3 files changed, 67 insertions, 1 deletions
diff --git a/llvm/lib/IR/Module.cpp b/llvm/lib/IR/Module.cpp
index 6a5b386c199..0f73d44ce45 100644
--- a/llvm/lib/IR/Module.cpp
+++ b/llvm/lib/IR/Module.cpp
@@ -24,6 +24,8 @@
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/LeakDetector.h"
 #include "llvm/Support/Dwarf.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/RandomNumberGenerator.h"
 #include <algorithm>
 #include <cstdarg>
 #include <cstdlib>
@@ -44,7 +46,7 @@ template class llvm::SymbolTableListTraits<GlobalAlias, Module>;
 //
 
 Module::Module(StringRef MID, LLVMContext &C)
-    : Context(C), Materializer(), ModuleID(MID), DL("") {
+    : Context(C), Materializer(), ModuleID(MID), RNG(nullptr), DL("") {
   ValSymTab = new ValueSymbolTable();
   NamedMDSymTab = new StringMap<NamedMDNode *>();
   Context.addModule(this);
@@ -59,6 +61,7 @@ Module::~Module() {
   NamedMDList.clear();
   delete ValSymTab;
   delete static_cast<StringMap<NamedMDNode *> *>(NamedMDSymTab);
+  delete RNG;
 }
 
 /// getNamedValue - Return the first global value in the module with
@@ -355,6 +358,16 @@ const DataLayout *Module::getDataLayout() const {
   return &DL;
 }
 
+// We want reproducible builds, but ModuleID may be a full path so we just use
+// the filename to salt the RNG (although it is not guaranteed to be unique).
+RandomNumberGenerator &Module::getRNG() const {
+  if (RNG == nullptr) {
+    StringRef Salt = sys::path::filename(ModuleID);
+    RNG = new RandomNumberGenerator(Salt);
+  }
+  return *RNG;
+}
+
 //===----------------------------------------------------------------------===//
 // Methods to control the materialization of GlobalValues in the Module.
 //
diff --git a/llvm/lib/Support/CMakeLists.txt b/llvm/lib/Support/CMakeLists.txt
index 2438d729d8d..eac95c262b5 100644
--- a/llvm/lib/Support/CMakeLists.txt
+++ b/llvm/lib/Support/CMakeLists.txt
@@ -41,6 +41,7 @@ add_llvm_library(LLVMSupport
   MD5.cpp
   PluginLoader.cpp
   PrettyStackTrace.cpp
+  RandomNumberGenerator.cpp
   Regex.cpp
   SmallPtrSet.cpp
   SmallVector.cpp
diff --git a/llvm/lib/Support/RandomNumberGenerator.cpp b/llvm/lib/Support/RandomNumberGenerator.cpp
new file mode 100644
index 00000000000..5513982e7b1
--- /dev/null
+++ b/llvm/lib/Support/RandomNumberGenerator.cpp
@@ -0,0 +1,52 @@
+//===-- 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"
+
+using namespace llvm;
+
+// Tracking BUG: 19665
+// http://llvm.org/bugs/show_bug.cgi?id=19665
+//
+// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
+static cl::opt<unsigned long long>
+Seed("rng-seed", cl::value_desc("seed"),
+     cl::desc("Seed for the random number generator"), cl::init(0));
+
+RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
+  DEBUG(
+    if (Seed == 0)
+      errs() << "Warning! Using unseeded random number generator.\n"
+  );
+
+  // Combine seed and salt using std::seed_seq.
+  // Entropy: Seed-low, Seed-high, Salt...
+  size_t Size = Salt.size() + 2;
+  uint32_t Data[Size];
+  Data[0] = Seed;
+  Data[1] = Seed >> 32;
+  std::copy_n(Salt.begin(), Salt.size(), Data + 2);
+
+  std::seed_seq SeedSeq(Data, Data + Size);
+  Generator.seed(SeedSeq);
+}
+
+uint64_t RandomNumberGenerator::next(uint64_t Max) {
+  std::uniform_int_distribution<uint64_t> distribution(0, Max - 1);
+  return distribution(Generator);
+}