lib/Sema/AnalysisBasedWarnings.cpp

//=- AnalysisBasedWarnings.cpp - Sema warnings based on libAnalysis -*- 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 defines analysis_warnings::[Policy,Executor].
// Together they are used by Sema to issue warnings based on inexpensive
// static analysis algorithms in libAnalysis.
//
//===----------------------------------------------------------------------===//

#include "clang/Sema/AnalysisBasedWarnings.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/EvaluatedExprVisitor.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ParentMap.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/StmtCXX.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/Analysis/Analyses/CFGReachabilityAnalysis.h"
#include "clang/Analysis/Analyses/Consumed.h"
#include "clang/Analysis/Analyses/ReachableCode.h"
#include "clang/Analysis/Analyses/ThreadSafety.h"
#include "clang/Analysis/Analyses/UninitializedValues.h"
#include "clang/Analysis/AnalysisDeclContext.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/CFGStmtMap.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/ScopeInfo.h"
#include "clang/Sema/SemaInternal.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Casting.h"
#include <algorithm>
#include <deque>
#include <iterator>

using namespace clang;

//===----------------------------------------------------------------------===//
// Unreachable code analysis.
//===----------------------------------------------------------------------===//

namespace {
  class UnreachableCodeHandler : public reachable_code::Callback {
    Sema &S;
    SourceRange PreviousSilenceableCondVal;

  public:
    UnreachableCodeHandler(Sema &s) : S(s) {}

    void HandleUnreachable(reachable_code::UnreachableKind UK,
                           SourceLocation L,
                           SourceRange SilenceableCondVal,
                           SourceRange R1,
                           SourceRange R2) override {
      // Avoid reporting multiple unreachable code diagnostics that are
      // triggered by the same conditional value.
      if (PreviousSilenceableCondVal.isValid() &&
          SilenceableCondVal.isValid() &&
          PreviousSilenceableCondVal == SilenceableCondVal)
        return;
      PreviousSilenceableCondVal = SilenceableCondVal;

      unsigned diag = diag::warn_unreachable;
      switch (UK) {
        case reachable_code::UK_Break:
          diag = diag::warn_unreachable_break;
          break;
        case reachable_code::UK_Return:
          diag = diag::warn_unreachable_return;
          break;
        case reachable_code::UK_Loop_Increment:
          diag = diag::warn_unreachable_loop_increment;
          break;
        case reachable_code::UK_Other:
          break;
      }

      S.Diag(L, diag) << R1 << R2;

      SourceLocation Open = SilenceableCondVal.getBegin();
      if (Open.isValid()) {
        SourceLocation Close = SilenceableCondVal.getEnd();
        Close = S.getLocForEndOfToken(Close);
        if (Close.isValid()) {
          S.Diag(Open, diag::note_unreachable_silence)
            << FixItHint::CreateInsertion(Open, "/* DISABLES CODE */ (")
            << FixItHint::CreateInsertion(Close, ")");
        }
      }
    }
  };
} // anonymous namespace

/// CheckUnreachable - Check for unreachable code.
static void CheckUnreachable(Sema &S, AnalysisDeclContext &AC) {
  // As a heuristic prune all diagnostics not in the main file.  Currently
  // the majority of warnings in headers are false positives.  These
  // are largely caused by configuration state, e.g. preprocessor
  // defined code, etc.
  //
  // Note that this is also a performance optimization.  Analyzing
  // headers many times can be expensive.
  if (!S.getSourceManager().isInMainFile(AC.getDecl()->getBeginLoc()))
    return;

  UnreachableCodeHandler UC(S);
  reachable_code::FindUnreachableCode(AC, S.getPreprocessor(), UC);
}

namespace {
/// Warn on logical operator errors in CFGBuilder
class LogicalErrorHandler : public CFGCallback {
  Sema &S;

public:
  LogicalErrorHandler(Sema &S) : CFGCallback(), S(S) {}

  static bool HasMacroID(const Expr *E) {
    if (E->getExprLoc().isMacroID())
      return true;

    // Recurse to children.
    for (const Stmt *SubStmt : E->children())
      if (const Expr *SubExpr = dyn_cast_or_null<Expr>(SubStmt))
        if (HasMacroID(SubExpr))
          return true;

    return false;
  }

  void compareAlwaysTrue(const BinaryOperator *B, bool isAlwaysTrue) override {
    if (HasMacroID(B))
      return;

    SourceRange DiagRange = B->getSourceRange();
    S.Diag(B->getExprLoc(), diag::warn_tautological_overlap_comparison)
        << DiagRange << isAlwaysTrue;
  }

  void compareBitwiseEquality(const BinaryOperator *B,
                              bool isAlwaysTrue) override {
    if (HasMacroID(B))
      return;

    SourceRange DiagRange = B->getSourceRange();
    S.Diag(B->getExprLoc(), diag::warn_comparison_bitwise_always)
        << DiagRange << isAlwaysTrue;
  }
};
} // anonymous namespace

//===----------------------------------------------------------------------===//
// Check for infinite self-recursion in functions
//===----------------------------------------------------------------------===//

// Returns true if the function is called anywhere within the CFGBlock.
// For member functions, the additional condition of being call from the
// this pointer is required.
static bool hasRecursiveCallInPath(const FunctionDecl *FD, CFGBlock &Block) {
  // Process all the Stmt's in this block to find any calls to FD.
  for (const auto &B : Block) {
    if (B.getKind() != CFGElement::Statement)
      continue;

    const CallExpr *CE = dyn_cast<CallExpr>(B.getAs<CFGStmt>()->getStmt());
    if (!CE || !CE->getCalleeDecl() ||
        CE->getCalleeDecl()->getCanonicalDecl() != FD)
      continue;

    // Skip function calls which are qualified with a templated class.
    if (const DeclRefExpr *DRE =
            dyn_cast<DeclRefExpr>(CE->getCallee()->IgnoreParenImpCasts())) {
      if (NestedNameSpecifier *NNS = DRE->getQualifier()) {
        if (NNS->getKind() == NestedNameSpecifier::TypeSpec &&
            isa<TemplateSpecializationType>(NNS->getAsType())) {
          continue;
        }
      }
    }

    const CXXMemberCallExpr *MCE = dyn_cast<CXXMemberCallExpr>(CE);
    if (!MCE || isa<CXXThisExpr>(MCE->getImplicitObjectArgument()) ||
        !MCE->getMethodDecl()->isVirtual())
      return true;
  }
  return false;
}

// Returns true if every path from the entry block passes through a call to FD.
static bool checkForRecursiveFunctionCall(const FunctionDecl *FD, CFG *cfg) {
  llvm::SmallPtrSet<CFGBlock *, 16> Visited;
  llvm::SmallVector<CFGBlock *, 16> WorkList;
  // Keep track of whether we found at least one recursive path.
  bool foundRecursion = false;

  const unsigned ExitID = cfg->getExit().getBlockID();

  // Seed the work list with the entry block.
  WorkList.push_back(&cfg->getEntry());

  while (!WorkList.empty()) {
    CFGBlock *Block = WorkList.pop_back_val();

    for (auto I = Block->succ_begin(), E = Block->succ_end(); I != E; ++I) {
      if (CFGBlock *SuccBlock = *I) {
        if (!Visited.insert(SuccBlock).second)
          continue;

        // Found a path to the exit node without a recursive call.
        if (ExitID == SuccBlock->getBlockID())
          return false;

        // If the successor block contains a recursive call, end analysis there.
        if (hasRecursiveCallInPath(FD, *SuccBlock)) {
          foundRecursion = true;
          continue;
        }

        WorkList.push_back(SuccBlock);
      }
    }
  }
  return foundRecursion;
}

static void checkRecursiveFunction(Sema &S, const FunctionDecl *FD,
                                   const Stmt *Body, AnalysisDeclContext &AC) {
  FD = FD->getCanonicalDecl();

  // Only run on non-templated functions and non-templated members of
  // templated classes.
  if (FD->getTemplatedKind() != FunctionDecl::TK_NonTemplate &&
      FD->getTemplatedKind() != FunctionDecl::TK_MemberSpecialization)
    return;

  CFG *cfg = AC.getCFG();
  if (!cfg) return;

  // If the exit block is unreachable, skip processing the function.
  if (cfg->getExit().pred_empty())
    return;

  // Emit diagnostic if a recursive function call is detected for all paths.
  if (checkForRecursiveFunctionCall(FD, cfg))
    S.Diag(Body->getBeginLoc(), diag::warn_infinite_recursive_function);
}

//===----------------------------------------------------------------------===//
// Check for throw in a non-throwing function.
//===----------------------------------------------------------------------===//

/// Determine whether an exception thrown by E, unwinding from ThrowBlock,
/// can reach ExitBlock.
static bool throwEscapes(Sema &S, const CXXThrowExpr *E, CFGBlock &ThrowBlock,
                         CFG *Body) {
  SmallVector<CFGBlock *, 16> Stack;
  llvm::BitVector Queued(Body->getNumBlockIDs());

  Stack.push_back(&ThrowBlock);
  Queued[ThrowBlock.getBlockID()] = true;

  while (!Stack.empty()) {
    CFGBlock &UnwindBlock = *Stack.back();
    Stack.pop_back();

    for (auto &Succ : UnwindBlock.succs()) {
      if (!Succ.isReachable() || Queued[Succ->getBlockID()])
        continue;

      if (Succ->getBlockID() == Body->getExit().getBlockID())
        return true;

      if (auto *Catch =
              dyn_cast_or_null<CXXCatchStmt>(Succ->getLabel())) {
        QualType Caught = Catch->getCaughtType();
        if (Caught.isNull() || // catch (...) catches everything
            !E->getSubExpr() || // throw; is considered cuaght by any handler
            S.handlerCanCatch(Caught, E->getSubExpr()->getType()))
          // Exception doesn't escape via this path.
          break;
      } else {
        Stack.push_back(Succ);
        Queued[Succ->getBlockID()] = true;
      }
    }
  }

  return false;
}

static void visitReachableThrows(
    CFG *BodyCFG,
    llvm::function_ref<void(const CXXThrowExpr *, CFGBlock &)> Visit) {
  llvm::BitVector Reachable(BodyCFG->getNumBlockIDs());
  clang::reachable_code::ScanReachableFromBlock(&BodyCFG->getEntry(), Reachable);
  for (CFGBlock *B : *BodyCFG) {
    if (!Reachable[B->getBlockID()])
      continue;
    for (CFGElement &E : *B) {
      Optional<CFGStmt> S = E.getAs<CFGStmt>();
      if (!S)
        continue;
      if (auto *Throw = dyn_cast<CXXThrowExpr>(S->getStmt()))
        Visit(Throw, *B);
    }
  }
}

static void EmitDiagForCXXThrowInNonThrowingFunc(Sema &S, SourceLocation OpLoc,
                                                 const FunctionDecl *FD) {
  if (!S.getSourceManager().isInSystemHeader(OpLoc) &&
      FD->getTypeSourceInfo()) {
    S.Diag(OpLoc, diag::warn_throw_in_noexcept_func) << FD;
    if (S.getLangOpts().CPlusPlus11 &&
        (isa<CXXDestructorDecl>(FD) ||
         FD->getDeclName().getCXXOverloadedOperator() == OO_Delete ||
         FD->getDeclName().getCXXOverloadedOperator() == OO_Array_Delete)) {
      if (const auto *Ty = FD->getTypeSourceInfo()->getType()->
                                         getAs<FunctionProtoType>())
        S.Diag(FD->getLocation(), diag::note_throw_in_dtor)
            << !isa<CXXDestructorDecl>(FD) << !Ty->hasExceptionSpec()
            << FD->getExceptionSpecSourceRange();
    } else
      S.Diag(FD->getLocation(), diag::note_throw_in_function)
          << FD->getExceptionSpecSourceRange();
  }
}

static void checkThrowInNonThrowingFunc(Sema &S, const FunctionDecl *FD,
                                        AnalysisDeclContext &AC) {
  CFG *BodyCFG = AC.getCFG();
  if (!BodyCFG)
    return;
  if (BodyCFG->getExit().pred_empty())
    return;
  visitReachableThrows(BodyCFG, [&](const CXXThrowExpr *Throw, CFGBlock &Block) {
    if (throwEscapes(S, Throw, Block, BodyCFG))
      EmitDiagForCXXThrowInNonThrowingFunc(S, Throw->getThrowLoc(), FD);
  });
}

static bool isNoexcept(const FunctionDecl *FD) {
  const auto *FPT = FD->getType()->castAs<FunctionProtoType>();
  if (FPT->isNothrow() || FD->hasAttr<NoThrowAttr>())
    return true;
  return false;
}

