diff --git a/lib/Frontend/VerifyDiagnosticsClient.cpp b/lib/Frontend/VerifyDiagnosticsClient.cpp
new file mode 100644
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--- /dev/null
+++ b/lib/Frontend/VerifyDiagnosticsClient.cpp
@@ -0,0 +1,346 @@
+//===--- VerifyDiagnosticsClient.cpp - Verifying Diagnostic Client --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This is a concrete diagnostic client, which buffers the diagnostic messages.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Frontend/VerifyDiagnosticsClient.h"
+#include "clang/Frontend/FrontendDiagnostic.h"
+#include "clang/Frontend/TextDiagnosticBuffer.h"
+#include "clang/Lex/Preprocessor.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace clang;
+
+VerifyDiagnosticsClient::VerifyDiagnosticsClient(Diagnostic &_Diags,
+                                                 DiagnosticClient *_Primary)
+  : Diags(_Diags), PrimaryClient(_Primary),
+    Buffer(new TextDiagnosticBuffer()), CurrentPreprocessor(0), NumErrors(0) {
+}
+
+VerifyDiagnosticsClient::~VerifyDiagnosticsClient() {
+  CheckDiagnostics();
+}
+
+// DiagnosticClient interface.
+
+void VerifyDiagnosticsClient::BeginSourceFile(const LangOptions &LangOpts,
+                                             const Preprocessor *PP) {
+  // FIXME: Const hack, we screw up the preprocessor but in practice its ok
+  // because it doesn't get reused. It would be better if we could make a copy
+  // though.
+  CurrentPreprocessor = const_cast<Preprocessor*>(PP);
+
+  PrimaryClient->BeginSourceFile(LangOpts, PP);
+}
+
+void VerifyDiagnosticsClient::EndSourceFile() {
+  CheckDiagnostics();
+
+  PrimaryClient->EndSourceFile();
+
+  CurrentPreprocessor = 0;
+}
+
+void VerifyDiagnosticsClient::HandleDiagnostic(Diagnostic::Level DiagLevel,
+                                              const DiagnosticInfo &Info) {
+  // Send the diagnostic to the buffer, we will check it once we reach the end
+  // of the source file (or are destructed).
+  Buffer->HandleDiagnostic(DiagLevel, Info);
+}
+
+// FIXME: It would be nice to just get this from the primary diagnostic client
+// or something.
+bool VerifyDiagnosticsClient::HadErrors() {
+  CheckDiagnostics();
+
+  return NumErrors != 0;
+}
+
+//===----------------------------------------------------------------------===//
+// Checking diagnostics implementation.
+//===----------------------------------------------------------------------===//
+
+typedef TextDiagnosticBuffer::DiagList DiagList;
+typedef TextDiagnosticBuffer::const_iterator const_diag_iterator;
+
+/// FindDiagnostics - Go through the comment and see if it indicates expected
+/// diagnostics. If so, then put them in a diagnostic list.
+///
+static void FindDiagnostics(const char *CommentStart, unsigned CommentLen,
+                            DiagList &ExpectedDiags,
+                            Preprocessor &PP, SourceLocation Pos,
+                            const char *ExpectedStr) {
+  const char *CommentEnd = CommentStart+CommentLen;
+  unsigned ExpectedStrLen = strlen(ExpectedStr);
+
+  // Find all expected-foo diagnostics in the string and add them to
+  // ExpectedDiags.
+  while (CommentStart != CommentEnd) {
+    CommentStart = std::find(CommentStart, CommentEnd, 'e');
+    if (unsigned(CommentEnd-CommentStart) < ExpectedStrLen) return;
+
+    // If this isn't expected-foo, ignore it.
+    if (memcmp(CommentStart, ExpectedStr, ExpectedStrLen)) {
+      ++CommentStart;
+      continue;
+    }
+
+    CommentStart += ExpectedStrLen;
+
+    // Skip whitespace.
+    while (CommentStart != CommentEnd &&
+           isspace(CommentStart[0]))
+      ++CommentStart;
+
+    // Default, if we find the '{' now, is 1 time.
+    int Times = 1;
+    int Temp = 0;
+    // In extended syntax, there could be a digit now.
+    while (CommentStart != CommentEnd &&
+           CommentStart[0] >= '0' && CommentStart[0] <= '9') {
+      Temp *= 10;
+      Temp += CommentStart[0] - '0';
+      ++CommentStart;
+    }
+    if (Temp > 0)
+      Times = Temp;
+
+    // Skip whitespace again.
+    while (CommentStart != CommentEnd &&
+           isspace(CommentStart[0]))
+      ++CommentStart;
+
+    // We should have a {{ now.
