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Re: [PATCH] Relax the requirement of reduction pattern in GCC vectorizer.


Ping..  Any comment on this patch?


thanks,
Cong


On Sat, Sep 28, 2013 at 9:34 AM, Xinliang David Li <davidxl@google.com> wrote:
> You can also add a test case of this form:
>
> int foo( int t, int n, int *dst)
> {
>    int j = 0;
>    int s = 1;
>    t++;
>    for (j = 0; j < n; j++)
>      {
>          dst[j] = t;
>          s *= t;
>      }
>
>    return s;
> }
>
> where without the fix the loop vectorization is missed.
>
> David
>
> On Fri, Sep 27, 2013 at 6:28 PM, Cong Hou <congh@google.com> wrote:
>> The current GCC vectorizer requires the following pattern as a simple
>> reduction computation:
>>
>>    loop_header:
>>      a1 = phi < a0, a2 >
>>      a3 = ...
>>      a2 = operation (a3, a1)
>>
>> But a3 can also be defined outside of the loop. For example, the
>> following loop can benefit from vectorization but the GCC vectorizer
>> fails to vectorize it:
>>
>>
>> int foo(int v)
>> {
>>   int s = 1;
>>   ++v;
>>   for (int i = 0; i < 100000; ++i)
>>     s *= v;
>>   return s;
>> }
>>
>>
>> This patch relaxes the original requirement by also considering the
>> following pattern:
>>
>>
>>    a3 = ...
>>    loop_header:
>>      a1 = phi < a0, a2 >
>>      a2 = operation (a3, a1)
>>
>>
>> A test case is also added. The patch is tested on x86-64.
>>
>>
>> thanks,
>> Cong
>>
>> ================================
>>
>> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
>> index 39c786e..45c1667 100644
>> --- a/gcc/ChangeLog
>> +++ b/gcc/ChangeLog
>> @@ -1,3 +1,9 @@
>> +2013-09-27  Cong Hou  <congh@google.com>
>> +
>> + * tree-vect-loop.c: Relax the requirement of the reduction
>> + pattern so that one operand of the reduction operation can
>> + come from outside of the loop.
>> +
>>  2013-09-25  Tom Tromey  <tromey@redhat.com>
>>
>>   * Makefile.in (PARTITION_H, LTO_SYMTAB_H, COMMON_TARGET_DEF_H)
>> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
>> index 09644d2..90496a2 100644
>> --- a/gcc/testsuite/ChangeLog
>> +++ b/gcc/testsuite/ChangeLog
>> @@ -1,3 +1,7 @@
>> +2013-09-27  Cong Hou  <congh@google.com>
>> +
>> + * gcc.dg/vect/vect-reduc-pattern-3.c: New test.
>> +
>>  2013-09-25  Marek Polacek  <polacek@redhat.com>
>>
>>   PR sanitizer/58413
>> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
>> index 2871ba1..3c51c3b 100644
>> --- a/gcc/tree-vect-loop.c
>> +++ b/gcc/tree-vect-loop.c
>> @@ -2091,6 +2091,13 @@ vect_is_slp_reduction (loop_vec_info loop_info,
>> gimple phi, gimple first_stmt)
>>       a3 = ...
>>       a2 = operation (a3, a1)
>>
>> +   or
>> +
>> +   a3 = ...
>> +   loop_header:
>> +     a1 = phi < a0, a2 >
>> +     a2 = operation (a3, a1)
>> +
>>     such that:
>>     1. operation is commutative and associative and it is safe to
>>        change the order of the computation (if CHECK_REDUCTION is true)
>> @@ -2451,6 +2458,7 @@ vect_is_simple_reduction_1 (loop_vec_info
>> loop_info, gimple phi,
>>    if (def2 && def2 == phi
>>        && (code == COND_EXPR
>>    || !def1 || gimple_nop_p (def1)
>> +  || !flow_bb_inside_loop_p (loop, gimple_bb (def1))
>>            || (def1 && flow_bb_inside_loop_p (loop, gimple_bb (def1))
>>                && (is_gimple_assign (def1)
>>    || is_gimple_call (def1)
>> @@ -2469,6 +2477,7 @@ vect_is_simple_reduction_1 (loop_vec_info
>> loop_info, gimple phi,
>>    if (def1 && def1 == phi
>>        && (code == COND_EXPR
>>    || !def2 || gimple_nop_p (def2)
>> +  || !flow_bb_inside_loop_p (loop, gimple_bb (def2))
>>            || (def2 && flow_bb_inside_loop_p (loop, gimple_bb (def2))
>>        && (is_gimple_assign (def2)
>>    || is_gimple_call (def2)
>> diff --git gcc/testsuite/gcc.dg/vect/vect-reduc-pattern-3.c
>> gcc/testsuite/gcc.dg/vect/vect-reduc-pattern-3.c
>> new file mode 100644
>> index 0000000..06a9416
>> --- /dev/null
>> +++ gcc/testsuite/gcc.dg/vect/vect-reduc-pattern-3.c
>> @@ -0,0 +1,41 @@
>> +/* { dg-require-effective-target vect_int } */
>> +
>> +#include <stdarg.h>
>> +#include "tree-vect.h"
>> +
>> +#define N 10
>> +#define RES 1024
>> +
>> +/* A reduction pattern in which there is no data ref in
>> +   the loop and one operand is defined outside of the loop.  */
>> +
>> +__attribute__ ((noinline)) int
>> +foo (int v)
>> +{
>> +  int i;
>> +  int result = 1;
>> +
>> +  ++v;
>> +  for (i = 0; i < N; i++)
>> +    result *= v;
>> +
>> +  return result;
>> +}
>> +
>> +int
>> +main (void)
>> +{
>> +  int res;
>> +
>> +  check_vect ();
>> +
>> +  res = foo (1);
>> +  if (res != RES)
>> +    abort ();
>> +
>> +  return 0;
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
>> +/* { dg-final { cleanup-tree-dump "vect" } } */
>> +


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