re PR libstdc++/87135 ([C++17] unordered containers violate iterator validity requirements)

2018-09-21  François Dumont  <fdumont@gcc.gnu.org>

	PR libstdc++/87135
	* src/c++11/hashtable_c++0x.cc (_Prime_rehash_policy::_M_next_bkt):
	Use __builtin_floor to compute _M_next_resize.
	* testsuite/23_containers/unordered_set/hash_policy/71181.cc: Adapt.
	* testsuite/23_containers/unordered_set/hash_policy/prime_rehash.cc:
	Adapt.

From-SVN: r264494

libstdc++-v3/ChangeLog

+2018-09-21  François Dumont  <fdumont@gcc.gnu.org>
+
+	PR libstdc++/87135
+	* src/c++11/hashtable_c++0x.cc (_Prime_rehash_policy::_M_next_bkt):
+	Use __builtin_floor to compute _M_next_resize.
+	* testsuite/23_containers/unordered_set/hash_policy/71181.cc: Adapt.
+	* testsuite/23_containers/unordered_set/hash_policy/prime_rehash.cc:
+	Adapt.
+
 2018-09-21  Jonathan Wakely  <jwakely@redhat.com>
 
 	* testsuite/26_numerics/headers/cmath/hypot-long-double.cc: Remove.

libstdc++-v3/src/c++11/hashtable_c++0x.cc

@@ -52,7 +52,7 @@ namespace __detail
     if (__n < sizeof(__fast_bkt))
       {
 	_M_next_resize =
-	  __builtin_ceil(__fast_bkt[__n] * (long double)_M_max_load_factor);
+	  __builtin_floor(__fast_bkt[__n] * (long double)_M_max_load_factor);
 	return __fast_bkt[__n];
       }
 
@@ -75,7 +75,7 @@ namespace __detail
       _M_next_resize = std::size_t(-1);
     else
       _M_next_resize =
-	__builtin_ceil(*__next_bkt * (long double)_M_max_load_factor);
+	__builtin_floor(*__next_bkt * (long double)_M_max_load_factor);
 
     return *__next_bkt;
   }

libstdc++-v3/testsuite/23_containers/unordered_set/hash_policy/71181.cc

@@ -30,7 +30,7 @@ template<typename _USet>
     auto bkts = us.bucket_count();
     for (int i = 0; i != threshold; ++i)
       {
-	if (i == nb_reserved)
+	if (i >= nb_reserved)
 	  {
 	    nb_reserved = bkts;
 	    us.reserve(nb_reserved);

libstdc++-v3/testsuite/23_containers/unordered_set/hash_policy/prime_rehash.cc

@@ -26,20 +26,22 @@ void test01()
 {
   std::__detail::_Prime_rehash_policy policy;
 
-  for (std::size_t i = 1;;)
+  // Starts at 4 because 2 & 3 are two consecutives primes that make this test
+  // fail.
+  for (std::size_t i = 4;;)
     {
       auto nxt = policy._M_next_bkt(i);
 
-      if (nxt == i)
+      if (nxt <= i)
 	{
-	  // Equals only when reaching max.
-	  constexpr auto mx = std::numeric_limits<std::size_t>::max() - 1;
+	  // Lower or equals only when reaching max prime.
+	  constexpr auto mx = std::numeric_limits<std::size_t>::max();
 	  VERIFY( nxt == policy._M_next_bkt(mx) );
 	  break;
 	}
 
       VERIFY( nxt > i );
-      i = nxt;
+      i = nxt + 1;
     }
 }