Random Number Generator (llvm)

Summary:
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

Reviewers: ahomescu, rinon, nicholas, jfb

Reviewed By: jfb

Subscribers: jfb, perl

Differential Revision: http://reviews.llvm.org/D3390

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211145 91177308-0d34-0410-b5e6-96231b3b80d8

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.
 //