On Fri, 3 Oct 2014, Jonathan Wakely wrote:
This is the patch I intend to commit to make std::list::size() O(1) as required by C++11.This is an ABI change, so std::list will get tagged with abi_tag("cxx11") so that it mangles differently.
Assuming a future where we have both _GLIBCXX_ABI_TAG_CXX11 and _GLIBCXX_ABI_TAG_CXX17, I don't really see how _GLIBCXX_DEFAULT_ABI_TAG is supposed to work. We don't want to define _GLIBCXX_DEFAULT_ABI_TAG to _GLIBCXX_ABI_TAG_CXX17 and suddenly have std::list change mangling. Should it be called _GLIBCXX_DEFAULT_ABI_TAG_CXX11, meaning _GLIBCXX_ABI_TAG_CXX11_IF_ENABLED_AND_NOTHING_OTHERWISE?
Defining a dummy _M_distance in the old abi case is a bit strange (we could protect the single use with #if _GLIBCXX_USE_CXX11_ABI), but why not...
Do you mind if I move (in a future patch once yours is committed) _M_size into _M_impl::_M_node as suggested in PR 61347?
-- Marc Glisse
