandlerBlock(), NewParentScope);

    }

    return;

  }

  case Stmt::SEHTryStmtClass: {

    SEHTryStmt *TS = cast<SEHTryStmt>(S);

    {

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_seh_try,

                                 diag::note_exits_seh_try,

                                 TS->getSourceRange().getBegin()));

      if (Stmt *TryBlock = TS->getTryBlock())

        BuildScopeInformation(TryBlock, NewParentScope);

    }

    // Jump from __except or __finally into the __try are not allowed either.

    if (SEHExceptStmt *Except = TS->getExceptHandler()) {

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_seh_except,

                                 diag::note_exits_seh_except,

                                 Except->getSourceRange().getBegin()));

      BuildScopeInformation(Except->getBlock(), NewParentScope);

    } else if (SEHFinallyStmt *Finally = TS->getFinallyHandler()) {

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_seh_finally,

                                 diag::note_exits_seh_finally,

                                 Finally->getSourceRange().getBegin()));

      BuildScopeInformation(Finally->getBlock(), NewParentScope);

    }

    return;

  }

  case Stmt::DeclStmtClass: {

    // If this is a declstmt with a VLA definition, it defines a scope from here

    // to the end of the containing context.

    DeclStmt *DS = cast<DeclStmt>(S);

    // The decl statement creates a scope if any of the decls in it are VLAs

    // or have the cleanup attribute.

    for (auto *I : DS->decls())

      BuildScopeInformation(I, origParentScope);

    return;

  }

  case Stmt::StmtExprClass: {

    // [GNU]

    // Jumping into a statement expression with goto or using

    // a switch statement outside the statement expression with

    // a case or default label inside the statement expression is not permitted.

    // Jumping out of a statement expression is permitted.

    StmtExpr *SE = cast<StmtExpr>(S);

    unsigned NewParentScope = Scopes.size();

    Scopes.push_back(GotoScope(ParentScope,

                               diag::note_enters_statement_expression,

                               /*OutDiag=*/0, SE->getBeginLoc()));

    BuildScopeInformation(SE->getSubStmt(), NewParentScope);

    return;

  }

  case Stmt::ObjCAtTryStmtClass: {

    // Disallow jumps into any part of an @try statement by pushing a scope and

    // walking all sub-stmts in that scope.

    ObjCAtTryStmt *AT = cast<ObjCAtTryStmt>(S);

    // Recursively walk the AST for the @try part.

    {

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_objc_try,

                                 diag::note_exits_objc_try,

                                 AT->getAtTryLoc()));

      if (Stmt *TryPart = AT->getTryBody())

        BuildScopeInformation(TryPart, NewParentScope);

    }

    // Jump from the catch to the finally or try is not valid.

    for (ObjCAtCatchStmt *AC : AT->catch_stmts()) {

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_objc_catch,

                                 diag::note_exits_objc_catch,

                                 AC->getAtCatchLoc()));

      // @catches are nested and it isn't

      BuildScopeInformation(AC->getCatchBody(), NewParentScope);

    }

    // Jump from the finally to the try or catch is not valid.

    if (ObjCAtFinallyStmt *AF = AT->getFinallyStmt()) {

      unsigned NewParentScope = Scopes.size();

      Scopes.push_back(GotoScope(ParentScope,

                                 diag::note_protected_by_objc_finally,

                                 diag::note_exits_objc_finally,

                                 AF->getAtFinallyLoc()));

      BuildScopeInformation(AF, NewParentScope);

    }

    return;

  }

  case Stmt::ObjCAtSynchronizedStmtClass: {

    // Disallow jumps into the protected statement of an @synchronized, but

    // allow jumps into the object expression it protects.

    ObjCAtSynchronizedStmt *AS = cast<ObjCAtSynchronizedStmt>(S);

    // Recursively walk the AST for the @synchronized object expr, it is

    // evaluated in the normal scope.

