diff --git a/clang/include/clang/Frontend/CompilerInvocation.h b/clang/include/clang/Frontend/CompilerInvocation.h
--- a/clang/include/clang/Frontend/CompilerInvocation.h
+++ b/clang/include/clang/Frontend/CompilerInvocation.h
@@ -55,10 +55,9 @@
 /// Args must have been created from the OptTable returned by
 /// createCC1OptTable().
 ///
-/// When errors are encountered, return false and, if Diags is non-null,
-/// report the error(s).
+/// When errors are encountered, return false and report the error(s).
 bool ParseDiagnosticArgs(DiagnosticOptions &Opts, llvm::opt::ArgList &Args,
-                         DiagnosticsEngine *Diags = nullptr,
+                         DiagnosticsEngine &Diags,
                          bool DefaultDiagColor = true);
 
 class CompilerInvocationBase {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -828,7 +828,7 @@
 
 static bool parseDiagnosticLevelMask(StringRef FlagName,
                                      const std::vector<std::string> &Levels,
-                                     DiagnosticsEngine *Diags,
+                                     DiagnosticsEngine &Diags,
                                      DiagnosticLevelMask &M) {
   bool Success = true;
   for (const auto &Level : Levels) {
@@ -841,8 +841,7 @@
         .Default(DiagnosticLevelMask::None);
     if (PM == DiagnosticLevelMask::None) {
       Success = false;
-      if (Diags)
-        Diags->Report(diag::err_drv_invalid_value) << FlagName << Level;
+      Diags.Report(diag::err_drv_invalid_value) << FlagName << Level;
     }
     M = M | PM;
   }
@@ -1381,7 +1380,7 @@
 }
 
 static bool checkVerifyPrefixes(const std::vector<std::string> &VerifyPrefixes,
-                                DiagnosticsEngine *Diags) {
+                                DiagnosticsEngine &Diags) {
   bool Success = true;
   for (const auto &Prefix : VerifyPrefixes) {
     // Every prefix must start with a letter and contain only alphanumeric
@@ -1391,17 +1390,15 @@
     });
     if (BadChar != Prefix.end() || !isLetter(Prefix[0])) {
       Success = false;
-      if (Diags) {
-        Diags->Report(diag::err_drv_invalid_value) << "-verify=" << Prefix;
-        Diags->Report(diag::note_drv_verify_prefix_spelling);
-      }
+      Diags.Report(diag::err_drv_invalid_value) << "-verify=" << Prefix;
+      Diags.Report(diag::note_drv_verify_prefix_spelling);
     }
   }
   return Success;
 }
 
 bool clang::ParseDiagnosticArgs(DiagnosticOptions &Opts, ArgList &Args,
-                                DiagnosticsEngine *Diags,
+                                DiagnosticsEngine &Diags,
                                 bool DefaultDiagColor) {
   bool Success = true;
 
@@ -1437,10 +1434,9 @@
     Opts.setShowOverloads(Ovl_All);
   else {
     Success = false;
-    if (Diags)
-      Diags->Report(diag::err_drv_invalid_value)
-      << Args.getLastArg(OPT_fshow_overloads_EQ)->getAsString(Args)
-      << ShowOverloads;
+    Diags.Report(diag::err_drv_invalid_value)
+        << Args.getLastArg(OPT_fshow_overloads_EQ)->getAsString(Args)
+        << ShowOverloads;
   }
 
   StringRef ShowCategory =
@@ -1453,10 +1449,9 @@
     Opts.ShowCategories = 2;
   else {
     Success = false;
-    if (Diags)
-      Diags->Report(diag::err_drv_invalid_value)
-      << Args.getLastArg(OPT_fdiagnostics_show_category)->getAsString(Args)
-      << ShowCategory;
+    Diags.Report(diag::err_drv_invalid_value)
+        << Args.getLastArg(OPT_fdiagnostics_show_category)->getAsString(Args)
+        << ShowCategory;
   }
 
