Revert r258473 as it's breaking the build with libc++

lib/Fuzzer/FuzzerInterface.h

public:
   FuzzerRandomBase(){}
   virtual ~FuzzerRandomBase(){};
   virtual void ResetSeed(unsigned int seed) = 0;
   // Return a random number.
   virtual size_t Rand() = 0;
   // Return a random number in range [0,n).
   size_t operator()(size_t n) { return n ? Rand() % n : 0; }
   bool RandBool() { return Rand() % 2; }
-
-  // The methods below is to satisfy UniformRandomNumberGenerator:
-  // http://en.cppreference.com/w/cpp/concept/UniformRandomNumberGenerator\
-
-  // Returns a random number between 0 and RAND_MAX inclusive.
-  double operator()() { return operator()(RAND_MAX); }
-
-  // Returns the smallest value that operator() may return.
-  double min() { return 0; }
-
-  // Returns the largest value that operator() may return.
-  double max() { return RAND_MAX; }
 };
 
 // Using libc's stand/rand.
 class FuzzerRandomLibc : public FuzzerRandomBase {
  public:
   FuzzerRandomLibc(unsigned int seed) { ResetSeed(seed); }
   void ResetSeed(unsigned int seed) override;
   ~FuzzerRandomLibc() override {};

lib/Fuzzer/FuzzerInternal.h

 #ifndef LLVM_FUZZER_INTERNAL_H
 #define LLVM_FUZZER_INTERNAL_H
 
 #include <cassert>
 #include <climits>
 #include <chrono>
 #include <cstddef>
 #include <cstdlib>
-#include <random>
 #include <string>
 #include <string.h>
 #include <vector>
 #include <unordered_set>
 
 #include "FuzzerInterface.h"
 
 namespace fuzzer {
struct FuzzingOptions {
     std::string ArtifactPrefix = "./";
     std::string ExactArtifactPath;
     bool SaveArtifacts = true;
     bool PrintNEW = true;  // Print a status line when new units are found;
     bool OutputCSV = false;
     bool PrintNewCovPcs = false;
   };
   Fuzzer(UserSuppliedFuzzer &USF, FuzzingOptions Options);
-  void AddToCorpus(const Unit &U) { Corpus.push_back(U); UpdateCorpusDistribution(); }
+  void AddToCorpus(const Unit &U) { Corpus.push_back(U); }
   size_t ChooseUnitIdxToMutate();
   const Unit &ChooseUnitToMutate() { return Corpus[ChooseUnitIdxToMutate()]; };
   void Loop();
   void Drill();
   void ShuffleAndMinimize();
   void InitializeTraceState();
   void AssignTaintLabels(uint8_t *Data, size_t Size);
   size_t CorpusSize() const { return Corpus.size(); }
private:
   void MutateAndTestOne();
   void ReportNewCoverage(const Unit &U);
   bool RunOne(const Unit &U);
   void RunOneAndUpdateCorpus(Unit &U);
   void WriteToOutputCorpus(const Unit &U);
   void WriteUnitToFileWithPrefix(const Unit &U, const char *Prefix);
   void PrintStats(const char *Where, const char *End = "\n");
   void PrintStatusForNewUnit(const Unit &U);
-  // Updates the probability distribution for the units in the corpus.
-  // Must be called whenever the corpus or unit weights are changed.
-  void UpdateCorpusDistribution();
 
   void SyncCorpus();
 
   size_t RecordBlockCoverage();
   size_t RecordCallerCalleeCoverage();
   void PrepareCoverageBeforeRun();
   bool CheckCoverageAfterRun();
 
private:
   // For UseCounters
   std::vector<uint8_t> CounterBitmap;
   size_t TotalBits() {  // Slow. Call it only for printing stats.
     size_t Res = 0;
     for (auto x : CounterBitmap) Res += __builtin_popcount(x);
     return Res;
   }
 
