Re: [PATCH] PR string/19907: Incorrect memcpy tests

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, May 9, 2016 at 5:51 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> 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 âimplsâ 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?
>

I checked it in.


-- 
H.J.