Re: [committed] libstdc++: Disable over-zealous warnings about std::string copies [PR103332]

[Jonathan Wakely <jwakely.gcc@gmail.com>]

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On Fri, 10 Dec 2021 at 00:39, Martin Sebor via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On 12/9/21 4:24 PM, Jonathan Wakely via Gcc-patches wrote:
> > These warnings are triggered by perfectly valid code using std::string.
> > They're particularly bad when --enable-fully-dynamic-string is used,
> > because even std::string().begin() will give a warning.
> >
> > Use pragmas to stop the troublesome warnings for copies done by
> > std::char_traits.
>
> I'm still experimenting with some of the approaches we discussed
> last week, but based on my findings so far this was going to be
> my suggestion at lest for now, until or unless the problem turns
> out to affect more code than just std::string.
>
> That said, I noticed a typo in the patch:
>
> >
> > libstdc++-v3/ChangeLog:
> >
> >       PR libstdc++/103332
> >       PR libstdc++/102958
> >       PR libstdc++/103483
> >       * include/bits/char_traits.h: Suppress stringop and array-bounds
> >       warnings.
> > ---
> >   libstdc++-v3/include/bits/char_traits.h | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/libstdc++-v3/include/bits/char_traits.h b/libstdc++-v3/include/bits/char_traits.h
> > index da3e0ffffaa..3f7befcf8b2 100644
> > --- a/libstdc++-v3/include/bits/char_traits.h
> > +++ b/libstdc++-v3/include/bits/char_traits.h
> > @@ -54,6 +54,11 @@ namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
> >   {
> >   _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wstringop-overflow"
> > +#pragma GCC diagnostic ignored "-Wstringop-overread"
> > +#pragma GCC diagnostic ignored "-Warray-bounds"
>
> (Just for reference, as I mentioned in my private mail, at -O1
> the same code also triggers -Wfree-nonheap-object.)
>
> > +
> >     /**
> >      *  @brief  Mapping from character type to associated types.
> >      *
> > @@ -990,6 +995,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >     } // namespace __detail
> >   #endif // C++20
> >
> > +#pragma GCC diagnostic push
>
> This should be pop.

Oops! thanks, fixed at r12-5888 by the attached patch. Tested
x86_64-linux, pushed to trunk.

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commit db184a3453b6fe810e2d9765ef8ed9028f96e968
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Dec 10 09:06:37 2021

    libstdc++: Fix diagnostic pragma push that should be pop
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/char_traits.h: Change pragma push to pop.

diff --git a/libstdc++-v3/include/bits/char_traits.h b/libstdc++-v3/include/bits/char_traits.h
index 3f7befcf8b2..13239580622 100644
--- a/libstdc++-v3/include/bits/char_traits.h
+++ b/libstdc++-v3/include/bits/char_traits.h
@@ -995,7 +995,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   } // namespace __detail
 #endif // C++20
 
-#pragma GCC diagnostic push
+#pragma GCC diagnostic pop
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace