[Bug tree-optimization/93004] New: Suspicious code in tree-ssa-loop-ivopts.c

[fxue at os dot amperecomputing.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93004

            Bug ID: 93004
           Summary: Suspicious code in tree-ssa-loop-ivopts.c
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fxue at os dot amperecomputing.com
  Target Milestone: ---

In function determine_group_iv_cost_address(),

  /* Uses in a group can share setup code, so only add setup cost once.  */
  cost -= cost.scratch;
  /* Compute and add costs for rest uses of this group.  */
  for (i = 1; i < group->vuses.length () && !sum_cost.infinite_cost_p (); i++)
    {
      struct iv_use *next = group->vuses[i];

      /* TODO: We could skip computing cost for sub iv_use when it has the
         same cost as the first iv_use, but the cost really depends on the
         offset and where the iv_use is.  */
        cost = get_computation_cost (data, next, cand, true,
                                     NULL, &can_autoinc, &inv_expr);
        if (inv_expr)
          {
            if (!inv_exprs)
              inv_exprs = BITMAP_ALLOC (NULL);

            bitmap_set_bit (inv_exprs, inv_expr->id);
          }
      sum_cost += cost;
    }

Change to "cost" ahead of loop is meaningless, since it will be refreshed
inside the loop. According to comment, I guess "cost -= cost.scratch" might be
placed after "cost = get_computation_cost()".