AnalysisBasedWarnings.cpp

//=- AnalysisBasedWarnings.cpp - Sema warnings based on libAnalysis -*- C++ -*-=//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/Sema/SemaInternal.h"
#include "clang/Sema/ScopeInfo.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Lex/Lexer.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtCXX.h"
#include "clang/AST/EvaluatedExprVisitor.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/Analysis/AnalysisContext.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/Analyses/ReachableCode.h"
#include "clang/Analysis/Analyses/CFGReachabilityAnalysis.h"
#include "clang/Analysis/Analyses/ThreadSafety.h"
#include "clang/Analysis/CFGStmtMap.h"
#include "clang/Analysis/Analyses/UninitializedValues.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/ImmutableMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Casting.h"
#include <algorithm>
#include <iterator>
#include <vector>
#include <deque>

using namespace clang;

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

namespace {
  class UnreachableCodeHandler : public reachable_code::Callback {
    Sema &S;
  public:
    UnreachableCodeHandler(Sema &s) : S(s) {}

    void HandleUnreachable(SourceLocation L, SourceRange R1, SourceRange R2) {
      S.Diag(L, diag::warn_unreachable) << R1 << R2;
    }
  };
}

/// CheckUnreachable - Check for unreachable code.
static void CheckUnreachable(Sema &S, AnalysisDeclContext &AC) {
  UnreachableCodeHandler UC(S);
  reachable_code::FindUnreachableCode(AC, UC);
}

//===----------------------------------------------------------------------===//
// 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 == 0) 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 (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
      CFGBlock &b = **I;
      if (!live[b.getBlockID()]) {
        if (b.pred_begin() == b.pred_end()) {
          if (b.getTerminator() && isa<CXXTryStmt>(b.getTerminator()))
            // 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 (isa<CFGStmt>(*ri))
        break;

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

    CFGStmt CS = cast<CFGStmt>(*ri);
    const Stmt *S = CS.getStmt();
    if (isa<ReturnStmt>(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 } 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 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 =
      diag::warn_suggest_noreturn_block;
    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.getDiagnosticLevel(diag::warn_maybe_falloff_nonvoid_function,
                                   FuncLoc) == DiagnosticsEngine::Ignored)
        && (!HasNoReturn ||
            D.getDiagnosticLevel(diag::warn_noreturn_function_has_return_expr,
                                 FuncLoc) == DiagnosticsEngine::Ignored)
        && (!ReturnsVoid ||
            D.getDiagnosticLevel(diag::warn_suggest_noreturn_block, FuncLoc)
              == DiagnosticsEngine::Ignored);
    }

    // For blocks / lambdas.
    return ReturnsVoid && !HasNoReturn
            && ((funMode == Lambda) ||
                D.getDiagnosticLevel(diag::warn_suggest_noreturn_block, FuncLoc)
                  == DiagnosticsEngine::Ignored);
  }
};

}

/// CheckFallThroughForFunctionDef - 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,
                                    const BlockExpr *blkExpr,
                                    const CheckFallThroughDiagnostics& CD,
                                    AnalysisDeclContext &AC) {

  bool ReturnsVoid = false;
  bool HasNoReturn = false;

  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
    ReturnsVoid = FD->getResultType()->isVoidType();
    HasNoReturn = FD->hasAttr<NoReturnAttr>() ||
       FD->getType()->getAs<FunctionType>()->getNoReturnAttr();
  }
  else if (const ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(D)) {
    ReturnsVoid = MD->getResultType()->isVoidType();
    HasNoReturn = MD->hasAttr<NoReturnAttr>();
  }
  else if (isa<BlockDecl>(D)) {
    QualType BlockTy = blkExpr->getType();
    if (const FunctionType *FT =
          BlockTy->getPointeeType()->getAs<FunctionType>()) {
      if (FT->getResultType()->isVoidType())
        ReturnsVoid = true;
      if (FT->getNoReturnAttr())
        HasNoReturn = true;
    }
  }

  DiagnosticsEngine &Diags = S.getDiagnostics();

  // Short circuit for compilation speed.
  if (CD.checkDiagnostics(Diags, ReturnsVoid, HasNoReturn))
      return;

