Index: include/clang/StaticAnalyzer/Core/AnalyzerOptions.h
===================================================================
--- include/clang/StaticAnalyzer/Core/AnalyzerOptions.h
+++ include/clang/StaticAnalyzer/Core/AnalyzerOptions.h
@@ -266,6 +266,9 @@
   /// \sa shouldWidenLoops
   Optional<bool> WidenLoops;
 
+  /// \sa shouldDisplayNotesAsEvents
+  Optional<bool> DisplayNotesAsEvents;
+
   /// A helper function that retrieves option for a given full-qualified
   /// checker name.
   /// Options for checkers can be specified via 'analyzer-config' command-line
@@ -534,6 +537,14 @@
   /// This is controlled by the 'widen-loops' config option.
   bool shouldWidenLoops();
 
+  /// Returns true if the bug reporter should transparently treat extra note
+  /// diagnostic pieces as event diagnostic pieces. Useful when the diagnostic
+  /// consumer doesn't support the extra note pieces.
+  ///
+  /// This is controlled by the 'extra-notes-as-events' option, which defaults
+  /// to false when unset.
+  bool shouldDisplayNotesAsEvents();
+
 public:
   AnalyzerOptions() :
     AnalysisStoreOpt(RegionStoreModel),
Index: include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h
===================================================================
--- include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h
+++ include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h
@@ -66,6 +66,8 @@
   typedef SmallVector<std::unique_ptr<BugReporterVisitor>, 8> VisitorList;
   typedef VisitorList::iterator visitor_iterator;
   typedef SmallVector<StringRef, 2> ExtraTextList;
+  typedef SmallVector<llvm::IntrusiveRefCntPtr<PathDiagnosticNotePiece>, 4>
+      NoteList;
 
 protected:
   friend class BugReporter;
@@ -82,7 +84,8 @@
   const ExplodedNode *ErrorNode;
   SmallVector<SourceRange, 4> Ranges;
   ExtraTextList ExtraText;
-  
+  NoteList Notes;
+
   typedef llvm::DenseSet<SymbolRef> Symbols;
   typedef llvm::DenseSet<const MemRegion *> Regions;
 
@@ -177,6 +180,18 @@
   const BugType& getBugType() const { return BT; }
   BugType& getBugType() { return BT; }
 
+  /// \brief True when the report has an execution path associated with it.
+  ///
+  /// A report is said to be path-sensitive if it was thrown against a
+  /// particular exploded node in the path-sensitive analysis graph.
+  /// Path-sensitive reports have their intermediate path diagnostics
+  /// auto-generated, perhaps with the help of checker-defined visitors,
+  /// and may contain extra notes.
+  /// Path-insensitive reports consist only of a single warning message
+  /// in a specific location, and perhaps extra notes.
+  /// Path-sensitive checkers are allowed to throw path-insensitive reports.
+  bool isPathSensitive() const { return ErrorNode != nullptr; }
+
   const ExplodedNode *getErrorNode() const { return ErrorNode; }
 
   StringRef getDescription() const { return Description; }
@@ -245,7 +260,27 @@
   void setDeclWithIssue(const Decl *declWithIssue) {
     DeclWithIssue = declWithIssue;
   }
-  
+
+  /// Add new item to the list of additional notes that need to be attached to
+  /// this path-insensitive report. If you want to add extra notes to a
+  /// path-sensitive report, you need to use a BugReporterVisitor because it
+  /// allows you to specify where exactly in the auto-generated path diagnostic
+  /// the extra note should appear.
+  void addNote(StringRef Msg, const PathDiagnosticLocation &Pos,
+                    ArrayRef<SourceRange> Ranges = {}) {
+    PathDiagnosticNotePiece *P =
+        new PathDiagnosticNotePiece(Pos, Msg);
+
+    for (const auto &R : Ranges)
+      P->addRange(R);
+
+    Notes.push_back(P);
+  }
+
+  virtual const NoteList &getNotes() {
+    return Notes;
+  }
+
   /// \brief This allows for addition of meta data to the diagnostic.
   ///
   /// Currently, only the HTMLDiagnosticClient knows how to display it. 
Index: include/clang/StaticAnalyzer/Core/BugReporter/PathDiagnostic.h
===================================================================
--- include/clang/StaticAnalyzer/Core/BugReporter/PathDiagnostic.h
+++ include/clang/StaticAnalyzer/Core/BugReporter/PathDiagnostic.h
@@ -336,7 +336,7 @@
 
