[PATCH] libstdc++: Optimize operator+(string/char*, string/char*) equally

[Jonathan Wakely]

On Wed, 24 Aug 2022 at 23:39, Alexandre Oliva <oliva@gnu.org> wrote:
>
> On Aug 24, 2022, Jonathan Wakely via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>
> >            * include/bits/basic_string.h (operator+(const string&,
> > const char*)):
> >            Remove naive implementation.
> >            * include/bits/basic_string.tcc (operator+(const string&,
> > const char*)):
> >            Add single-allocation implementation.
>
> ISTM this requires the following additional tweak:
>
> diff --git a/libstdc++-v3/src/c++11/string-inst.cc b/libstdc++-v3/src/c++11/string-inst.cc
> index bfae6d902a1dd..2ec0e9d85f947 100644
> --- a/libstdc++-v3/src/c++11/string-inst.cc
> +++ b/libstdc++-v3/src/c++11/string-inst.cc
> @@ -58,6 +58,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>    template class basic_string<C>;
>    template S operator+(const C*, const S&);
> +  template S operator+(const S&, const C*);
>    template S operator+(C, const S&);
>    template S operator+(const S&, const S&);
>
>
> Without this, I'm getting undefined references to this specialization in
> libstdc++.so, that I tracked down to a std::system_error ctor in
> cxx11-ios_failure.o.  I got this while testing another patch that might
> be the reason why the template instantiation doesn't get inlined, but...
> we can't depend on its being inlined, can we?

Right. But adding that will cause another symbol to be exported,
probably with the wrong symbol version.

To fix https://gcc.gnu.org/PR106735 I'm just going to revert it for
now, and revisit in the morning.