Re: How to handle loop iterator variable?

[Sandeep Maram]

Hi,

 My function is working properly for the below case -

for (i = 1; i < N ; i++)
    {
      a[i] = 1;
    }
  for (i = 1; i < N ; i++)
    {
      j = a[i];
    }

But I am required to add additional phi node for j in the following case -

for (i = 1; i < N ; i++)
    {
      a[i] = 1;
    }
  for (i = 1; i < N ; i++)
    {
      j = j + a[i];
    }

  I am trying to understand how it is done in create_iv. I have tried
using merge_blocks() of cfghooks.c to fuse the loop headers. Using
code

/* The following function fuses two loops.  */

void
fuse_loops (struct loop *loop_a, struct loop *loop_b)
{
  basic_block *bbs_a, *bbs_b;
  struct loop *new_loop;
  bbs_a = get_loop_body (loop_a);
  bbs_b = get_loop_body (loop_b);
  debug_loop (loop_a, 10);
  debug_loop (loop_b, 10);
  merge_blocks (bbs_b[0], bbs_a[0]);
  debug_loop (loop_a, 10);
  debug_loop (loop_b, 10);
  cancel_loop_tree (loop_a);

}

 But the I get an internal compiler error -

loop.c: In function 'main':
loop.c:8: internal compiler error: in single_succ_edge, at basic-block.h:638

The function merge_blocks()  merges blocks only with single successors
and predecessors. But the blocks in loops have 2 each.

Can you please suggest what is the right thing to do here?

Thanks,
Sandeep.