[Bug tree-optimization/66851] New: support double reduction in parloops

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66851

            Bug ID: 66851
           Summary: support double reduction in parloops
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

outer-4.c contains an xfail:
...
/* { dg-do compile } */
/* { dg-options "-O2 -ftree-parallelize-loops=4 -fdump-tree-parloops-details
-fdump-tree-optimized" } */

void abort (void);

int g_sum=0;
int x[500][500];

__attribute__((noinline))
void parloop (int N)
{
  int i, j;
  int sum;

  /* Double reduction is currently not supported, outer loop is not
     parallelized.  Inner reduction is detected, inner loop is
     parallelized.  */
  sum = 0;
  for (i = 0; i < N; i++)
    for (j = 0; j < N; j++)
      sum += x[i][j];

  g_sum = sum;
}

int main(void)
{
  parloop(500);

  return 0;
}


/* { dg-final { scan-tree-dump-times "parallelizing outer loop" 1 "parloops" {
xfail *-*-* } } } */
/* { dg-final { scan-tree-dump-times "loopfn" 4 "optimized" } } */
...