diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -1537,15 +1537,29 @@
 }
 
 static StringRef ArgPrefix = "  -";
+static StringRef ArgPrefixLong = "  --";
 static StringRef ArgHelpPrefix = " - ";
-static size_t ArgPrefixesSize = ArgPrefix.size() + ArgHelpPrefix.size();
+
+static size_t argPrefixesSize(size_t len) {
+  if (len == 1)
+    return ArgPrefix.size() + ArgHelpPrefix.size();
+  return ArgPrefixLong.size() + ArgHelpPrefix.size();
+}
+
+static StringRef argPrefix(size_t len) {
+  if (len == 1)
+    return ArgPrefix;
+  return ArgPrefixLong;
+}
 
 //===----------------------------------------------------------------------===//
 // cl::alias class implementation
 //
 
 // Return the width of the option tag for printing...
-size_t alias::getOptionWidth() const { return ArgStr.size() + ArgPrefixesSize; }
+size_t alias::getOptionWidth() const {
+  return ArgStr.size() + argPrefixesSize(ArgStr.size());
+}
 
 void Option::printHelpStr(StringRef HelpStr, size_t Indent,
                           size_t FirstLineIndentedBy) {
@@ -1561,8 +1575,9 @@
 
 // Print out the option for the alias.
 void alias::printOptionInfo(size_t GlobalWidth) const {
-  outs() << ArgPrefix << ArgStr;
-  printHelpStr(HelpStr, GlobalWidth, ArgStr.size() + ArgPrefixesSize);
+  outs() << argPrefix(ArgStr.size()) << ArgStr;
+  printHelpStr(HelpStr, GlobalWidth,
+               ArgStr.size() + argPrefixesSize(ArgStr.size()));
 }
 
 //===----------------------------------------------------------------------===//
@@ -1583,7 +1598,7 @@
     Len += getValueStr(O, ValName).size() + FormattingLen;
   }
 
-  return Len + ArgPrefixesSize;
+  return Len + argPrefixesSize(O.ArgStr.size());
 }
 
 // printOptionInfo - Print out information about this option.  The
@@ -1591,7 +1606,7 @@
 //
 void basic_parser_impl::printOptionInfo(const Option &O,
                                         size_t GlobalWidth) const {
-  outs() << ArgPrefix << O.ArgStr;
+  outs() << argPrefix(O.ArgStr.size()) << O.ArgStr;
 
   auto ValName = getValueName();
   if (!ValName.empty()) {
@@ -1607,7 +1622,7 @@
 
 void basic_parser_impl::printOptionName(const Option &O,
                                         size_t GlobalWidth) const {
-  outs() << ArgPrefix << O.ArgStr;
+  outs() << argPrefix(O.ArgStr.size()) << O.ArgStr;
   outs().indent(GlobalWidth - O.ArgStr.size());
 }
 
@@ -1739,7 +1754,8 @@
 // Return the width of the option tag for printing...
 size_t generic_parser_base::getOptionWidth(const Option &O) const {
   if (O.hasArgStr()) {
-    size_t Size = O.ArgStr.size() + ArgPrefixesSize + EqValue.size();
+    size_t Size =
+        O.ArgStr.size() + argPrefixesSize(O.ArgStr.size()) + EqValue.size();
     for (unsigned i = 0, e = getNumOptions(); i != e; ++i) {
       StringRef Name = getOption(i);
       if (!shouldPrintOption(Name, getDescription(i), O))
@@ -1767,17 +1783,19 @@
     if (O.getValueExpectedFlag() == ValueOptional) {
       for (unsigned i = 0, e = getNumOptions(); i != e; ++i) {
         if (getOption(i).empty()) {
-          outs() << ArgPrefix << O.ArgStr;
+          outs() << argPrefix(O.ArgStr.size()) << O.ArgStr;
           Option::printHelpStr(O.HelpStr, GlobalWidth,
-                               O.ArgStr.size() + ArgPrefixesSize);
+                               O.ArgStr.size() +
+                                   argPrefixesSize(O.ArgStr.size()));
           break;
         }
       }
     }
 
-    outs() << ArgPrefix << O.ArgStr << EqValue;
+    outs() << argPrefix(O.ArgStr.size()) << O.ArgStr << EqValue;
     Option::printHelpStr(O.HelpStr, GlobalWidth,
-                         O.ArgStr.size() + EqValue.size() + ArgPrefixesSize);
+                         O.ArgStr.size() + EqValue.size() +
+                             argPrefixesSize(O.ArgStr.size()));
     for (unsigned i = 0, e = getNumOptions(); i != e; ++i) {
       StringRef OptionName = getOption(i);
       StringRef Description = getDescription(i);