+    if (CommentEnd-CommentStart < 2 ||
+        CommentStart[0] != '{' || CommentStart[1] != '{') {
+      if (std::find(CommentStart, CommentEnd, '{') != CommentEnd)
+        PP.Diag(Pos, diag::err_verify_bogus_characters);
+      else
+        PP.Diag(Pos, diag::err_verify_missing_start);
+      return;
+    }
+    CommentStart += 2;
+
+    // Find the }}.
+    const char *ExpectedEnd = CommentStart;
+    while (1) {
+      ExpectedEnd = std::find(ExpectedEnd, CommentEnd, '}');
+      if (CommentEnd-ExpectedEnd < 2) {
+        PP.Diag(Pos, diag::err_verify_missing_end);
+        return;
+      }
+
+      if (ExpectedEnd[1] == '}')
+        break;
+
+      ++ExpectedEnd;  // Skip over singular }'s
+    }
+
+    std::string Msg(CommentStart, ExpectedEnd);
+    std::string::size_type FindPos;
+    while ((FindPos = Msg.find("\\n")) != std::string::npos)
+      Msg.replace(FindPos, 2, "\n");
+    // Add is possibly multiple times.
+    for (int i = 0; i < Times; ++i)
+      ExpectedDiags.push_back(std::make_pair(Pos, Msg));
+
+    CommentStart = ExpectedEnd;
+  }
+}
+
+/// FindExpectedDiags - Lex the main source file to find all of the
+//   expected errors and warnings.
+static void FindExpectedDiags(Preprocessor &PP,
+                              DiagList &ExpectedErrors,
+                              DiagList &ExpectedWarnings,
+                              DiagList &ExpectedNotes) {
+  // Create a raw lexer to pull all the comments out of the main file.  We don't
+  // want to look in #include'd headers for expected-error strings.
+  SourceManager &SM = PP.getSourceManager();
+  FileID FID = SM.getMainFileID();
+  if (SM.getMainFileID().isInvalid())
+    return;
+
+  // Create a lexer to lex all the tokens of the main file in raw mode.
+  const llvm::MemoryBuffer *FromFile = SM.getBuffer(FID);
+  Lexer RawLex(FID, FromFile, SM, PP.getLangOptions());
+
+  // Return comments as tokens, this is how we find expected diagnostics.
+  RawLex.SetCommentRetentionState(true);
+
+  Token Tok;
+  Tok.setKind(tok::comment);
+  while (Tok.isNot(tok::eof)) {
+    RawLex.Lex(Tok);
+    if (!Tok.is(tok::comment)) continue;
+
+    std::string Comment = PP.getSpelling(Tok);
+    if (Comment.empty()) continue;
+
+    // Find all expected errors.
+    FindDiagnostics(&Comment[0], Comment.size(), ExpectedErrors, PP,
+                    Tok.getLocation(), "expected-error");
+
+    // Find all expected warnings.
+    FindDiagnostics(&Comment[0], Comment.size(), ExpectedWarnings, PP,
+                    Tok.getLocation(), "expected-warning");
+
+    // Find all expected notes.
+    FindDiagnostics(&Comment[0], Comment.size(), ExpectedNotes, PP,
+                    Tok.getLocation(), "expected-note");
+  };
+}
+
+/// PrintProblem - This takes a diagnostic map of the delta between expected and
+/// seen diagnostics. If there's anything in it, then something unexpected
+/// happened. Print the map out in a nice format and return "true". If the map
+/// is empty and we're not going to print things, then return "false".
+///
+static unsigned PrintProblem(Diagnostic &Diags, SourceManager *SourceMgr,
+                             const_diag_iterator diag_begin,
+                             const_diag_iterator diag_end,
+                             const char *Kind, bool Expected) {
+  if (diag_begin == diag_end) return 0;
+
+  llvm::SmallString<256> Fmt;
+  llvm::raw_svector_ostream OS(Fmt);
+  for (const_diag_iterator I = diag_begin, E = diag_end; I != E; ++I) {
+    if (I->first.isInvalid() || !SourceMgr)
+      OS << "\n  (frontend)";
+    else
+      OS << "\n  Line " << SourceMgr->getInstantiationLineNumber(I->first);
+    OS << ": " << I->second;
+  }
+
+  Diags.Report(diag::err_verify_inconsistent_diags)
+    << Kind << !Expected << OS.str();
+  return std::distance(diag_begin, diag_end);
+}
+
+/// CompareDiagLists - Compare two diagnostic lists and return the difference
+/// between them.
