Re: fragile test case ivopt_infer_2.c

[Richard Biener <richard dot guenther at gmail dot com>]

On Wed, Jun 19, 2013 at 12:35 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
> On Wed, Jun 19, 2013 at 4:43 PM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> On Wed, Jun 19, 2013 at 10:04 AM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>>> Hi,
>>> For test case gcc.dg/tree-ssa/ivopt_inter_2.c
>>>
>>> #ifndef TYPE
>>> #define TYPE char*
>>> #endif
>>>
>>> extern char a[];
>>>
>>> /* Can not infer loop iteration from array -- exit test can not be replaced.  */
>>> void foo (unsigned int i_width, TYPE dst)
>>> {
>>>   unsigned long long i = 0;
>>>   unsigned long long j = 0;
>>>   for ( ; j < i_width; )
>>>     {
>>>       *dst = a[i];
>>>       dst++;
>>>       i += 2;
>>>       j += 1;
>>>     }
>>> }
>>>
>>> /* { dg-final { scan-tree-dump-times "Replacing" 0 "ivopts"} } */
>>> /* { dg-final { cleanup-tree-dump "ivopts" } } */
>>>
>>> It checks whether the test is eliminated by address iv candidate,
>>> which is fragile.
>>> Giving the ivopt dump file :
>>>
>>> foo (unsigned int i_width, char * dst)
>>> {
>>>   long long unsigned int j;
>>>   long long unsigned int i;
>>>   long long unsigned int _4;
>>>   char _9;
>>>   long long unsigned int _18;
>>>
>>>   <bb 2>:
>>>   _18 = (long long unsigned int) i_width_7(D);
>>>   if (_18 != 0)
>>>     goto <bb 3>;
>>>   else
>>>     goto <bb 7>;
>>>
>>>   <bb 3>:
>>>
>>>   <bb 4>:
>>>   # j_21 = PHI <j_13(5), 0(3)>
>>>   _9 = MEM[symbol: a, index: j_21, step: 2, offset: 0B];
>>>   MEM[base: dst_5(D), index: j_21, offset: 0B] = _9;
>>>   j_13 = j_21 + 1;
>>>   if (j_13 < _18)
>>>     goto <bb 5>;
>>>   else
>>>     goto <bb 6>;
>>>
>>>   <bb 5>:
>>>   goto <bb 4>;
>>>
>>>   <bb 6>:
>>>
>>>   <bb 7>:
>>>   return;
>>> }
>>>
>>> It's possible to have  "if (j_13 < _18)" eliminated into "if (j_13 !=
>>> _18)", and the case would fail because of dump message "Replacing exit
>>> test: if (j_13 < _18)"
>>>
>>> Same story for ivopt_mult_3.c
>>>
>>> Any idea how it should be handled?
>>
>> Probably by checking for the real issue - I suppose at some point
>> the number of iterations was infered to be zero or one.
>>
> But the analyze result of loop is:
>
>
> Analyzing # of iterations of loop 1
>   exit condition [1, + , 1] < (long long unsigned int) i_width_7(D)
>   bounds on difference of bases: 0 ... 18446744073709551614
>   result:
>     # of iterations (long long unsigned int) i_width_7(D) +
> 18446744073709551615, bounded by 18446744073709551614
>   number of iterations (long long unsigned int) i_width_7(D) +
> 18446744073709551615

Which looks correct.

Richard.

>
> --
> Best Regards.