Index: include/llvm/Support/RandomNumberGenerator.h
===================================================================
--- /dev/null
+++ include/llvm/Support/RandomNumberGenerator.h
@@ -0,0 +1,54 @@
+//==- llvm/Support/RandomNumberGenerator.h - RNG for diversity ---*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines an abstraction for random number generation (RNG).
+// Note that the current implementation is not cryptographically secure
+// as it uses the C++11 <random> facilities.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
+#define LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
+
+#include "llvm/ADT/StringRef.h"
+#include <string>
+#include <random>
+
+namespace llvm {
+
+class RandomNumberGenerator {
+public:
+  /// \brief Add additional personalization data to the RNG seed.
+  ///
+  /// This function should be used to add deterministic command line
+  /// argument data to the RNG initialization, resulting in a
+  /// different stream of random numbers for each invocation during a
+  /// build. The input to this function should be unique per
+  /// compilation unit.
+  static void SetSalt(const StringRef &Salt);
+
+  static RandomNumberGenerator *Get();
+
+  /// \brief Returns a random number in the range [0, Max).
+  uint64_t Random(uint64_t Max);
+
+private:
+  std::default_random_engine generator;
+
+  void Seed(StringRef Salt, uint64_t Seed);
+
+  RandomNumberGenerator();
+  // Noncopyable.
+  RandomNumberGenerator(const RandomNumberGenerator &other) = delete;
+  RandomNumberGenerator &
+  operator=(const RandomNumberGenerator &other) = delete;
+};
+}
+
+#endif
Index: lib/Support/CMakeLists.txt
===================================================================
--- lib/Support/CMakeLists.txt
+++ lib/Support/CMakeLists.txt
@@ -40,6 +40,7 @@
   MD5.cpp
   PluginLoader.cpp
   PrettyStackTrace.cpp
+  RandomNumberGenerator.cpp
   Regex.cpp
   SmallPtrSet.cpp
   SmallVector.cpp
Index: lib/Support/RandomNumberGenerator.cpp
===================================================================
--- /dev/null
+++ lib/Support/RandomNumberGenerator.cpp
@@ -0,0 +1,86 @@
+//===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements random number generation (RNG).
+// The current implementation is NOT cryptographically secure as it uses
+// the C++11 <random> facilities.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "rng"
+#include "llvm/Support/RandomNumberGenerator.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/ThreadLocal.h"
+
+using namespace llvm;
+
+// Initialized once, then only read by threads, so no locking required.
+static std::string SaltData;
+
+// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
+static cl::opt<unsigned long long>
+RandomSeed("rng-seed", cl::value_desc("seed"),
+           cl::desc("Seed for the random number generator"), cl::init(0));
+
+static cl::opt<std::string, true>
+SaltDataOpt("salt-data",
+            cl::desc("Salt data for the RNG (testing only, should be set "
+                     "by command line options"),
+            cl::Hidden, cl::location(SaltData));
+
+static ManagedStatic<sys::ThreadLocal<const RandomNumberGenerator> > Instance;
+
+void RandomNumberGenerator::SetSalt(const StringRef &Salt) {
+  SaltData = Salt;
+}
+
+RandomNumberGenerator *RandomNumberGenerator::Get() {
+  RandomNumberGenerator *RNG =
+      const_cast<RandomNumberGenerator *>(Instance->get());
+
+  if (RNG == nullptr) {
+    RNG = new RandomNumberGenerator;
+    Instance->set(RNG);
+  }
+
+  return RNG;
+}
+
+// Note that every new RNG will produce the same stream of
+// pseudo-random numbers, unless SetSalt is called again.
+RandomNumberGenerator::RandomNumberGenerator() {
+  if (RandomSeed == 0 && SaltData.empty())
+    DEBUG(errs()
+          << "Warning! Using unseeded and unsalted random number generator\n");
+
+  Seed(SaltData, RandomSeed);
+}
+
+uint64_t RandomNumberGenerator::Random(uint64_t Max) {
+  std::uniform_int_distribution<uint64_t> distribution(0, Max - 1);
+  return distribution(generator);
+}
+
+void RandomNumberGenerator::Seed(StringRef Salt, uint64_t Seed) {
+  DEBUG(dbgs() << "Re-Seeding RNG from salt and seed\n");
+  DEBUG(dbgs() << "Salt: " << Salt << "\n");
+  DEBUG(dbgs() << "Seed: " << Seed << "\n");
+
+  // Sequence: Seed-low, Seed-high, Salt...
+  size_t SeedSize = Salt.size() + 2;
+  uint32_t Seeds[SeedSize];
+  Seeds[0] = Seed;
+  Seeds[1] = Seed >> 32;
+  std::copy_n(Salt.begin(), Salt.size(), Seeds + 2);
+
+  std::seed_seq SeedSeq(Seeds, Seeds + SeedSize);
+  generator.seed(SeedSeq);
+}