On Fri, Apr 7, 2017 at 11:32 AM, Bernd Edlinger <bernd.edlin...@hotmail.de> wrote: > On 04/07/17 17:10, Richard Biener wrote: >> On April 7, 2017 3:37:30 PM GMT+02:00, Bernd Edlinger >> <bernd.edlin...@hotmail.de> wrote: >>> On 04/07/17 08:54, Richard Biener wrote: >>>> On Thu, 6 Apr 2017, Bernd Edlinger wrote: >>>>> I think get_alias_set(t) will return 0 for typeless_storage >>>>> types, and therefore has_zero_child will be set anyway. >>>>> I think both mean the same thing in the end, but it depends on >>>>> what typeless_storage should actually mean, and we have >>>>> not yet the same idea about it. >>>> >>>> But has_zero_child does not do what we like it to because otherwise >>>> in the PR using the char[] array member would have worked! >>>> >>>> has_zero_child doesn't do that on purpose of course, but this means >>>> returing alias-set zero for the typeless storage _member_ doesn't >>>> suffice. >>>> >>> >>> I see you have a certain idea how to solve the C++17 issue. >>> And yes, I apologize, if I tried to pee on your tree :) >> >> We do have the need to support this part of the C++ standard. For other >> user code may_alias suffices and I see no reason to haste inventing sth new >> without a single convincing testcase. GCC/Language extensions should not be >> added without a good reason. >> >> I didn't propose to expose the type flag to users at all. >> >> Richard. >> > > Well, actually you did: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671#c100 > > But I won't argue if you prefer to do it as you like, > after all TBAA is your area. So that is fine for me. > > Attached is the latest version of my patch, I fixed > the issue with the type-flag conversion, and it is > already fully functional.
I agree that we don't want a new attribute. This should not be limited to C++17 mode; std::aligned_storage is in C++11 and we might as well have the same behavior in C++98 mode. Jason