-  std::piecewise_constant_distribution<double> CorpusDistribution;
   UserSuppliedFuzzer &USF;
   FuzzingOptions Options;
   system_clock::time_point ProcessStartTime = system_clock::now();
   system_clock::time_point LastExternalSync = system_clock::now();
   system_clock::time_point UnitStartTime;
   long TimeOfLongestUnitInSeconds = 0;
   long EpochOfLastReadOfOutputCorpus = 0;
   size_t LastRecordedBlockCoverage = 0;

lib/Fuzzer/FuzzerLoop.cpp

void Fuzzer::RereadOutputCorpus() {
   if (Options.Verbosity >= 2)
     Printf("Reload: read %zd new units.\n",  AdditionalCorpus.size());
   for (auto &X : AdditionalCorpus) {
     if (X.size() > (size_t)Options.MaxLen)
       X.resize(Options.MaxLen);
     if (UnitHashesAddedToCorpus.insert(Hash(X)).second) {
       if (RunOne(X)) {
         Corpus.push_back(X);
-        UpdateCorpusDistribution();
         PrintStats("RELOAD");
       }
     }
   }
 }
 
 void Fuzzer::ShuffleAndMinimize() {
   bool PreferSmall = (Options.PreferSmallDuringInitialShuffle == 1 ||
for (size_t First = 0; First < 1; First++) {
       if (RunOne(U)) {
         NewCorpus.push_back(U);
         if (Options.Verbosity >= 2)
           Printf("NEW0: %zd L %zd\n", LastRecordedBlockCoverage, U.size());
       }
     }
   }
   Corpus = NewCorpus;
-  UpdateCorpusDistribution();
   for (auto &X : Corpus)
     UnitHashesAddedToCorpus.insert(Hash(X));
   PrintStats("INITED");
 }
 
 bool Fuzzer::RunOne(const Unit &U) {
   UnitStartTime = system_clock::now();
   TotalNumberOfRuns++;
if (Options.Verbosity) {
     Printf(" L: %zd ", U.size());
     USF.GetMD().PrintMutationSequence();
     Printf("\n");
   }
 }
 
 void Fuzzer::ReportNewCoverage(const Unit &U) {
   Corpus.push_back(U);
-  UpdateCorpusDistribution();
   UnitHashesAddedToCorpus.insert(Hash(U));
   USF.GetMD().RecordSuccessfulMutationSequence();
   PrintStatusForNewUnit(U);
   WriteToOutputCorpus(U);
   if (Options.ExitOnFirst)
     exit(0);
 }
 
if (i == 0)
       StartTraceRecording();
     RunOneAndUpdateCorpus(U);
     StopTraceRecording();
   }
 }
 
 // Returns an index of random unit from the corpus to mutate.
 // Hypothesis: units added to the corpus last are more likely to be interesting.
-// This function gives more weight to the more recent units.
+// This function gives more wieght to the more recent units.
 size_t Fuzzer::ChooseUnitIdxToMutate() {
-    size_t Idx = static_cast<size_t>(CorpusDistribution(USF.GetRand()));
-    assert(Idx < Corpus.size());
-    return Idx;
+    size_t N = Corpus.size();
+    size_t Total = (N + 1) * N / 2;
+    size_t R = USF.GetRand()(Total);
+    size_t IdxBeg = 0, IdxEnd = N;
+    // Binary search.
+    while (IdxEnd - IdxBeg >= 2) {
+      size_t Idx = IdxBeg + (IdxEnd - IdxBeg) / 2;
+      if (R > (Idx + 1) * Idx / 2)
+        IdxBeg = Idx;
+      else
+        IdxEnd = Idx;
+    }
+    assert(IdxBeg < N);
+    return IdxBeg;
 }
 
 // Experimental search heuristic: drilling.
 // - Read, shuffle, execute and minimize the corpus.
 // - Choose one random unit.
 // - Reset the coverage.
 // - Start fuzzing as if the chosen unit was the only element of the corpus.
 // - When done, reset the coverage again.
 // - Merge the newly created corpus into the original one.
 void Fuzzer::Drill() {
   // The corpus is already read, shuffled, and minimized.
   assert(!Corpus.empty());
   Options.PrintNEW = false;  // Don't print NEW status lines when drilling.
 
