diff --git a/llvm/include/llvm/ADT/StringMap.h b/llvm/include/llvm/ADT/StringMap.h
--- a/llvm/include/llvm/ADT/StringMap.h
+++ b/llvm/include/llvm/ADT/StringMap.h
@@ -14,12 +14,16 @@
 #ifndef LLVM_ADT_STRINGMAP_H
 #define LLVM_ADT_STRINGMAP_H
 
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringMapEntry.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/Support/AllocatorBase.h"
+#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
 #include <initializer_list>
 #include <iterator>
+#include <ostream>
+#include <sstream>
 
 namespace llvm {
 
@@ -483,6 +487,27 @@
   StringRef operator*() const { return this->wrapped()->getKey(); }
 };
 
+template <typename T>
+std::ostream &operator<<(std::ostream &OS, const StringMap<T> &M) {
+  if (M.empty()) {
+    return OS << "{ }";
+  }
+
+  std::vector<std::string> Lines;
+  for (const auto &E : M) {
+    std::ostringstream SS;
+    SS << E << ",";
+    Lines.push_back(SS.str());
+  }
+  llvm::sort(Lines.begin(), Lines.end());
+  Lines.insert(Lines.begin(), "{");
+  Lines.insert(Lines.end(), "}");
+
+  return OS << llvm::formatv("{0:$[\n]}",
+                             make_range(Lines.begin(), Lines.end()))
+                   .str();
+}
+
 } // end namespace llvm
 
 #endif // LLVM_ADT_STRINGMAP_H
diff --git a/llvm/include/llvm/ADT/StringMapEntry.h b/llvm/include/llvm/ADT/StringMapEntry.h
--- a/llvm/include/llvm/ADT/StringMapEntry.h
+++ b/llvm/include/llvm/ADT/StringMapEntry.h
@@ -17,8 +17,9 @@
 #define LLVM_ADT_STRINGMAPENTRY_H
 
 #include "llvm/ADT/None.h"
-#include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/StringRef.h"
+#include <ostream>
+#include <type_traits>
 
 namespace llvm {
 
@@ -145,6 +146,25 @@
   }
 };
 
+template <typename T, typename = std::void_t<>>
+struct CanStream : std::false_type {};
+
+template <typename T>
+struct CanStream<
+    T, std::void_t<decltype(std::declval<std::ostream>() << std::declval<T>())>>
+    : std::true_type {};
+
+template <typename T>
+std::ostream &operator<<(std::ostream &OS, const StringMapEntry<T> &S) {
+  OS << "{\"" << S.getKey().data() << "\": ";
+  if constexpr (CanStream<T>::value) {
+    OS << S.getValue();
+  } else {
+    OS << "some value ...";
+  }
+  return OS << "}";
+}
+
 } // end namespace llvm
 
 #endif // LLVM_ADT_STRINGMAPENTRY_H
diff --git a/llvm/unittests/ADT/StringMapTest.cpp b/llvm/unittests/ADT/StringMapTest.cpp
--- a/llvm/unittests/ADT/StringMapTest.cpp
+++ b/llvm/unittests/ADT/StringMapTest.cpp
@@ -12,6 +12,8 @@
 #include "llvm/Support/DataTypes.h"
 #include "gtest/gtest.h"
 #include <limits>
+#include <ostream>
+#include <sstream>
 #include <tuple>
 using namespace llvm;
 
@@ -635,4 +637,40 @@
   EXPECT_EQ(LargeValue, Key.size());
 }
 
+TEST(StringMapCustomTest, StringMapEntryStream) {
+  std::ostringstream OS;
+  StringMap<int> Map;
+  Map["A"] = 42;
+  Map["Z"] = 35;
+  Map["B"] = 7;
+
+  OS << Map;
+  EXPECT_EQ(OS.str(), R"({
+{"A": 42},
+{"B": 7},
+{"Z": 35},
+})");
+}
+
+TEST(StringMapCustomTest, NestedStringMapEntryStream) {
+  std::ostringstream OS;
+  StringMap<StringMap<int>> Map;
+  Map["Z"];
+  Map["A"]["Apple"] = 5;
+  Map["B"]["Bee"] = 3;
+  Map["A"]["Axe"] = 3;
+
+  OS << Map;
+  EXPECT_EQ(OS.str(), R"({
+{"A": {
+{"Apple": 5},
+{"Axe": 3},
+}},
+{"B": {
+{"Bee": 3},
+}},
+{"Z": { }},
+})");
+}
+
 } // end anonymous namespace