Re: [PATCH v2] target/i386: Remove compilation errors when -Werror=maybe-uninitialized

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 22/12/22 11:07, Eric Auger wrote:
> Hi Philippe,
> 
> On 12/22/22 10:01, Philippe Mathieu-Daudé wrote:
>> On 22/12/22 09:18, Paolo Bonzini wrote:
>>> On 12/21/22 17:36, Eric Auger wrote:
>>>> To avoid compilation errors when -Werror=maybe-uninitialized is used,
>>>> replace 'case 3' by 'default'.
>>>>
>>>> Otherwise we get:
>>>>
>>>> ../target/i386/ops_sse.h: In function ‘helper_vpermdq_ymm’:
>>>> ../target/i386/ops_sse.h:2495:13: error: ‘r3’ may be used
>>>> uninitialized in this function [-Werror=maybe-uninitialized]
>>>>      2495 |     d->Q(3) = r3;
>>>>           |     ~~~~~~~~^~~~
>>>> ../target/i386/ops_sse.h:2494:13: error: ‘r2’ may be used
>>>> uninitialized in this function [-Werror=maybe-uninitialized]
>>>>      2494 |     d->Q(2) = r2;
>>>>           |     ~~~~~~~~^~~~
>>>> ../target/i386/ops_sse.h:2493:13: error: ‘r1’ may be used
>>>> uninitialized in this function [-Werror=maybe-uninitialized]
>>>>      2493 |     d->Q(1) = r1;
>>>>           |     ~~~~~~~~^~~~
>>>> ../target/i386/ops_sse.h:2492:13: error: ‘r0’ may be used
>>>> uninitialized in this function [-Werror=maybe-uninitialized]
>>>>      2492 |     d->Q(0) = r0;
>>>>           |     ~~~~~~~~^~~~
>>
>> With what compiler? Is that a supported one?
> https://lore.kernel.org/qemu-devel/3aab489e-9d90-c1ad-0b6b-b2b5d80db723@redhat.com/

Adding the compiler version in the commit description would help:

--
Using GCC 11.3.1 "cc (GCC) 11.3.1 20220421 (Red Hat 11.3.1-2)" we get:
--

>>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>>> Suggested-by: Stefan Weil <sw@weilnetz.de>
>>>> Fixes: 790684776861 ("target/i386: reimplement 0x0f 0x3a, add AVX")
>>>> ---
>>>>    target/i386/ops_sse.h | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/target/i386/ops_sse.h b/target/i386/ops_sse.h
>>>> index 3cbc36a59d..c442c8c10c 100644
>>>> --- a/target/i386/ops_sse.h
>>>> +++ b/target/i386/ops_sse.h
>>>> @@ -2466,7 +2466,7 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg
>>>> *s, uint32_t order)
>>>>            r0 = s->Q(0);
>>>>            r1 = s->Q(1);
>>>>            break;
>>>> -    case 3:
>>>> +    default:
>>>>            r0 = s->Q(2);
>>>>            r1 = s->Q(3);
>>>>            break;
>>>> @@ -2484,7 +2484,7 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg
>>>> *s, uint32_t order)
>>>>            r2 = s->Q(0);
>>>>            r3 = s->Q(1);
>>>>            break;
>>>> -    case 3:
>>>> +    default:
>>>>            r2 = s->Q(2);
>>>>            r3 = s->Q(3);
>>>>            break;
>>>
>>> Queued, but this compiler sucks. :)
>>
>> Can't we simply add a dumb 'default' case? So when reviewing we don't
>> have to evaluate 'default' means 3 here.
>>
>> -- >8 --
>> --- a/target/i386/ops_sse.h
>> +++ b/target/i386/ops_sse.h
>> @@ -2470,6 +2470,8 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg *s,
>> uint32_t order)
>>           r0 = s->Q(2);
>>           r1 = s->Q(3);
>>           break;
>> +    default:
>> +        qemu_build_not_reached();
>>       }
>>       switch ((order >> 4) & 3) {
>>       case 0:
>> @@ -2488,6 +2490,8 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg *s,
>> uint32_t order)
>>           r2 = s->Q(2);
>>           r3 = s->Q(3);
>>           break;
>> +    default:
>> +        qemu_build_not_reached();
>>       }
> I guess this won't fix the fact r0, r1, r2, r3 are not initialized, will it?

Well my compiler (Apple clang version 14.0.0 (clang-1400.0.29.202))
doesn't display the warning, I don't have yours handy to test it :)