Re: [PATCH] restore ancient -Waddress for weak symbols [PR33925]

[Eric Gallager <egall@gwmail.gwu.edu>]

On Mon, Oct 4, 2021 at 2:43 PM Martin Sebor via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> While resolving the recent -Waddress enhancement request (PR
> PR102103) I came across a 2007 problem report about GCC 4 having
> stopped warning for using the address of inline functions in
> equality comparisons with null.  With inline functions being
> commonplace in C++ this seems like an important use case for
> the warning.
>
> The change that resulted in suppressing the warning in these
> cases was introduced inadvertently in a fix for PR 22252.
>
> To restore the warning, the attached patch enhances
> the decl_with_nonnull_addr_p() function to return true also for
> weak symbols for which a definition has been provided.
>
> Tested on x86_64-linux and by comparing the GCC output for new
> test cases to Clang's which diagnoses all but one instance of
> these cases with either -Wtautological-pointer-compare or
> -Wpointer-bool-conversion, depending on context.

Would it make sense to use the same names as clang's flags here, too,
instead of dumping them all under -Waddress? I think the additional
granularity could be helpful for people who only want some warnings,
but not others.

> The one case where Clang doesn't issue a warning but GCC
> with the patch does is for a symbol explicitly declared with
> attribute weak for which a definition has been provided.
> I believe the address of such symbols is necessarily nonnull and
> so issuing the warning is helpful
> (both GCC and Clang fold such comparisons to a constant).
>
> Martin