Re: [PATCH] libstdc++: Implement C++20 atomic<shared_ptr> and atomic<weak_ptr>

[Jonathan Wakely <jwakely@redhat.com>]

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On Mon, 17 Jan 2022 at 09:39, Stephan Bergmann <sbergman@redhat.com> wrote:

> On 1/17/22 01:12, Jonathan Wakely via Libstdc++ wrote:
> > Here's the finished version of that patch, which is all inline in the
> > header, and performs faster too.
> >
> > Tested powerpc64le-linux and x86_64-linux.
> > Pushed to trunk.
>
> FYI, recent Clang still requires typename in two places to compile
> <memory> with -std=c++20,
>
> > diff --git a/libstdc++-v3/include/bits/shared_ptr_atomic.h
> b/libstdc++-v3/include/bits/shared_ptr_atomic.h
> > index 900499bae32..50aa46370ca 100644
> > --- a/libstdc++-v3/include/bits/shared_ptr_atomic.h
> > +++ b/libstdc++-v3/include/bits/shared_ptr_atomic.h
> > @@ -456,8 +456,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >        typename _Tp::element_type* _M_ptr;
> >        _Atomic_count _M_refcount;
> >
> > -      static _Atomic_count::pointer
> > -      _S_add_ref(_Atomic_count::pointer __p)
> > +      static typename _Atomic_count::pointer
> > +      _S_add_ref(typename _Atomic_count::pointer __p)
> >        {
> >       if (__p)
> >         {
>

Sigh, yes, I already noticed this myself. Clang is wrong (P0634R0 gives an
example *very* similar to this as motivation for the change), but we need
to keep writing the code in C++17 style if we want to be compatible with
released versions of Clang.

Fixed by the attached patch, tested x86_64-linux and pushed to trunk.

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commit a923345c72aef9ebb6b32f81f4825acc11085803
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jan 17 09:42:35 2022

    libstdc++: Add 'typename' to dependent types in atomic<shared_ptr<T>>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/shared_ptr_atomic.h (_Sp_atomic): Add typename
            to qualified-id for dependent type.

diff --git a/libstdc++-v3/include/bits/shared_ptr_atomic.h b/libstdc++-v3/include/bits/shared_ptr_atomic.h
index 900499bae32..50aa46370ca 100644
--- a/libstdc++-v3/include/bits/shared_ptr_atomic.h
+++ b/libstdc++-v3/include/bits/shared_ptr_atomic.h
@@ -456,8 +456,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typename _Tp::element_type* _M_ptr;
       _Atomic_count _M_refcount;
 
-      static _Atomic_count::pointer
-      _S_add_ref(_Atomic_count::pointer __p)
+      static typename _Atomic_count::pointer
+      _S_add_ref(typename _Atomic_count::pointer __p)
       {
 	if (__p)
 	  {