Random Number Generator Refactoring (removing from Module)

This patch removes the RNG from Module. Passes should instead create a new RNG for their use as needed.

Patch by Stephen Crane @rinon.

Differential revision: http://reviews.llvm.org/D4377

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224444 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/RandomNumberGenerator.h

@@ -7,9 +7,9 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// 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.
+// This file defines an abstraction for deterministic random number
+// generation (RNG).  Note that the current implementation is not
+// cryptographically secure as it uses the C++11 <random> facilities.
 //
 //===----------------------------------------------------------------------===//
 
@@ -24,26 +24,27 @@
 namespace llvm {
 
 /// A random number generator.
-/// Instances of this class should not be shared across threads.
+///
+/// Instances of this class should not be shared across threads. The
+/// seed should be set by passing the -rng-seed=<uint64> option. Use
+/// Module::createRNG to create a new RNG instance for use with that
+/// module.
 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);
+  uint_fast64_t operator()();
 
 private:
+  /// Seeds and salts the underlying RNG engine.
+  ///
+  /// This constructor should not be used directly. Instead use
+  /// Module::createRNG to create a new RNG salted with the Module ID.
+  RandomNumberGenerator(StringRef Salt);
+
   // 64-bit Mersenne Twister by Matsumoto and Nishimura, 2000
   // http://en.cppreference.com/w/cpp/numeric/random/mersenne_twister_engine
+  // This RNG is deterministically portable across C++11
+  // implementations.
   std::mt19937_64 Generator;
 
   // Noncopyable.
@@ -51,6 +52,8 @@ private:
       LLVM_DELETED_FUNCTION;
   RandomNumberGenerator &
   operator=(const RandomNumberGenerator &other) LLVM_DELETED_FUNCTION;
+
+  friend class Module;
 };
 }