  // FIXME: Function try block
  if (const CompoundStmt *Compound = dyn_cast<CompoundStmt>(Body)) {
    switch (CheckFallThrough(AC)) {
      case UnknownFallThrough:
        break;

      case MaybeFallThrough:
        if (HasNoReturn)
          S.Diag(Compound->getRBracLoc(),
                 CD.diag_MaybeFallThrough_HasNoReturn);
        else if (!ReturnsVoid)
          S.Diag(Compound->getRBracLoc(),
                 CD.diag_MaybeFallThrough_ReturnsNonVoid);
        break;
      case AlwaysFallThrough:
        if (HasNoReturn)
          S.Diag(Compound->getRBracLoc(),
                 CD.diag_AlwaysFallThrough_HasNoReturn);
        else if (!ReturnsVoid)
          S.Diag(Compound->getRBracLoc(),
                 CD.diag_AlwaysFallThrough_ReturnsNonVoid);
        break;
      case NeverFallThroughOrReturn:
        if (ReturnsVoid && !HasNoReturn && CD.diag_NeverFallThroughOrReturn) {
          if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
            S.Diag(Compound->getLBracLoc(), CD.diag_NeverFallThroughOrReturn)
              << 0 << FD;
          } else if (const ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(D)) {
            S.Diag(Compound->getLBracLoc(), CD.diag_NeverFallThroughOrReturn)
              << 1 << MD;
          } else {
            S.Diag(Compound->getLBracLoc(), 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 EvaluatedExprVisitor<ContainsReference> {
  bool FoundReference;
  const DeclRefExpr *Needle;

public:
  ContainsReference(ASTContext &Context, const DeclRefExpr *Needle)
    : EvaluatedExprVisitor<ContainsReference>(Context),
      FoundReference(false), Needle(Needle) {}

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

    EvaluatedExprVisitor<ContainsReference>::VisitExpr(E);
  }

  void VisitDeclRefExpr(DeclRefExpr *E) {
    if (E == Needle)
      FoundReference = true;
    else
      EvaluatedExprVisitor<ContainsReference>::VisitDeclRefExpr(E);
  }

  bool doesContainReference() const { return FoundReference; }
};
}

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

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

  SourceLocation Loc = S.PP.getLocForEndOfToken(VD->getLocEnd());
  
  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->getLocStart(),
                                      Then->getLocStart()));
    if (Else) {
      SourceLocation ElseKwLoc = Lexer::getLocForEndOfToken(
          Then->getLocEnd(), 0, S.getSourceManager(), S.getLangOpts());
      Fixit2 = FixItHint::CreateRemoval(
          SourceRange(ElseKwLoc, Else->getLocEnd()));
    }
  } else {
    // If condition is always false, remove all but the 'else'.
    if (Else)
      Fixit1 = FixItHint::CreateRemoval(
          CharSourceRange::getCharRange(If->getLocStart(),
                                        Else->getLocStart()));
    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;

  // 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;
    const char *Str;
    SourceRange Range;

    // FixIts to suppress the diagnosic 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->getStmtClass()) {
    default:
      // Don't know how to report this. Just fall back to 'may be used
      // uninitialized'. This happens for range-based for, which the user
      // can't explicitly fix.
      // FIXME: This also happens if the first use of a variable is always
      // uninitialized, eg "for (int n; n < 10; ++n)". We should report that
      // with the 'is uninitialized' diagnostic.
      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->getLocStart(),
                                                      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;

    // "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->getLocStart(), 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()->getLocStart(),
           Use.getKind() == UninitUse::Always ? diag::warn_uninit_var
                                              : 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(const_cast<Expr*>(Initializer));
      if (CR.doesContainReference()) {
        S.Diag(DRE->getLocStart(),
               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->getLocStart(),
             diag::warn_uninit_byref_blockvar_captured_by_block)
        << VD->getDeclName();
    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->getLocStart(), diag::note_uninit_var_def)
      << 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;
    }

    bool checkFallThroughIntoBlock(const CFGBlock &B, int &AnnotatedCnt) {
      int UnannotatedCnt = 0;
      AnnotatedCnt = 0;

      std::deque<const CFGBlock*> BlockQueue;

      std::copy(B.pred_begin(), B.pred_end(), std::back_inserter(BlockQueue));

      while (!BlockQueue.empty()) {
        const CFGBlock *P = BlockQueue.front();
        BlockQueue.pop_front();

        const Stmt *Term = P->getTerminator();
        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.

        if (P->pred_begin() == P->pred_end()) {  // The block is unreachable.
          // This only catches trivially unreachable blocks.
          for (CFGBlock::const_iterator ElIt = P->begin(), ElEnd = P->end();
               ElIt != ElEnd; ++ElIt) {
            if (const CFGStmt *CS = ElIt->getAs<CFGStmt>()){
              if (const AttributedStmt *AS = asFallThroughAttr(CS->getStmt())) {
                S.Diag(AS->getLocStart(),
                       diag::warn_fallthrough_attr_unreachable);
                markFallthroughVisited(AS);
                ++AnnotatedCnt;
              }
              // 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;
    }