 class PathDiagnosticPiece : public RefCountedBaseVPTR {
 public:
-  enum Kind { ControlFlow, Event, Macro, Call };
+  enum Kind { ControlFlow, Event, Macro, Call, Note };
   enum DisplayHint { Above, Below };
 
 private:
@@ -452,7 +452,8 @@
   void Profile(llvm::FoldingSetNodeID &ID) const override;
 
   static bool classof(const PathDiagnosticPiece *P) {
-    return P->getKind() == Event || P->getKind() == Macro;
+    return P->getKind() == Event || P->getKind() == Macro ||
+           P->getKind() == Note;
   }
 };
 
@@ -710,6 +711,23 @@
   void Profile(llvm::FoldingSetNodeID &ID) const override;
 };
 
+class PathDiagnosticNotePiece: public PathDiagnosticSpotPiece {
+public:
+  PathDiagnosticNotePiece(const PathDiagnosticLocation &Pos, StringRef S,
+                               bool AddPosRange = true)
+      : PathDiagnosticSpotPiece(Pos, S, Note, AddPosRange) {}
+
+  ~PathDiagnosticNotePiece() override;
+
+  static inline bool classof(const PathDiagnosticPiece *P) {
+    return P->getKind() == Note;
+  }
+
+  void dump() const override;
+
+  void Profile(llvm::FoldingSetNodeID &ID) const override;
+};
+
 /// PathDiagnostic - PathDiagnostic objects represent a single path-sensitive
 ///  diagnostic.  It represents an ordered-collection of PathDiagnosticPieces,
 ///  each which represent the pieces of the path.
Index: lib/Rewrite/HTMLRewrite.cpp
===================================================================
--- lib/Rewrite/HTMLRewrite.cpp
+++ lib/Rewrite/HTMLRewrite.cpp
@@ -324,6 +324,7 @@
       " .msgT { padding:0x; spacing:0x }\n"
       " .msgEvent { background-color:#fff8b4; color:#000000 }\n"
       " .msgControl { background-color:#bbbbbb; color:#000000 }\n"
+      " .msgNote { background-color:#ddeeff; color:#000000 }\n"
       " .mrange { background-color:#dfddf3 }\n"
       " .mrange { border-bottom:1px solid #6F9DBE }\n"
       " .PathIndex { font-weight: bold; padding:0px 5px; "
@@ -343,8 +344,12 @@
       "   border-collapse: collapse; border-spacing: 0px;\n"
       " }\n"
       " td.rowname {\n"
-      "   text-align:right; font-weight:bold; color:#444444;\n"
-      "   padding-right:2ex; }\n"
+      "   text-align: right;\n"
+      "   vertical-align: top;\n"
+      "   font-weight: bold;\n"
+      "   color:#444444;\n"
+      "   padding-right:2ex;\n"
+      " }\n"
       "</style>\n</head>\n<body>";
 
   // Generate header
Index: lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
===================================================================
--- lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
+++ lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
@@ -344,3 +344,10 @@
     WidenLoops = getBooleanOption("widen-loops", /*Default=*/false);
   return WidenLoops.getValue();
 }
+
+bool AnalyzerOptions::shouldDisplayNotesAsEvents() {
+  if (!DisplayNotesAsEvents.hasValue())
+    DisplayNotesAsEvents =
+        getBooleanOption("notes-as-events", /*Default=*/false);
+  return DisplayNotesAsEvents.getValue();
+}
Index: lib/StaticAnalyzer/Core/BugReporter.cpp
===================================================================
--- lib/StaticAnalyzer/Core/BugReporter.cpp
+++ lib/StaticAnalyzer/Core/BugReporter.cpp
@@ -112,15 +112,15 @@
     path.pop_front();
 