   Unit U = ChooseUnitToMutate();
 
   CHECK_WEAK_API_FUNCTION(__sanitizer_reset_coverage);
   __sanitizer_reset_coverage();
 
   std::vector<Unit> SavedCorpus;
   SavedCorpus.swap(Corpus);
   Corpus.push_back(U);
-  UpdateCorpusDistribution();
   assert(Corpus.size() == 1);
   RunOne(U);
   PrintStats("DRILL ");
   std::string SavedOutputCorpusPath; // Don't write new units while drilling.
   SavedOutputCorpusPath.swap(Options.OutputCorpus);
   Loop();
 
   __sanitizer_reset_coverage();
void Fuzzer::SyncCorpus() {
   auto Now = system_clock::now();
   if (duration_cast<seconds>(Now - LastExternalSync).count() <
       Options.SyncTimeout)
     return;
   LastExternalSync = Now;
   ExecuteCommand(Options.SyncCommand + " " + Options.OutputCorpus);
 }
 
-void Fuzzer::UpdateCorpusDistribution() {
-  size_t N = Corpus.size();
-  std::vector<double> Intervals(N+1);
-  std::vector<double> Weights(N);
-  std::iota(Intervals.begin(), Intervals.end(), 0);
-  std::iota(Weights.begin(), Weights.end(), 1);
-  CorpusDistribution = std::piecewise_constant_distribution<double>(
-      Intervals.begin(), Intervals.end(), Weights.begin());
-}
-
 }  // namespace fuzzer

lib/Fuzzer/test/FuzzerUnittest.cpp

 #include "FuzzerInternal.h"
 #include "gtest/gtest.h"
 #include <set>
 
 using namespace fuzzer;
 
 // For now, have LLVMFuzzerTestOneInput just to make it link.
 // Later we may want to make unittests that actually call LLVMFuzzerTestOneInput.
-extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+extern "C" void LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   abort();
 }
 
 TEST(Fuzzer, CrossOver) {
   FuzzerRandomLibc Rand(0);
   MutationDispatcher MD(Rand);
   Unit A({0, 1, 2}), B({5, 6, 7});
   Unit C;
TEST(FuzzerUtil, Base64) {
   EXPECT_EQ("YWI=", Base64({'a', 'b'}));
   EXPECT_EQ("eHk=", Base64({'x', 'y'}));
   EXPECT_EQ("YWJj", Base64({'a', 'b', 'c'}));
   EXPECT_EQ("eHl6", Base64({'x', 'y', 'z'}));
   EXPECT_EQ("YWJjeA==", Base64({'a', 'b', 'c', 'x'}));
   EXPECT_EQ("YWJjeHk=", Base64({'a', 'b', 'c', 'x', 'y'}));
   EXPECT_EQ("YWJjeHl6", Base64({'a', 'b', 'c', 'x', 'y', 'z'}));
 }
-
-TEST(Corpus, Distribution) {
-  FuzzerRandomLibc Rand(0);
-  SimpleUserSuppliedFuzzer USF(&Rand, LLVMFuzzerTestOneInput);
-  Fuzzer::FuzzingOptions Options;
-  Fuzzer Fuzz(USF, Options);
-  size_t N = 10;
-  size_t TriesPerUnit = 1<<20;
-  for (size_t i = 0; i < N; i++) {
-    Fuzz.AddToCorpus(Unit{ static_cast<uint8_t>(i) });
-  }
-  std::vector<size_t> Hist(N);
-  for (size_t i = 0; i < N * TriesPerUnit; i++) {
-    Hist[Fuzz.ChooseUnitIdxToMutate()]++;
-  }
-  for (size_t i = 0; i < N; i++) {
-    // A weak sanity check that every unit gets invoked.
-    EXPECT_GT(Hist[i], TriesPerUnit / N / 3);
-  }
-}