+///
+static unsigned CompareDiagLists(Diagnostic &Diags,
+                                 SourceManager &SourceMgr,
+                                 const_diag_iterator d1_begin,
+                                 const_diag_iterator d1_end,
+                                 const_diag_iterator d2_begin,
+                                 const_diag_iterator d2_end,
+                                 const char *Label) {
+  DiagList LeftOnly;
+  DiagList Left(d1_begin, d1_end);
+  DiagList Right(d2_begin, d2_end);
+
+  for (const_diag_iterator I = Left.begin(), E = Left.end(); I != E; ++I) {
+    unsigned LineNo1 = SourceMgr.getInstantiationLineNumber(I->first);
+    const std::string &Diag1 = I->second;
+
+    DiagList::iterator II, IE;
+    for (II = Right.begin(), IE = Right.end(); II != IE; ++II) {
+      unsigned LineNo2 = SourceMgr.getInstantiationLineNumber(II->first);
+      if (LineNo1 != LineNo2) continue;
+
+      const std::string &Diag2 = II->second;
+      if (Diag2.find(Diag1) != std::string::npos ||
+          Diag1.find(Diag2) != std::string::npos) {
+        break;
+      }
+    }
+    if (II == IE) {
+      // Not found.
+      LeftOnly.push_back(*I);
+    } else {
+      // Found. The same cannot be found twice.
+      Right.erase(II);
+    }
+  }
+  // Now all that's left in Right are those that were not matched.
+
+  return (PrintProblem(Diags, &SourceMgr,
+                      LeftOnly.begin(), LeftOnly.end(), Label, true) +
+          PrintProblem(Diags, &SourceMgr,
+                       Right.begin(), Right.end(), Label, false));
+}
+
+/// CheckResults - This compares the expected results to those that
+/// were actually reported. It emits any discrepencies. Return "true" if there
+/// were problems. Return "false" otherwise.
+///
+static unsigned CheckResults(Diagnostic &Diags, SourceManager &SourceMgr,
+                             const TextDiagnosticBuffer &Buffer,
+                             const DiagList &ExpectedErrors,
+                             const DiagList &ExpectedWarnings,
+                             const DiagList &ExpectedNotes) {
+  // We want to capture the delta between what was expected and what was
+  // seen.
+  //
+  //   Expected \ Seen - set expected but not seen
+  //   Seen \ Expected - set seen but not expected
+  unsigned NumProblems = 0;
+
+  // See if there are error mismatches.
+  NumProblems += CompareDiagLists(Diags, SourceMgr,
+                                  ExpectedErrors.begin(), ExpectedErrors.end(),
+                                  Buffer.err_begin(), Buffer.err_end(),
+                                  "error");
+
+  // See if there are warning mismatches.
+  NumProblems += CompareDiagLists(Diags, SourceMgr,
+                                  ExpectedWarnings.begin(),
+                                  ExpectedWarnings.end(),
+                                  Buffer.warn_begin(), Buffer.warn_end(),
+                                  "warning");
+
+  // See if there are note mismatches.
+  NumProblems += CompareDiagLists(Diags, SourceMgr,
+                                  ExpectedNotes.begin(),
+                                  ExpectedNotes.end(),
+                                  Buffer.note_begin(), Buffer.note_end(),
+                                  "note");
+
+  return NumProblems;
+}
+
+
+void VerifyDiagnosticsClient::CheckDiagnostics() {
+  DiagList ExpectedErrors, ExpectedWarnings, ExpectedNotes;
+
+  // Ensure any diagnostics go to the primary client.
+  DiagnosticClient *CurClient = Diags.getClient();
+  Diags.setClient(PrimaryClient.get());
+
+  // If we have a preprocessor, scan the source for expected diagnostic
+  // markers. If not then any diagnostics are unexpected.
+  if (CurrentPreprocessor) {
+    FindExpectedDiags(*CurrentPreprocessor, ExpectedErrors, ExpectedWarnings,
+                      ExpectedNotes);
+
+    // Check that the expected diagnostics occurred.
+    NumErrors += CheckResults(Diags, CurrentPreprocessor->getSourceManager(),
+                              *Buffer,
+                              ExpectedErrors, ExpectedWarnings, ExpectedNotes);
+  } else {
+    NumErrors += (PrintProblem(Diags, 0,
+                               Buffer->err_begin(), Buffer->err_end(),
+                               "error", false) +
+                  PrintProblem(Diags, 0,
+                               Buffer->warn_begin(), Buffer->warn_end(),
+                               "warn", false) +
+                  PrintProblem(Diags, 0,
+                               Buffer->note_begin(), Buffer->note_end(),
+                               "note", false));
+  }
+
+  Diags.setClient(CurClient);
+
+  // Reset the buffer, we have processed all the diagnostics in it.
+  Buffer.reset(new TextDiagnosticBuffer());
+}