     switch (piece->getKind()) {
-      case clang::ento::PathDiagnosticPiece::Call:
+      case PathDiagnosticPiece::Call:
         removeRedundantMsgs(cast<PathDiagnosticCallPiece>(piece)->path);
         break;
-      case clang::ento::PathDiagnosticPiece::Macro:
+      case PathDiagnosticPiece::Macro:
         removeRedundantMsgs(cast<PathDiagnosticMacroPiece>(piece)->subPieces);
         break;
-      case clang::ento::PathDiagnosticPiece::ControlFlow:
+      case PathDiagnosticPiece::ControlFlow:
         break;
-      case clang::ento::PathDiagnosticPiece::Event: {
+      case PathDiagnosticPiece::Event: {
         if (i == N-1)
           break;
 
@@ -140,6 +140,8 @@
         }
         break;
       }
+      case PathDiagnosticPiece::Note:
+        break;
     }
     path.push_back(piece);
   }
@@ -197,6 +199,9 @@
       }
       case PathDiagnosticPiece::ControlFlow:
         break;
+
+      case PathDiagnosticPiece::Note:
+        break;
     }
 
     pieces.push_back(piece);
@@ -3403,25 +3408,28 @@
       exampleReport->getUniqueingLocation(),
       exampleReport->getUniqueingDecl()));
 
-  MaxBugClassSize = std::max(bugReports.size(),
-                             static_cast<size_t>(MaxBugClassSize));
+  if (exampleReport->isPathSensitive()) {
+    // Generate the full path diagnostic, using the generation scheme
+    // specified by the PathDiagnosticConsumer. Note that we have to generate
+    // path diagnostics even for consumers which do not support paths, because
+    // the BugReporterVisitors may mark this bug as a false positive.
+    assert(!bugReports.empty());
+
+    MaxBugClassSize =
+        std::max(bugReports.size(), static_cast<size_t>(MaxBugClassSize));
 
-  // Generate the full path diagnostic, using the generation scheme
-  // specified by the PathDiagnosticConsumer. Note that we have to generate
-  // path diagnostics even for consumers which do not support paths, because
-  // the BugReporterVisitors may mark this bug as a false positive.
-  if (!bugReports.empty())
     if (!generatePathDiagnostic(*D.get(), PD, bugReports))
       return;
 
-  MaxValidBugClassSize = std::max(bugReports.size(),
-                                  static_cast<size_t>(MaxValidBugClassSize));
+    MaxValidBugClassSize =
+        std::max(bugReports.size(), static_cast<size_t>(MaxValidBugClassSize));
 
-  // Examine the report and see if the last piece is in a header. Reset the
-  // report location to the last piece in the main source file.
-  AnalyzerOptions& Opts = getAnalyzerOptions();
-  if (Opts.shouldReportIssuesInMainSourceFile() && !Opts.AnalyzeAll)
-    D->resetDiagnosticLocationToMainFile();
+    // Examine the report and see if the last piece is in a header. Reset the
+    // report location to the last piece in the main source file.
+    AnalyzerOptions &Opts = getAnalyzerOptions();
+    if (Opts.shouldReportIssuesInMainSourceFile() && !Opts.AnalyzeAll)
+      D->resetDiagnosticLocationToMainFile();
+  }
 
   // If the path is empty, generate a single step path with the location
   // of the issue.
@@ -3434,6 +3442,27 @@
     D->setEndOfPath(std::move(piece));
   }
 