//===----------------------------------------------------------------------===//
// Check for missing return value.
//===----------------------------------------------------------------------===//

enum ControlFlowKind {
  UnknownFallThrough,
  NeverFallThrough,
  MaybeFallThrough,
  AlwaysFallThrough,
  NeverFallThroughOrReturn
};

/// CheckFallThrough - Check that we don't fall off the end of a
/// Statement that should return a value.
///
/// \returns AlwaysFallThrough iff we always fall off the end of the statement,
/// MaybeFallThrough iff we might or might not fall off the end,
/// NeverFallThroughOrReturn iff we never fall off the end of the statement or
/// return.  We assume NeverFallThrough iff we never fall off the end of the
/// statement but we may return.  We assume that functions not marked noreturn
/// will return.
static ControlFlowKind CheckFallThrough(AnalysisDeclContext &AC) {
  CFG *cfg = AC.getCFG();
  if (!cfg) return UnknownFallThrough;

  // The CFG leaves in dead things, and we don't want the dead code paths to
  // confuse us, so we mark all live things first.
  llvm::BitVector live(cfg->getNumBlockIDs());
  unsigned count = reachable_code::ScanReachableFromBlock(&cfg->getEntry(),
                                                          live);

  bool AddEHEdges = AC.getAddEHEdges();
  if (!AddEHEdges && count != cfg->getNumBlockIDs())
    // When there are things remaining dead, and we didn't add EH edges
    // from CallExprs to the catch clauses, we have to go back and
    // mark them as live.
    for (const auto *B : *cfg) {
      if (!live[B->getBlockID()]) {
        if (B->pred_begin() == B->pred_end()) {
          const Stmt *Term = B->getTerminatorStmt();
          if (Term && isa<CXXTryStmt>(Term))
            // When not adding EH edges from calls, catch clauses
            // can otherwise seem dead.  Avoid noting them as dead.
            count += reachable_code::ScanReachableFromBlock(B, live);
          continue;
        }
      }
    }

  // Now we know what is live, we check the live precessors of the exit block
  // and look for fall through paths, being careful to ignore normal returns,
  // and exceptional paths.
  bool HasLiveReturn = false;
  bool HasFakeEdge = false;
  bool HasPlainEdge = false;
  bool HasAbnormalEdge = false;

  // Ignore default cases that aren't likely to be reachable because all
  // enums in a switch(X) have explicit case statements.
  CFGBlock::FilterOptions FO;
  FO.IgnoreDefaultsWithCoveredEnums = 1;

  for (CFGBlock::filtered_pred_iterator I =
           cfg->getExit().filtered_pred_start_end(FO);
       I.hasMore(); ++I) {
    const CFGBlock &B = **I;
    if (!live[B.getBlockID()])
      continue;

    // Skip blocks which contain an element marked as no-return. They don't
    // represent actually viable edges into the exit block, so mark them as
    // abnormal.
    if (B.hasNoReturnElement()) {
      HasAbnormalEdge = true;
      continue;
    }

    // Destructors can appear after the 'return' in the CFG.  This is
    // normal.  We need to look pass the destructors for the return
    // statement (if it exists).
    CFGBlock::const_reverse_iterator ri = B.rbegin(), re = B.rend();

    for ( ; ri != re ; ++ri)
      if (ri->getAs<CFGStmt>())
        break;

    // No more CFGElements in the block?
    if (ri == re) {
      const Stmt *Term = B.getTerminatorStmt();
      if (Term && isa<CXXTryStmt>(Term)) {
        HasAbnormalEdge = true;
        continue;
      }
      // A labeled empty statement, or the entry block...
      HasPlainEdge = true;
      continue;
    }

    CFGStmt CS = ri->castAs<CFGStmt>();
    const Stmt *S = CS.getStmt();
    if (isa<ReturnStmt>(S) || isa<CoreturnStmt>(S)) {
      HasLiveReturn = true;
      continue;
    }
    if (isa<ObjCAtThrowStmt>(S)) {
      HasFakeEdge = true;
      continue;
    }
    if (isa<CXXThrowExpr>(S)) {
      HasFakeEdge = true;
      continue;
    }
    if (isa<MSAsmStmt>(S)) {
      // TODO: Verify this is correct.
      HasFakeEdge = true;
      HasLiveReturn = true;
      continue;
    }
    if (isa<CXXTryStmt>(S)) {
      HasAbnormalEdge = true;
      continue;
    }
    if (std::find(B.succ_begin(), B.succ_end(), &cfg->getExit())
        == B.succ_end()) {
      HasAbnormalEdge = true;
      continue;
    }

    HasPlainEdge = true;
  }
  if (!HasPlainEdge) {
    if (HasLiveReturn)
      return NeverFallThrough;
    return NeverFallThroughOrReturn;
  }
  if (HasAbnormalEdge || HasFakeEdge || HasLiveReturn)
    return MaybeFallThrough;
  // This says AlwaysFallThrough for calls to functions that are not marked
  // noreturn, that don't return.  If people would like this warning to be more
  // accurate, such functions should be marked as noreturn.
  return AlwaysFallThrough;
}

namespace {

struct CheckFallThroughDiagnostics {
  unsigned diag_MaybeFallThrough_HasNoReturn;
  unsigned diag_MaybeFallThrough_ReturnsNonVoid;
  unsigned diag_AlwaysFallThrough_HasNoReturn;
  unsigned diag_AlwaysFallThrough_ReturnsNonVoid;
  unsigned diag_NeverFallThroughOrReturn;
  enum { Function, Block, Lambda, Coroutine } funMode;
  SourceLocation FuncLoc;

  static CheckFallThroughDiagnostics MakeForFunction(const Decl *Func) {
    CheckFallThroughDiagnostics D;
    D.FuncLoc = Func->getLocation();
    D.diag_MaybeFallThrough_HasNoReturn =
      diag::warn_falloff_noreturn_function;
    D.diag_MaybeFallThrough_ReturnsNonVoid =
      diag::warn_maybe_falloff_nonvoid_function;
    D.diag_AlwaysFallThrough_HasNoReturn =
      diag::warn_falloff_noreturn_function;
    D.diag_AlwaysFallThrough_ReturnsNonVoid =
      diag::warn_falloff_nonvoid_function;

    // Don't suggest that virtual functions be marked "noreturn", since they
    // might be overridden by non-noreturn functions.
    bool isVirtualMethod = false;
    if (const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Func))
      isVirtualMethod = Method->isVirtual();

    // Don't suggest that template instantiations be marked "noreturn"
    bool isTemplateInstantiation = false;
    if (const FunctionDecl *Function = dyn_cast<FunctionDecl>(Func))
      isTemplateInstantiation = Function->isTemplateInstantiation();

    if (!isVirtualMethod && !isTemplateInstantiation)
      D.diag_NeverFallThroughOrReturn =
        diag::warn_suggest_noreturn_function;
    else
      D.diag_NeverFallThroughOrReturn = 0;

    D.funMode = Function;
    return D;
  }

  static CheckFallThroughDiagnostics MakeForCoroutine(const Decl *Func) {
    CheckFallThroughDiagnostics D;
    D.FuncLoc = Func->getLocation();
    D.diag_MaybeFallThrough_HasNoReturn = 0;
    D.diag_MaybeFallThrough_ReturnsNonVoid =
        diag::warn_maybe_falloff_nonvoid_coroutine;
    D.diag_AlwaysFallThrough_HasNoReturn = 0;
    D.diag_AlwaysFallThrough_ReturnsNonVoid =
        diag::warn_falloff_nonvoid_coroutine;
    D.funMode = Coroutine;
    return D;
  }

  static CheckFallThroughDiagnostics MakeForBlock() {
    CheckFallThroughDiagnostics D;
    D.diag_MaybeFallThrough_HasNoReturn =
      diag::err_noreturn_block_has_return_expr;
    D.diag_MaybeFallThrough_ReturnsNonVoid =
      diag::err_maybe_falloff_nonvoid_block;
    D.diag_AlwaysFallThrough_HasNoReturn =
      diag::err_noreturn_block_has_return_expr;
    D.diag_AlwaysFallThrough_ReturnsNonVoid =
      diag::err_falloff_nonvoid_block;
    D.diag_NeverFallThroughOrReturn = 0;
    D.funMode = Block;
    return D;
  }

  static CheckFallThroughDiagnostics MakeForLambda() {
    CheckFallThroughDiagnostics D;
    D.diag_MaybeFallThrough_HasNoReturn =
      diag::err_noreturn_lambda_has_return_expr;
    D.diag_MaybeFallThrough_ReturnsNonVoid =
      diag::warn_maybe_falloff_nonvoid_lambda;
    D.diag_AlwaysFallThrough_HasNoReturn =
      diag::err_noreturn_lambda_has_return_expr;
    D.diag_AlwaysFallThrough_ReturnsNonVoid =
      diag::warn_falloff_nonvoid_lambda;
    D.diag_NeverFallThroughOrReturn = 0;
    D.funMode = Lambda;
    return D;
  }

  bool checkDiagnostics(DiagnosticsEngine &D, bool ReturnsVoid,
                        bool HasNoReturn) const {
    if (funMode == Function) {
      return (ReturnsVoid ||
              D.isIgnored(diag::warn_maybe_falloff_nonvoid_function,
                          FuncLoc)) &&
             (!HasNoReturn ||
              D.isIgnored(diag::warn_noreturn_function_has_return_expr,
                          FuncLoc)) &&
             (!ReturnsVoid ||
              D.isIgnored(diag::warn_suggest_noreturn_block, FuncLoc));
    }
    if (funMode == Coroutine) {
      return (ReturnsVoid ||
              D.isIgnored(diag::warn_maybe_falloff_nonvoid_function, FuncLoc) ||
              D.isIgnored(diag::warn_maybe_falloff_nonvoid_coroutine,
                          FuncLoc)) &&
             (!HasNoReturn);
    }
    // For blocks / lambdas.
    return ReturnsVoid && !HasNoReturn;
  }
};

