disable -Warray-bounds in libgo (PR 101374)

[Richard Biener]

On Thu, Jul 8, 2021 at 8:02 PM Martin Sebor via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi Ian,
>
> Yesterday's enhancement to -Warray-bounds has exposed a couple of
> issues in libgo where the code writes into an invalid constant
> address that the warning is designed to flag.
>
> On the assumption that those invalid addresses are deliberate,
> the attached patch suppresses these instances by using #pragma
> GCC diagnostic but I don't think I'm supposed to commit it (at
> least Git won't let me).  To avoid Go bootstrap failures please
> either apply the patch or otherwise suppress the warning (e.g.,
> by using a volatile pointer temporary).

Btw, I don't think we should diagnose things like

                *(int*)0x21 = 0x21;

when somebody literally writes that he'll be just annoyed by diagnostics.

Of course the above might be able to use __builtin_trap (); - it looks
like it is placed where control flow should never end, kind of a
__builtin_unreachable (), which means abort () might do as well.

Richard.

> Thanks
> Martin