On 03/06/2024 18:20, Jonathan Wakely wrote:
On Mon, 3 Jun 2024 at 05:56, François Dumont <frs.dum...@gmail.com> wrote:
I hadn't try to make my patch as limited as possible to fix the problem,
indeed.
libstdc++: Fix -Wstringop-overflow warning coming from std::vector
[PR109849]
libstdc++-v3/ChangeLog:
PR libstdc++/109849
* include/bits/vector.tcc
(std::vector<>::_M_range_insert(iterator, _FwdIt, _FwdIt,
forward_iterator_tag)): Add __builtin_unreachable
expression to tell
the compiler that the allocated buffer is large enough to
receive current
elements plus the range to insert.
Tested under Linux x64, ok to commit ?
Does the !__builtin_constant_p(__len) in this version do anything?
If it's a constant, then the compiler can already provide it's in
range, so the __builtin_unreachable() is redundant, but doesn't do any
harm.
Yes, it prevents some constexpr test failure because
__builtin_unreachable is not a constexpr (at least not for some C++
Standard versions).
But it wasn't a nice way to avoid this regression. Here is another
proposal that activate the __builtin_unreachable only for pre-c++11
modes. C++03 had no problem neither but I haven't found any occurrence
of __cplusplus checks against the C++03 version so I prefer not to add any.
libstdc++: Fix -Wstringop-overflow warning coming from std::vector
[PR109849]
libstdc++-v3/ChangeLog:
PR libstdc++/109849
* include/bits/vector.tcc
(std::vector<>::_M_range_insert(iterator, _FwdIt, _FwdIt,
forward_iterator_tag))[__cplusplus < 2011103L]: Add
__builtin_unreachable
expression to tell the compiler that the allocated buffer
is large enough to
receive current elements plus the elements of the range to
insert.
Ok to commit ?
François
diff --git a/libstdc++-v3/include/bits/vector.tcc
b/libstdc++-v3/include/bits/vector.tcc
index 36b27dce7b9..c500aab9e56 100644
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -933,6 +933,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
const size_type __len =
_M_check_len(__n, "vector::_M_range_insert");
+#if __cplusplus < 201103LL
+ if (__len < (__n + (__old_start - __old_finish)))
+ __builtin_unreachable();
+#endif
+
pointer __new_start(this->_M_allocate(__len));
pointer __new_finish(__new_start);
__try
