PATCH to fix -Wrestrict ICE (PR middle-end/83463)

[Martin Sebor]

On 12/18/2017 11:32 AM, Bernd Edlinger wrote:
> Hi Martin,
>
>> In all cases all the information necessary to detect and diagnose
>> or even avoid the problem is available.  In fact, one might argue
>> that optimizing such calls (expanding them inline) would be
>> preferable to doing nothing and allowing the undefined behavior
>> to cause a bug at runtime.
>
> I think the right thing to do here would emit a warning for
> declaring the builtin with the wrong prototype.
>
> If you try to do the equivalent in C++ you get this:
>
> cat test.cc
> extern "C" void* memcpy (...);
>
> void p (void *d, const void *s)
> {
>   memcpy (d, s, 0);
> }
>
>  g++ -S  test.cc
> test.cc:1:18: warning: declaration of ‘void* memcpy(...)’ conflicts with built-in declaration ‘void* memcpy(void*, const void*, long unsigned int)’ [-Wbuiltin-declaration-mismatch]
>  extern "C" void* memcpy (...);
>                   ^~~~~~
>
> You get the same warning in C when the Prototype does not match,
> but unfortunately not when the prototype is missing.
>
> I would prefer the same warning in C whenever the declaration does
> not match.

That sounds good to me.

I do think that, in addition, issuing another warning for calls
with arguments of the wrong type (or wrong number) would be useful
as well, or in fact even more so.  It will make it possible to
distinguish safe calls to such functions from unsafe ones.  These
two could be part of the same enhancement or independent of one
another.

Martin