On 23/05/2024 15:31, Jonathan Wakely wrote:
On 23/05/24 06:55 +0200, François Dumont wrote:
As explained in this email:
https://gcc.gnu.org/pipermail/libstdc++/2024-April/058552.html
I experimented -Wfree-nonheap-object because of my enhancements on
algos.
So here is a patch to extend the usage of the _Guard type to other
parts of vector.
Nice, that fixes the warning you were seeing?
Yes ! I indeed forgot to say so :-)
We recently got a bug report about -Wfree-nonheap-object in
std::vector, but that is coming from _M_realloc_append which already
uses the RAII guard :-(
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115016
Note that I also had to move call to __uninitialized_copy_a before
assigning this->_M_impl._M_start so get rid of the -Wfree-nonheap-object
warn. But _M_realloc_append is already doing potentially throwing
operations before assigning this->_M_impl so it must be something else.
Though it made me notice another occurence of _Guard in this method. Now
replaced too in this new patch.
libstdc++: Use RAII to replace try/catch blocks
Move _Guard into std::vector declaration and use it to guard all
calls to
vector _M_allocate.
Doing so the compiler has more visibility on what is done with the
pointers
and do not raise anymore the -Wfree-nonheap-object warning.
libstdc++-v3/ChangeLog:
* include/bits/vector.tcc (_Guard): Move all the nested
duplicated class...
* include/bits/stl_vector.h (_Guard_alloc): ...here.
(_M_allocate_and_copy): Use latter.
(_M_initialize_dispatch): Likewise and set _M_finish first
from the result
of __uninitialize_fill_n_a that can throw.
(_M_range_initialize): Likewise.
diff --git a/libstdc++-v3/include/bits/stl_vector.h
b/libstdc++-v3/include/bits/stl_vector.h
index 31169711a48..4ea74e3339a 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -1607,6 +1607,39 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
clear() _GLIBCXX_NOEXCEPT
{ _M_erase_at_end(this->_M_impl._M_start); }
+ private:
+ // RAII guard for allocated storage.
+ struct _Guard
If it's being defined at class scope instead of locally in a member
function, I think a better name would be good. Maybe _Ptr_guard or
_Dealloc_guard or something.
_Guard_alloc chosen.
+ {
+ pointer _M_storage; // Storage to deallocate
+ size_type _M_len;
+ _Base& _M_vect;
+
+ _GLIBCXX20_CONSTEXPR
+ _Guard(pointer __s, size_type __l, _Base& __vect)
+ : _M_storage(__s), _M_len(__l), _M_vect(__vect)
+ { }
+
+ _GLIBCXX20_CONSTEXPR
+ ~_Guard()
+ {
+ if (_M_storage)
+ _M_vect._M_deallocate(_M_storage, _M_len);
+ }
+
+ _GLIBCXX20_CONSTEXPR
+ pointer
+ _M_release()
+ {
+ pointer __res = _M_storage;
+ _M_storage = 0;
I don't think the NullablePointer requirements include assigning 0,
only from nullptr, which isn't valid in C++98.
https://en.cppreference.com/w/cpp/named_req/NullablePointer
Please use _M_storage = pointer() instead.
I forgot about user fancy pointer, fixed.
+ return __res;
+ }
+
+ private:
+ _Guard(const _Guard&);
+ };
+
protected:
/**
* Memory expansion handler. Uses the member allocation
function to
@@ -1618,18 +1651,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
_M_allocate_and_copy(size_type __n,
_ForwardIterator __first, _ForwardIterator __last)
{
- pointer __result = this->_M_allocate(__n);
- __try
- {
- std::__uninitialized_copy_a(__first, __last, __result,
- _M_get_Tp_allocator());
- return __result;
- }
- __catch(...)
- {
- _M_deallocate(__result, __n);
- __throw_exception_again;
- }
+ _Guard __guard(this->_M_allocate(__n), __n, *this);
+ std::__uninitialized_copy_a
+ (__first, __last, __guard._M_storage, _M_get_Tp_allocator());
+ return __guard._M_release();
}
@@ -1642,13 +1667,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// 438. Ambiguity in the "do the right thing" clause
template<typename _Integer>
void
- _M_initialize_dispatch(_Integer __n, _Integer __value, __true_type)
+ _M_initialize_dispatch(_Integer __int_n, _Integer __value,
__true_type)
{
- this->_M_impl._M_start = _M_allocate(_S_check_init_len(
- static_cast<size_type>(__n), _M_get_Tp_allocator()));
- this->_M_impl._M_end_of_storage =
- this->_M_impl._M_start + static_cast<size_type>(__n);
- _M_fill_initialize(static_cast<size_type>(__n), __value);
Please fix the comment on _M_fill_initialize if you're removing the
use of it here.
Already done in this initial patch proposal, see below.
+ const size_type __n = static_cast<size_type>(__int_n);
+ _Guard __guard(_M_allocate(_S_check_init_len(
+ __n, _M_get_Tp_allocator())), __n, *this);
I think this would be easier to read if the _S_check_init_len call was
done first, and maybe the allocation too, since we are going to need a
local __start later anyway. So maybe like this:
template<typename _Integer>
void
_M_initialize_dispatch(_Integer __ni, _Integer __value, __true_type)
{
const size_type __n = static_cast<size_type>(__ni);
pointer __start = _M_allocate(_S_check_init_len(__n),
_M_get_Tp_allocator());
_Guard __guard(__start, __n, *this);
this->_M_impl._M_start = __start;
_M_fill_initialize(__n, __value);
this->_M_impl._M_end_of_storage = __start + __n;
(void) __guard._M_release();
}
Or inline the __uninitialized_fill_n_a call if you want to (but then
fix the comment on _M_fill_initialize). Inlining it does make this
function more consistent with the next one, which calls
__uninitialized_copy_a directly.
Yes, this is why I called __uninitialized_fill_n_a instead and also to
do so *before* assigning _M_impl._M_start.
Ok to commit ?
