Re: [PATCH] Simple fix to enhance outer-loop vectorization.

[Richard Biener <richard.guenther@gmail.com>]

On Thu, May 28, 2015 at 5:51 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
> Richard,
>
> First of all, I don't think that it is possible to write out test for
> outer-loop vectorization with zero-step reference because of possible
> loop-carried dependencies and run-time aliasing is not supported for
> outer-loop. If there are no such dependencies pre or pdse does
> hoisting (sinking) of such invariant references. So I add a check on
> it to accept zero-step references for outer loop marked with
> forc-vectorize flag to guarantee absence of loop-carried dependencies
> between inner-loop iterations.
> I included run-time test that checks vectorization correctness.
>
> Update patch is attached.

Please don't use fprintf from testcases but just call abort () when
you detect an error.  gcc.dg/vect testcases shouldn't have an
explicit dg-do run, just drop it, it is implicit.

Ok with that changes.

Thanks,
Richard.



> Yuri..
>
> 2015-05-28 14:39 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>> On Thu, May 28, 2015 at 1:00 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>> Hi All,
>>>
>>> Here is a simple patch which removes restriction on outer-loop
>>> vectorization -  allow references in inner-loop with zero step. This
>>> case was found in one important benchmark.
>>>
>>> Bootstrap and regression testing did not show any new failures.
>>> Is it OK for trunk.
>>>
>>> ChangeLog:
>>> 2015-05-28  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>
>>> * tree-vect-data-refs.c (vect_analyze_data_ref_access): Allow
>>> consecutive accesses within outer-loop vectorization for references
>>> with zero step in inner-loop.
>>>
>>> gcc/testsuite/ChangeLog:
>>> * gcc.dg/vect/fast-math-vect-outer-1.c: New test.
>>
>> Can you please add a non-omp-simd testcase that triggers this as well and that
>> is a runtime testcase verifying the transform is correct?
>>
>> Also please don't add to the strange testcase-name machinery but just
>> use { dg-additional-options "-ffast-math" }
>>
>> Index: tree-vect-data-refs.c
>> ===================================================================
>> --- tree-vect-data-refs.c       (revision 223653)
>> +++ tree-vect-data-refs.c       (working copy)
>> @@ -2261,7 +2261,6 @@
>>    return true;
>>  }
>>
>> -
>>  /* Analyze the access pattern of the data-reference DR.
>>     In case of non-consecutive accesses call vect_analyze_group_access() to
>>     analyze groups of accesses.  */
>>
>> spurious white-space change
>>
>>
>> @@ -2291,14 +2290,8 @@
>>    if (loop_vinfo && integer_zerop (step))
>>
>> Surely the comment before this needs updating now.
>>
>>      {
>>        GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt)) = NULL;
>> -      if (nested_in_vect_loop_p (loop, stmt))
>> -       {
>> -         if (dump_enabled_p ())
>> -           dump_printf_loc (MSG_NOTE, vect_location,
>> -                            "zero step in inner loop of nest\n");
>> -         return false;
>> -       }
>> -      return DR_IS_READ (dr);
>> +      if (!nested_in_vect_loop_p (loop, stmt))
>> +       return DR_IS_READ (dr);
>>      }
>>
>>    if (loop && nested_in_vect_loop_p (loop, stmt))
>>
>> so what happens after the patch?  It would be nice to have a comment
>> explaining what happens in the nested_in_vect_loop_p case for
>> the case when the outer-loop step is zero and when it is not zero.
>>
>> In particular as you don't need any code generation changes - this hints
>> at that you may miss something ;)
>>
>> Otherwise of course the patch is ok - lifting restrictions is good.
>>
>> Thanks,
>> Richard.