[Bug tree-optimization/113239] [13 regression] After 822a11a1e64, bogus -Warray-bounds warnings in std::vector

["dimitry@unified-streaming.com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113239

Dimitry Andric <dimitry@unified-streaming.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com

--- Comment #2 from Dimitry Andric <dimitry@unified-streaming.com> ---
I reduced a preprocessed version of the test case to a more minimal version,
which does not include the full <vector> header. Bisecting with the
preprocessed and reduced test case again shows that it regressed with commit
e7310e24b1c0ca67b1bb507c1330b2bf39e59e32 ("Make ranger vrp1 default").

New test case:

// g++ -std=c++17 -Wall -O2 -c pr113239-preproc.cpp

struct __is_move_iterator
{
  enum
  {
    __value
  };
};
template <typename _Iterator, typename> struct __normal_iterator
{
  _Iterator _M_current;
  __normal_iterator (_Iterator __i) : _M_current (__i) {}
  _Iterator
  base ()
  {
    return _M_current;
  }
};
template <typename _Iterator, typename _Container>
bool
operator== (__normal_iterator<_Iterator, _Container> __lhs,
            __normal_iterator<_Iterator, _Container> __rhs)
{
  return __lhs.base () == __rhs.base ();
}
template <typename _Iterator, typename _Container>
_Iterator __niter_base (__normal_iterator<_Iterator, _Container>);
struct __copy_move
{
  template <typename _Tp, typename _Up>
  static void
  __assign_one (_Tp __to, _Up __from)
  {
    *__to = *__from;
  }
  template <typename _Tp, typename _Up>
  static _Up *
  __copy_m (_Tp *__last, _Up *__result)
  {
    _Tp __first;
    long _Num = __last - &__first;
    __assign_one (__result, &__first);
    return __result + _Num;
  }
};
template <int, typename _II, typename _OI>
_OI
__copy_move_a2 (_II __last, _OI __result)
{
  return __copy_move::__copy_m (__last, __result);
}
template <int _IsMove, typename _II, typename _OI>
_OI
__copy_move_a1 (_II __last, _OI __result)
{
  return __copy_move_a2<_IsMove> (__last, __result);
}
template <int _IsMove, typename _II, typename _OI>
_OI
__copy_move_a (_II __last, _OI __result)
{
  _OI __trans_tmp_1
      = __copy_move_a1<_IsMove> (__niter_base (__last), __result);
  return __trans_tmp_1;
}
template <typename _II, typename _OI>
void
copy (_II __last, _OI __result)
{
  __copy_move_a<__is_move_iterator::__value> (__last, __result);
}
template <typename _Tp> struct __new_allocator
{
# 125
"/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h"
3
  unsigned char *
  allocate (long __n)
  {

    if (alignof (char))

      std::align_val_t __al ((sizeof (_Tp), __al));

    return static_cast<unsigned char *> (operator new (__n));
  }
};
template <typename> struct allocator_traits;
template <typename _Tp> struct allocator_traits<__new_allocator<_Tp> >
{
  using allocator_type = __new_allocator<_Tp>;
  using pointer = _Tp *;
  using const_pointer = _Tp *;
  using size_type = long;
  template <typename _Up> using rebind_alloc = __new_allocator<_Up>;
  static pointer
  allocate (allocator_type __a, size_type __n)
  {
    return __a.allocate (__n);
  }
};
struct __alloc_traits : allocator_traits<__new_allocator<unsigned char> >
{
  struct rebind
  {
    typedef rebind_alloc<unsigned char> other;
  };
};
struct __uninitialized_copy
{
  template <typename _InputIterator, typename _ForwardIterator>
  static __uninit_copy (_InputIterator __last, _ForwardIterator __result)
  {
    copy (__last, __result);
  }
};
template <typename _InputIterator, typename _ForwardIterator>
uninitialized_copy (_InputIterator __last, _ForwardIterator __result)
{
  __uninitialized_copy::__uninit_copy (__last, __result);
}
template <typename _InputIterator, typename _ForwardIterator, typename _Tp>
__uninitialized_copy_a (_InputIterator, _InputIterator __last,
                        _ForwardIterator __result, _Tp)
{
  uninitialized_copy (__last, __result);
}
struct _Vector_base
{
  typedef __alloc_traits::rebind::other _Tp_alloc_type;
  typedef __alloc_traits::pointer pointer;
  struct _Vector_impl_data
  {
    pointer _M_start;
    pointer _M_finish;
  };
  struct _Vector_impl : _Tp_alloc_type, _Vector_impl_data
  {
    _Vector_impl (_Tp_alloc_type);
  };
  _Vector_base (long __n, __new_allocator<unsigned char> __a) : _M_impl (__a)
  {
    _M_impl._M_start = _M_allocate (__n);
  }
  _Vector_impl _M_impl;
  pointer
  _M_allocate (unsigned long __n)
  {
    return __n ? __alloc_traits::allocate (_M_impl, __n) : pointer ();
  }
};
struct vector : _Vector_base
{
  typedef __normal_iterator<__alloc_traits::const_pointer, int> const_iterator;
  vector ();
  _Tp_alloc_type __trans_tmp_5;
  vector (vector &__x) : _Vector_base (__x.size (), __trans_tmp_5)
  {
    _Tp_alloc_type __trans_tmp_4;
    const_iterator __trans_tmp_2 = 0, __trans_tmp_3 = 0;
    __uninitialized_copy_a (__trans_tmp_2, __trans_tmp_3, _M_impl._M_start,
                            __trans_tmp_4);
  }
  const_iterator
  begin ()
  {
    return _M_impl._M_start;
  }
  const_iterator
  end ()
  {
    return _M_impl._M_finish;
  }
  size () { return _M_impl._M_finish - _M_impl._M_start; }
  empty () { return begin () == end (); }
};
struct frame_t
{
  frame_t () : pts_ (0), timescale_ (0), data_ () {}
  long pts_;
  int timescale_;
  vector data_;
};
struct frame_source_t
{
  virtual frame_t get ();
};
struct frame_filter_t : frame_source_t
{
  frame_t
  get ()
  {
    if (current_frame_.data_.empty ())
      return current_frame_;
  }
  frame_t current_frame_;
};
create_frame_filter () { frame_filter_t (); }