    BuildScopeInformation(AS->getSynchExpr(), ParentScope);

    // Recursively walk the AST for the @synchronized part, protected by a new

    // scope.

    unsigned NewParentScope = Scopes.size();

    Scopes.push_back(GotoScope(ParentScope,

                               diag::note_protected_by_objc_synchronized,

                               diag::note_exits_objc_synchronized,

                               AS->getAtSynchronizedLoc()));

    BuildScopeInformation(AS->getSynchBody(), NewParentScope);

    return;

  }

  case Stmt::ObjCAutoreleasePoolStmtClass: {

    // Disallow jumps into the protected statement of an @autoreleasepool.

    ObjCAutoreleasePoolStmt *AS = cast<ObjCAutoreleasePoolStmt>(S);

    // Recursively walk the AST for the @autoreleasepool part, protected by a

    // new scope.

    unsigned NewParentScope = Scopes.size();

    Scopes.push_back(GotoScope(ParentScope,

                               diag::note_protected_by_objc_autoreleasepool,

                               diag::note_exits_objc_autoreleasepool,

                               AS->getAtLoc()));

    BuildScopeInformation(AS->getSubStmt(), NewParentScope);

    return;

  }

  case Stmt::ExprWithCleanupsClass: {

    // Disallow jumps past full-expressions that use blocks with

    // non-trivial cleanups of their captures.  This is theoretically

    // implementable but a lot of work which we haven't felt up to doing.

    ExprWithCleanups *EWC = cast<ExprWithCleanups>(S);

    for (unsigned i = 0, e = EWC->getNumObjects(); i != e; ++i) {

      if (auto *BDecl = EWC->getObject(i).dyn_cast<BlockDecl *>())

        for (const auto &CI : BDecl->captures()) {

          VarDecl *variable = CI.getVariable();

          BuildScopeInformation(variable, BDecl, origParentScope);

        }

      else if (auto *CLE = EWC->getObject(i).dyn_cast<CompoundLiteralExpr *>())

        BuildScopeInformation(CLE, origParentScope);

      else

        llvm_unreachable("unexpected cleanup object type");

    }

    break;

  }

  case Stmt::MaterializeTemporaryExprClass: {

    // Disallow jumps out of scopes containing temporaries lifetime-extended to

    // automatic storage duration.

    MaterializeTemporaryExpr *MTE = cast<MaterializeTemporaryExpr>(S);

    if (MTE->getStorageDuration() == SD_Automatic) {

      SmallVector<const Expr *, 4> CommaLHS;

      SmallVector<SubobjectAdjustment, 4> Adjustments;

      const Expr *ExtendedObject =

          MTE->getSubExpr()->skipRValueSubobjectAdjustments(CommaLHS,

                                                            Adjustments);

      if (ExtendedObject->getType().isDestructedType()) {

        Scopes.push_back(GotoScope(ParentScope, 0,

                                   diag::note_exits_temporary_dtor,

                                   ExtendedObject->getExprLoc()));

        origParentScope = Scopes.size()-1;

      }

    }

    break;

  }

  case Stmt::CaseStmtClass:

  case Stmt::DefaultStmtClass:

  case Stmt::LabelStmtClass:

    LabelAndGotoScopes[S] = ParentScope;

    break;

  case Stmt::AttributedStmtClass: {

    AttributedStmt *AS = cast<AttributedStmt>(S);

    if (GetMustTailAttr(AS)) {

      LabelAndGotoScopes[AS] = ParentScope;

      MustTailStmts.push_back(AS);

    }

    break;

  }

  default:

    if (auto *ED = dyn_cast<OMPExecutableDirective>(S)) {

      if (!ED->isStandaloneDirective()) {

        unsigned NewParentScope = Scopes.size();

        Scopes.emplace_back(ParentScope,

                            diag::note_omp_protected_structured_block,

                            diag::note_omp_exits_structured_block,

                            ED->getStructuredBlock()->getBeginLoc());

        BuildScopeInformation(ED->getStructuredBlock(), NewParentScope);

        return;

      }

    }

    break;

  }

  for (Stmt *SubStmt : S->children()) {

    if (!SubStmt)

        continue;

    if (StmtsToSkip) {

      --StmtsToSkip;

      continue;

    }

    // Cases, labels, and defaults aren't "scope parents".  It's also

    // important to handle these iteratively instead of recursively in

    // order to avoid blowing out the stack.

    while (true) {

      Stmt *Next;

      if (SwitchCase *SC = dyn_cast<SwitchCase>(SubStmt))

        Next = SC->getSubStmt();

      else if (LabelStmt *LS = dyn_cast<LabelStmt>(SubStmt))

        Next = LS->getSubStmt();

      else

        break;

      LabelAndGotoScopes[SubStmt] = ParentScope;

      SubStmt = Next;

    }

    // Recursively walk the AST.