+  PathPieces &Pieces = D->getMutablePieces();
+  if (getAnalyzerOptions().shouldDisplayNotesAsEvents()) {
+    // For path diagnostic consumers that don't support extra notes,
+    // we may optionally convert those to path notes.
+    for (auto I = exampleReport->getNotes().rbegin(),
+              E = exampleReport->getNotes().rend(); I != E; ++I) {
+      PathDiagnosticNotePiece *Piece = I->get();
+      PathDiagnosticEventPiece *ConvertedPiece =
+          new PathDiagnosticEventPiece(Piece->getLocation(),
+                                       Piece->getString());
+      for (const auto &R: Piece->getRanges())
+        ConvertedPiece->addRange(R);
+
+      Pieces.push_front(ConvertedPiece);
+    }
+  } else {
+    for (auto I = exampleReport->getNotes().rbegin(),
+              E = exampleReport->getNotes().rend(); I != E; ++I)
+      Pieces.push_front(*I);
+  }
+
   // Get the meta data.
   const BugReport::ExtraTextList &Meta = exampleReport->getExtraText();
   for (BugReport::ExtraTextList::const_iterator i = Meta.begin(),
@@ -3518,6 +3547,13 @@
   // FIXME: Print which macro is being invoked.
 }
 
+LLVM_DUMP_METHOD void PathDiagnosticNotePiece::dump() const {
+  llvm::errs() << "NOTE\n--------------\n";
+  llvm::errs() << getString() << "\n";
+  llvm::errs() << " ---- at ----\n";
+  getLocation().dump();
+}
+
 LLVM_DUMP_METHOD void PathDiagnosticLocation::dump() const {
   if (!isValid()) {
     llvm::errs() << "<INVALID>\n";
Index: lib/StaticAnalyzer/Core/HTMLDiagnostics.cpp
===================================================================
--- lib/StaticAnalyzer/Core/HTMLDiagnostics.cpp
+++ lib/StaticAnalyzer/Core/HTMLDiagnostics.cpp
@@ -152,13 +152,30 @@
   }
 
   // Process the path.
-  unsigned n = path.size();
-  unsigned max = n;
-
-  for (PathPieces::const_reverse_iterator I = path.rbegin(),
-       E = path.rend();
-        I != E; ++I, --n)
-    HandlePiece(R, FID, **I, n, max);
+  // Maintain the counts of extra note pieces separately.
+  unsigned TotalPieces = path.size();
+  unsigned TotalNotePieces =
+      std::count_if(path.begin(), path.end(),
+                    [](const IntrusiveRefCntPtr<PathDiagnosticPiece> &p) {
+                      return isa<PathDiagnosticNotePiece>(p.get());
+                    });
+
+  unsigned TotalRegularPieces = TotalPieces - TotalNotePieces;
+  unsigned NumRegularPieces = TotalRegularPieces;
+  unsigned NumNotePieces = TotalNotePieces;
+
+  for (auto I = path.rbegin(), E = path.rend(); I != E; ++I) {
+    if (isa<PathDiagnosticNotePiece>(I->get())) {
+      // This adds diagnostic bubbles, but not navigation.
+      // Navigation through note pieces would be added later,
+      // as a separate pass through the piece list.
+      HandlePiece(R, FID, **I, NumNotePieces, TotalNotePieces);
+      --NumNotePieces;
+    } else {
+      HandlePiece(R, FID, **I, NumRegularPieces, TotalRegularPieces);
+      --NumRegularPieces;
+    }
+  }
 
   // Add line numbers, header, footer, etc.
 
@@ -192,24 +209,38 @@
   int ColumnNumber = path.back()->getLocation().asLocation().getExpansionColumnNumber();
 
   // Add the name of the file as an <h1> tag.
-
   {
     std::string s;
     llvm::raw_string_ostream os(s);
 
