From: "François Dumont" <frs.dumont@gmail.com>
To: Jonathan Wakely <jwakely@redhat.com>
Cc: libstdc++ <libstdc++@gcc.gnu.org>, gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Avoid vector -Wfree-nonheap-object warnings
Date: Thu, 23 May 2024 19:37:56 +0200 [thread overview]
Message-ID: <a07d81c6-7a3e-4f0d-9547-d6e2b4406723@gmail.com> (raw)
In-Reply-To: <Zk9FLceo0aCxnWfS@zen.kayari.org>
[-- Attachment #1: Type: text/plain, Size: 7183 bytes --]
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.
>> - // Called by the first initialize_dispatch above and by the
>> - // vector(n,value,a) constructor.
>> + // Called by the vector(n,value,a) constructor.
See, it's here :-)
Ok to commit ?
François
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diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index 31169711a48..30d7201c613 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_alloc
+ {
+ pointer _M_storage; // Storage to deallocate
+ size_type _M_len;
+ _Base& _M_vect;
+
+ _GLIBCXX20_CONSTEXPR
+ _Guard_alloc(pointer __s, size_type __l, _Base& __vect)
+ : _M_storage(__s), _M_len(__l), _M_vect(__vect)
+ { }
+
+ _GLIBCXX20_CONSTEXPR
+ ~_Guard_alloc()
+ {
+ if (_M_storage)
+ _M_vect._M_deallocate(_M_storage, _M_len);
+ }
+
+ _GLIBCXX20_CONSTEXPR
+ pointer
+ _M_release()
+ {
+ pointer __res = _M_storage;
+ _M_storage = pointer();
+ return __res;
+ }
+
+ private:
+ _Guard_alloc(const _Guard_alloc&);
+ };
+
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_alloc __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 +1667,17 @@ _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);
+ const size_type __n = static_cast<size_type>(__int_n);
+ pointer __start =
+ _M_allocate(_S_check_init_len(__n, _M_get_Tp_allocator()));
+ _Guard_alloc __guard(__start, __n, *this);
+ this->_M_impl._M_finish = std::__uninitialized_fill_n_a
+ (__start, __n, __value, _M_get_Tp_allocator());
+ this->_M_impl._M_start = __start;
+ (void)__guard._M_release();
+ this->_M_impl._M_end_of_storage = __start + __n;
}
// Called by the range constructor to implement [23.1.1]/9
@@ -1690,17 +1719,17 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
std::forward_iterator_tag)
{
const size_type __n = std::distance(__first, __last);
- this->_M_impl._M_start
- = this->_M_allocate(_S_check_init_len(__n, _M_get_Tp_allocator()));
- this->_M_impl._M_end_of_storage = this->_M_impl._M_start + __n;
- this->_M_impl._M_finish =
- std::__uninitialized_copy_a(__first, __last,
- this->_M_impl._M_start,
- _M_get_Tp_allocator());
+ pointer __start =
+ this->_M_allocate(_S_check_init_len(__n, _M_get_Tp_allocator()));
+ _Guard_alloc __guard(__start, __n, *this);
+ this->_M_impl._M_finish = std::__uninitialized_copy_a
+ (__first, __last, __start, _M_get_Tp_allocator());
+ this->_M_impl._M_start = __start;
+ (void) __guard._M_release();
+ this->_M_impl._M_end_of_storage = __start + __n;
}
- // Called by the first initialize_dispatch above and by the
- // vector(n,value,a) constructor.
+ // Called by the vector(n,value,a) constructor.
_GLIBCXX20_CONSTEXPR
void
_M_fill_initialize(size_type __n, const value_type& __value)
diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
index 25df060beee..36b27dce7b9 100644
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -467,32 +467,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
pointer __new_start(this->_M_allocate(__len));
pointer __new_finish(__new_start);
- // RAII guard for allocated storage.
- struct _Guard
{
- pointer _M_storage; // Storage to deallocate
- size_type _M_len;
- _Tp_alloc_type& _M_alloc;
-
- _GLIBCXX20_CONSTEXPR
- _Guard(pointer __s, size_type __l, _Tp_alloc_type& __a)
- : _M_storage(__s), _M_len(__l), _M_alloc(__a)
- { }
-
- _GLIBCXX20_CONSTEXPR
- ~_Guard()
- {
- if (_M_storage)
- __gnu_cxx::__alloc_traits<_Tp_alloc_type>::
- deallocate(_M_alloc, _M_storage, _M_len);
- }
-
- private:
- _Guard(const _Guard&);
- };
-
- {
- _Guard __guard(__new_start, __len, _M_impl);
+ _Guard_alloc __guard(__new_start, __len, *this);
// The order of the three operations is dictated by the C++11
// case, where the moves could alter a new element belonging
@@ -596,32 +572,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
pointer __new_start(this->_M_allocate(__len));
pointer __new_finish(__new_start);
- // RAII guard for allocated storage.
- struct _Guard
{
- pointer _M_storage; // Storage to deallocate
- size_type _M_len;
- _Tp_alloc_type& _M_alloc;
-
- _GLIBCXX20_CONSTEXPR
- _Guard(pointer __s, size_type __l, _Tp_alloc_type& __a)
- : _M_storage(__s), _M_len(__l), _M_alloc(__a)
- { }
-
- _GLIBCXX20_CONSTEXPR
- ~_Guard()
- {
- if (_M_storage)
- __gnu_cxx::__alloc_traits<_Tp_alloc_type>::
- deallocate(_M_alloc, _M_storage, _M_len);
- }
-
- private:
- _Guard(const _Guard&);
- };
-
- {
- _Guard __guard(__new_start, __len, _M_impl);
+ _Guard_alloc __guard(__new_start, __len, *this);
// The order of the three operations is dictated by the C++11
// case, where the moves could alter a new element belonging
@@ -833,32 +785,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
_M_check_len(__n, "vector::_M_default_append");
pointer __new_start(this->_M_allocate(__len));
- // RAII guard for allocated storage.
- struct _Guard
- {
- pointer _M_storage; // Storage to deallocate
- size_type _M_len;
- _Tp_alloc_type& _M_alloc;
-
- _GLIBCXX20_CONSTEXPR
- _Guard(pointer __s, size_type __l, _Tp_alloc_type& __a)
- : _M_storage(__s), _M_len(__l), _M_alloc(__a)
- { }
-
- _GLIBCXX20_CONSTEXPR
- ~_Guard()
- {
- if (_M_storage)
- __gnu_cxx::__alloc_traits<_Tp_alloc_type>::
- deallocate(_M_alloc, _M_storage, _M_len);
- }
-
- private:
- _Guard(const _Guard&);
- };
-
{
- _Guard __guard(__new_start, __len, _M_impl);
+ _Guard_alloc __guard(__new_start, __len, *this);
std::__uninitialized_default_n_a(__new_start + __size, __n,
_M_get_Tp_allocator());
next prev parent reply other threads:[~2024-05-23 17:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-23 4:55 François Dumont
2024-05-23 13:31 ` Jonathan Wakely
2024-05-23 17:37 ` François Dumont [this message]
2024-05-24 14:17 ` Jonathan Wakely
2024-05-25 9:59 ` François Dumont
2024-05-27 4:37 ` François Dumont
2024-05-28 10:30 ` Jonathan Wakely
2024-05-28 20:53 ` François Dumont
2024-05-29 9:35 ` Jonathan Wakely
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