Commit bfebc63a authored by Alex Lorenz's avatar Alex Lorenz
Browse files

[ADT][Expensive checks] Create a std::random_device seed only once when shuffling before sorting 

This speeds up the build of compiler-rt with an expensive checks enabled clang by an order of
1 or 2 magnitudes on my machine. I was hoping this would also fix the 'large.test' libFuzzer
timeout on the expensive checks bot on green dragon http://lab.llvm.org:8080/green/job/clang-stage1-cmake-RA-expensive/,
but the fuzzer test still takes too long to compile because of other IR/MIR verification inefficiencies.

Differential Revision: https://reviews.llvm.org/D70288
parent 77f8a332

llvm/include/llvm/ADT/STLExtras.h

+21 −8
Original line number Diff line number Diff line
@@ -1053,6 +1053,23 @@ inline int (*get_array_pod_sort_comparator(const T &)) 
  return array_pod_sort_comparator<T>;

}



#ifdef EXPENSIVE_CHECKS

namespace detail {



inline unsigned presortShuffleEntropy() {

  static unsigned Result(std::random_device{}());

  return Result;

}



template <class IteratorTy>

inline void presortShuffle(IteratorTy Start, IteratorTy End) {

  std::mt19937 Generator(presortShuffleEntropy());

  std::shuffle(Start, End, Generator);

}



} // end namespace detail

#endif



/// array_pod_sort - This sorts an array with the specified start and end

/// extent.  This is just like std::sort, except that it calls qsort instead of

/// using an inlined template.  qsort is slightly slower than std::sort, but
@@ -1074,8 +1091,7 @@ inline void array_pod_sort(IteratorTy Start, IteratorTy End) { 
  auto NElts = End - Start;

  if (NElts <= 1) return;

#ifdef EXPENSIVE_CHECKS

  std::mt19937 Generator(std::random_device{}());

  std::shuffle(Start, End, Generator);

  detail::presortShuffle<IteratorTy>(Start, End);

#endif

  qsort(&*Start, NElts, sizeof(*Start), get_array_pod_sort_comparator(*Start));

}
@@ -1091,8 +1107,7 @@ inline void array_pod_sort( 
  auto NElts = End - Start;

  if (NElts <= 1) return;

#ifdef EXPENSIVE_CHECKS

  std::mt19937 Generator(std::random_device{}());

  std::shuffle(Start, End, Generator);

  detail::presortShuffle<IteratorTy>(Start, End);

#endif

  qsort(&*Start, NElts, sizeof(*Start),

        reinterpret_cast<int (*)(const void *, const void *)>(Compare));
@@ -1103,8 +1118,7 @@ inline void array_pod_sort( 
template <typename IteratorTy>

inline void sort(IteratorTy Start, IteratorTy End) {

#ifdef EXPENSIVE_CHECKS

  std::mt19937 Generator(std::random_device{}());

  std::shuffle(Start, End, Generator);

  detail::presortShuffle<IteratorTy>(Start, End);

#endif

  std::sort(Start, End);

}
@@ -1116,8 +1130,7 @@ template <typename Container> inline void sort(Container &&C) { 
template <typename IteratorTy, typename Compare>

inline void sort(IteratorTy Start, IteratorTy End, Compare Comp) {

#ifdef EXPENSIVE_CHECKS

  std::mt19937 Generator(std::random_device{}());

  std::shuffle(Start, End, Generator);

  detail::presortShuffle<IteratorTy>(Start, End);

#endif

  std::sort(Start, End, Comp);

}