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libstdc++: Add hint to compiler about vector invariants [PR106434]

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The PR shows a bogus warning where jump threading generates code for the
undefined case that the insertion point is a value-initialized iterator
but _M_finish and _M_end_of_storage are unequal (so at least one must be
non-null). Using __builtin_unreachable() removes the bogus warning. Also
add an assertion to diagnose undefined misuses of a null iterator here,
so we don't just silently optimize that undefined code to something
unsafe.

libstdc++-v3/ChangeLog:

	PR c++/106434
	* include/bits/vector.tcc (insert(const_iterator, const T&)):
	Add assertion and optimization hint that the iterator for the
	insertion point must be non-null.
This commit is contained in:
Jonathan Wakely 2022-12-05 12:53:42 +00:00
parent af177d7280
commit 4ba94abf14
1 changed files with 23 additions and 17 deletions
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40
libstdc++-v3/include/bits/vector.tcc
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@ -139,26 +139,32 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
{
const size_type __n = __position - begin();
if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
if (__position == end())
{
_GLIBCXX_ASAN_ANNOTATE_GROW(1);
_Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
__x);
++this->_M_impl._M_finish;
_GLIBCXX_ASAN_ANNOTATE_GREW(1);
}
else
{
{
__glibcxx_assert(__position != const_iterator());
if (!(__position != const_iterator()))
__builtin_unreachable(); // PR 106434
if (__position == end())
{
_GLIBCXX_ASAN_ANNOTATE_GROW(1);
_Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
__x);
++this->_M_impl._M_finish;
_GLIBCXX_ASAN_ANNOTATE_GREW(1);
}
else
{
#if __cplusplus >= 201103L
const auto __pos = begin() + (__position - cbegin());
// __x could be an existing element of this vector, so make a
// copy of it before _M_insert_aux moves elements around.
_Temporary_value __x_copy(this, __x);
_M_insert_aux(__pos, std::move(__x_copy._M_val()));
const auto __pos = begin() + (__position - cbegin());
// __x could be an existing element of this vector, so make a
// copy of it before _M_insert_aux moves elements around.
_Temporary_value __x_copy(this, __x);
_M_insert_aux(__pos, std::move(__x_copy._M_val()));
#else
_M_insert_aux(__position, __x);
_M_insert_aux(__position, __x);
#endif
}
}
}
else
#if __cplusplus >= 201103L
_M_realloc_insert(begin() + (__position - cbegin()), __x);