https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127089
Bug ID: 127089
Summary: [[assume(!v.empty())]] does not suppress
-Warray-bounds on vector::pop_back, unlike if
(empty()) std::unreachable()
Product: gcc
Version: 16.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rogerio.souza at gmail dot com
Target Milestone: ---
The following testcase produces a -Warray-bounds warning for
std::vector::pop_back() even when the vector's non-emptiness is explicitly
provided using the standard C++23 [[assume]] attribute:
testcase-assume.cpp:
===============================
#include <vector>
struct H;
const H* const* beg();
const H* const* end();
void assumed(const H* x)
{
std::vector<const H*> v(beg(), end());
[[assume(!v.empty())]];
v.pop_back();
v.push_back(x);
}
void unreachable(const H* x)
{
std::vector<const H*> v(beg(), end());
if (v.empty())
std::unreachable();
v.pop_back();
v.push_back(x);
}
===============================
Compile with:
===============================
$ g++ -c -std=c++23 -O2 -Wall testcase-assume.cpp
===============================
GCC emits this warning for assumed:
===============================
.../bits/stl_construct.h:88:9: warning: array subscript -1 is outside array
bounds of 'const H* [1152921504606846975]' [-Warray-bounds=]
88 | __location->~_Tp();
| ~~~~~~~~~~~~~~~~^~
... inlined from 'constexpr void std::vector<_Tp, _Alloc>::pop_back()'
... inlined from 'void assumed(const H*)' at testcase-assume.cpp:12:15
===============================
Version results
The unguarded pop_back() testcase was compiled with -std=c++23 -Wall:
g++ -O1 -O2 -O3
12.4.0 clean warns warns
14.2.0 clean warns warns
14.3.0 clean warns warns
15.2.0 clean clean clean
15.3.0 clean clean clean
16.1.0 clean warns warns
The behavior is independent of the selected language mode in the tested range
(-std=c++17 through -std=c++26).
