[PATCH] D70288: [ADT][Expensive checks] Create a /dev/random seed only once when shuffling the range before sorting it to avoid bot timeouts

[Alex Lorenz via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGbfebc63a3dbd: [ADT][Expensive checks] Create a std::random_device seed only once when… (authored by arphaman).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D70288/new/

https://reviews.llvm.org/D70288

Files:
  llvm/include/llvm/ADT/STLExtras.h


Index: llvm/include/llvm/ADT/STLExtras.h
===================================================================
--- llvm/include/llvm/ADT/STLExtras.h
+++ llvm/include/llvm/ADT/STLExtras.h
@@ -1053,6 +1053,23 @@
   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 @@
   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 @@
   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 @@
 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 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);
 }


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