} // anonymous namespace

/// CheckFallThroughForBody - Check that we don't fall off the end of a
/// function that should return a value.  Check that we don't fall off the end
/// of a noreturn function.  We assume that functions and blocks not marked
/// noreturn will return.
static void CheckFallThroughForBody(Sema &S, const Decl *D, const Stmt *Body,
                                    QualType BlockType,
                                    const CheckFallThroughDiagnostics &CD,
                                    AnalysisDeclContext &AC,
                                    sema::FunctionScopeInfo *FSI) {

  bool ReturnsVoid = false;
  bool HasNoReturn = false;
  bool IsCoroutine = FSI->isCoroutine();

  if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
    if (const auto *CBody = dyn_cast<CoroutineBodyStmt>(Body))
      ReturnsVoid = CBody->getFallthroughHandler() != nullptr;
    else
      ReturnsVoid = FD->getReturnType()->isVoidType();
    HasNoReturn = FD->isNoReturn();
  }
  else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
    ReturnsVoid = MD->getReturnType()->isVoidType();
    HasNoReturn = MD->hasAttr<NoReturnAttr>();
  }
  else if (isa<BlockDecl>(D)) {
    if (const FunctionType *FT =
          BlockType->getPointeeType()->getAs<FunctionType>()) {
      if (FT->getReturnType()->isVoidType())
        ReturnsVoid = true;
      if (FT->getNoReturnAttr())
        HasNoReturn = true;
    }
  }

  DiagnosticsEngine &Diags = S.getDiagnostics();

  // Short circuit for compilation speed.
  if (CD.checkDiagnostics(Diags, ReturnsVoid, HasNoReturn))
      return;
  SourceLocation LBrace = Body->getBeginLoc(), RBrace = Body->getEndLoc();
  auto EmitDiag = [&](SourceLocation Loc, unsigned DiagID) {
    if (IsCoroutine)
      S.Diag(Loc, DiagID) << FSI->CoroutinePromise->getType();
    else
      S.Diag(Loc, DiagID);
  };

  // cpu_dispatch functions permit empty function bodies for ICC compatibility.
  if (D->getAsFunction() && D->getAsFunction()->isCPUDispatchMultiVersion())
    return;

  // Either in a function body compound statement, or a function-try-block.
  switch (CheckFallThrough(AC)) {
    case UnknownFallThrough:
      break;

    case MaybeFallThrough:
      if (HasNoReturn)
        EmitDiag(RBrace, CD.diag_MaybeFallThrough_HasNoReturn);
      else if (!ReturnsVoid)
        EmitDiag(RBrace, CD.diag_MaybeFallThrough_ReturnsNonVoid);
      break;
    case AlwaysFallThrough:
      if (HasNoReturn)
        EmitDiag(RBrace, CD.diag_AlwaysFallThrough_HasNoReturn);
      else if (!ReturnsVoid)
        EmitDiag(RBrace, CD.diag_AlwaysFallThrough_ReturnsNonVoid);
      break;
    case NeverFallThroughOrReturn:
      if (ReturnsVoid && !HasNoReturn && CD.diag_NeverFallThroughOrReturn) {
        if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
          S.Diag(LBrace, CD.diag_NeverFallThroughOrReturn) << 0 << FD;
        } else if (const ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(D)) {
          S.Diag(LBrace, CD.diag_NeverFallThroughOrReturn) << 1 << MD;
        } else {
          S.Diag(LBrace, CD.diag_NeverFallThroughOrReturn);
        }
      }
      break;
    case NeverFallThrough:
      break;
  }
}

//===----------------------------------------------------------------------===//
// -Wuninitialized
//===----------------------------------------------------------------------===//

namespace {
/// ContainsReference - A visitor class to search for references to
/// a particular declaration (the needle) within any evaluated component of an
/// expression (recursively).
class ContainsReference : public ConstEvaluatedExprVisitor<ContainsReference> {
  bool FoundReference;
  const DeclRefExpr *Needle;

public:
  typedef ConstEvaluatedExprVisitor<ContainsReference> Inherited;

  ContainsReference(ASTContext &Context, const DeclRefExpr *Needle)
    : Inherited(Context), FoundReference(false), Needle(Needle) {}

  void VisitExpr(const Expr *E) {
    // Stop evaluating if we already have a reference.
    if (FoundReference)
      return;

    Inherited::VisitExpr(E);
  }

  void VisitDeclRefExpr(const DeclRefExpr *E) {
    if (E == Needle)
      FoundReference = true;
    else
      Inherited::VisitDeclRefExpr(E);
  }

  bool doesContainReference() const { return FoundReference; }
};
} // anonymous namespace

static bool SuggestInitializationFixit(Sema &S, const VarDecl *VD) {
  QualType VariableTy = VD->getType().getCanonicalType();
  if (VariableTy->isBlockPointerType() &&
      !VD->hasAttr<BlocksAttr>()) {
    S.Diag(VD->getLocation(), diag::note_block_var_fixit_add_initialization)
        << VD->getDeclName()
        << FixItHint::CreateInsertion(VD->getLocation(), "__block ");
    return true;
  }

  // Don't issue a fixit if there is already an initializer.
  if (VD->getInit())
    return false;

  // Don't suggest a fixit inside macros.
  if (VD->getEndLoc().isMacroID())
    return false;

  SourceLocation Loc = S.getLocForEndOfToken(VD->getEndLoc());

  // Suggest possible initialization (if any).
  std::string Init = S.getFixItZeroInitializerForType(VariableTy, Loc);
  if (Init.empty())
    return false;

  S.Diag(Loc, diag::note_var_fixit_add_initialization) << VD->getDeclName()
    << FixItHint::CreateInsertion(Loc, Init);
  return true;
}

/// Create a fixit to remove an if-like statement, on the assumption that its
/// condition is CondVal.
static void CreateIfFixit(Sema &S, const Stmt *If, const Stmt *Then,
                          const Stmt *Else, bool CondVal,
                          FixItHint &Fixit1, FixItHint &Fixit2) {
  if (CondVal) {
    // If condition is always true, remove all but the 'then'.
    Fixit1 = FixItHint::CreateRemoval(
        CharSourceRange::getCharRange(If->getBeginLoc(), Then->getBeginLoc()));
    if (Else) {
      SourceLocation ElseKwLoc = S.getLocForEndOfToken(Then->getEndLoc());
      Fixit2 =
          FixItHint::CreateRemoval(SourceRange(ElseKwLoc, Else->getEndLoc()));
    }
  } else {
    // If condition is always false, remove all but the 'else'.
    if (Else)
      Fixit1 = FixItHint::CreateRemoval(CharSourceRange::getCharRange(
          If->getBeginLoc(), Else->getBeginLoc()));
    else
      Fixit1 = FixItHint::CreateRemoval(If->getSourceRange());
  }
}

/// DiagUninitUse -- Helper function to produce a diagnostic for an
/// uninitialized use of a variable.
static void DiagUninitUse(Sema &S, const VarDecl *VD, const UninitUse &Use,
                          bool IsCapturedByBlock) {
  bool Diagnosed = false;

  switch (Use.getKind()) {
  case UninitUse::Always:
    S.Diag(Use.getUser()->getBeginLoc(), diag::warn_uninit_var)
        << VD->getDeclName() << IsCapturedByBlock
        << Use.getUser()->getSourceRange();
    return;

  case UninitUse::AfterDecl:
  case UninitUse::AfterCall:
    S.Diag(VD->getLocation(), diag::warn_sometimes_uninit_var)
      << VD->getDeclName() << IsCapturedByBlock
      << (Use.getKind() == UninitUse::AfterDecl ? 4 : 5)
      << const_cast<DeclContext*>(VD->getLexicalDeclContext())
      << VD->getSourceRange();
    S.Diag(Use.getUser()->getBeginLoc(), diag::note_uninit_var_use)
        << IsCapturedByBlock << Use.getUser()->getSourceRange();
    return;

  case UninitUse::Maybe:
  case UninitUse::Sometimes:
    // Carry on to report sometimes-uninitialized branches, if possible,
    // or a 'may be used uninitialized' diagnostic otherwise.
    break;
  }

  // Diagnose each branch which leads to a sometimes-uninitialized use.
  for (UninitUse::branch_iterator I = Use.branch_begin(), E = Use.branch_end();
       I != E; ++I) {
    assert(Use.getKind() == UninitUse::Sometimes);

    const Expr *User = Use.getUser();
    const Stmt *Term = I->Terminator;

    // Information used when building the diagnostic.
    unsigned DiagKind;
    StringRef Str;
    SourceRange Range;

    // FixIts to suppress the diagnostic by removing the dead condition.
    // For all binary terminators, branch 0 is taken if the condition is true,
    // and branch 1 is taken if the condition is false.
    int RemoveDiagKind = -1;
    const char *FixitStr =
        S.getLangOpts().CPlusPlus ? (I->Output ? "true" : "false")
                                  : (I->Output ? "1" : "0");
    FixItHint Fixit1, Fixit2;

    switch (Term ? Term->getStmtClass() : Stmt::DeclStmtClass) {
    default:
      // Don't know how to report this. Just fall back to 'may be used
      // uninitialized'. FIXME: Can this happen?
      continue;

    // "condition is true / condition is false".
    case Stmt::IfStmtClass: {
      const IfStmt *IS = cast<IfStmt>(Term);
      DiagKind = 0;
      Str = "if";
      Range = IS->getCond()->getSourceRange();
      RemoveDiagKind = 0;
      CreateIfFixit(S, IS, IS->getThen(), IS->getElse(),
                    I->Output, Fixit1, Fixit2);
      break;
    }
    case Stmt::ConditionalOperatorClass: {
      const ConditionalOperator *CO = cast<ConditionalOperator>(Term);
      DiagKind = 0;
      Str = "?:";
      Range = CO->getCond()->getSourceRange();
      RemoveDiagKind = 0;
      CreateIfFixit(S, CO, CO->getTrueExpr(), CO->getFalseExpr(),
                    I->Output, Fixit1, Fixit2);
      break;
    }
    case Stmt::BinaryOperatorClass: {
      const BinaryOperator *BO = cast<BinaryOperator>(Term);
      if (!BO->isLogicalOp())
        continue;
      DiagKind = 0;
      Str = BO->getOpcodeStr();
      Range = BO->getLHS()->getSourceRange();
      RemoveDiagKind = 0;
      if ((BO->getOpcode() == BO_LAnd && I->Output) ||
          (BO->getOpcode() == BO_LOr && !I->Output))
        // true && y -> y, false || y -> y.
        Fixit1 = FixItHint::CreateRemoval(
            SourceRange(BO->getBeginLoc(), BO->getOperatorLoc()));
      else
        // false && y -> false, true || y -> true.
        Fixit1 = FixItHint::CreateReplacement(BO->getSourceRange(), FixitStr);
      break;
    }

