On 31/05/17 22:28 +0200, François Dumont wrote:
Unless I made a mistake it revealed that restoring explicit call to
_Bit_alloc_type() in default constructor was not enough. G++ doesn't
transform it into a value-init if needed. I don't know if it is a
compiler bug but I had to do just like presented in the Standard to
achieve the expected behavior.
That really shouldn't be necessary (see blow).
This value-init is specific to post-C++11 right ? Maybe I could remove
the useless explicit call to _Bit_alloc_type() in pre-C++11 mode ?
No, because C++03 also requires the allocator to be value-initialized.
Now I wonder if I really introduced a regression in rb_tree...
Yes, I think you did. Could you try to verify that using the new
default_init_allocator?
+ struct _Bvector_impl
+ : public _Bit_alloc_type, public _Bvector_impl_data
+ {
+ public:
+#if __cplusplus >= 201103L
+ _Bvector_impl()
+ noexcept( noexcept(_Bit_alloc_type())
+ && noexcept(_Bvector_impl(declval<const
_Bit_alloc_type&>())) )
This second condition is not needed, because that constructor should
be noexcept (see below).
+ : _Bvector_impl(_Bit_alloc_type())
This should not be necessary...
+ { }
+#else
_Bvector_impl()
- : _Bit_alloc_type(), _M_start(), _M_finish(), _M_end_of_storage()
+ : _Bit_alloc_type()
{ }
+#endif
I would expect the constructor to look like this:
_Bvector_impl()
_GLIBCXX_NOEXCEPT_IF( noexcept(_Bit_alloc_type()) )
: _Bit_alloc_type()
{ }
What happens when you do that?
_Bvector_impl(const _Bit_alloc_type& __a)
- : _Bit_alloc_type(__a), _M_start(), _M_finish(), _M_end_of_storage()
+ _GLIBCXX_NOEXCEPT_IF( noexcept(_Bit_alloc_type(__a)) )
Copying the allocator is not allowed to throw. You can use simply
_GLIBCXX_NOEXCEPT here.
+void test01()
+{
+ typedef default_init_allocator<T> alloc_type;
+ typedef std::vector<T, alloc_type> test_type;
+
+ test_type v1;
+ v1.push_back(T());
+
+ VERIFY( !v1.empty() );
+ VERIFY( !v1.get_allocator().state );
This is unlikely to ever fail, because the stack is probably full of
zeros anyway. Did you confirm whether the test fails without your
fixes to value-initialize the allocator?
One possible way to make it fail would be to construct the
vector<bool> using placement new, into a buffer filled with non-zero
values. (Valgrind or a sanitizer should also tell us, but we can't
rely on them in the testsuite).
