Index: include/llvm/Support/RandomNumberGenerator.h
===================================================================
--- include/llvm/Support/RandomNumberGenerator.h
+++ include/llvm/Support/RandomNumberGenerator.h
@@ -19,6 +19,7 @@
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/DataTypes.h" // Needed for uint64_t on Windows.
 #include <random>
+#include <system_error>
 
 namespace llvm {
 class StringRef;
@@ -53,6 +54,9 @@
 
   friend class Module;
 };
+
+// Get random vector of specified size
+std::error_code getRandomBytes(void *Buffer, size_t Size);
 }
 
 #endif
Index: lib/Support/RandomNumberGenerator.cpp
===================================================================
--- lib/Support/RandomNumberGenerator.cpp
+++ lib/Support/RandomNumberGenerator.cpp
@@ -17,6 +17,11 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#ifdef LLVM_ON_WIN32
+#include "Windows/WindowsSupport.h"
+#else
+#include "Unix/Unix.h"
+#endif
 
 using namespace llvm;
 
@@ -55,3 +60,24 @@
 uint_fast64_t RandomNumberGenerator::operator()() {
   return Generator();
 }
+
+// Get random vector of specified size
+std::error_code getRandomBytes(void *Buffer, size_t Size) {
+#ifdef LLVM_ON_WIN32
+  HCRYPTPROV hProvider;
+  if (CryptAcquireContextW(&hProvider, 0, 0, PROV_RSA_FULL,
+                           CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
+    ScopedCryptContext ScopedHandle(hProvider);
+    if (CryptGenRandom(hProvider, Size, Buffer))
+      return std::error_code();
+  }
+  return std::error_code(GetLastError(), std::system_category());
+#else
+  int Fd = open("/dev/urandom", O_RDONLY);
+  if (Fd == -1)
+    return std::error_code(errno, std::system_category());
+  read(Fd, Buffer, Size);
+  close(Fd);
+  return std::error_code();
+#endif
+}
Index: lib/Support/Unix/Unix.h
===================================================================
--- lib/Support/Unix/Unix.h
+++ lib/Support/Unix/Unix.h
@@ -48,6 +48,10 @@
 # include <dlfcn.h>
 #endif
 
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+
 /// This function builds an error message into \p ErrMsg using the \p prefix
 /// string and the Unix error number given by \p errnum. If errnum is -1, the
 /// default then the value of errno is used.