    // "loop is entered / loop is exited".
    case Stmt::WhileStmtClass:
      DiagKind = 1;
      Str = "while";
      Range = cast<WhileStmt>(Term)->getCond()->getSourceRange();
      RemoveDiagKind = 1;
      Fixit1 = FixItHint::CreateReplacement(Range, FixitStr);
      break;
    case Stmt::ForStmtClass:
      DiagKind = 1;
      Str = "for";
      Range = cast<ForStmt>(Term)->getCond()->getSourceRange();
      RemoveDiagKind = 1;
      if (I->Output)
        Fixit1 = FixItHint::CreateRemoval(Range);
      else
        Fixit1 = FixItHint::CreateReplacement(Range, FixitStr);
      break;
    case Stmt::CXXForRangeStmtClass:
      if (I->Output == 1) {
        // The use occurs if a range-based for loop's body never executes.
        // That may be impossible, and there's no syntactic fix for this,
        // so treat it as a 'may be uninitialized' case.
        continue;
      }
      DiagKind = 1;
      Str = "for";
      Range = cast<CXXForRangeStmt>(Term)->getRangeInit()->getSourceRange();
      break;

    // "condition is true / loop is exited".
    case Stmt::DoStmtClass:
      DiagKind = 2;
      Str = "do";
      Range = cast<DoStmt>(Term)->getCond()->getSourceRange();
      RemoveDiagKind = 1;
      Fixit1 = FixItHint::CreateReplacement(Range, FixitStr);
      break;

    // "switch case is taken".
    case Stmt::CaseStmtClass:
      DiagKind = 3;
      Str = "case";
      Range = cast<CaseStmt>(Term)->getLHS()->getSourceRange();
      break;
    case Stmt::DefaultStmtClass:
      DiagKind = 3;
      Str = "default";
      Range = cast<DefaultStmt>(Term)->getDefaultLoc();
      break;
    }

    S.Diag(Range.getBegin(), diag::warn_sometimes_uninit_var)
      << VD->getDeclName() << IsCapturedByBlock << DiagKind
      << Str << I->Output << Range;
    S.Diag(User->getBeginLoc(), diag::note_uninit_var_use)
        << IsCapturedByBlock << User->getSourceRange();
    if (RemoveDiagKind != -1)
      S.Diag(Fixit1.RemoveRange.getBegin(), diag::note_uninit_fixit_remove_cond)
        << RemoveDiagKind << Str << I->Output << Fixit1 << Fixit2;

    Diagnosed = true;
  }

  if (!Diagnosed)
    S.Diag(Use.getUser()->getBeginLoc(), diag::warn_maybe_uninit_var)
        << VD->getDeclName() << IsCapturedByBlock
        << Use.getUser()->getSourceRange();
}

/// DiagnoseUninitializedUse -- Helper function for diagnosing uses of an
/// uninitialized variable. This manages the different forms of diagnostic
/// emitted for particular types of uses. Returns true if the use was diagnosed
/// as a warning. If a particular use is one we omit warnings for, returns
/// false.
static bool DiagnoseUninitializedUse(Sema &S, const VarDecl *VD,
                                     const UninitUse &Use,
                                     bool alwaysReportSelfInit = false) {
  if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Use.getUser())) {
    // Inspect the initializer of the variable declaration which is
    // being referenced prior to its initialization. We emit
    // specialized diagnostics for self-initialization, and we
    // specifically avoid warning about self references which take the
    // form of:
    //
    //   int x = x;
    //
    // This is used to indicate to GCC that 'x' is intentionally left
    // uninitialized. Proven code paths which access 'x' in
    // an uninitialized state after this will still warn.
    if (const Expr *Initializer = VD->getInit()) {
      if (!alwaysReportSelfInit && DRE == Initializer->IgnoreParenImpCasts())
        return false;

      ContainsReference CR(S.Context, DRE);
      CR.Visit(Initializer);
      if (CR.doesContainReference()) {
        S.Diag(DRE->getBeginLoc(), diag::warn_uninit_self_reference_in_init)
            << VD->getDeclName() << VD->getLocation() << DRE->getSourceRange();
        return true;
      }
    }

    DiagUninitUse(S, VD, Use, false);
  } else {
    const BlockExpr *BE = cast<BlockExpr>(Use.getUser());
    if (VD->getType()->isBlockPointerType() && !VD->hasAttr<BlocksAttr>())
      S.Diag(BE->getBeginLoc(),
             diag::warn_uninit_byref_blockvar_captured_by_block)
          << VD->getDeclName()
          << VD->getType().getQualifiers().hasObjCLifetime();
    else
      DiagUninitUse(S, VD, Use, true);
  }

  // Report where the variable was declared when the use wasn't within
  // the initializer of that declaration & we didn't already suggest
  // an initialization fixit.
  if (!SuggestInitializationFixit(S, VD))
    S.Diag(VD->getBeginLoc(), diag::note_var_declared_here)
        << VD->getDeclName();

  return true;
}

namespace {
  class FallthroughMapper : public RecursiveASTVisitor<FallthroughMapper> {
  public:
    FallthroughMapper(Sema &S)
      : FoundSwitchStatements(false),
        S(S) {
    }

    bool foundSwitchStatements() const { return FoundSwitchStatements; }

    void markFallthroughVisited(const AttributedStmt *Stmt) {
      bool Found = FallthroughStmts.erase(Stmt);
      assert(Found);
      (void)Found;
    }

    typedef llvm::SmallPtrSet<const AttributedStmt*, 8> AttrStmts;

    const AttrStmts &getFallthroughStmts() const {
      return FallthroughStmts;
    }

    void fillReachableBlocks(CFG *Cfg) {
      assert(ReachableBlocks.empty() && "ReachableBlocks already filled");
      std::deque<const CFGBlock *> BlockQueue;

      ReachableBlocks.insert(&Cfg->getEntry());
      BlockQueue.push_back(&Cfg->getEntry());
      // Mark all case blocks reachable to avoid problems with switching on
      // constants, covered enums, etc.
      // These blocks can contain fall-through annotations, and we don't want to
      // issue a warn_fallthrough_attr_unreachable for them.
      for (const auto *B : *Cfg) {
        const Stmt *L = B->getLabel();
        if (L && isa<SwitchCase>(L) && ReachableBlocks.insert(B).second)
          BlockQueue.push_back(B);
      }

      while (!BlockQueue.empty()) {
        const CFGBlock *P = BlockQueue.front();
        BlockQueue.pop_front();
        for (CFGBlock::const_succ_iterator I = P->succ_begin(),
                                           E = P->succ_end();
             I != E; ++I) {
          if (*I && ReachableBlocks.insert(*I).second)
            BlockQueue.push_back(*I);
        }
      }
    }

    bool checkFallThroughIntoBlock(const CFGBlock &B, int &AnnotatedCnt,
                                   bool IsTemplateInstantiation) {
      assert(!ReachableBlocks.empty() && "ReachableBlocks empty");

      int UnannotatedCnt = 0;
      AnnotatedCnt = 0;

      std::deque<const CFGBlock*> BlockQueue(B.pred_begin(), B.pred_end());
      while (!BlockQueue.empty()) {
        const CFGBlock *P = BlockQueue.front();
        BlockQueue.pop_front();
        if (!P) continue;

        const Stmt *Term = P->getTerminatorStmt();
        if (Term && isa<SwitchStmt>(Term))
          continue; // Switch statement, good.

        const SwitchCase *SW = dyn_cast_or_null<SwitchCase>(P->getLabel());
        if (SW && SW->getSubStmt() == B.getLabel() && P->begin() == P->end())
          continue; // Previous case label has no statements, good.

        const LabelStmt *L = dyn_cast_or_null<LabelStmt>(P->getLabel());
        if (L && L->getSubStmt() == B.getLabel() && P->begin() == P->end())
          continue; // Case label is preceded with a normal label, good.

        if (!ReachableBlocks.count(P)) {
          for (CFGBlock::const_reverse_iterator ElemIt = P->rbegin(),
                                                ElemEnd = P->rend();
               ElemIt != ElemEnd; ++ElemIt) {
            if (Optional<CFGStmt> CS = ElemIt->getAs<CFGStmt>()) {
              if (const AttributedStmt *AS = asFallThroughAttr(CS->getStmt())) {
                // Don't issue a warning for an unreachable fallthrough
                // attribute in template instantiations as it may not be
                // unreachable in all instantiations of the template.
                if (!IsTemplateInstantiation)
                  S.Diag(AS->getBeginLoc(),
                         diag::warn_fallthrough_attr_unreachable);
                markFallthroughVisited(AS);
                ++AnnotatedCnt;
                break;
              }
              // Don't care about other unreachable statements.
            }
          }
          // If there are no unreachable statements, this may be a special
          // case in CFG:
          // case X: {
          //    A a;  // A has a destructor.
          //    break;
          // }
          // // <<<< This place is represented by a 'hanging' CFG block.
          // case Y:
          continue;
        }

        const Stmt *LastStmt = getLastStmt(*P);
        if (const AttributedStmt *AS = asFallThroughAttr(LastStmt)) {
          markFallthroughVisited(AS);
          ++AnnotatedCnt;
          continue; // Fallthrough annotation, good.
        }

        if (!LastStmt) { // This block contains no executable statements.
          // Traverse its predecessors.
          std::copy(P->pred_begin(), P->pred_end(),
                    std::back_inserter(BlockQueue));
          continue;
        }

        ++UnannotatedCnt;
      }
      return !!UnannotatedCnt;
    }

    // RecursiveASTVisitor setup.
    bool shouldWalkTypesOfTypeLocs() const { return false; }

    bool VisitAttributedStmt(AttributedStmt *S) {
      if (asFallThroughAttr(S))
        FallthroughStmts.insert(S);
      return true;
    }

    bool VisitSwitchStmt(SwitchStmt *S) {
      FoundSwitchStatements = true;
      return true;
    }

    // We don't want to traverse local type declarations. We analyze their
    // methods separately.
    bool TraverseDecl(Decl *D) { return true; }

