std::string add nullptr attribute

[Marc Glisse]

On Mon, 20 Feb 2023, Gabriel Ravier via Gcc-help wrote:

> This is the kind of thing that makes me wonder why there isn't some kind of 
> `__builtin_unreachable_do_not_optimize()` builtin that allows one to mark 
> places in code that should never be reached and should thus be warned about 
> if such a thing happens while at the same time never doing any optimization 
> on the basis of the presence of the call.

-fsanitize=unreachable -fsanitize=null and others prevent the kind of 
optimization you are worried about.

-- 
Marc Glisse