Re: [PATCH v1] libstdc++: Optimize removal from unique assoc containers [PR112934]

["Barnabás Pőcze" <pobrn@protonmail.com>]

Hi


2024. március 13., szerda 12:43 keltezéssel, Jonathan Wakely <jwakely@redhat.com> írta:

> On Mon, 11 Mar 2024 at 23:36, Barnabás Pőcze <pobrn@protonmail.com> wrote:
> >
> > Previously, calling erase(key) on both std::map and std::set
> > would execute that same code that std::multi{map,set} would.
> > However, doing that is unnecessary because std::{map,set}
> > guarantee that all elements are unique.
> >
> > It is reasonable to expect that erase(key) is equivalent
> > or better than:
> >
> >   auto it = m.find(key);
> >   if (it != m.end())
> >     m.erase(it);
> >
> > However, this was not the case. Fix that by adding a new
> > function _Rb_tree<>::_M_erase_unique() that is essentially
> > equivalent to the above snippet, and use this from both
> > std::map and std::set.
> 
> Hi, this change looks reasonable, thanks for the patch. Please note
> that GCC is currently in "stage 3" of its dev process so this change
> would have to wait until after GCC 14 branches from trunk, due in a
> few weeks.

As far as I can see GCC 14 has been released, so I pulled and ran the test suite
again:

  make check-target-libstdc++-v3 RUNTESTFLAGS="conformance.exp=23_containers/*"

and it reported no failures. Is there anything else I should do?


Regards,
Barnabás Pőcze

> 
> I assume you ran the testsuite with no regressions. Do you have
> benchmarks to show this making a difference?
> 
> 
> >
> > libstdc++-v3/ChangeLog:
> >
> >         PR libstdc++/112934
> >         * include/bits/stl_tree.h (_Rb_tree<>::_M_erase_unique): Add.
> >         * include/bits/stl_map.h (map<>::erase): Use _M_erase_unique.
> >         * include/bits/stl_set.h (set<>::erase): Likewise.
> > ---
> >  libstdc++-v3/include/bits/stl_map.h  |  2 +-
> >  libstdc++-v3/include/bits/stl_set.h  |  2 +-
> >  libstdc++-v3/include/bits/stl_tree.h | 17 +++++++++++++++++
> >  3 files changed, 19 insertions(+), 2 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/bits/stl_map.h b/libstdc++-v3/include/bits/stl_map.h
> > index ad58a631af5..229643b77fd 100644
> > --- a/libstdc++-v3/include/bits/stl_map.h
> > +++ b/libstdc++-v3/include/bits/stl_map.h
> > @@ -1115,7 +1115,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> >         */
> >        size_type
> >        erase(const key_type& __x)
> > -      { return _M_t.erase(__x); }
> > +      { return _M_t._M_erase_unique(__x); }
> >
> >  #if __cplusplus >= 201103L
> >        // _GLIBCXX_RESOLVE_LIB_DEFECTS
> > diff --git a/libstdc++-v3/include/bits/stl_set.h b/libstdc++-v3/include/bits/stl_set.h
> > index c0eb4dbf65f..51a1717ec62 100644
> > --- a/libstdc++-v3/include/bits/stl_set.h
> > +++ b/libstdc++-v3/include/bits/stl_set.h
> > @@ -684,7 +684,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> >         */
> >        size_type
> >        erase(const key_type& __x)
> > -      { return _M_t.erase(__x); }
> > +      { return _M_t._M_erase_unique(__x); }
> >
> >  #if __cplusplus >= 201103L
> >        // _GLIBCXX_RESOLVE_LIB_DEFECTS
> > diff --git a/libstdc++-v3/include/bits/stl_tree.h b/libstdc++-v3/include/bits/stl_tree.h
> > index 6f470f04f6a..9e80d449c7e 100644
> > --- a/libstdc++-v3/include/bits/stl_tree.h
> > +++ b/libstdc++-v3/include/bits/stl_tree.h
> > @@ -1225,6 +1225,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >        size_type
> >        erase(const key_type& __x);
> >
> > +      size_type
> > +      _M_erase_unique(const key_type& __x);
> > +
> >  #if __cplusplus >= 201103L
> >        // _GLIBCXX_RESOLVE_LIB_DEFECTS
> >        // DR 130. Associative erase should return an iterator.
> > @@ -2518,6 +2521,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >        return __old_size - size();
> >      }
> >
> > +  template<typename _Key, typename _Val, typename _KeyOfValue,
> > +          typename _Compare, typename _Alloc>
> > +    typename _Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::size_type
> > +    _Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::
> > +    _M_erase_unique(const _Key& __x)
> > +    {
> > +      iterator __it = find(__x);
> > +      if (__it == end())
> > +       return 0;
> > +
> > +      _M_erase_aux(__it);
> > +      return 1;
> > +    }
> > +
> >    template<typename _Key, typename _Val, typename _KeyOfValue,
> >            typename _Compare, typename _Alloc>
> >      typename _Rb_tree<_Key, _Val, _KeyOfValue,
> > --
> > 2.44.0
> >
> >
>