    // We analyze lambda bodies separately. Skip them here.
    bool TraverseLambdaExpr(LambdaExpr *LE) {
      // Traverse the captures, but not the body.
      for (const auto &C : zip(LE->captures(), LE->capture_inits()))
        TraverseLambdaCapture(LE, &std::get<0>(C), std::get<1>(C));
      return true;
    }

  private:

    static const AttributedStmt *asFallThroughAttr(const Stmt *S) {
      if (const AttributedStmt *AS = dyn_cast_or_null<AttributedStmt>(S)) {
        if (hasSpecificAttr<FallThroughAttr>(AS->getAttrs()))
          return AS;
      }
      return nullptr;
    }

    static const Stmt *getLastStmt(const CFGBlock &B) {
      if (const Stmt *Term = B.getTerminatorStmt())
        return Term;
      for (CFGBlock::const_reverse_iterator ElemIt = B.rbegin(),
                                            ElemEnd = B.rend();
                                            ElemIt != ElemEnd; ++ElemIt) {
        if (Optional<CFGStmt> CS = ElemIt->getAs<CFGStmt>())
          return CS->getStmt();
      }
      // Workaround to detect a statement thrown out by CFGBuilder:
      //   case X: {} case Y:
      //   case X: ; case Y:
      if (const SwitchCase *SW = dyn_cast_or_null<SwitchCase>(B.getLabel()))
        if (!isa<SwitchCase>(SW->getSubStmt()))
          return SW->getSubStmt();

      return nullptr;
    }

    bool FoundSwitchStatements;
    AttrStmts FallthroughStmts;
    Sema &S;
    llvm::SmallPtrSet<const CFGBlock *, 16> ReachableBlocks;
  };
} // anonymous namespace

static StringRef getFallthroughAttrSpelling(Preprocessor &PP,
                                            SourceLocation Loc) {
  TokenValue FallthroughTokens[] = {
    tok::l_square, tok::l_square,
    PP.getIdentifierInfo("fallthrough"),
    tok::r_square, tok::r_square
  };

  TokenValue ClangFallthroughTokens[] = {
    tok::l_square, tok::l_square, PP.getIdentifierInfo("clang"),
    tok::coloncolon, PP.getIdentifierInfo("fallthrough"),
    tok::r_square, tok::r_square
  };

  bool PreferClangAttr = !PP.getLangOpts().CPlusPlus17;

  StringRef MacroName;
  if (PreferClangAttr)
    MacroName = PP.getLastMacroWithSpelling(Loc, ClangFallthroughTokens);
  if (MacroName.empty())
    MacroName = PP.getLastMacroWithSpelling(Loc, FallthroughTokens);
  if (MacroName.empty() && !PreferClangAttr)
    MacroName = PP.getLastMacroWithSpelling(Loc, ClangFallthroughTokens);
  if (MacroName.empty())
    MacroName = PreferClangAttr ? "[[clang::fallthrough]]" : "[[fallthrough]]";
  return MacroName;
}

static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
                                            bool PerFunction) {
  // Only perform this analysis when using [[]] attributes. There is no good
  // workflow for this warning when not using C++11. There is no good way to
  // silence the warning (no attribute is available) unless we are using
  // [[]] attributes. One could use pragmas to silence the warning, but as a
  // general solution that is gross and not in the spirit of this warning.
  //
  // NOTE: This an intermediate solution. There are on-going discussions on
  // how to properly support this warning outside of C++11 with an annotation.
  if (!AC.getASTContext().getLangOpts().DoubleSquareBracketAttributes)
    return;

  FallthroughMapper FM(S);
  FM.TraverseStmt(AC.getBody());

  if (!FM.foundSwitchStatements())
    return;

  if (PerFunction && FM.getFallthroughStmts().empty())
    return;

  CFG *Cfg = AC.getCFG();

  if (!Cfg)
    return;

  FM.fillReachableBlocks(Cfg);

  for (const CFGBlock *B : llvm::reverse(*Cfg)) {
    const Stmt *Label = B->getLabel();

    if (!Label || !isa<SwitchCase>(Label))
      continue;

    int AnnotatedCnt;

    bool IsTemplateInstantiation = false;
    if (const FunctionDecl *Function = dyn_cast<FunctionDecl>(AC.getDecl()))
      IsTemplateInstantiation = Function->isTemplateInstantiation();
    if (!FM.checkFallThroughIntoBlock(*B, AnnotatedCnt,
                                      IsTemplateInstantiation))
      continue;

    S.Diag(Label->getBeginLoc(),
           PerFunction ? diag::warn_unannotated_fallthrough_per_function
                       : diag::warn_unannotated_fallthrough);

    if (!AnnotatedCnt) {
      SourceLocation L = Label->getBeginLoc();
      if (L.isMacroID())
        continue;
      if (S.getLangOpts().CPlusPlus11) {
        const Stmt *Term = B->getTerminatorStmt();
        // Skip empty cases.
        while (B->empty() && !Term && B->succ_size() == 1) {
          B = *B->succ_begin();
          Term = B->getTerminatorStmt();
        }
        if (!(B->empty() && Term && isa<BreakStmt>(Term))) {
          Preprocessor &PP = S.getPreprocessor();
          StringRef AnnotationSpelling = getFallthroughAttrSpelling(PP, L);
          SmallString<64> TextToInsert(AnnotationSpelling);
          TextToInsert += "; ";
          S.Diag(L, diag::note_insert_fallthrough_fixit) <<
              AnnotationSpelling <<
              FixItHint::CreateInsertion(L, TextToInsert);
        }
      }
      S.Diag(L, diag::note_insert_break_fixit) <<
        FixItHint::CreateInsertion(L, "break; ");
    }
  }

  for (const auto *F : FM.getFallthroughStmts())
    S.Diag(F->getBeginLoc(), diag::err_fallthrough_attr_invalid_placement);
}

static bool isInLoop(const ASTContext &Ctx, const ParentMap &PM,
                     const Stmt *S) {
  assert(S);

  do {
    switch (S->getStmtClass()) {
    case Stmt::ForStmtClass:
    case Stmt::WhileStmtClass:
    case Stmt::CXXForRangeStmtClass:
    case Stmt::ObjCForCollectionStmtClass:
      return true;
    case Stmt::DoStmtClass: {
      Expr::EvalResult Result;
      if (!cast<DoStmt>(S)->getCond()->EvaluateAsInt(Result, Ctx))
        return true;
      return Result.Val.getInt().getBoolValue();
    }
    default:
      break;
    }
  } while ((S = PM.getParent(S)));

  return false;
}

static void diagnoseRepeatedUseOfWeak(Sema &S,
                                      const sema::FunctionScopeInfo *CurFn,
                                      const Decl *D,
                                      const ParentMap &PM) {
  typedef sema::FunctionScopeInfo::WeakObjectProfileTy WeakObjectProfileTy;
  typedef sema::FunctionScopeInfo::WeakObjectUseMap WeakObjectUseMap;
  typedef sema::FunctionScopeInfo::WeakUseVector WeakUseVector;
  typedef std::pair<const Stmt *, WeakObjectUseMap::const_iterator>
  StmtUsesPair;

  ASTContext &Ctx = S.getASTContext();

  const WeakObjectUseMap &WeakMap = CurFn->getWeakObjectUses();

  // Extract all weak objects that are referenced more than once.
  SmallVector<StmtUsesPair, 8> UsesByStmt;
  for (WeakObjectUseMap::const_iterator I = WeakMap.begin(), E = WeakMap.end();
       I != E; ++I) {
    const WeakUseVector &Uses = I->second;

    // Find the first read of the weak object.
    WeakUseVector::const_iterator UI = Uses.begin(), UE = Uses.end();
    for ( ; UI != UE; ++UI) {
      if (UI->isUnsafe())
        break;
    }

    // If there were only writes to this object, don't warn.
    if (UI == UE)
      continue;

    // If there was only one read, followed by any number of writes, and the
    // read is not within a loop, don't warn. Additionally, don't warn in a
    // loop if the base object is a local variable -- local variables are often
    // changed in loops.
    if (UI == Uses.begin()) {
      WeakUseVector::const_iterator UI2 = UI;
      for (++UI2; UI2 != UE; ++UI2)
        if (UI2->isUnsafe())
          break;

      if (UI2 == UE) {
        if (!isInLoop(Ctx, PM, UI->getUseExpr()))
          continue;

        const WeakObjectProfileTy &Profile = I->first;
        if (!Profile.isExactProfile())
          continue;

        const NamedDecl *Base = Profile.getBase();
        if (!Base)
          Base = Profile.getProperty();
        assert(Base && "A profile always has a base or property.");

        if (const VarDecl *BaseVar = dyn_cast<VarDecl>(Base))
          if (BaseVar->hasLocalStorage() && !isa<ParmVarDecl>(Base))
            continue;
      }
    }

    UsesByStmt.push_back(StmtUsesPair(UI->getUseExpr(), I));
  }

  if (UsesByStmt.empty())
    return;

  // Sort by first use so that we emit the warnings in a deterministic order.
  SourceManager &SM = S.getSourceManager();
  llvm::sort(UsesByStmt,
             [&SM](const StmtUsesPair &LHS, const StmtUsesPair &RHS) {
               return SM.isBeforeInTranslationUnit(LHS.first->getBeginLoc(),
                                                   RHS.first->getBeginLoc());
             });

  // Classify the current code body for better warning text.
  // This enum should stay in sync with the cases in
  // warn_arc_repeated_use_of_weak and warn_arc_possible_repeated_use_of_weak.
  // FIXME: Should we use a common classification enum and the same set of
  // possibilities all throughout Sema?
  enum {
    Function,
    Method,
    Block,
    Lambda
  } FunctionKind;

  if (isa<sema::BlockScopeInfo>(CurFn))
    FunctionKind = Block;
  else if (isa<sema::LambdaScopeInfo>(CurFn))
    FunctionKind = Lambda;
  else if (isa<ObjCMethodDecl>(D))
    FunctionKind = Method;
  else
    FunctionKind = Function;

  // Iterate through the sorted problems and emit warnings for each.
  for (const auto &P : UsesByStmt) {
    const Stmt *FirstRead = P.first;
    const WeakObjectProfileTy &Key = P.second->first;
    const WeakUseVector &Uses = P.second->second;

    // For complicated expressions like 'a.b.c' and 'x.b.c', WeakObjectProfileTy
    // may not contain enough information to determine that these are different
    // properties. We can only be 100% sure of a repeated use in certain cases,
    // and we adjust the diagnostic kind accordingly so that the less certain
    // case can be turned off if it is too noisy.
    unsigned DiagKind;
    if (Key.isExactProfile())
      DiagKind = diag::warn_arc_repeated_use_of_weak;
    else
      DiagKind = diag::warn_arc_possible_repeated_use_of_weak;

    // Classify the weak object being accessed for better warning text.
    // This enum should stay in sync with the cases in
    // warn_arc_repeated_use_of_weak and warn_arc_possible_repeated_use_of_weak.
    enum {
      Variable,
      Property,
      ImplicitProperty,
      Ivar
    } ObjectKind;

    const NamedDecl *KeyProp = Key.getProperty();
    if (isa<VarDecl>(KeyProp))
      ObjectKind = Variable;
    else if (isa<ObjCPropertyDecl>(KeyProp))
      ObjectKind = Property;
    else if (isa<ObjCMethodDecl>(KeyProp))
      ObjectKind = ImplicitProperty;
    else if (isa<ObjCIvarDecl>(KeyProp))
      ObjectKind = Ivar;
    else
      llvm_unreachable("Unexpected weak object kind!");

    // Do not warn about IBOutlet weak property receivers being set to null
    // since they are typically only used from the main thread.
    if (const ObjCPropertyDecl *Prop = dyn_cast<ObjCPropertyDecl>(KeyProp))
      if (Prop->hasAttr<IBOutletAttr>())
        continue;