     os << "<!-- REPORTHEADER -->\n"
-      << "<h3>Bug Summary</h3>\n<table class=\"simpletable\">\n"
+       << "<h3>Bug Summary</h3>\n<table class=\"simpletable\">\n"
           "<tr><td class=\"rowname\">File:</td><td>"
-      << html::EscapeText(DirName)
-      << html::EscapeText(Entry->getName())
-      << "</td></tr>\n<tr><td class=\"rowname\">Location:</td><td>"
-         "<a href=\"#EndPath\">line "
-      << LineNumber
-      << ", column "
-      << ColumnNumber
-      << "</a></td></tr>\n"
-         "<tr><td class=\"rowname\">Description:</td><td>"
-      << D.getVerboseDescription() << "</td></tr>\n";
+       << html::EscapeText(DirName)
+       << html::EscapeText(Entry->getName())
+       << "</td></tr>\n<tr><td class=\"rowname\">Warning:</td><td>"
+          "<a href=\"#EndPath\">line "
+       << LineNumber
+       << ", column "
+       << ColumnNumber
+       << "</a><br />"
+       << D.getVerboseDescription() << "</td></tr>\n";
+
+    // The navigation across the extra notes pieces.
+    unsigned NumExtraPieces = 0;
+    for (const auto &Piece : path) {
+      if (const auto *P = dyn_cast<PathDiagnosticNotePiece>(Piece.get())) {
+        int LineNumber =
+            P->getLocation().asLocation().getExpansionLineNumber();
+        int ColumnNumber =
+            P->getLocation().asLocation().getExpansionColumnNumber();
+        os << "<tr><td class=\"rowname\">Note:</td><td>"
+           << "<a href=\"#Note" << NumExtraPieces << "\">line "
+           << LineNumber << ", column " << ColumnNumber << "</a><br />"
+           << P->getString() << "</td></tr>";
+        ++NumExtraPieces;
+      }
+    }
 
     // Output any other meta data.
 
@@ -385,13 +416,20 @@
   // Create the html for the message.
 
   const char *Kind = nullptr;
+  bool IsNote = false;
+  bool SuppressIndex = (max == 1);
   switch (P.getKind()) {
   case PathDiagnosticPiece::Call:
-      llvm_unreachable("Calls should already be handled");
+      llvm_unreachable("Calls and extra notes should already be handled");
   case PathDiagnosticPiece::Event:  Kind = "Event"; break;
   case PathDiagnosticPiece::ControlFlow: Kind = "Control"; break;
     // Setting Kind to "Control" is intentional.
   case PathDiagnosticPiece::Macro: Kind = "Control"; break;
+  case PathDiagnosticPiece::Note:
+    Kind = "Note";
+    IsNote = true;
+    SuppressIndex = true;
+    break;
   }
 
   std::string sbuf;
@@ -399,7 +437,9 @@
 
   os << "\n<tr><td class=\"num\"></td><td class=\"line\"><div id=\"";
 
-  if (num == max)
+  if (IsNote)
+    os << "Note" << num;
+  else if (num == max)
     os << "EndPath";
   else
     os << "Path" << num;
@@ -461,7 +501,7 @@
 
   os << "\">";
 
-  if (max > 1) {
+  if (!SuppressIndex) {
     os << "<table class=\"msgT\"><tr><td valign=\"top\">";
     os << "<div class=\"PathIndex";
     if (Kind) os << " PathIndex" << Kind;
@@ -501,7 +541,7 @@
 
     os << "':\n";
 
-    if (max > 1) {
+    if (!SuppressIndex) {
       os << "</td>";
       if (num < max) {
         os << "<td><div class=\"PathNav\"><a href=\"#";
@@ -523,7 +563,7 @@
   else {
     os << html::EscapeText(P.getString());
 
-    if (max > 1) {
+    if (!SuppressIndex) {
       os << "</td>";
       if (num < max) {
         os << "<td><div class=\"PathNav\"><a href=\"#";
Index: lib/StaticAnalyzer/Core/PathDiagnostic.cpp
===================================================================
--- lib/StaticAnalyzer/Core/PathDiagnostic.cpp
+++ lib/StaticAnalyzer/Core/PathDiagnostic.cpp
@@ -60,6 +60,7 @@
 PathDiagnosticCallPiece::~PathDiagnosticCallPiece() {}
 PathDiagnosticControlFlowPiece::~PathDiagnosticControlFlowPiece() {}
 PathDiagnosticMacroPiece::~PathDiagnosticMacroPiece() {}
+PathDiagnosticNotePiece::~PathDiagnosticNotePiece() {}
 
