Index: lib/LTO/LTOCodeGenerator.cpp
===================================================================
--- lib/LTO/LTOCodeGenerator.cpp
+++ lib/LTO/LTOCodeGenerator.cpp
@@ -64,16 +64,32 @@
 #endif
 }

-static void handleLTODiagnostic(const DiagnosticInfo &DI) {
-  DiagnosticPrinterRawOStream DP(errs());
-  DI.print(DP);
-  errs() << "\n";
+static const char *
+getLTODiagnosticPrefix(lto_codegen_diagnostic_severity_t Severity) {
+  switch (Severity) {
+  case LTO_DS_NOTE:
+    return "note: ";
+  case LTO_DS_REMARK:
+    return "remark: ";
+  case LTO_DS_ERROR:
+    return "error: ";
+  case LTO_DS_WARNING:
+    return "warning: ";
+  default:
+    return "";
+  }
 }

+static void handleLTODiagnostic(lto_codegen_diagnostic_severity_t Severity,
+                                const char *Msg, void *) {
+  errs() << getLTODiagnosticPrefix(Severity) << Msg << "\n";
+}
+
 LTOCodeGenerator::LTOCodeGenerator()
     : Context(getGlobalContext()),
       MergedModule(new Module("ld-temp.o", Context)),
-      IRLinker(MergedModule.get(), handleLTODiagnostic) {
+      IRLinker(MergedModule.get()) {
+  setDiagnosticHandler(handleLTODiagnostic, nullptr);
   initializeLTOPasses();
 }

@@ -80,7 +96,8 @@
 LTOCodeGenerator::LTOCodeGenerator(std::unique_ptr<LLVMContext> Context)
     : OwnedContext(std::move(Context)), Context(*OwnedContext),
       MergedModule(new Module("ld-temp.o", *OwnedContext)),
-      IRLinker(MergedModule.get(), handleLTODiagnostic) {
+      IRLinker(MergedModule.get()) {
+  setDiagnosticHandler(handleLTODiagnostic, nullptr);
   initializeLTOPasses();
 }

Index: tools/lto/lto.cpp
===================================================================
--- tools/lto/lto.cpp
+++ tools/lto/lto.cpp
@@ -85,13 +85,21 @@

 namespace {

+static void handleLibLTODiagnostic(lto_codegen_diagnostic_severity_t Severity,
+                                   const char *Msg, void *) {
+  sLastErrorString = Msg;
+  sLastErrorString += "\n";
+}
+
 // This derived class owns the native object file. This helps implement the
 // libLTO API semantics, which require that the code generator owns the object
 // file.
 struct LibLTOCodeGenerator : LTOCodeGenerator {
-  LibLTOCodeGenerator() {}
+  LibLTOCodeGenerator() {
+    setDiagnosticHandler(handleLibLTODiagnostic, nullptr); }
   LibLTOCodeGenerator(std::unique_ptr<LLVMContext> Context)
-      : LTOCodeGenerator(std::move(Context)) {}
+      : LTOCodeGenerator(std::move(Context)) {
+    setDiagnosticHandler(handleLibLTODiagnostic, nullptr); }

   std::unique_ptr<MemoryBuffer> NativeObjectFile;
 };