Index: include/clang/Frontend/TextDiagnosticBuffer.h
===================================================================
--- include/clang/Frontend/TextDiagnosticBuffer.h
+++ include/clang/Frontend/TextDiagnosticBuffer.h
@@ -29,6 +29,11 @@
   typedef DiagList::const_iterator const_iterator;
 private:
   DiagList Errors, Warnings, Remarks, Notes;
+  /// All - All diagnostics in the order in which they were generated.  That
+  /// order likely doesn't correspond to user input order, but it at least
+  /// keeps notes in the right places.  Each pair in the vector is a diagnostic
+  /// level and an index into the corresponding DiagList above.
+  std::vector<std::pair<DiagnosticsEngine::Level, size_t>> All;
 public:
   const_iterator err_begin() const  { return Errors.begin(); }
   const_iterator err_end() const    { return Errors.end(); }
Index: lib/Frontend/TextDiagnosticBuffer.cpp
===================================================================
--- lib/Frontend/TextDiagnosticBuffer.cpp
+++ lib/Frontend/TextDiagnosticBuffer.cpp
@@ -30,34 +30,45 @@
   default: llvm_unreachable(
                          "Diagnostic not handled during diagnostic buffering!");
   case DiagnosticsEngine::Note:
+    All.emplace_back(Level, Notes.size());
     Notes.emplace_back(Info.getLocation(), Buf.str());
     break;
   case DiagnosticsEngine::Warning:
+    All.emplace_back(Level, Warnings.size());
     Warnings.emplace_back(Info.getLocation(), Buf.str());
     break;
   case DiagnosticsEngine::Remark:
+    All.emplace_back(Level, Remarks.size());
     Remarks.emplace_back(Info.getLocation(), Buf.str());
     break;
   case DiagnosticsEngine::Error:
   case DiagnosticsEngine::Fatal:
+    All.emplace_back(Level, Errors.size());
     Errors.emplace_back(Info.getLocation(), Buf.str());
     break;
   }
 }
 
 void TextDiagnosticBuffer::FlushDiagnostics(DiagnosticsEngine &Diags) const {
-  // FIXME: Flush the diagnostics in order.
-  for (const_iterator it = err_begin(), ie = err_end(); it != ie; ++it)
-    Diags.Report(Diags.getCustomDiagID(DiagnosticsEngine::Error, "%0"))
-        << it->second;
-  for (const_iterator it = warn_begin(), ie = warn_end(); it != ie; ++it)
-    Diags.Report(Diags.getCustomDiagID(DiagnosticsEngine::Warning, "%0"))
-        << it->second;
-  for (const_iterator it = remark_begin(), ie = remark_end(); it != ie; ++it)
-    Diags.Report(Diags.getCustomDiagID(DiagnosticsEngine::Remark, "%0"))
-        << it->second;
-  for (const_iterator it = note_begin(), ie = note_end(); it != ie; ++it)
-    Diags.Report(Diags.getCustomDiagID(DiagnosticsEngine::Note, "%0"))
-        << it->second;
+  for (auto it = All.begin(), ie = All.end(); it != ie; ++it) {
+    auto Diag = Diags.Report(Diags.getCustomDiagID(it->first, "%0"));
+    switch (it->first) {
+    default: llvm_unreachable(
+                           "Diagnostic not handled during diagnostic flushing!");
+    case DiagnosticsEngine::Note:
+      Diag << Notes[it->second].second;
+      break;
+    case DiagnosticsEngine::Warning:
+      Diag << Warnings[it->second].second;
+      break;
+    case DiagnosticsEngine::Remark:
+      Diag << Remarks[it->second].second;
+      break;
+    case DiagnosticsEngine::Error:
+    case DiagnosticsEngine::Fatal:
+      Diag << Errors[it->second].second;
+      break;
+    }
+  }
 }
 
Index: test/Frontend/diagnostics-order.c
===================================================================
--- test/Frontend/diagnostics-order.c
+++ test/Frontend/diagnostics-order.c
@@ -0,0 +1,10 @@
+// Make sure a note stays with its associated command-line argument diagnostic.
+// Previously, these diagnostics were grouped by diagnostic level with all
+// notes last.
+//
+// RUN: not %clang_cc1 -O999 -std=bogus %s 2> %t
+// RUN: FileCheck < %t %s
+//
+// CHECK: warning: optimization level '-O999' is not supported
+// CHECK-NEXT: error: invalid value 'bogus' in '-std=bogus'
+// CHECK-NEXT: note: use {{.*}} for {{.*}} standard