https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110060
Bug ID: 110060
Summary: Adding optimizer hints to std::vector causes a new
-Wstringop-overread false positive
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Blocks: 97048
Target Milestone: ---
Created attachment 55223
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55223&action=edit
Preprocessed source for FAIL 23_containers/vector/types/1.cc
As discussed on IRC recently, I want to add optimization hints to
std::vector::size() and std::vector::capacity() so that gcc knows there will be
no reallocation here:
vec.assign(vec.size(), 0);
The call to assign will not reallocate because size() <= capacity() is always
true. We can express that invariant in the code.
However, doing so causes a new testsuite FAIL:
FAIL: 23_containers/vector/types/1.cc (test for excess errors)
$ ~/gcc/latest/bin/g++ -O2 -Wall a-1.ii
In file included from /home/jwakely/gcc/14/include/c++/14.0.0/vector:62,
from
/home/jwakely/src/gcc/gcc/libstdc++-v3/testsuite/23_containers/vector/types/1.cc:23:
In static member function ‘static _Up* std::__copy_move<_IsMove, true,
std::random_access_iterator_tag>::__copy_m(_Tp*, _Tp*, _Up*) [with _Tp =
greedy_ops::X; _Up = greedy_ops::X; bool _IsMove = false]’,
inlined from ‘_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove =
false; _II = greedy_ops::X*; _OI = greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:506:30,
inlined from ‘_OI std::__copy_move_a1(_II, _II, _OI) [with bool _IsMove =
false; _II = greedy_ops::X*; _OI = greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:533:42,
inlined from ‘_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove =
false; _II = greedy_ops::X*; _OI = greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:540:31,
inlined from ‘_OI std::copy(_II, _II, _OI) [with _II = greedy_ops::X*; _OI
= greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:633:7,
inlined from ‘std::vector<_Tp, _Alloc>& std::vector<_Tp,
_Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = greedy_ops::X;
_Alloc = std::allocator<greedy_ops::X>]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/vector.tcc:255:17,
inlined from ‘int main()’ at
/home/jwakely/src/gcc/gcc/libstdc++-v3/testsuite/23_containers/vector/types/1.cc:35:7:
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:437:30: warning:
‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ forming offset
1 is out of the bounds [0, 1] [-Warray-bounds=]
437 | __builtin_memmove(__result, __first, sizeof(_Tp) * _Num);
| ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In static member function ‘static _Up* std::__copy_move<_IsMove, true,
std::random_access_iterator_tag>::__copy_m(_Tp*, _Tp*, _Up*) [with _Tp =
greedy_ops::X; _Up = greedy_ops::X; bool _IsMove = false]’,
inlined from ‘_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove =
false; _II = greedy_ops::X*; _OI = greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:506:30,
inlined from ‘_OI std::__copy_move_a1(_II, _II, _OI) [with bool _IsMove =
false; _II = greedy_ops::X*; _OI = greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:533:42,
inlined from ‘_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove =
false; _II = greedy_ops::X*; _OI = greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:540:31,
inlined from ‘_OI std::copy(_II, _II, _OI) [with _II = greedy_ops::X*; _OI
= greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:633:7,
inlined from ‘static _ForwardIterator
std::__uninitialized_copy<true>::__uninit_copy(_InputIterator, _InputIterator,
_ForwardIterator) [with _InputIterator = greedy_ops::X*; _ForwardIterator =
greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_uninitialized.h:147:27,
inlined from ‘_ForwardIterator std::uninitialized_copy(_InputIterator,
_InputIterator, _ForwardIterator) [with _InputIterator = greedy_ops::X*;
_ForwardIterator = greedy_ops::X*]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_uninitialized.h:185:15,
inlined from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator,
_InputIterator, _ForwardIterator, allocator<_Tp>&) [with _InputIterator =
greedy_ops::X*; _ForwardIterator = greedy_ops::X*; _Tp = greedy_ops::X]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_uninitialized.h:373:37,
inlined from ‘std::vector<_Tp, _Alloc>& std::vector<_Tp,
_Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = greedy_ops::X;
_Alloc = std::allocator<greedy_ops::X>]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/vector.tcc:257:35,
inlined from ‘int main()’ at
/home/jwakely/src/gcc/gcc/libstdc++-v3/testsuite/23_containers/vector/types/1.cc:35:7:
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_algobase.h:437:30: warning:
‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ reading between
2 and 9223372036854775807 bytes from a region of size 1 [-Wstringop-overread]
437 | __builtin_memmove(__result, __first, sizeof(_Tp) * _Num);
| ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/gcc/14/include/c++/14.0.0/x86_64-pc-linux-gnu/bits/c++allocator.h:33,
from
/home/jwakely/gcc/14/include/c++/14.0.0/bits/allocator.h:46,
from /home/jwakely/gcc/14/include/c++/14.0.0/vector:63:
In member function ‘_Tp* std::__new_allocator<_Tp>::allocate(size_type, const
void*) [with _Tp = greedy_ops::X]’,
inlined from ‘static _Tp* std::allocator_traits<std::allocator<_Tp1>
>::allocate(allocator_type&, size_type) [with _Tp = greedy_ops::X]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/alloc_traits.h:482:28,
inlined from ‘std::_Vector_base<_Tp, _Alloc>::pointer
std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp =
greedy_ops::X; _Alloc = std::allocator<greedy_ops::X>]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_vector.h:378:33,
inlined from ‘std::_Vector_base<_Tp, _Alloc>::pointer
std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp =
greedy_ops::X; _Alloc = std::allocator<greedy_ops::X>]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_vector.h:375:7,
inlined from ‘void std::_Vector_base<_Tp,
_Alloc>::_M_create_storage(std::size_t) [with _Tp = greedy_ops::X; _Alloc =
std::allocator<greedy_ops::X>]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_vector.h:413:44,
inlined from ‘std::_Vector_base<_Tp, _Alloc>::_Vector_base(std::size_t,
const allocator_type&) [with _Tp = greedy_ops::X; _Alloc =
std::allocator<greedy_ops::X>]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_vector.h:332:26,
inlined from ‘std::vector<_Tp, _Alloc>::vector(size_type, const
allocator_type&) [with _Tp = greedy_ops::X; _Alloc =
std::allocator<greedy_ops::X>]’ at
/home/jwakely/gcc/14/include/c++/14.0.0/bits/stl_vector.h:572:47,
inlined from ‘int main()’ at
/home/jwakely/src/gcc/gcc/libstdc++-v3/testsuite/23_containers/vector/types/1.cc:29:39:
/home/jwakely/gcc/14/include/c++/14.0.0/bits/new_allocator.h:147:48: note:
source object of size 1 allocated by ‘operator new’
147 | return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n *
sizeof(_Tp)));
| ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
The preprocessed source of the test is attached (with the proposed new hints
added to the std::vector code). There's no warning with -O1 or -O3, only -O2.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97048
[Bug 97048] [meta-bug] bogus/missing -Wstringop-overread warnings