    BuildScopeInformation(SubStmt, ParentScope);

  }

}

/// VerifyJumps - Verify each element of the Jumps array to see if they are

/// valid, emitting diagnostics if not.

void JumpScopeChecker::VerifyJumps() {

  while (!Jumps.empty()) {

    Stmt *Jump = Jumps.pop_back_val();

    // With a goto,

    if (GotoStmt *GS = dyn_cast<GotoStmt>(Jump)) {

      // The label may not have a statement if it's coming from inline MS ASM.

      if (GS->getLabel()->getStmt()) {

        CheckJump(GS, GS->getLabel()->getStmt(), GS->getGotoLoc(),

                  diag::err_goto_into_protected_scope,

                  diag::ext_goto_into_protected_scope,

                  diag::warn_cxx98_compat_goto_into_protected_scope);

      }

      CheckGotoStmt(GS);

      continue;

    }

    // If an asm goto jumps to a different scope, things like destructors or

    // initializers might not be run which may be suprising to users. Perhaps

    // this behavior can be changed in the future, but today Clang will not

    // generate such code. Produce a diagnostic instead. See also the

    // discussion here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110728.

    if (auto *G = dyn_cast<GCCAsmStmt>(Jump)) {

      for (AddrLabelExpr *L : G->labels()) {

        LabelDecl *LD = L->getLabel();

        unsigned JumpScope = LabelAndGotoScopes[G];

        unsigned TargetScope = LabelAndGotoScopes[LD->getStmt()];

        if (JumpScope != TargetScope)

          DiagnoseIndirectOrAsmJump(G, JumpScope, LD, TargetScope);

      }

      continue;

    }

    // We only get indirect gotos here when they have a constant target.

    if (IndirectGotoStmt *IGS = dyn_cast<IndirectGotoStmt>(Jump)) {

      LabelDecl *Target = IGS->getConstantTarget();

      CheckJump(IGS, Target->getStmt(), IGS->getGotoLoc(),

                diag::err_goto_into_protected_scope,

                diag::ext_goto_into_protected_scope,

                diag::warn_cxx98_compat_goto_into_protected_scope);

      continue;

    }

    SwitchStmt *SS = cast<SwitchStmt>(Jump);

    for (SwitchCase *SC = SS->getSwitchCaseList(); SC;

         SC = SC->getNextSwitchCase()) {

      if (CHECK_PERMISSIVE(!LabelAndGotoScopes.count(SC)))

        continue;

      SourceLocation Loc;

      if (CaseStmt *CS = dyn_cast<CaseStmt>(SC))

        Loc = CS->getBeginLoc();

      else if (DefaultStmt *DS = dyn_cast<DefaultStmt>(SC))

        Loc = DS->getBeginLoc();

      else

        Loc = SC->getBeginLoc();

      CheckJump(SS, SC, Loc, diag::err_switch_into_protected_scope, 0,

                diag::warn_cxx98_compat_switch_into_protected_scope);

    }

  }

}

/// VerifyIndirectJumps - Verify whether any possible indirect goto jump might

/// cross a protection boundary.  Unlike direct jumps, indirect goto jumps

/// count cleanups as protection boundaries: since there's no way to know where

/// the jump is going, we can't implicitly run the right cleanups the way we

/// can with direct jumps.  Thus, an indirect/asm jump is "trivial" if it

/// bypasses no initializations and no teardowns.  More formally, an

/// indirect/asm jump from A to B is trivial if the path out from A to DCA(A,B)

/// is trivial and the path in from DCA(A,B) to B is trivial, where DCA(A,B) is

/// the deepest common ancestor of A and B.  Jump-triviality is transitive but

/// asymmetric.

