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libstdc++: Fix -Warray-bounds warning in std::vector::resize [PR114945]

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This is yet another false positive warning fix. This time the compiler
can't prove that when the vector has sufficient excess capacity to
append new elements, the pointer to the existing storage is not null.

libstdc++-v3/ChangeLog:

	PR libstdc++/114945
	* include/bits/vector.tcc (vector::_M_default_append): Add
	unreachable condition so the compiler knows that _M_finish is
	not null.
	* testsuite/23_containers/vector/capacity/114945.cc: New test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

(cherry picked from commit 844eed3364309bd20cbb7d6793a16b7c6b889ba4)
This commit is contained in:
Jonathan Wakely 2025-03-31 12:30:44 +01:00 committed by Jonathan Wakely
parent c839965c2e
commit 6b11aed73f
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2 changed files with 39 additions and 0 deletions
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3
libstdc++-v3/include/bits/vector.tcc
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@ -816,6 +816,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
if (__navail >= __n)
{
if (!this->_M_impl._M_finish)
__builtin_unreachable();
_GLIBCXX_ASAN_ANNOTATE_GROW(__n);
this->_M_impl._M_finish =
std::__uninitialized_default_n_a(this->_M_impl._M_finish,

36
libstdc++-v3/testsuite/23_containers/vector/capacity/114945.cc Normal file
View File

@ -0,0 +1,36 @@
// { dg-options "-O2 -Werror=stringop-overflow -Werror=array-bounds" }
// { dg-do compile { target c++11 } }
// Bug libstdc++/114945
// Sporadic std::vector::resize() -Wstringop-overflow or -Warray-bounds warning
#include <stdint.h>
#include <vector>
template <typename a> struct b {
void resize(std::size_t c) { d.resize(c); }
template <typename e> void f(a, e);
std::vector<char> d;
};
#include <regex>
std::regex g;
uint64_t h;
uint32_t i;
struct s {
enum class j : size_t;
void k();
using l = b<j>;
std::vector<l> m;
};
enum class s::j : size_t { n };
void o() { g = ""; }
void s::k() {
l p;
auto q = uint32_t(), r = uint32_t();
if (h)
r = i;
b<size_t> t;
if (q || r)
p.f(j::n, 5);
t.resize(4);
m.push_back(p);
}