https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109717
Bug ID: 109717
Summary: -Warray-bound error with gnu++20 and fmt library
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: psmith at gnu dot org
Target Milestone: ---
Created attachment 54983
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54983&action=edit
fmt1.i preprocessor output (compressed)
I found SO MANY issues related to -Warray-bound, many of them reported with GCC
11 or so. I can't tell if this is a duplicate or not, although this issue
doesn't reproduce for me with GCC 11.3.
I have built my own GCC 13.1 from source on x86_64 GNU/Linux (as I've been
doing for >10 years) and it works great except for one thing. When I use some
parts of the fmt 9.1.0 library, and "-O2 -Werror-builds -std=gnu++20" (removing
any one of those, or changing to -std=gnu++17, makes the error go away).
I try to compile this:
#include <vector>
#include <iterator>
#include <fmt/format.h>
void add_info(std::vector<char>& buf)
{
fmt::format_to(std::back_inserter(buf), "hello {}", "there");
}
and I get this output:
$ g++-13.1 -I/data/src/build/common/fmt/include -std=gnu++20 -Warray-bounds -O2
-c -o /tmp/fmt1.o /tmp/fmt1.cpp
In file included from
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/vector:62,
from /tmp/fmt1.cpp:1:
In static member function 'static constexpr _Up* std::__copy_move<_IsMove,
true, std::random_access_iterator_tag>::__copy_m(_Tp*, _Tp*, _Up*) [with _Tp =
unsigned int; _Up = unsigned int; bool _IsMove = false]',
inlined from 'constexpr _OI std::__copy_move_a2(_II, _II, _OI) [with bool
_IsMove = false; _II = unsigned int*; _OI = unsigned int*]' at
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/bits/stl_algobase.h:506:30,
inlined from 'constexpr _OI std::__copy_move_a1(_II, _II, _OI) [with bool
_IsMove = false; _II = unsigned int*; _OI = unsigned int*]' at
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/bits/stl_algobase.h:533:42,
inlined from 'constexpr _OI std::__copy_move_a(_II, _II, _OI) [with bool
_IsMove = false; _II = unsigned int*; _OI = unsigned int*]' at
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/bits/stl_algobase.h:540:31,
inlined from 'constexpr _OI std::copy(_II, _II, _OI) [with _II = unsigned
int*; _OI = unsigned int*]' at
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/bits/stl_algobase.h:633:7,
inlined from 'static _ForwardIterator
std::__uninitialized_copy<true>::__uninit_copy(_InputIterator, _InputIterator,
_ForwardIterator) [with _InputIterator = unsigned int*; _ForwardIterator =
unsigned int*]' at
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/bits/stl_uninitialized.h:147:27,
inlined from '_ForwardIterator std::uninitialized_copy(_InputIterator,
_InputIterator, _ForwardIterator) [with _InputIterator = unsigned int*;
_ForwardIterator = unsigned int*]' at
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/bits/stl_uninitialized.h:185:15,
inlined from 'constexpr void fmt::v9::basic_memory_buffer<T, SIZE,
Allocator>::grow(size_t) [with T = unsigned int; long unsigned int SIZE = 32;
Allocator = std::allocator<unsigned int>]' at
/data/src/build/common/fmt/include/fmt/format.h:925:26,
inlined from 'constexpr void
fmt::v9::detail::buffer<T>::try_reserve(size_t) [with T = unsigned int]' at
/data/src/build/common/fmt/include/fmt/core.h:928:39,
inlined from 'constexpr void
fmt::v9::detail::buffer<T>::try_reserve(size_t) [with T = unsigned int]' at
/data/src/build/common/fmt/include/fmt/core.h:927:24,
inlined from 'constexpr void fmt::v9::detail::buffer<T>::try_resize(size_t)
[with T = unsigned int]' at
/data/src/build/common/fmt/include/fmt/core.h:919:16,
inlined from 'constexpr void fmt::v9::basic_memory_buffer<T, SIZE,
Allocator>::resize(size_t) [with T = unsigned int; long unsigned int SIZE = 32;
Allocator = std::allocator<unsigned int>]' at
/data/src/build/common/fmt/include/fmt/format.h:897:63,
inlined from 'constexpr void fmt::v9::detail::bigint::assign(UInt) [with
UInt = long unsigned int; typename std::enable_if<(std::is_same<UInt, long
unsigned int>::value || std::is_same<UInt, __int128 unsigned>::value),
int>::type <anonymous> = 0]' at
/data/src/build/common/fmt/include/fmt/format.h:2792:19,
inlined from 'constexpr void fmt::v9::detail::bigint::operator=(Int) [with
Int = int]' at /data/src/build/common/fmt/include/fmt/format.h:2813:11,
inlined from 'constexpr void fmt::v9::detail::bigint::assign_pow10(int)' at
/data/src/build/common/fmt/include/fmt/format.h:2886:32:
/data/src/build/x86_64-linux/cc/unknown/x86_64-unknown-linux-gnu/include/c++/13.1.0/bits/stl_algobase.h:437:30:
warning: 'void* __builtin_memmove(void*, const void*, long unsigned int)'
forming offset 4 is out of the bounds [0, 4] [-Warray-bounds=]
437 | __builtin_memmove(__result, __first, sizeof(_Tp) * _Num);
| ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's very strange that it says "offset 4" is out of bounds for [0, 4] but maybe
I just don't understand the error.
The code in fmt/format.h line 2886 is:
// Assigns pow(10, exp) to this bigint.
FMT_CONSTEXPR20 void assign_pow10(int exp) {
FMT_ASSERT(exp >= 0, "");
if (exp == 0) return *this = 1; //<== line 2886
If I don't use the fmt::format_to() function (just normal fmt::print etc.) then
it works fine.
Also I should point out that for some reason I can't reproduce this with
godbolt using GCC 13.1 and fmt 9.1.0. I also can't reproduce it with my
previous build, GCC 11.3 (but all else the same).
I'll add the postprocessed output (where I still see the above error) as an
attachment.
