[PATCH] PR string/19907: Incorrect memcpy tests

[H.J. Lu]

On Sun, May 8, 2016 at 12:35 PM, Florian Weimer <fw@deneb.enyo.de> wrote:
> * H. J. Lu:
>
>> On Sun, May 8, 2016 at 10:14 AM, Florian Weimer <fw@deneb.enyo.de> wrote:
>>> * H. J. Lu:
>>>
>>>> +  /* Must clear the destination buffer set by the previous run.  */
>>>> +  for (i = 0; i < len; i++)
>>>> +    dst[i] = 0;
>>>
>>> Doesn't this need some sort of compiler barrier so that GCC will not
>>> eliminate the dead stores if it recognizes a memset-style loop?
>>
>> The code looks like:
>>
>>  /* Must clear the destination buffer set by the previous run.  */
>>   for (i = 0; i < len; i++)
>>     dst[i] = 0;
>>
>>   if (CALL (impl, dst, src, len) != MEMCPY_RESULT (dst, len))
>>     {
>>
>> Compiler doesn't know what CALL (impl, dst, src, len) does
>> and won't optimize it out.
>
> I looked at the underlying mechanism and there's an indirection
> through the “impls” section.  You are right that it's going to take a
> while until the compiler will see through that.  In any case, it's a
> pre-existing problem, not related to your change.

Any other comments, feedbacks, objections?

-- 
H.J.