///

/// A path in is trivial if none of the entered scopes have an InDiag.

/// A path out is trivial is none of the exited scopes have an OutDiag.

///

/// Under these definitions, this function checks that the indirect

/// jump between A and B is trivial for every indirect goto statement A

/// and every label B whose address was taken in the function.

void JumpScopeChecker::VerifyIndirectJumps() {

  if (IndirectJumps.empty())

    return;

  // If there aren't any address-of-label expressions in this function,

  // complain about the first indirect goto.

  if (IndirectJumpTargets.empty()) {

    S.Diag(IndirectJumps[0]->getBeginLoc(),

           diag::err_indirect_goto_without_addrlabel);

    return;

  }

  // Collect a single representative of every scope containing an indirect

  // goto.  For most code bases, this substantially cuts down on the number of

  // jump sites we'll have to consider later.

  using JumpScope = std::pair<unsigned, Stmt *>;

  SmallVector<JumpScope, 32> JumpScopes;

  {

    llvm::DenseMap<unsigned, Stmt*> JumpScopesMap;

    for (Stmt *IG : IndirectJumps) {

      if (CHECK_PERMISSIVE(!LabelAndGotoScopes.count(IG)))

        continue;

      unsigned IGScope = LabelAndGotoScopes[IG];

      if (!JumpScopesMap.contains(IGScope))

        JumpScopesMap[IGScope] = IG;

    }

    JumpScopes.reserve(JumpScopesMap.size());

    for (auto &Pair : JumpScopesMap)

      JumpScopes.emplace_back(Pair);

  }

  // Collect a single representative of every scope containing a

  // label whose address was taken somewhere in the function.

  // For most code bases, there will be only one such scope.

  llvm::DenseMap<unsigned, LabelDecl*> TargetScopes;

  for (LabelDecl *TheLabel : IndirectJumpTargets) {

    if (CHECK_PERMISSIVE(!LabelAndGotoScopes.count(TheLabel->getStmt())))

      continue;

    unsigned LabelScope = LabelAndGotoScopes[TheLabel->getStmt()];

    if (!TargetScopes.contains(LabelScope))

      TargetScopes[LabelScope] = TheLabel;

  }

  // For each target scope, make sure it's trivially reachable from

  // every scope containing a jump site.

  //

  // A path between scopes always consists of exitting zero or more

  // scopes, then entering zero or more scopes.  We build a set of

  // of scopes S from which the target scope can be trivially

  // entered, then verify that every jump scope can be trivially

  // exitted to reach a scope in S.

  llvm::BitVector Reachable(Scopes.size(), false);

  for (auto [TargetScope, TargetLabel] : TargetScopes) {

    Reachable.reset();

    // Mark all the enclosing scopes from which you can safely jump

    // into the target scope.  'Min' will end up being the index of

    // the shallowest such scope.

    unsigned Min = TargetScope;

    while (true) {

      Reachable.set(Min);

      // Don't go beyond the outermost scope.

      if (Min == 0) break;

      // Stop if we can't trivially enter the current scope.

      if (Scopes[Min].InDiag) break;

      Min = Scopes[Min].ParentScope;

    }

    // Walk through all the jump sites, checking that they can trivially

    // reach this label scope.

    for (auto [JumpScope, JumpStmt] : JumpScopes) {

      unsigned Scope = JumpScope;

      // Walk out the "scope chain" for this scope, looking for a scope

      // we've marked reachable.  For well-formed code this amortizes

      // to O(JumpScopes.size() / Scopes.size()):  we only iterate

      // when we see something unmarked, and in well-formed code we

      // mark everything we iterate past.

      bool IsReachable = false;

      while (true) {

        if (Reachable.test(Scope)) {

          // If we find something reachable, mark all the scopes we just

          // walked through as reachable.

          for (unsigned S = JumpScope; S != Scope; S = Scopes[S].ParentScope)

            Reachable.set(S);

          IsReachable = true;

          break;

        }

        // Don't walk out if we've reached the top-level scope or we've

        // gotten shallower than the shallowest reachable scope.

