[committed] libstdc++: Do not use memset in _Hashtable::clear()

[Jonathan Wakely]

Tested x86_64-linux. Pushed to trunk.

-- >8 --

Using memset is incorrect if the __bucket_ptr type is non-trivial, or
does not use an all-zero bit pattern for its null value.

Replace the three uses of memset with std::fill_n to set the pointers to
nullptr.

libstdc++-v3/ChangeLog:

        * include/bits/hashtable.h (_Hashtable::clear): Do not use
        memset to zero out bucket pointers.
        (_Hashtable::_M_assign_elements): Likewise.
---
 libstdc++-v3/include/bits/hashtable.h | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/include/bits/hashtable.h 
b/libstdc++-v3/include/bits/hashtable.h
index 6e78cb7d9c0..983aa909d6c 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -34,6 +34,7 @@
 
 #include <bits/hashtable_policy.h>
 #include <bits/enable_special_members.h>
+#include <bits/stl_algobase.h> // fill_n
 #include <bits/stl_function.h> // __has_is_transparent_t
 #if __cplusplus > 201402L
 # include <bits/node_handle.h>
@@ -1376,8 +1377,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
            _M_bucket_count = __ht._M_bucket_count;
          }
        else
-         __builtin_memset(_M_buckets, 0,
-                          _M_bucket_count * sizeof(__node_base_ptr));
+         std::fill_n(_M_buckets, _M_bucket_count, nullptr);
 
        __try
          {
@@ -1400,8 +1400,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                _M_buckets = __former_buckets;
                _M_bucket_count = __former_bucket_count;
              }
-           __builtin_memset(_M_buckets, 0,
-                            _M_bucket_count * sizeof(__node_base_ptr));
+           std::fill_n(_M_buckets, _M_bucket_count, nullptr);
            __throw_exception_again;
          }
       }
@@ -2582,8 +2581,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     clear() noexcept
     {
       this->_M_deallocate_nodes(_M_begin());
-      __builtin_memset(_M_buckets, 0,
-                      _M_bucket_count * sizeof(__node_base_ptr));
+      std::fill_n(_M_buckets, _M_bucket_count, nullptr);
       _M_element_count = 0;
       _M_before_begin._M_nxt = nullptr;
     }
-- 
2.45.1