  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 0;
    }

    static const Stmt *getLastStmt(const CFGBlock &B) {
      if (const Stmt *Term = B.getTerminator())
        return Term;
      for (CFGBlock::const_reverse_iterator ElemIt = B.rbegin(),
                                            ElemEnd = B.rend();
                                            ElemIt != ElemEnd; ++ElemIt) {
        if (const 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 0;
    }

    bool FoundSwitchStatements;
    AttrStmts FallthroughStmts;
    Sema &S;
  };
}

static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
                                            bool PerFunction) {
  FallthroughMapper FM(S);
  FM.TraverseStmt(AC.getBody());

  if (!FM.foundSwitchStatements())
    return;

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

  CFG *Cfg = AC.getCFG();

  if (!Cfg)
    return;

  int AnnotatedCnt;

  for (CFG::reverse_iterator I = Cfg->rbegin(), E = Cfg->rend(); I != E; ++I) {
    const CFGBlock &B = **I;
    const Stmt *Label = B.getLabel();

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

    if (!FM.checkFallThroughIntoBlock(B, AnnotatedCnt))
      continue;

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

    if (!AnnotatedCnt) {
      SourceLocation L = Label->getLocStart();
      if (L.isMacroID())
        continue;
      if (S.getLangOpts().CPlusPlus0x) {
        const Stmt *Term = B.getTerminator();
        if (!(B.empty() && Term && isa<BreakStmt>(Term))) {
          S.Diag(L, diag::note_insert_fallthrough_fixit) <<
            FixItHint::CreateInsertion(L, "[[clang::fallthrough]]; ");
        }
      }
      S.Diag(L, diag::note_insert_break_fixit) <<
        FixItHint::CreateInsertion(L, "break; ");
    }
  }

  const FallthroughMapper::AttrStmts &Fallthroughs = FM.getFallthroughStmts();
  for (FallthroughMapper::AttrStmts::const_iterator I = Fallthroughs.begin(),
                                                    E = Fallthroughs.end();
                                                    I != E; ++I) {
    S.Diag((*I)->getLocStart(), diag::warn_fallthrough_attr_invalid_placement);
  }

}

namespace {
struct SLocSort {
  bool operator()(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();
    SourceLocation aLoc = a.getUser()->getLocStart();
    SourceLocation bLoc = b.getUser()->getLocStart();
    return aLoc.getRawEncoding() < bLoc.getRawEncoding();
  }
};

class UninitValsDiagReporter : public UninitVariablesHandler {
  Sema &S;
  typedef SmallVector<UninitUse, 2> UsesVec;
  typedef llvm::DenseMap<const VarDecl *, std::pair<UsesVec*, bool> > UsesMap;
  UsesMap *uses;
  
public:
  UninitValsDiagReporter(Sema &S) : S(S), uses(0) {}
  ~UninitValsDiagReporter() { 
    flushDiagnostics();
  }

  std::pair<UsesVec*, bool> &getUses(const VarDecl *vd) {
    if (!uses)
      uses = new UsesMap();

    UsesMap::mapped_type &V = (*uses)[vd];
    UsesVec *&vec = V.first;
    if (!vec)
      vec = new UsesVec();
    
    return V;
  }
  
  void handleUseOfUninitVariable(const VarDecl *vd, const UninitUse &use) {
    getUses(vd).first->push_back(use);
  }
  
  void handleSelfInit(const VarDecl *vd) {
    getUses(vd).second = true;    
  }
  
  void flushDiagnostics() {
    if (!uses)
      return;
    
    // FIXME: This iteration order, and thus the resulting diagnostic order,
    //        is nondeterministic.
    for (UsesMap::iterator i = uses->begin(), e = uses->end(); i != e; ++i) {
      const VarDecl *vd = i->first;
      const UsesMap::mapped_type &V = i->second;

      UsesVec *vec = V.first;
      bool hasSelfInit = V.second;

      // 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.
        std::sort(vec->begin(), vec->end(), SLocSort());
        
        for (UsesVec::iterator vi = vec->begin(), ve = vec->end(); vi != ve;
             ++vi) {
          // If we have self-init, downgrade all uses to 'may be uninitialized'.
          UninitUse Use = hasSelfInit ? UninitUse(vi->getUser(), false) : *vi;

          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;
    }
    delete uses;
  }

private:
  static bool hasAlwaysUninitializedUse(const UsesVec* vec) {
  for (UsesVec::const_iterator i = vec->begin(), e = vec->end(); i != e; ++i) {
    if (i->getKind() == UninitUse::Always) {
      return true;
    }
  }
  return false;
}
};
}


//===----------------------------------------------------------------------===//
// -Wthread-safety
//===----------------------------------------------------------------------===//
namespace clang {
namespace thread_safety {
typedef llvm::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);
  }
};

namespace {
class ThreadSafetyReporter : public clang::thread_safety::ThreadSafetyHandler {
  Sema &S;
  DiagList Warnings;
  SourceLocation FunLocation, FunEndLocation;