[PATCH] libstdc++: Fix-self element self-assigments when insertint an empty range [PR121313]

[Jonathan Wakely]

On Thu, 14 Aug 2025, 15:31 Patrick Palka, <ppalka@redhat.com> wrote:

> On Thu, 14 Aug 2025, Tomasz Kamiński wrote:
>
> Typo in subject line, "inserting"
>
> > For __n == 0, the elements where self move-assigned by
> > std::move_backward(__ins, __old_finish - __n, __old_finish).
>
> s/where/were?
>
> LGTM besides that.
>

Yeah, ok for trunk and gcc-15 with those tweaks.




> >
> >       PR libstdc++/121313
> >
> > libstdc++-v3/ChangeLog:
> >
> >       * include/bits/vector.tcc (vector::insert_range): Add check for
> >       empty size.
> >       * testsuite/23_containers/vector/modifiers/insert/insert_range.cc:
> >       New tests.
> > ---
> > Testing on x86_64-linux. Newly added test passed.
> >
> > OK for trunk and v15.
> >
> >  libstdc++-v3/include/bits/vector.tcc          | 10 ++--
> >  .../vector/modifiers/insert/insert_range.cc   | 50 +++++++++++++++++++
> >  2 files changed, 57 insertions(+), 3 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/bits/vector.tcc
> b/libstdc++-v3/include/bits/vector.tcc
> > index 70ead1d7083..1543ce9cd77 100644
> > --- a/libstdc++-v3/include/bits/vector.tcc
> > +++ b/libstdc++-v3/include/bits/vector.tcc
> > @@ -1007,17 +1007,21 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> >
> >       if constexpr (ranges::forward_range<_Rg>)
> >         {
> > +         const auto __ins_idx = __pos - cbegin();
> > +         // Number of new elements to insert:
> > +         const auto __n = size_type(ranges::distance(__rg));
> > +         if (__n == 0)
> > +           return begin() + __ins_idx;
> > +
> >           // Start of existing elements:
> >           pointer __old_start = this->_M_impl._M_start;
> >           // End of existing elements:
> >           pointer __old_finish = this->_M_impl._M_finish;
> >           // Insertion point:
> > -         const auto __ins_idx = __pos - cbegin();
> >           pointer __ins = __old_start + __ins_idx;
> > -         // Number of new elements to insert:
> > -         const auto __n = size_type(ranges::distance(__rg));
> >           // Number of elements that can fit in unused capacity:
> >           const auto __cap = this->_M_impl._M_end_of_storage -
> __old_finish;
> > +
> >           if (__cap >= __n)
> >             {
> >               // Number of existing elements after insertion point:
> > diff --git
> a/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/insert_range.cc
> b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/insert_range.cc
> > index 506bebbe519..e4b5982188f 100644
> > ---
> a/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/insert_range.cc
> > +++
> b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/insert_range.cc
> > @@ -99,8 +99,58 @@ test_ranges()
> >    return true;
> >  }
> >
> > +struct SelfAssignChecker {
> > +  static int moveCounter;
> > +  static int copyCounter;
> > +
> > +  SelfAssignChecker() = default;
> > +  constexpr SelfAssignChecker(int v) : val(v) { }
> > +  SelfAssignChecker(const SelfAssignChecker&) = default;
> > +  SelfAssignChecker(SelfAssignChecker&&) = default;
> > +
> > +  SelfAssignChecker operator=(const SelfAssignChecker& rhs)
> > +  {
> > +    if (this == &rhs)
> > +      ++copyCounter;
> > +    this->val = rhs.val;
> > +    return *this;
> > +  }
> > +
> > +  SelfAssignChecker operator=(SelfAssignChecker&& rhs)
> > +  {
> > +    if (this == &rhs)
> > +      ++moveCounter;
> > +    this->val = rhs.val;
> > +    return *this;
> > +  }
> > +
> > +  int val;
> > +
> > +  friend bool operator==(SelfAssignChecker, SelfAssignChecker) =
> default;
> > +};
> > +
> > +int SelfAssignChecker::moveCounter = 0;
> > +int SelfAssignChecker::copyCounter = 0;
> > +
> > +void
> > +test_pr121313()
> > +{
> > +  using namespace __gnu_test;
> > +
> > +  SelfAssignChecker::copyCounter = SelfAssignChecker::moveCounter = 0;
> > +  do_test<test_forward_range<int>, std::allocator<SelfAssignChecker>>();
> > +  VERIFY( SelfAssignChecker::moveCounter == 0 );
> > +  VERIFY( SelfAssignChecker::copyCounter == 0 );
> > +
> > +  SelfAssignChecker::copyCounter = SelfAssignChecker::moveCounter = 0;
> > +  do_test<test_input_range<int>, std::allocator<SelfAssignChecker>>();
> > +  VERIFY( SelfAssignChecker::moveCounter == 0 );
> > +  VERIFY( SelfAssignChecker::copyCounter == 0 );
> > +}
> > +
> >  int main()
> >  {
> >    test_ranges();
> > +  test_pr121313();
> >    static_assert( test_ranges() );
> >  }
> > --
> > 2.49.0
> >
> >
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