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libstdc++: Fix -Wstringop-overread warning in std::vector<bool> [PR114758]

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As in r13-4393-gcca06f0d6d76b0 and a few other commits, we can avoid
bogus warnings in std::vector<bool> by hoisting some loads to before the
allocation that calls operator new. This means that the compiler has
enough info to remove the dead branches that trigger bogus warnings.

On trunk this is only needed with -fno-assume-sane-operators-new-delete
but it will help on the branches where that option doesn't exist.

libstdc++-v3/ChangeLog:

	PR libstdc++/114758
	* include/bits/vector.tcc (vector<bool, A>::_M_fill_insert):
	Hoist loads of begin() and end() before allocation.
	* testsuite/23_containers/vector/bool/capacity/114758.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 97cbe3cd5f
commit 1f6c19f307
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2 changed files with 15 additions and 2 deletions
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5
libstdc++-v3/include/bits/vector.tcc
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@ -1134,11 +1134,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
{
const size_type __len =
_M_check_len(__n, "vector<bool>::_M_fill_insert");
iterator __begin = begin(), __end = end();
_Bit_pointer __q = this->_M_allocate(__len);
iterator __start(std::__addressof(*__q), 0);
iterator __i = _M_copy_aligned(begin(), __position, __start);
iterator __i = _M_copy_aligned(__begin, __position, __start);
std::fill(__i, __i + difference_type(__n), __x);
iterator __finish = std::copy(__position, end(),
iterator __finish = std::copy(__position, __end,
__i + difference_type(__n));
this->_M_deallocate();
this->_M_impl._M_end_of_storage = __q + _S_nword(__len);

12
libstdc++-v3/testsuite/23_containers/vector/bool/capacity/114758.cc Normal file
View file

@ -0,0 +1,12 @@
// { dg-options "-O3 -Werror=stringop-overread -fno-assume-sane-operators-new-delete" }
// { dg-do compile }
// Bug libstdc++/114758 The layout of a std::vector<bool> reports a warning
#include <vector>
void pr114758(std::vector<bool>& v)
{
v.resize(3);
v = std::vector<bool>(3, false);
}