 void PathPieces::flattenTo(PathPieces &Primary, PathPieces &Current,
                            bool ShouldFlattenMacros) const {
@@ -95,6 +96,7 @@
     }
     case PathDiagnosticPiece::Event:
     case PathDiagnosticPiece::ControlFlow:
+    case PathDiagnosticPiece::Note:
       Current.push_back(Piece);
       break;
     }
@@ -342,15 +344,16 @@
   }
 
   switch (X.getKind()) {
-    case clang::ento::PathDiagnosticPiece::ControlFlow:
+    case PathDiagnosticPiece::ControlFlow:
       return compareControlFlow(cast<PathDiagnosticControlFlowPiece>(X),
                                 cast<PathDiagnosticControlFlowPiece>(Y));
-    case clang::ento::PathDiagnosticPiece::Event:
+    case PathDiagnosticPiece::Event:
+    case PathDiagnosticPiece::Note:
       return None;
-    case clang::ento::PathDiagnosticPiece::Macro:
+    case PathDiagnosticPiece::Macro:
       return compareMacro(cast<PathDiagnosticMacroPiece>(X),
                           cast<PathDiagnosticMacroPiece>(Y));
-    case clang::ento::PathDiagnosticPiece::Call:
+    case PathDiagnosticPiece::Call:
       return compareCall(cast<PathDiagnosticCallPiece>(X),
                          cast<PathDiagnosticCallPiece>(Y));
   }
@@ -1098,6 +1101,10 @@
     ID.Add(**I);
 }
 
+void PathDiagnosticNotePiece::Profile(llvm::FoldingSetNodeID &ID) const {
+  PathDiagnosticSpotPiece::Profile(ID);
+}
+
 void PathDiagnostic::Profile(llvm::FoldingSetNodeID &ID) const {
   ID.Add(getLocation());
   ID.AddString(BugType);
Index: lib/StaticAnalyzer/Core/PlistDiagnostics.cpp
===================================================================
--- lib/StaticAnalyzer/Core/PlistDiagnostics.cpp
+++ lib/StaticAnalyzer/Core/PlistDiagnostics.cpp
@@ -281,6 +281,9 @@
       ReportMacro(o, cast<PathDiagnosticMacroPiece>(P), FM, SM, LangOpts,
                   indent, depth);
       break;
+    case PathDiagnosticPiece::Note:
+      // FIXME: Extend the plist format to support those.
+      break;
   }
 }
 
Index: lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp
===================================================================
--- lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp
+++ lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp
@@ -113,16 +113,28 @@
       Diag.Report(WarnLoc, WarnID) << PD->getShortDescription()
                                    << PD->path.back()->getRanges();
 
+      // First, add extra notes, even if paths should not be included.
+      for (const auto &Piece : PD->path) {
+        if (!isa<PathDiagnosticNotePiece>(Piece.get()))
+          continue;
+
+        SourceLocation NoteLoc = Piece->getLocation().asLocation();
+        Diag.Report(NoteLoc, NoteID) << Piece->getString()
+                                     << Piece->getRanges();
+      }
+
       if (!IncludePath)
         continue;
 
+      // Then, add the path notes if necessary.
       PathPieces FlatPath = PD->path.flatten(/*ShouldFlattenMacros=*/true);
-      for (PathPieces::const_iterator PI = FlatPath.begin(),
-                                      PE = FlatPath.end();
-           PI != PE; ++PI) {
-        SourceLocation NoteLoc = (*PI)->getLocation().asLocation();
-        Diag.Report(NoteLoc, NoteID) << (*PI)->getString()
-                                     << (*PI)->getRanges();
+      for (const auto &Piece : FlatPath) {
+        if (isa<PathDiagnosticNotePiece>(Piece.get()))
+          continue;
+
+        SourceLocation NoteLoc = Piece->getLocation().asLocation();
+        Diag.Report(NoteLoc, NoteID) << Piece->getString()
+                                     << Piece->getRanges();
       }
     }
   }