mizvekov added a comment.
In D104500#2865849 <https://reviews.llvm.org/D104500#2865849>, @Quuxplusone
wrote:
> @mizvekov, I don't understand what you mean by "yet another" mechanism. This
> is just asking to restore Clang's C++98/03 extension (that supports move
> constructors even in C++03). It's asking to //remove// special-case code you
> added, right? Find the line where you're saying "oh but if it's C++03 then
> //don't// do the usual rvalue lookup," and remove that.
>
> My naive guess is line 3459:
>
> if (getLangOpts().CPlusPlus11 && !getLangOpts().CPlusPlus2b &&
> NRInfo.isMoveEligible()) {
>
> should maybe be just
>
> if (!getLangOpts().CPlusPlus2b && NRInfo.isMoveEligible()) {
>
> Could you look into that?
With that change, you get the full P1825 <https://reviews.llvm.org/P1825>
implicit move in C++98, which modifies the semantics of pure C++98 programs.
Like I said in the commit message, this can change which copy constructor is
picked, between non-const and const ones.
To continue supporting C++98, we would need to keep the old C++11 implicit move
code around.
>> And I think libc++ is in the process of ditching support for C++98
>> completely, though I might be mistaken about the extent here.
>
> Nope, untrue. I've been making some patches to ditch libc++'s
> `_LIBCPP_CXX03_LANG` macro, but I'm doing that precisely because the only
> compiler we support in C++03 mode is Clang, and on Clang we //can// actually
> use rvalue references and variadic templates and so on, even in C++03 mode.
> That is, this extension (that was broken by this patch) is actually //the
> only reason libc++ works in C++03 mode at all!// So it's important to
> preserve the extension. (And presumably there might be clients relying on the
> extension, besides just libc++.)
Well I thought that meant exactly that libc++ does not support C++98, it only
works on clang because it provides so much of C++11 as an extension.
I did not remove this just on my own whim by the way, the information I had and
the reason the patch was approved as is, is because as I said, those extensions
were considered best effort and not officially supported.
@rsmith thoughts?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D104500/new/
https://reviews.llvm.org/D104500
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