RFC: Followup to PR91593

[Jerry DeLisle]

On 10/1/19 12:40 PM, Martin Sebor wrote:
> On 9/30/19 9:40 PM, Jerry DeLisle wrote:
>> Copying gcc list for additional thoughts on a possible bogus warning.
>>
>> On 9/29/19 9:02 AM, Jerry DeLisle wrote:

--- snip ---
> 
> In case it helps, the warning is for the access:
> 
>  Â  # .MEM_68 = VDEF <.MEM_71>
>  Â  MEM[(char *)_86] = 0;
> 
> where _86 is set to
> 
>  Â  _86 = &itoa_buf + _43;
> 
> and _43 has the range [136, 17179869176].  (The warning needs to
> be enhanced a bit to mention the accessed object in this case.)
> itoa_buf's DECL_SIZE_UNIT evaluates to 129.
> 
> The call to btoa_big in write_b:
> 
>  Â Â Â Â Â  p = btoa_big (source, itoa_buf, len, &n);
> 
> is made with len > 16.  If len > sizeof itoa_buf  / 8 then it does
> look like btoa_big would write past the end of itoa_buf because it
> writes len * 8 bytes into it.  I don't know if the function can be
> called with len that large but if not, adding this just above
> the call suppresses the warning.
> 
>  Â Â Â Â Â  if (len > sizeof itoa_buf / 8)
>  Â Â Â Â __builtin_unreachable ();
> 
> Martin
> 

Thanks Martin, this does help me understand why the warning. Yes, len cannot be 
greater than 16. I decided to just use memset in write_b where the buffer is 
created to avoid the assignment that triggers the warning. Your suggestion may 
likewise work. In my comments describing the warning as bogus, by bogus, I mean 
"not applicable" to the situation.

I notice many warnings flying by when building gcc/gfortran. My preference would 
be to clear as many off as possible so that we can actually notice warnings when 
they are applicable and not miss them among a crowd of warnings.

I don't know if this makes sense to anyone and I do appreciate your response.

Jerry