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libstdc++: Fix -Warray-bounds warning in std::vector<bool> [PR110498]

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In this case, we need to tell the compiler that the current size is not
larger than the new size so that all the existing elements can be copied
to the new storage. This avoids bogus warnings about overflowing the new
storage when the compiler can't tell that that cannot happen.

We might as well also hoist the loads of begin() and end() before the
allocation too. All callers will have loaded at least begin() before
calling _M_reallocate.

libstdc++-v3/ChangeLog:

	PR libstdc++/110498
	* include/bits/vector.tcc (vector<bool, A>::_M_reallocate):
	Hoist loads of begin() and end() before allocation and use them
	to state an unreachable condition.
	* testsuite/23_containers/vector/bool/capacity/110498.cc: New
	test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
This commit is contained in:
Jonathan Wakely 2025-03-28 15:41:41 +00:00 • committed by Jonathan Wakely
parent 1f6c19f307
commit aa3aaf2bfb
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2 changed files with 22 additions and 1 deletions
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5
libstdc++-v3/include/bits/vector.tcc
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@ -1106,9 +1106,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
vector<bool, _Alloc>::
_M_reallocate(size_type __n)
{
const iterator __begin = begin(), __end = end();
if (size_type(__end - __begin) > __n)
__builtin_unreachable();
_Bit_pointer __q = this->_M_allocate(__n);
iterator __start(std::__addressof(*__q), 0);
iterator __finish(_M_copy_aligned(begin(), end(), __start));
iterator __finish(_M_copy_aligned(__begin, __end, __start));
this->_M_deallocate();
this->_M_impl._M_start = __start;
this->_M_impl._M_finish = __finish;

18
libstdc++-v3/testsuite/23_containers/vector/bool/capacity/110498.cc Normal file
View file

@ -0,0 +1,18 @@
// { dg-options "-O3 -Werror=array-bounds -fno-assume-sane-operators-new-delete" }
// { dg-do compile }
// Bug libstdc++/110498
// Spurious warnings stringop-overflow and array-bounds copying data as bytes
// into vector::reserve
#include <vector>
void f(std::vector<bool>& v)
{
// Warning emitted when set to any number in the range [1,64].
const std::size_t reserve_size = 30;
v.reserve(reserve_size);
v.push_back(0);
}