https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111250
Bug ID: 111250
Summary: __glibcxx_requires_subscript assertions are not
checked during constant evaluation
Product: gcc
Version: 13.2.1
Status: UNCONFIRMED
Keywords: accepts-invalid
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
This means the following example from Peter Dimov only fails with
-D_GLIBCXX_ASSERTIONS or -D_GLIBCXX_DEBUG:
#include <vector>
constexpr bool f()
{
std::vector<int> v{ 1, 2, 3 };
return &v[3] == &v.front();
}
constexpr bool b = f();
The __glibcxx_assert macro expands to a __glibcxx_constexpr_assert check that
is always checked during constant evaluation, even without
-D_GLIBCXX_ASSERTIONS. However, the __glibcxx_requires_subscript macro does not
use __glibcxx_assert and just expands to nothing. See <debug/assertions.h>:
#ifndef _GLIBCXX_ASSERTIONS
# define __glibcxx_requires_non_empty_range(_First,_Last)
# define __glibcxx_requires_nonempty()
# define __glibcxx_requires_subscript(_N)
#else
// Verify that [_First, _Last) forms a non-empty iterator range.
# define __glibcxx_requires_non_empty_range(_First,_Last) \
__glibcxx_assert(_First != _Last)
# define __glibcxx_requires_subscript(_N) \
__glibcxx_assert(_N < this->size())
// Verify that the container is nonempty
# define __glibcxx_requires_nonempty() \
__glibcxx_assert(!this->empty())
#endif
I think we should remove the #ifndef and just always expand those to
__glibcxx_assert expressions. That will mean they're checked during constant
evaluation.
