Committed with the advised changes.
Ok, I'll backport next week.
Thanks
On 19/10/2023 10:05, Jonathan Wakely wrote:
On Thursday, 19 October 2023, François Dumont <frs.dum...@gmail.com>
wrote:
> libstdc++: [_Hashtable] Do not reuse untrusted cached hash code
>
> On merge reuse merged node cached hash code only if we are on the
same type of
> hash and this hash is stateless. Usage of function pointers or
std::function as
> hash functor will prevent this optimization.
I found this first sentence a little hard to parse. How about:
On merge, reuse a merged node's cached hash code only if we are on the
same
type of
hash and this hash is stateless.
And for the second sentence, would it be clearer to say "will prevent
reusing cached hash codes" instead of "will prevent this optimization"?
And for the comment on the new function, I think this reads better:
"Only use the node's (possibly cached) hash code if its hash function
_H2 matches _Hash. Otherwise recompute it using _Hash."
The code and tests look good, so if you're happy with the
comment+changelog suggestions, this is ok for trunk.
This seems like a bug fix that should be backported too, after some
time on trunk.
>
> libstdc++-v3/ChangeLog
>
> * include/bits/hashtable_policy.h
> (_Hash_code_base::_M_hash_code(const _Hash&, const
_Hash_node_value<>&)): Remove.
> (_Hash_code_base::_M_hash_code<_H2>(const _H2&, const
_Hash_node_value<>&)): Remove.
> * include/bits/hashtable.h
> (_M_src_hash_code<_H2>(const _H2&, const key_type&, const
__node_value_type&)): New.
> (_M_merge_unique<>, _M_merge_multi<>): Use latter.
> * testsuite/23_containers/unordered_map/modifiers/merge.cc
> (test04, test05, test06): New test cases.
>
> Tested under Linux x86_64, ok to commit ?
>
> François
>
>
