Index: lib/Support/Signals.cpp
===================================================================
--- lib/Support/Signals.cpp
+++ lib/Support/Signals.cpp
@@ -20,6 +20,8 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FileUtilities.h"
 #include "llvm/Support/Format.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/FormatAdapters.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Mutex.h"
@@ -155,7 +157,7 @@
   }
 
   Optional<StringRef> Redirects[] = {StringRef(InputFile),
-                                     StringRef(OutputFile), llvm::None};
+                                     StringRef(OutputFile), ""};
   StringRef Args[] = {"llvm-symbolizer", "--functions=linkage", "--inlining",
 #ifdef _WIN32
                       // Pass --relative-address on Windows so that we don't
@@ -180,8 +182,14 @@
   auto CurLine = Lines.begin();
   int frame_no = 0;
   for (int i = 0; i < Depth; i++) {
+    auto PrintLineHeader = [&]() {
+      OS << right_justify(formatv("#{0}", frame_no++).str(),
+                          std::log10(Depth) + 2)
+         << ' ' << format_ptr(StackTrace[i]) << ' ';
+    };
     if (!Modules[i]) {
-      OS << '#' << frame_no++ << ' ' << format_ptr(StackTrace[i]) << '\n';
+      PrintLineHeader();
+      OS << '\n';
       continue;
     }
     // Read pairs of lines (function name and file/line info) until we
@@ -192,7 +200,7 @@
       StringRef FunctionName = *CurLine++;
       if (FunctionName.empty())
         break;
-      OS << '#' << frame_no++ << ' ' << format_ptr(StackTrace[i]) << ' ';
+      PrintLineHeader();
       if (!FunctionName.startswith("??"))
         OS << FunctionName << ' ';
       if (CurLine == Lines.end())