From b4840d7a4d357b3f79071cccdeaadefe278b912a Mon Sep 17 00:00:00 2001
From: JF Bastien <jfb@google.com>
Date: Wed, 25 Jun 2014 15:21:42 +0000
Subject: Random Number Generator (llvm)

Provides an abstraction for a random number generator (RNG) that produces a stream of pseudo-random numbers.
The current implementation uses C++11 facilities and is therefore not cryptographically secure.

The RNG is salted with the text of the current command line invocation.
In addition, a user may specify a seed (reproducible builds).

In clang, the seed can be set via

-frandom-seed=X
In the back end, the seed can be set via

-rng-seed=X
This is the llvm part of the patch.
clang part: D3391

URL: http://reviews.llvm.org/D3390
Author: yln

I'm landing this for the second time, it broke Windows bots the first time around.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211705 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/IR/Module.h                     |  8 +++++
 include/llvm/Support/RandomNumberGenerator.h | 54 ++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 include/llvm/Support/RandomNumberGenerator.h

(limited to 'include')

diff --git a/include/llvm/IR/Module.h b/include/llvm/IR/Module.h
index 7230df9f79..77e5d21e29 100644
--- a/include/llvm/IR/Module.h
+++ b/include/llvm/IR/Module.h
@@ -29,6 +29,7 @@ namespace llvm {
 class FunctionType;
 class GVMaterializer;
 class LLVMContext;
+class RandomNumberGenerator;
 class StructType;
 template<typename T> struct DenseMapInfo;
 template<typename KeyT, typename ValueT, typename KeyInfoT> class DenseMap;
@@ -201,6 +202,8 @@ private:
   std::string ModuleID;           ///< Human readable identifier for the module
   std::string TargetTriple;       ///< Platform target triple Module compiled on
   void *NamedMDSymTab;            ///< NamedMDNode names.
+  // Allow lazy initialization in const method.
+  mutable RandomNumberGenerator *RNG; ///< The random number generator for this module.
 
   // We need to keep the string because the C API expects us to own the string
   // representation.
@@ -249,6 +252,11 @@ public:
   /// @returns a string containing the module-scope inline assembly blocks.
   const std::string &getModuleInlineAsm() const { return GlobalScopeAsm; }
 
+  /// Get the RandomNumberGenerator for this module. The RNG can be
+  /// seeded via -rng-seed=<uint64> and is salted with the ModuleID.
+  /// The returned RNG should not be shared across threads.
+  RandomNumberGenerator &getRNG() const;
+
 /// @}
 /// @name Module Level Mutators
 /// @{
diff --git a/include/llvm/Support/RandomNumberGenerator.h b/include/llvm/Support/RandomNumberGenerator.h
new file mode 100644
index 0000000000..1ec2c7eca9
--- /dev/null
+++ b/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 "llvm/Support/DataTypes.h" // Needed for uint64_t on Windows.
+#include <random>
+
+namespace llvm {
+
+/// A random number generator.
+/// Instances of this class should not be shared across threads.
+class RandomNumberGenerator {
+public:
+  /// Seeds and salts the underlying RNG engine. The salt of type StringRef
+  /// is passed into the constructor. The seed can be set on the command
+  /// line via -rng-seed=<uint64>.
+  /// The reason for the salt is to ensure different random streams even if
+  /// the same seed is used for multiple invocations of the compiler.
+  /// A good salt value should add additional entropy and be constant across
+  /// different machines (i.e., no paths) to allow for reproducible builds.
+  /// An instance of this class can be retrieved from the current Module.
+  /// \see Module::getRNG
+  RandomNumberGenerator(StringRef Salt);
+
+  /// Returns a random number in the range [0, Max).
+  uint64_t next(uint64_t Max);
+
+private:
+  // 64-bit Mersenne Twister by Matsumoto and Nishimura, 2000
+  // http://en.cppreference.com/w/cpp/numeric/random/mersenne_twister_engine
+  std::mt19937_64 Generator;
+
+  // Noncopyable.
+  RandomNumberGenerator(const RandomNumberGenerator &other) = delete;
+  RandomNumberGenerator &operator=(const RandomNumberGenerator &other) = delete;
+};
+}
+
+#endif
-- 
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