    // Show the first time the object was read.
    S.Diag(FirstRead->getBeginLoc(), DiagKind)
        << int(ObjectKind) << KeyProp << int(FunctionKind)
        << FirstRead->getSourceRange();

    // Print all the other accesses as notes.
    for (const auto &Use : Uses) {
      if (Use.getUseExpr() == FirstRead)
        continue;
      S.Diag(Use.getUseExpr()->getBeginLoc(),
             diag::note_arc_weak_also_accessed_here)
          << Use.getUseExpr()->getSourceRange();
    }
  }
}

namespace {
class UninitValsDiagReporter : public UninitVariablesHandler {
  Sema &S;
  typedef SmallVector<UninitUse, 2> UsesVec;
  typedef llvm::PointerIntPair<UsesVec *, 1, bool> MappedType;
  // Prefer using MapVector to DenseMap, so that iteration order will be
  // the same as insertion order. This is needed to obtain a deterministic
  // order of diagnostics when calling flushDiagnostics().
  typedef llvm::MapVector<const VarDecl *, MappedType> UsesMap;
  UsesMap uses;

public:
  UninitValsDiagReporter(Sema &S) : S(S) {}
  ~UninitValsDiagReporter() override { flushDiagnostics(); }

  MappedType &getUses(const VarDecl *vd) {
    MappedType &V = uses[vd];
    if (!V.getPointer())
      V.setPointer(new UsesVec());
    return V;
  }

  void handleUseOfUninitVariable(const VarDecl *vd,
                                 const UninitUse &use) override {
    getUses(vd).getPointer()->push_back(use);
  }

  void handleSelfInit(const VarDecl *vd) override {
    getUses(vd).setInt(true);
  }

  void flushDiagnostics() {
    for (const auto &P : uses) {
      const VarDecl *vd = P.first;
      const MappedType &V = P.second;

      UsesVec *vec = V.getPointer();
      bool hasSelfInit = V.getInt();

      // Specially handle the case where we have uses of an uninitialized
      // variable, but the root cause is an idiomatic self-init.  We want
      // to report the diagnostic at the self-init since that is the root cause.
      if (!vec->empty() && hasSelfInit && hasAlwaysUninitializedUse(vec))
        DiagnoseUninitializedUse(S, vd,
                                 UninitUse(vd->getInit()->IgnoreParenCasts(),
                                           /* isAlwaysUninit */ true),
                                 /* alwaysReportSelfInit */ true);
      else {
        // Sort the uses by their SourceLocations.  While not strictly
        // guaranteed to produce them in line/column order, this will provide
        // a stable ordering.
        llvm::sort(vec->begin(), vec->end(),
                   [](const UninitUse &a, const UninitUse &b) {
          // Prefer a more confident report over a less confident one.
          if (a.getKind() != b.getKind())
            return a.getKind() > b.getKind();
          return a.getUser()->getBeginLoc() < b.getUser()->getBeginLoc();
        });

        for (const auto &U : *vec) {
          // If we have self-init, downgrade all uses to 'may be uninitialized'.
          UninitUse Use = hasSelfInit ? UninitUse(U.getUser(), false) : U;

          if (DiagnoseUninitializedUse(S, vd, Use))
            // Skip further diagnostics for this variable. We try to warn only
            // on the first point at which a variable is used uninitialized.
            break;
        }
      }

      // Release the uses vector.
      delete vec;
    }

    uses.clear();
  }

private:
  static bool hasAlwaysUninitializedUse(const UsesVec* vec) {
    return std::any_of(vec->begin(), vec->end(), [](const UninitUse &U) {
      return U.getKind() == UninitUse::Always ||
             U.getKind() == UninitUse::AfterCall ||
             U.getKind() == UninitUse::AfterDecl;
    });
  }
};
} // anonymous namespace

namespace clang {
namespace {
typedef SmallVector<PartialDiagnosticAt, 1> OptionalNotes;
typedef std::pair<PartialDiagnosticAt, OptionalNotes> DelayedDiag;
typedef std::list<DelayedDiag> DiagList;

struct SortDiagBySourceLocation {
  SourceManager &SM;
  SortDiagBySourceLocation(SourceManager &SM) : SM(SM) {}

  bool operator()(const DelayedDiag &left, const DelayedDiag &right) {
    // Although this call will be slow, this is only called when outputting
    // multiple warnings.
    return SM.isBeforeInTranslationUnit(left.first.first, right.first.first);
  }
};
} // anonymous namespace
} // namespace clang

//===----------------------------------------------------------------------===//
// -Wthread-safety
//===----------------------------------------------------------------------===//
namespace clang {
namespace threadSafety {
namespace {
class ThreadSafetyReporter : public clang::threadSafety::ThreadSafetyHandler {
  Sema &S;
  DiagList Warnings;
  SourceLocation FunLocation, FunEndLocation;

  const FunctionDecl *CurrentFunction;
  bool Verbose;

  OptionalNotes getNotes() const {
    if (Verbose && CurrentFunction) {
      PartialDiagnosticAt FNote(CurrentFunction->getBody()->getBeginLoc(),
                                S.PDiag(diag::note_thread_warning_in_fun)
                                    << CurrentFunction);
      return OptionalNotes(1, FNote);
    }
    return OptionalNotes();
  }

  OptionalNotes getNotes(const PartialDiagnosticAt &Note) const {
    OptionalNotes ONS(1, Note);
    if (Verbose && CurrentFunction) {
      PartialDiagnosticAt FNote(CurrentFunction->getBody()->getBeginLoc(),
                                S.PDiag(diag::note_thread_warning_in_fun)
                                    << CurrentFunction);
      ONS.push_back(std::move(FNote));
    }
    return ONS;
  }

  OptionalNotes getNotes(const PartialDiagnosticAt &Note1,
                         const PartialDiagnosticAt &Note2) const {
    OptionalNotes ONS;
    ONS.push_back(Note1);
    ONS.push_back(Note2);
    if (Verbose && CurrentFunction) {
      PartialDiagnosticAt FNote(CurrentFunction->getBody()->getBeginLoc(),
                                S.PDiag(diag::note_thread_warning_in_fun)
                                    << CurrentFunction);
      ONS.push_back(std::move(FNote));
    }
    return ONS;
  }

  OptionalNotes makeLockedHereNote(SourceLocation LocLocked, StringRef Kind) {
    return LocLocked.isValid()
               ? getNotes(PartialDiagnosticAt(
                     LocLocked, S.PDiag(diag::note_locked_here) << Kind))
               : getNotes();
  }

 public:
  ThreadSafetyReporter(Sema &S, SourceLocation FL, SourceLocation FEL)
    : S(S), FunLocation(FL), FunEndLocation(FEL),
      CurrentFunction(nullptr), Verbose(false) {}

  void setVerbose(bool b) { Verbose = b; }

  /// Emit all buffered diagnostics in order of sourcelocation.
  /// We need to output diagnostics produced while iterating through
  /// the lockset in deterministic order, so this function orders diagnostics
  /// and outputs them.
  void emitDiagnostics() {
    Warnings.sort(SortDiagBySourceLocation(S.getSourceManager()));
    for (const auto &Diag : Warnings) {
      S.Diag(Diag.first.first, Diag.first.second);
      for (const auto &Note : Diag.second)
        S.Diag(Note.first, Note.second);
    }
  }

  void handleInvalidLockExp(StringRef Kind, SourceLocation Loc) override {
    PartialDiagnosticAt Warning(Loc, S.PDiag(diag::warn_cannot_resolve_lock)
                                         << Loc);
    Warnings.emplace_back(std::move(Warning), getNotes());
  }

  void handleUnmatchedUnlock(StringRef Kind, Name LockName,
                             SourceLocation Loc) override {
    if (Loc.isInvalid())
      Loc = FunLocation;
    PartialDiagnosticAt Warning(Loc, S.PDiag(diag::warn_unlock_but_no_lock)
                                         << Kind << LockName);
    Warnings.emplace_back(std::move(Warning), getNotes());
  }

  void handleIncorrectUnlockKind(StringRef Kind, Name LockName,
                                 LockKind Expected, LockKind Received,
                                 SourceLocation LocLocked,
                                 SourceLocation LocUnlock) override {
    if (LocUnlock.isInvalid())
      LocUnlock = FunLocation;
    PartialDiagnosticAt Warning(
        LocUnlock, S.PDiag(diag::warn_unlock_kind_mismatch)
                       << Kind << LockName << Received << Expected);
    Warnings.emplace_back(std::move(Warning),
                          makeLockedHereNote(LocLocked, Kind));
  }

  void handleDoubleLock(StringRef Kind, Name LockName, SourceLocation LocLocked,
                        SourceLocation LocDoubleLock) override {
    if (LocDoubleLock.isInvalid())
      LocDoubleLock = FunLocation;
    PartialDiagnosticAt Warning(LocDoubleLock, S.PDiag(diag::warn_double_lock)
                                                   << Kind << LockName);
    Warnings.emplace_back(std::move(Warning),
                          makeLockedHereNote(LocLocked, Kind));
  }

  void handleMutexHeldEndOfScope(StringRef Kind, Name LockName,
                                 SourceLocation LocLocked,
                                 SourceLocation LocEndOfScope,
                                 LockErrorKind LEK) override {
    unsigned DiagID = 0;
    switch (LEK) {
      case LEK_LockedSomePredecessors:
        DiagID = diag::warn_lock_some_predecessors;
        break;
      case LEK_LockedSomeLoopIterations:
        DiagID = diag::warn_expecting_lock_held_on_loop;
        break;
      case LEK_LockedAtEndOfFunction:
        DiagID = diag::warn_no_unlock;
        break;
      case LEK_NotLockedAtEndOfFunction:
        DiagID = diag::warn_expecting_locked;
        break;
    }
    if (LocEndOfScope.isInvalid())
      LocEndOfScope = FunEndLocation;