        if (Scope == 0 || Scope < Min) break;

        // Don't walk out through an out-diagnostic.

        if (Scopes[Scope].OutDiag) break;

        Scope = Scopes[Scope].ParentScope;

      }

      // Only diagnose if we didn't find something.

      if (IsReachable) continue;

      DiagnoseIndirectOrAsmJump(JumpStmt, JumpScope, TargetLabel, TargetScope);

    }

  }

}

/// Return true if a particular error+note combination must be downgraded to a

/// warning in Microsoft mode.

static bool IsMicrosoftJumpWarning(unsigned JumpDiag, unsigned InDiagNote) {

  return (JumpDiag == diag::err_goto_into_protected_scope &&

         (InDiagNote == diag::note_protected_by_variable_init ||

          InDiagNote == diag::note_protected_by_variable_nontriv_destructor));

}

/// Return true if a particular note should be downgraded to a compatibility

/// warning in C++11 mode.

static bool IsCXX98CompatWarning(Sema &S, unsigned InDiagNote) {

  return S.getLangOpts().CPlusPlus11 &&

         InDiagNote == diag::note_protected_by_variable_non_pod;

}

/// Produce primary diagnostic for an indirect jump statement.

static void DiagnoseIndirectOrAsmJumpStmt(Sema &S, Stmt *Jump,

                                          LabelDecl *Target, bool &Diagnosed) {

  if (Diagnosed)

    return;

  bool IsAsmGoto = isa<GCCAsmStmt>(Jump);

  S.Diag(Jump->getBeginLoc(), diag::err_indirect_goto_in_protected_scope)

      << IsAsmGoto;

  S.Diag(Target->getStmt()->getIdentLoc(), diag::note_indirect_goto_target)

      << IsAsmGoto;

  Diagnosed = true;

}

/// Produce note diagnostics for a jump into a protected scope.

void JumpScopeChecker::NoteJumpIntoScopes(ArrayRef<unsigned> ToScopes) {

  if (CHECK_PERMISSIVE(ToScopes.empty()))

    return;

  for (unsigned I = 0, E = ToScopes.size(); I != E; ++I)

    if (Scopes[ToScopes[I]].InDiag)

      S.Diag(Scopes[ToScopes[I]].Loc, Scopes[ToScopes[I]].InDiag);

}

/// Diagnose an indirect jump which is known to cross scopes.

void JumpScopeChecker::DiagnoseIndirectOrAsmJump(Stmt *Jump, unsigned JumpScope,

                                                 LabelDecl *Target,

                                                 unsigned TargetScope) {

  if (CHECK_PERMISSIVE(JumpScope == TargetScope))

    return;

  unsigned Common = GetDeepestCommonScope(JumpScope, TargetScope);

  bool Diagnosed = false;

  // Walk out the scope chain until we reach the common ancestor.

  for (unsigned I = JumpScope; I != Common; I = Scopes[I].ParentScope)

    if (Scopes[I].OutDiag) {

      DiagnoseIndirectOrAsmJumpStmt(S, Jump, Target, Diagnosed);

      S.Diag(Scopes[I].Loc, Scopes[I].OutDiag);

    }

  SmallVector<unsigned, 10> ToScopesCXX98Compat;

  // Now walk into the scopes containing the label whose address was taken.

  for (unsigned I = TargetScope; I != Common; I = Scopes[I].ParentScope)

    if (IsCXX98CompatWarning(S, Scopes[I].InDiag))

      ToScopesCXX98Compat.push_back(I);

    else if (Scopes[I].InDiag) {

      DiagnoseIndirectOrAsmJumpStmt(S, Jump, Target, Diagnosed);

      S.Diag(Scopes[I].Loc, Scopes[I].InDiag);

    }

  // Diagnose this jump if it would be ill-formed in C++98.

  if (!Diagnosed && !ToScopesCXX98Compat.empty()) {

    bool IsAsmGoto = isa<GCCAsmStmt>(Jump);

    S.Diag(Jump->getBeginLoc(),

           diag::warn_cxx98_compat_indirect_goto_in_protected_scope)

        << IsAsmGoto;