// EOT

With gcc-13-3595-g7b1cdca6d6d:

$ ~/ins/gcc-13-3595-g7b1cdca6d6d/bin/g++ -std=c++17 -O2 -Wall -Werror -c
pr113239-preproc.cpp
(no warning)

With gcc-13-3596-ge7310e24b1c/bin/g++:

$ ~/ins/gcc-13-3596-ge7310e24b1c/bin/g++  -std=c++17 -O2 -Wall -Werror -c
pr113239-preproc.cpp
In static member function 'static void __copy_move::__assign_one(_Tp, _Up)
[with _Tp = unsigned char*; _Up = unsigned char*]',
    inlined from 'static _Up* __copy_move::__copy_m(_Tp*, _Up*) [with _Tp =
unsigned char; _Up = unsigned char]' at pr113239-preproc.cpp:41:18,
    inlined from '_OI __copy_move_a2(_II, _OI) [with int <anonymous> = 0; _II =
unsigned char*; _OI = unsigned char*]' at pr113239-preproc.cpp:49:32,
    inlined from '_OI __copy_move_a1(_II, _OI) [with int _IsMove = 0; _II =
unsigned char*; _OI = unsigned char*]' at pr113239-preproc.cpp:55:34,
    inlined from '_OI __copy_move_a(_II, _OI) [with int _IsMove = 0; _II =
__normal_iterator<unsigned char*, int>; _OI = unsigned char*]' at
pr113239-preproc.cpp:62:33,
    inlined from 'void copy(_II, _OI) [with _II = __normal_iterator<unsigned
char*, int>; _OI = unsigned char*]' at pr113239-preproc.cpp:69:46,
    inlined from 'static int
__uninitialized_copy::__uninit_copy(_InputIterator, _ForwardIterator) [with
_InputIterator = __normal_iterator<unsigned char*, int>; _ForwardIterator =
unsigned char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:162:10,
    inlined from 'int uninitialized_copy(_InputIterator, _ForwardIterator)
[with _InputIterator = __normal_iterator<unsigned char*, int>; _ForwardIterator
= unsigned char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:168:39,
    inlined from 'int __uninitialized_copy_a(_InputIterator, _InputIterator,
_ForwardIterator, _Tp) [with _InputIterator = __normal_iterator<unsigned char*,
int>; _ForwardIterator = unsigned char*; _Tp = __new_allocator<unsigned char>]'
at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:174:22,
    inlined from 'vector::vector(vector&)' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:209:28,
    inlined from 'frame_t::frame_t(frame_t&)' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:225:8,
    inlined from 'virtual frame_t frame_filter_t::get()' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:242:14:
pr113239-preproc.cpp:33:11: error: array subscript 0 is outside array bounds of
'unsigned char [0]' [-Werror=array-bounds]
   33 |     *__to = *__from;
      |     ~~~~~~^~~~~~~~~
In member function 'unsigned char* __new_allocator<_Tp>::allocate(long int)
[with _Tp = unsigned char]',
    inlined from 'static _Tp* allocator_traits<__new_allocator<_Tp>
>::allocate(allocator_type, size_type) [with _Tp = unsigned char]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:147:25,
    inlined from 'unsigned char* _Vector_base::_M_allocate(long unsigned int)'
at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:197:43,
    inlined from '_Vector_base::_Vector_base(long int, __new_allocator<unsigned
char>)' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:191:36,
    inlined from 'vector::vector(vector&)' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:205:66,
    inlined from 'frame_t::frame_t(frame_t&)' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:225:8,
    inlined from 'virtual frame_t frame_filter_t::get()' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:242:14:
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:133:55:
note: object of size 0 allocated by 'operator new'
  133 |
      |                                                       ^
cc1plus: all warnings being treated as errors

So there seems to be some problem in the "ranger" vrp1 pass. I'm CC'ing the
author of that commit.

I could try to use --param=vrp1-mode=vrp to see if that makes the warning go
away... :)