Re: Regression with recent change

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/14/2021 8:53 AM, Aldy Hernandez wrote:
>
>
> On 9/14/21 4:13 PM, Michael Matz wrote:
>> Hello,
>>
>> On Mon, 13 Sep 2021, Aldy Hernandez via Gcc-patches wrote:
>>
>> The testcase still tests what it's supposed to test with ...
>>
>>>> typedef unsigned short uint16_t;
>>>>
>>>> uint16_t a, b;
>>>>
>>>> int *j_global;
>>>> uint16_t f(void)
>>>> {
>>>>     int c, **p;
>>>>     short d = 2, e = 4;
>>>>
>>
>> ... "c = a;" added here (i.e. it still hangs before the pr55107 change).
>>
>>>>     for (;; b++)
>>>>       {
>>>>         int *j = j_global, k = 0;
>>>>
>>>>         for (; *j; j++)
>>>>        {
>>>>          for(; c; c++)
>>>>            for(; k < 1; k++)
>>>>              {
>>>>                short *f = &d;
>>>>
>>>>                if(b)
>>>>                  return *f;
>>>>              }
>>>>        }
>>>>
>>>>         if(!c)
>>>>        d *= e;
>>>>
>>>>         a = d;
>>>>         if ((a ? b = 0 : (**p ? : 1) != (d != 1 ? 1 : (b = 0))) != 
>>>> ((k ? a
>>> : 0)
>>>>          < (a * (c = k))))
>>>>        **p = 0;
>>>>       }
>>>> }
>>>>
>>>
>>> Thanks for getting rid of the noise here.
>>>
>>> I've simplified the above to show what's going on in the warning on
>>> nds32-elf:
>>>
>>> int george, *global;
>>> int stuff(), readme();
>>>
>>> int
>>> f (void)
>>> {
>>>     int store;
>>>
>>>     for (;;)
>>>       {
>>>         int k = 0;
>>>
>>>         while (global)
>>>          {
>>>            for (; store; ++store)
>>
>> Yeah, that seems a correct warning, your 'store' (the 'c' in the 
>> original
>> testcase) is really used uninitialized (when 'global' aka '*j_global' is
>> non-zero).  Sorry for not noticing earlier, I was only getting rid of
>> warnings, not carefully looking at the testcase itself.  I think with
>> above initialization of 'c' it's conforming, and still a correct test 
>> for
>> the original bug.
>
> This is good news.  So far, every single warning/problem that has 
> surfaced with the backward threader rewrite has been a latent bug 
> elsewhere (or a bad test) :-).
Always good news :-)

>
> Would you mind checking in your changes to the testcase?
Yes, please do.

jeff