[PATCH GCC]Fix memory leak and wrong invariant dependence computation in IVOPT

[Bin Cheng]

Hi,
When address iv uses grouping was introduced, I also introduced memory leak
and wrong computation of depends_on bitmap.  The intention is to skip
`depends_on' computation for sub address type iv uses.  Unfortunately, the
code is wrong because depends_on is freed in subsequent calls to
get_computation_cost for a grouped iv use.  This results in loss of
depends_on information, as well memory leaks for depends_on bitmap.

I think this is an obvious fix to the issue.  Bootstrap and test on x86_64.
OK?

Thanks,
bin

2015-10-27  Bin Cheng  <bin.ch...@arm.com>

        * tree-ssa-loop-ivopts.c (split_address_cost): Check depends_on.
        (get_computation_cost_at): Ditto.
        (determine_use_iv_cost_address): Pass NULL for arguments depends_on
        and inv_expr_id.


diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 945d34b..91f7284 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -4328,7 +4328,9 @@ split_address_cost (struct ivopts_data *data,
       *symbol_present = false;
       *var_present = true;
       fd_ivopts_data = data;
-      walk_tree (&addr, find_depends, depends_on, NULL);
+      if (depends_on)
+       walk_tree (&addr, find_depends, depends_on, NULL);
+
       return new_cost (target_spill_cost[data->speed], 0);
     }
 
@@ -4616,7 +4618,8 @@ get_computation_cost_at (struct ivopts_data *data,
                                ? TYPE_MODE (TREE_TYPE (*use->op_p))
                                : VOIDmode);
 
-  *depends_on = NULL;
+  if (depends_on)
+    *depends_on = NULL;
 
   /* Only consider real candidates.  */
   if (!cand->iv)
@@ -4908,9 +4911,9 @@ determine_use_iv_cost_address (struct ivopts_data *data,
        sub_use && !infinite_cost_p (cost);
        sub_use = sub_use->next)
     {
-       sub_cost = get_computation_cost (data, sub_use, cand, true, &depends_on,
-                                       &can_autoinc, &inv_expr_id);
-       cost = add_costs (cost, sub_cost);
+      sub_cost = get_computation_cost (data, sub_use, cand, true, NULL,
+                                      &can_autoinc, NULL);
+      cost = add_costs (cost, sub_cost);
     }
 
   set_use_iv_cost (data, use, cand, cost, depends_on, NULL_TREE, ERROR_MARK,