    PartialDiagnosticAt Warning(LocEndOfScope, S.PDiag(DiagID) << Kind
                                                               << LockName);
    Warnings.emplace_back(std::move(Warning),
                          makeLockedHereNote(LocLocked, Kind));
  }

  void handleExclusiveAndShared(StringRef Kind, Name LockName,
                                SourceLocation Loc1,
                                SourceLocation Loc2) override {
    PartialDiagnosticAt Warning(Loc1,
                                S.PDiag(diag::warn_lock_exclusive_and_shared)
                                    << Kind << LockName);
    PartialDiagnosticAt Note(Loc2, S.PDiag(diag::note_lock_exclusive_and_shared)
                                       << Kind << LockName);
    Warnings.emplace_back(std::move(Warning), getNotes(Note));
  }

  void handleNoMutexHeld(StringRef Kind, const NamedDecl *D,
                         ProtectedOperationKind POK, AccessKind AK,
                         SourceLocation Loc) override {
    assert((POK == POK_VarAccess || POK == POK_VarDereference) &&
           "Only works for variables");
    unsigned DiagID = POK == POK_VarAccess?
                        diag::warn_variable_requires_any_lock:
                        diag::warn_var_deref_requires_any_lock;
    PartialDiagnosticAt Warning(Loc, S.PDiag(DiagID)
      << D << getLockKindFromAccessKind(AK));
    Warnings.emplace_back(std::move(Warning), getNotes());
  }

  void handleMutexNotHeld(StringRef Kind, const NamedDecl *D,
                          ProtectedOperationKind POK, Name LockName,
                          LockKind LK, SourceLocation Loc,
                          Name *PossibleMatch) override {
    unsigned DiagID = 0;
    if (PossibleMatch) {
      switch (POK) {
        case POK_VarAccess:
          DiagID = diag::warn_variable_requires_lock_precise;
          break;
        case POK_VarDereference:
          DiagID = diag::warn_var_deref_requires_lock_precise;
          break;
        case POK_FunctionCall:
          DiagID = diag::warn_fun_requires_lock_precise;
          break;
        case POK_PassByRef:
          DiagID = diag::warn_guarded_pass_by_reference;
          break;
        case POK_PtPassByRef:
          DiagID = diag::warn_pt_guarded_pass_by_reference;
          break;
      }
      PartialDiagnosticAt Warning(Loc, S.PDiag(DiagID) << Kind
                                                       << D
                                                       << LockName << LK);
      PartialDiagnosticAt Note(Loc, S.PDiag(diag::note_found_mutex_near_match)
                                        << *PossibleMatch);
      if (Verbose && POK == POK_VarAccess) {
        PartialDiagnosticAt VNote(D->getLocation(),
                                 S.PDiag(diag::note_guarded_by_declared_here)
                                     << D->getNameAsString());
        Warnings.emplace_back(std::move(Warning), getNotes(Note, VNote));
      } else
        Warnings.emplace_back(std::move(Warning), getNotes(Note));
    } else {
      switch (POK) {
        case POK_VarAccess:
          DiagID = diag::warn_variable_requires_lock;
          break;
        case POK_VarDereference:
          DiagID = diag::warn_var_deref_requires_lock;
          break;
        case POK_FunctionCall:
          DiagID = diag::warn_fun_requires_lock;
          break;
        case POK_PassByRef:
          DiagID = diag::warn_guarded_pass_by_reference;
          break;
        case POK_PtPassByRef:
          DiagID = diag::warn_pt_guarded_pass_by_reference;
          break;
      }
      PartialDiagnosticAt Warning(Loc, S.PDiag(DiagID) << Kind
                                                       << D
                                                       << LockName << LK);
      if (Verbose && POK == POK_VarAccess) {
        PartialDiagnosticAt Note(D->getLocation(),
                                 S.PDiag(diag::note_guarded_by_declared_here));
        Warnings.emplace_back(std::move(Warning), getNotes(Note));
      } else
        Warnings.emplace_back(std::move(Warning), getNotes());
    }
  }

  void handleNegativeNotHeld(StringRef Kind, Name LockName, Name Neg,
                             SourceLocation Loc) override {
    PartialDiagnosticAt Warning(Loc,
        S.PDiag(diag::warn_acquire_requires_negative_cap)
        << Kind << LockName << Neg);
    Warnings.emplace_back(std::move(Warning), getNotes());
  }

  void handleFunExcludesLock(StringRef Kind, Name FunName, Name LockName,
                             SourceLocation Loc) override {
    PartialDiagnosticAt Warning(Loc, S.PDiag(diag::warn_fun_excludes_mutex)
                                         << Kind << FunName << LockName);
    Warnings.emplace_back(std::move(Warning), getNotes());
  }

  void handleLockAcquiredBefore(StringRef Kind, Name L1Name, Name L2Name,
                                SourceLocation Loc) override {
    PartialDiagnosticAt Warning(Loc,
      S.PDiag(diag::warn_acquired_before) << Kind << L1Name << L2Name);
    Warnings.emplace_back(std::move(Warning), getNotes());
  }

  void handleBeforeAfterCycle(Name L1Name, SourceLocation Loc) override {
    PartialDiagnosticAt Warning(Loc,
      S.PDiag(diag::warn_acquired_before_after_cycle) << L1Name);
    Warnings.emplace_back(std::move(Warning), getNotes());
  }

  void enterFunction(const FunctionDecl* FD) override {
    CurrentFunction = FD;
  }

  void leaveFunction(const FunctionDecl* FD) override {
    CurrentFunction = nullptr;
  }
};
} // anonymous namespace
} // namespace threadSafety
} // namespace clang

//===----------------------------------------------------------------------===//
// -Wconsumed
//===----------------------------------------------------------------------===//

namespace clang {
namespace consumed {
namespace {
class ConsumedWarningsHandler : public ConsumedWarningsHandlerBase {

  Sema &S;
  DiagList Warnings;

public:

  ConsumedWarningsHandler(Sema &S) : S(S) {}

  void emitDiagnostics() override {
    Warnings.sort(SortDiagBySourceLocation(S.getSourceManager()));
    for (const auto &Diag : Warnings) {
      S.Diag(Diag.first.first, Diag.first.second);
      for (const auto &Note : Diag.second)
        S.Diag(Note.first, Note.second);
    }
  }

  void warnLoopStateMismatch(SourceLocation Loc,
                             StringRef VariableName) override {
    PartialDiagnosticAt Warning(Loc, S.PDiag(diag::warn_loop_state_mismatch) <<
      VariableName);

    Warnings.emplace_back(std::move(Warning), OptionalNotes());
  }

  void warnParamReturnTypestateMismatch(SourceLocation Loc,
                                        StringRef VariableName,
                                        StringRef ExpectedState,
                                        StringRef ObservedState) override {

    PartialDiagnosticAt Warning(Loc, S.PDiag(
      diag::warn_param_return_typestate_mismatch) << VariableName <<
        ExpectedState << ObservedState);

    Warnings.emplace_back(std::move(Warning), OptionalNotes());
  }

  void warnParamTypestateMismatch(SourceLocation Loc, StringRef ExpectedState,
                                  StringRef ObservedState) override {

    PartialDiagnosticAt Warning(Loc, S.PDiag(
      diag::warn_param_typestate_mismatch) << ExpectedState << ObservedState);

    Warnings.emplace_back(std::move(Warning), OptionalNotes());
  }

  void warnReturnTypestateForUnconsumableType(SourceLocation Loc,
                                              StringRef TypeName) override {
    PartialDiagnosticAt Warning(Loc, S.PDiag(
      diag::warn_return_typestate_for_unconsumable_type) << TypeName);

    Warnings.emplace_back(std::move(Warning), OptionalNotes());
  }

  void warnReturnTypestateMismatch(SourceLocation Loc, StringRef ExpectedState,
                                   StringRef ObservedState) override {

    PartialDiagnosticAt Warning(Loc, S.PDiag(
      diag::warn_return_typestate_mismatch) << ExpectedState << ObservedState);

    Warnings.emplace_back(std::move(Warning), OptionalNotes());
  }

  void warnUseOfTempInInvalidState(StringRef MethodName, StringRef State,
                                   SourceLocation Loc) override {

    PartialDiagnosticAt Warning(Loc, S.PDiag(
      diag::warn_use_of_temp_in_invalid_state) << MethodName << State);

    Warnings.emplace_back(std::move(Warning), OptionalNotes());
  }

  void warnUseInInvalidState(StringRef MethodName, StringRef VariableName,
                             StringRef State, SourceLocation Loc) override {

    PartialDiagnosticAt Warning(Loc, S.PDiag(diag::warn_use_in_invalid_state) <<
                                MethodName << VariableName << State);

    Warnings.emplace_back(std::move(Warning), OptionalNotes());
  }
};
} // anonymous namespace
} // namespace consumed
} // namespace clang

//===----------------------------------------------------------------------===//
// AnalysisBasedWarnings - Worker object used by Sema to execute analysis-based
//  warnings on a function, method, or block.
//===----------------------------------------------------------------------===//

clang::sema::AnalysisBasedWarnings::Policy::Policy() {
  enableCheckFallThrough = 1;
  enableCheckUnreachable = 0;
  enableThreadSafetyAnalysis = 0;
  enableConsumedAnalysis = 0;
}

static unsigned isEnabled(DiagnosticsEngine &D, unsigned diag) {
  return (unsigned)!D.isIgnored(diag, SourceLocation());
}

clang::sema::AnalysisBasedWarnings::AnalysisBasedWarnings(Sema &s)
  : S(s),
    NumFunctionsAnalyzed(0),
    NumFunctionsWithBadCFGs(0),
    NumCFGBlocks(0),
    MaxCFGBlocksPerFunction(0),
    NumUninitAnalysisFunctions(0),
    NumUninitAnalysisVariables(0),
    MaxUninitAnalysisVariablesPerFunction(0),
    NumUninitAnalysisBlockVisits(0),
    MaxUninitAnalysisBlockVisitsPerFunction(0) {

  using namespace diag;
  DiagnosticsEngine &D = S.getDiagnostics();

  DefaultPolicy.enableCheckUnreachable =
    isEnabled(D, warn_unreachable) ||
    isEnabled(D, warn_unreachable_break) ||
    isEnabled(D, warn_unreachable_return) ||
    isEnabled(D, warn_unreachable_loop_increment);

  DefaultPolicy.enableThreadSafetyAnalysis =
    isEnabled(D, warn_double_lock);

  DefaultPolicy.enableConsumedAnalysis =
    isEnabled(D, warn_use_in_invalid_state);
}

static void flushDiagnostics(Sema &S, const sema::FunctionScopeInfo *fscope) {
  for (const auto &D : fscope->PossiblyUnreachableDiags)
    S.Diag(D.Loc, D.PD);
}

void clang::sema::
AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
                                     sema::FunctionScopeInfo *fscope,
                                     const Decl *D, QualType BlockType) {

  // We avoid doing analysis-based warnings when there are errors for
  // two reasons:
  // (1) The CFGs often can't be constructed (if the body is invalid), so
  //     don't bother trying.
  // (2) The code already has problems; running the analysis just takes more
  //     time.
  DiagnosticsEngine &Diags = S.getDiagnostics();

  // Do not do any analysis if we are going to just ignore them.
  if (Diags.getIgnoreAllWarnings() ||
      (Diags.getSuppressSystemWarnings() &&
       S.SourceMgr.isInSystemHeader(D->getLocation())))
    return;

  // For code in dependent contexts, we'll do this at instantiation time.
  if (cast<DeclContext>(D)->isDependentContext())
    return;

  if (Diags.hasUncompilableErrorOccurred()) {
    // Flush out any possibly unreachable diagnostics.
    flushDiagnostics(S, fscope);
    return;
  }

  const Stmt *Body = D->getBody();
  assert(Body);

  // Construct the analysis context with the specified CFG build options.
  AnalysisDeclContext AC(/* AnalysisDeclContextManager */ nullptr, D);

