[llvm] r224444 - Random Number Generator Refactoring (removing from Module)
JF Bastien
jfb at google.com
Wed Dec 17 10:12:11 PST 2014
Author: jfb
Date: Wed Dec 17 12:12:10 2014
New Revision: 224444
URL: http://llvm.org/viewvc/llvm-project?rev=224444&view=rev
Log:
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
Modified:
llvm/trunk/include/llvm/IR/Module.h
llvm/trunk/include/llvm/Support/RandomNumberGenerator.h
llvm/trunk/lib/IR/Module.cpp
llvm/trunk/lib/Support/RandomNumberGenerator.cpp
Modified: llvm/trunk/include/llvm/IR/Module.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/Module.h?rev=224444&r1=224443&r2=224444&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/Module.h (original)
+++ llvm/trunk/include/llvm/IR/Module.h Wed Dec 17 12:12:10 2014
@@ -219,8 +219,6 @@ private:
std::string TargetTriple; ///< Platform target triple Module compiled on
///< Format: (arch)(sub)-(vendor)-(sys0-(abi)
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.
@@ -269,10 +267,16 @@ 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;
+ /// Get a RandomNumberGenerator salted for use with this module. The
+ /// RNG can be seeded via -rng-seed=<uint64> and is salted with the
+ /// ModuleID and the provided pass salt. The returned RNG should not
+ /// be shared across threads or passes.
+ ///
+ /// A unique RNG per pass ensures a reproducible random stream even
+ /// when other randomness consuming passes are added or removed. In
+ /// addition, the random stream will be reproducible across LLVM
+ /// versions when the pass does not change.
+ RandomNumberGenerator *createRNG(const Pass* P) const;
/// @}
/// @name Module Level Mutators
Modified: llvm/trunk/include/llvm/Support/RandomNumberGenerator.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/RandomNumberGenerator.h?rev=224444&r1=224443&r2=224444&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/RandomNumberGenerator.h (original)
+++ llvm/trunk/include/llvm/Support/RandomNumberGenerator.h Wed Dec 17 12:12:10 2014
@@ -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;
};
}
Modified: llvm/trunk/lib/IR/Module.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Module.cpp?rev=224444&r1=224443&r2=224444&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Module.cpp (original)
+++ llvm/trunk/lib/IR/Module.cpp Wed Dec 17 12:12:10 2014
@@ -47,7 +47,7 @@ template class llvm::SymbolTableListTrai
//
Module::Module(StringRef MID, LLVMContext &C)
- : Context(C), Materializer(), ModuleID(MID), RNG(nullptr), DL("") {
+ : Context(C), Materializer(), ModuleID(MID), DL("") {
ValSymTab = new ValueSymbolTable();
NamedMDSymTab = new StringMap<NamedMDNode *>();
Context.addModule(this);
@@ -62,9 +62,27 @@ Module::~Module() {
NamedMDList.clear();
delete ValSymTab;
delete static_cast<StringMap<NamedMDNode *> *>(NamedMDSymTab);
- delete RNG;
}
+RandomNumberGenerator *Module::createRNG(const Pass* P) const {
+ SmallString<32> Salt(P->getPassName());
+
+ // This RNG is guaranteed to produce the same random stream only
+ // when the Module ID and thus the input filename is the same. This
+ // might be problematic if the input filename extension changes
+ // (e.g. from .c to .bc or .ll).
+ //
+ // We could store this salt in NamedMetadata, but this would make
+ // the parameter non-const. This would unfortunately make this
+ // interface unusable by any Machine passes, since they only have a
+ // const reference to their IR Module. Alternatively we can always
+ // store salt metadata from the Module constructor.
+ Salt += sys::path::filename(getModuleIdentifier());
+
+ return new RandomNumberGenerator(Salt);
+}
+
+
/// getNamedValue - Return the first global value in the module with
/// the specified name, of arbitrary type. This method returns null
/// if a global with the specified name is not found.
@@ -374,16 +392,6 @@ const DataLayout *Module::getDataLayout(
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.
//
Modified: llvm/trunk/lib/Support/RandomNumberGenerator.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/RandomNumberGenerator.cpp?rev=224444&r1=224443&r2=224444&view=diff
==============================================================================
--- llvm/trunk/lib/Support/RandomNumberGenerator.cpp (original)
+++ llvm/trunk/lib/Support/RandomNumberGenerator.cpp Wed Dec 17 12:12:10 2014
@@ -7,16 +7,16 @@
//
//===----------------------------------------------------------------------===//
//
-// This file implements random number generation (RNG).
+// This file implements deterministic 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/RandomNumberGenerator.h"
using namespace llvm;
@@ -31,31 +31,25 @@ Seed("rng-seed", cl::value_desc("seed"),
RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
DEBUG(
if (Seed == 0)
- errs() << "Warning! Using unseeded random number generator.\n"
+ dbgs() << "Warning! Using unseeded random number generator.\n"
);
- // Combine seed and salt using std::seed_seq.
- // Entropy: Seed-low, Seed-high, Salt...
+ // Combine seed and salts using std::seed_seq.
+ // Data: Seed-low, Seed-high, Salt
+ // Note: std::seed_seq can only store 32-bit values, even though we
+ // are using a 64-bit RNG. This isn't a problem since the Mersenne
+ // twister constructor copies these correctly into its initial state.
std::vector<uint32_t> Data;
- Data.reserve(2 + Salt.size()/4 + 1);
+ Data.reserve(2 + Salt.size());
Data.push_back(Seed);
Data.push_back(Seed >> 32);
- uint32_t Pack = 0;
- for (size_t I = 0; I < Salt.size(); ++I) {
- Pack <<= 8;
- Pack += Salt[I];
-
- if (I%4 == 3)
- Data.push_back(Pack);
- }
- Data.push_back(Pack);
+ std::copy(Salt.begin(), Salt.end(), Data.end());
std::seed_seq SeedSeq(Data.begin(), Data.end());
Generator.seed(SeedSeq);
}
-uint64_t RandomNumberGenerator::next(uint64_t Max) {
- std::uniform_int_distribution<uint64_t> distribution(0, Max - 1);
- return distribution(Generator);
+uint_fast64_t RandomNumberGenerator::operator()() {
+ return Generator();
}
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