[PATCH PR95700] Use nullptr instead of NULL as a sentinel value

[Richard Biener]

On Wed, Jun 24, 2020 at 4:14 PM Jonathan Wakely via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On 24/06/20 12:31 +0200, Ilya Leoshkevich wrote:
> >Bootstrapped and regtested on x86_64-redhat-linux, ppc64le-redhat-linux
> >and s390x-redhat-linux.
> >
> >Ok for master?
> >
> >---
> >
> >Bootstrap with musl libc fails with numerous "missing sentinel in
> >function call" errors.  This is because musl defines NULL as 0L for C++,
> >but gcc requires sentinel value to be a pointer or __null.
> >
> >Jonathan Wakely says:
> >
> >    To be really safe during stage 1, GCC should not use NULL as a
> >    pointer sentinel in C++ code anyway.
> >
> >    The bootstrap compiler could define it to 0 or 0u, neither of which
> >    is guaranteed to be OK to pass as a varargs sentinel where a null
> >    pointer is expected.  Any of (void*)0 or (void*)NULL or nullptr
> >    would be safe.
> >
> >Therefore, fix by replacing NULL sentinels with nullptr.
>
> For some additional context, the C++ standard guarantees that passing
> nullptr to a varargs function will convert to (void*)0. That has been
> true since nullptr was added in C++11.

Is there a diagnostic option that we can turn on so no NULLs will creep
in in such position?   Without that we'll bitrot quickly?

Richard.

>