   StringRef Format =
@@ -1472,10 +1467,9 @@
     Opts.setFormat(DiagnosticOptions::Vi);
   else {
     Success = false;
-    if (Diags)
-      Diags->Report(diag::err_drv_invalid_value)
-      << Args.getLastArg(OPT_fdiagnostics_format)->getAsString(Args)
-      << Format;
+    Diags.Report(diag::err_drv_invalid_value)
+        << Args.getLastArg(OPT_fdiagnostics_format)->getAsString(Args)
+        << Format;
   }
 
   Opts.ShowSourceRanges = Args.hasArg(OPT_fdiagnostics_print_source_range_info);
@@ -1521,9 +1515,8 @@
                                     DiagnosticOptions::DefaultTabStop, Diags);
   if (Opts.TabStop == 0 || Opts.TabStop > DiagnosticOptions::MaxTabStop) {
     Opts.TabStop = DiagnosticOptions::DefaultTabStop;
-    if (Diags)
-      Diags->Report(diag::warn_ignoring_ftabstop_value)
-      << Opts.TabStop << DiagnosticOptions::DefaultTabStop;
+    Diags.Report(diag::warn_ignoring_ftabstop_value)
+        << Opts.TabStop << DiagnosticOptions::DefaultTabStop;
   }
   Opts.MessageLength =
       getLastArgIntValue(Args, OPT_fmessage_length_EQ, 0, Diags);
@@ -3056,7 +3049,7 @@
     Diags.Report(diag::err_fe_dependency_file_requires_MT);
     Success = false;
   }
-  Success &= ParseDiagnosticArgs(Res.getDiagnosticOpts(), Args, &Diags,
+  Success &= ParseDiagnosticArgs(Res.getDiagnosticOpts(), Args, Diags,
                                  /*DefaultDiagColor=*/false);
   ParseCommentArgs(LangOpts.CommentOpts, Args);
   // FIXME: We shouldn't have to pass the DashX option around here
diff --git a/clang/lib/Tooling/Tooling.cpp b/clang/lib/Tooling/Tooling.cpp
--- a/clang/lib/Tooling/Tooling.cpp
+++ b/clang/lib/Tooling/Tooling.cpp
@@ -328,7 +328,9 @@
   unsigned MissingArgIndex, MissingArgCount;
   llvm::opt::InputArgList ParsedArgs = driver::getDriverOptTable().ParseArgs(
       ArrayRef<const char *>(Argv).slice(1), MissingArgIndex, MissingArgCount);
-  ParseDiagnosticArgs(*DiagOpts, ParsedArgs);
+  DiagnosticsEngine DummyDiags(new DiagnosticIDs(), new DiagnosticOptions(),
+                               new IgnoringDiagConsumer());
+  ParseDiagnosticArgs(*DiagOpts, ParsedArgs, DummyDiags);
   TextDiagnosticPrinter DiagnosticPrinter(
       llvm::errs(), &*DiagOpts);
   DiagnosticsEngine Diagnostics(
diff --git a/clang/tools/driver/driver.cpp b/clang/tools/driver/driver.cpp
--- a/clang/tools/driver/driver.cpp
+++ b/clang/tools/driver/driver.cpp
@@ -281,7 +281,9 @@
   // We ignore MissingArgCount and the return value of ParseDiagnosticArgs.
   // Any errors that would be diagnosed here will also be diagnosed later,
   // when the DiagnosticsEngine actually exists.
-  (void)ParseDiagnosticArgs(*DiagOpts, Args);
+  DiagnosticsEngine DummyDiags(new DiagnosticIDs(), new DiagnosticOptions(),
+                               new IgnoringDiagConsumer());
+  (void)ParseDiagnosticArgs(*DiagOpts, Args, DummyDiags);
 
   UseNewCC1Process =
       Args.hasFlag(clang::driver::options::OPT_fno_integrated_cc1,