  // Don't generate EH edges for CallExprs as we'd like to avoid the n^2
  // explosion for destructors that can result and the compile time hit.
  AC.getCFGBuildOptions().PruneTriviallyFalseEdges = true;
  AC.getCFGBuildOptions().AddEHEdges = false;
  AC.getCFGBuildOptions().AddInitializers = true;
  AC.getCFGBuildOptions().AddImplicitDtors = true;
  AC.getCFGBuildOptions().AddTemporaryDtors = true;
  AC.getCFGBuildOptions().AddCXXNewAllocator = false;
  AC.getCFGBuildOptions().AddCXXDefaultInitExprInCtors = true;

  // Force that certain expressions appear as CFGElements in the CFG.  This
  // is used to speed up various analyses.
  // FIXME: This isn't the right factoring.  This is here for initial
  // prototyping, but we need a way for analyses to say what expressions they
  // expect to always be CFGElements and then fill in the BuildOptions
  // appropriately.  This is essentially a layering violation.
  if (P.enableCheckUnreachable || P.enableThreadSafetyAnalysis ||
      P.enableConsumedAnalysis) {
    // Unreachable code analysis and thread safety require a linearized CFG.
    AC.getCFGBuildOptions().setAllAlwaysAdd();
  }
  else {
    AC.getCFGBuildOptions()
      .setAlwaysAdd(Stmt::BinaryOperatorClass)
      .setAlwaysAdd(Stmt::CompoundAssignOperatorClass)
      .setAlwaysAdd(Stmt::BlockExprClass)
      .setAlwaysAdd(Stmt::CStyleCastExprClass)
      .setAlwaysAdd(Stmt::DeclRefExprClass)
      .setAlwaysAdd(Stmt::ImplicitCastExprClass)
      .setAlwaysAdd(Stmt::UnaryOperatorClass)
      .setAlwaysAdd(Stmt::AttributedStmtClass);
  }

  // Install the logical handler for -Wtautological-overlap-compare
  llvm::Optional<LogicalErrorHandler> LEH;
  if (!Diags.isIgnored(diag::warn_tautological_overlap_comparison,
                       D->getBeginLoc())) {
    LEH.emplace(S);
    AC.getCFGBuildOptions().Observer = &*LEH;
  }

  // Emit delayed diagnostics.
  if (!fscope->PossiblyUnreachableDiags.empty()) {
    bool analyzed = false;

    // Register the expressions with the CFGBuilder.
    for (const auto &D : fscope->PossiblyUnreachableDiags) {
      for (const Stmt *S : D.Stmts)
        AC.registerForcedBlockExpression(S);
    }

    if (AC.getCFG()) {
      analyzed = true;
      for (const auto &D : fscope->PossiblyUnreachableDiags) {
        bool AllReachable = true;
        for (const Stmt *S : D.Stmts) {
          const CFGBlock *block = AC.getBlockForRegisteredExpression(S);
          CFGReverseBlockReachabilityAnalysis *cra =
              AC.getCFGReachablityAnalysis();
          // FIXME: We should be able to assert that block is non-null, but
          // the CFG analysis can skip potentially-evaluated expressions in
          // edge cases; see test/Sema/vla-2.c.
          if (block && cra) {
            // Can this block be reached from the entrance?
            if (!cra->isReachable(&AC.getCFG()->getEntry(), block)) {
              AllReachable = false;
              break;
            }
          }
          // If we cannot map to a basic block, assume the statement is
          // reachable.
        }

        if (AllReachable)
          S.Diag(D.Loc, D.PD);
      }
    }

    if (!analyzed)
      flushDiagnostics(S, fscope);
  }

  // Warning: check missing 'return'
  if (P.enableCheckFallThrough) {
    const CheckFallThroughDiagnostics &CD =
        (isa<BlockDecl>(D)
             ? CheckFallThroughDiagnostics::MakeForBlock()
             : (isa<CXXMethodDecl>(D) &&
                cast<CXXMethodDecl>(D)->getOverloadedOperator() == OO_Call &&
                cast<CXXMethodDecl>(D)->getParent()->isLambda())
                   ? CheckFallThroughDiagnostics::MakeForLambda()
                   : (fscope->isCoroutine()
                          ? CheckFallThroughDiagnostics::MakeForCoroutine(D)
                          : CheckFallThroughDiagnostics::MakeForFunction(D)));
    CheckFallThroughForBody(S, D, Body, BlockType, CD, AC, fscope);
  }

  // Warning: check for unreachable code
  if (P.enableCheckUnreachable) {
    // Only check for unreachable code on non-template instantiations.
    // Different template instantiations can effectively change the control-flow
    // and it is very difficult to prove that a snippet of code in a template
    // is unreachable for all instantiations.
    bool isTemplateInstantiation = false;
    if (const FunctionDecl *Function = dyn_cast<FunctionDecl>(D))
      isTemplateInstantiation = Function->isTemplateInstantiation();
    if (!isTemplateInstantiation)
      CheckUnreachable(S, AC);
  }

  // Check for thread safety violations
  if (P.enableThreadSafetyAnalysis) {
    SourceLocation FL = AC.getDecl()->getLocation();
    SourceLocation FEL = AC.getDecl()->getEndLoc();
    threadSafety::ThreadSafetyReporter Reporter(S, FL, FEL);
    if (!Diags.isIgnored(diag::warn_thread_safety_beta, D->getBeginLoc()))
      Reporter.setIssueBetaWarnings(true);
    if (!Diags.isIgnored(diag::warn_thread_safety_verbose, D->getBeginLoc()))
      Reporter.setVerbose(true);

    threadSafety::runThreadSafetyAnalysis(AC, Reporter,
                                          &S.ThreadSafetyDeclCache);
    Reporter.emitDiagnostics();
  }

  // Check for violations of consumed properties.
  if (P.enableConsumedAnalysis) {
    consumed::ConsumedWarningsHandler WarningHandler(S);
    consumed::ConsumedAnalyzer Analyzer(WarningHandler);
    Analyzer.run(AC);
  }

  if (!Diags.isIgnored(diag::warn_uninit_var, D->getBeginLoc()) ||
      !Diags.isIgnored(diag::warn_sometimes_uninit_var, D->getBeginLoc()) ||
      !Diags.isIgnored(diag::warn_maybe_uninit_var, D->getBeginLoc())) {
    if (CFG *cfg = AC.getCFG()) {
      UninitValsDiagReporter reporter(S);
      UninitVariablesAnalysisStats stats;
      std::memset(&stats, 0, sizeof(UninitVariablesAnalysisStats));
      runUninitializedVariablesAnalysis(*cast<DeclContext>(D), *cfg, AC,
                                        reporter, stats);

      if (S.CollectStats && stats.NumVariablesAnalyzed > 0) {
        ++NumUninitAnalysisFunctions;
        NumUninitAnalysisVariables += stats.NumVariablesAnalyzed;
        NumUninitAnalysisBlockVisits += stats.NumBlockVisits;
        MaxUninitAnalysisVariablesPerFunction =
            std::max(MaxUninitAnalysisVariablesPerFunction,
                     stats.NumVariablesAnalyzed);
        MaxUninitAnalysisBlockVisitsPerFunction =
            std::max(MaxUninitAnalysisBlockVisitsPerFunction,
                     stats.NumBlockVisits);
      }
    }
  }

  bool FallThroughDiagFull =
      !Diags.isIgnored(diag::warn_unannotated_fallthrough, D->getBeginLoc());
  bool FallThroughDiagPerFunction = !Diags.isIgnored(
      diag::warn_unannotated_fallthrough_per_function, D->getBeginLoc());
  if (FallThroughDiagFull || FallThroughDiagPerFunction ||
      fscope->HasFallthroughStmt) {
    DiagnoseSwitchLabelsFallthrough(S, AC, !FallThroughDiagFull);
  }

  if (S.getLangOpts().ObjCWeak &&
      !Diags.isIgnored(diag::warn_arc_repeated_use_of_weak, D->getBeginLoc()))
    diagnoseRepeatedUseOfWeak(S, fscope, D, AC.getParentMap());


  // Check for infinite self-recursion in functions
  if (!Diags.isIgnored(diag::warn_infinite_recursive_function,
                       D->getBeginLoc())) {
    if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
      checkRecursiveFunction(S, FD, Body, AC);
    }
  }

  // Check for throw out of non-throwing function.
  if (!Diags.isIgnored(diag::warn_throw_in_noexcept_func, D->getBeginLoc()))
    if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
      if (S.getLangOpts().CPlusPlus && isNoexcept(FD))
        checkThrowInNonThrowingFunc(S, FD, AC);

  // If none of the previous checks caused a CFG build, trigger one here
  // for -Wtautological-overlap-compare
  if (!Diags.isIgnored(diag::warn_tautological_overlap_comparison,
                       D->getBeginLoc())) {
    AC.getCFG();
  }

  // Collect statistics about the CFG if it was built.
  if (S.CollectStats && AC.isCFGBuilt()) {
    ++NumFunctionsAnalyzed;
    if (CFG *cfg = AC.getCFG()) {
      // If we successfully built a CFG for this context, record some more
      // detail information about it.
      NumCFGBlocks += cfg->getNumBlockIDs();
      MaxCFGBlocksPerFunction = std::max(MaxCFGBlocksPerFunction,
                                         cfg->getNumBlockIDs());
    } else {
      ++NumFunctionsWithBadCFGs;
    }
  }
}

void clang::sema::AnalysisBasedWarnings::PrintStats() const {
  llvm::errs() << "\n*** Analysis Based Warnings Stats:\n";

  unsigned NumCFGsBuilt = NumFunctionsAnalyzed - NumFunctionsWithBadCFGs;
  unsigned AvgCFGBlocksPerFunction =
      !NumCFGsBuilt ? 0 : NumCFGBlocks/NumCFGsBuilt;
  llvm::errs() << NumFunctionsAnalyzed << " functions analyzed ("
               << NumFunctionsWithBadCFGs << " w/o CFGs).\n"
               << "  " << NumCFGBlocks << " CFG blocks built.\n"
               << "  " << AvgCFGBlocksPerFunction
               << " average CFG blocks per function.\n"
               << "  " << MaxCFGBlocksPerFunction
               << " max CFG blocks per function.\n";

  unsigned AvgUninitVariablesPerFunction = !NumUninitAnalysisFunctions ? 0
      : NumUninitAnalysisVariables/NumUninitAnalysisFunctions;
  unsigned AvgUninitBlockVisitsPerFunction = !NumUninitAnalysisFunctions ? 0
      : NumUninitAnalysisBlockVisits/NumUninitAnalysisFunctions;
  llvm::errs() << NumUninitAnalysisFunctions
               << " functions analyzed for uninitialiazed variables\n"
               << "  " << NumUninitAnalysisVariables << " variables analyzed.\n"
               << "  " << AvgUninitVariablesPerFunction
               << " average variables per function.\n"
               << "  " << MaxUninitAnalysisVariablesPerFunction
               << " max variables per function.\n"
               << "  " << NumUninitAnalysisBlockVisits << " block visits.\n"
               << "  " << AvgUninitBlockVisitsPerFunction
               << " average block visits per function.\n"
               << "  " << MaxUninitAnalysisBlockVisitsPerFunction
               << " max block visits per function.\n";
}