[Bug libstdc++/109442] Dead local copy of std::vector not removed from function

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109442

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Smith from comment #14)
> If I understand correctly, you're looking for documentation that
> 
>   __builtin_operator_new(size)
> 
> has the exact same semantics and permits the same optimizations as `::new T`
> for a trivially-constructible non-array type `T` whose size is `size` and
> that
> 
>   __builtin_operator_delete(p)
> 
> has the exact same semantics and permits the same optimizations as `::delete
> p` for a trivially-destructible non-array type `T` whose size is `size`,
> with `p` of type `T*` -- and similarly for the other (aligned, nothrow)
> variants?
> 
> That is the intent; I can look into getting Clang's documentation updated to
> say that more explicitly if that's useful to you.

I was specifically looking at C++20 7.6.2.7/10 to /14 (but maybe also
others and of course the relevant parts of the delete expression).  In
particular the extra leeway the standard provides to new/delete _expressions_
vs. calls of the global replaceable operators directly - do the
__builtin_operator_{new,delete} in this regard behave like new/delete
_expressions_ or like direct calls to the operators?

Do the builtins call one of the replaceable global new/delete operators
and thus users can reliably override them?

How do the builtins behave during constexpr evaluation?  new/delete
expressions have their behavior documented in the standard.