Re: [PATCH] Fix bogus -Wstringop-overflow warning

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/13/22 06:06, Eric Botcazou via Gcc-patches wrote:
> Hi,
>
> if you compile the attached testcase with -O2 -fno-inline -Wall, you get:
>
> In function 'process_array3':
> cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [-
> Wstringop-overflow=]
> cc1: note: referencing argument 1 of type 'char[4]'
> t.c:6:6: note: in a call to function 'process_array4'
>      6 | void process_array4 (char a[4], int n)
>        |      ^~~~~~~~~~~~~~
> cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [-
> Wstringop-overflow=]
> cc1: note: referencing argument 1 of type 'char[4]'
> t.c:6:6: note: in a call to function 'process_array4'
>
> That's because the ICF IPA pass has identified the two functions and turned
> process_array3 into a wrapper of process_array4.  This looks sensible to me
> given that the only difference between them is an "access" attribute on their
> type describing the access size of the parameter and the "access" attribute
> does not affect type identity (struct attribute_spec.affects_type_identity).
>
> Hence the proposed fix, tested on x86-64/Linux, OK for the mainline?
>
>
> 2022-10-13  Eric Botcazou  <ebotcazou@adacore.com>
>
> 	* gimple-ssa-warn-access.cc (pass_waccess::check_call): Return
> 	early for calls made from thunks.
>
>
> 2022-10-13  Eric Botcazou  <ebotcazou@adacore.com>
>
> 	* gcc.dg/Wstringop-overflow-89.c: New test.

Not a fan as it could potentially hide a real issue, but I don't really 
have a better solution.  I pondered suggesting "access" affect type 
identity, but the cases where that's really important are probably 
better handled by the "fn spec" attribute, leaving "access" strictly 
impacting diagnostics.

OK

jeff