[PATCH GCC][refacor]Manage allocation of struct iv in obstack.

[Bin Cheng]

Hi,
GCC avoids multi-pointers/dangling-pointers of struct iv by allocating
multiple copies of the structure.  This patch is an obvious fix to the issue
by managing iv structures in obstack.

Bootstrap on x86_64, will apply to trunk if no objection.

Thanks,
bin

2015-06-26  Bin Cheng  <bin.ch...@arm.com>

        * tree-ssa-loop-ivopts.c (struct ivopts_data): New field iv_obstack.
        (tree_ssa_iv_optimize_init): Initialize iv_obstack.
        (alloc_iv): New parameter.  Allocate struct iv using obstack_alloc.
        (set_iv, find_interesting_uses_address, add_candidate_1): New
        argument.
        (find_interesting_uses_op): Don't duplicate struct iv.
        (free_loop_data): Don't free iv structure explicitly.
        (tree_ssa_iv_optimize_finalize): Free iv_obstack.

Index: gcc/tree-ssa-loop-ivopts.c
===================================================================
--- gcc/tree-ssa-loop-ivopts.c  (revision 224930)
+++ gcc/tree-ssa-loop-ivopts.c  (working copy)
@@ -352,6 +352,9 @@ struct ivopts_data
   /* The maximum invariant id.  */
   unsigned max_inv_id;
 
+  /* Obstack for iv structure.  */
+  struct obstack iv_obstack;
+
   /* Whether to consider just related and important candidates when replacing a
      use.  */
   bool consider_all_candidates;
@@ -912,6 +915,7 @@ tree_ssa_iv_optimize_init (struct ivopts_data *dat
   data->inv_expr_id = 0;
   data->name_expansion_cache = NULL;
   decl_rtl_to_reset.create (20);
+  gcc_obstack_init (&data->iv_obstack);
 }
 
 /* Returns a memory object to that EXPR points.  In case we are able to
@@ -995,10 +999,12 @@ contain_complex_addr_expr (tree expr)
    for loop LOOP.  NO_OVERFLOW implies the iv doesn't overflow.  */
 
 static struct iv *
-alloc_iv (tree base, tree step, bool no_overflow = false)
+alloc_iv (struct ivopts_data *data, tree base, tree step,
+         bool no_overflow = false)
 {
   tree expr = base;
-  struct iv *iv = XCNEW (struct iv);
+  struct iv *iv = (struct iv*) obstack_alloc (&data->iv_obstack,
+                                             sizeof (struct iv));
   gcc_assert (step != NULL_TREE);
 
   /* Lower address expression in base except ones with DECL_P as operand.
@@ -1039,7 +1045,7 @@ set_iv (struct ivopts_data *data, tree iv, tree ba
   gcc_assert (!info->iv);
 
   bitmap_set_bit (data->relevant, SSA_NAME_VERSION (iv));
-  info->iv = alloc_iv (base, step, no_overflow);
+  info->iv = alloc_iv (data, base, step, no_overflow);
   info->iv->ssa_name = iv;
 }
 
@@ -1430,7 +1432,6 @@ static struct iv_use *
 find_interesting_uses_op (struct ivopts_data *data, tree op)
 {
   struct iv *iv;
-  struct iv *civ;
   gimple stmt;
   struct iv_use *use;
 
@@ -1456,14 +1457,11 @@ find_interesting_uses_op (struct ivopts_data *data
     }
   iv->have_use_for = true;
 
-  civ = XNEW (struct iv);
-  *civ = *iv;
-
   stmt = SSA_NAME_DEF_STMT (op);
   gcc_assert (gimple_code (stmt) == GIMPLE_PHI
              || is_gimple_assign (stmt));
 
-  use = record_use (data, NULL, civ, stmt, USE_NONLINEAR_EXPR);
+  use = record_use (data, NULL, iv, stmt, USE_NONLINEAR_EXPR);
   iv->use_id = use->id;
 
   return use;
@@ -2038,7 +2036,7 @@ find_interesting_uses_address (struct ivopts_data
        }
     }
 
-  civ = alloc_iv (base, step);
+  civ = alloc_iv (data, base, step);
   record_group_use (data, op_p, civ, stmt, USE_ADDRESS);
   return;
 
@@ -2681,7 +2679,7 @@ add_candidate_1 (struct ivopts_data *data,
       if (!base && !step)
        cand->iv = NULL;
       else
-       cand->iv = alloc_iv (base, step);
+       cand->iv = alloc_iv (data, base, step);
 
       cand->pos = pos;
       if (pos != IP_ORIGINAL && cand->iv)
@@ -7188,7 +7186,6 @@ free_loop_data (struct ivopts_data *data)
       struct version_info *info;
 
       info = ver_info (data, i);
-      free (info->iv);
       info->iv = NULL;
       info->has_nonlin_use = false;
       info->preserve_biv = false;
@@ -7207,13 +7204,11 @@ free_loop_data (struct ivopts_data *data)
          gcc_assert (sub->related_cands == NULL);
          gcc_assert (sub->n_map_members == 0 && sub->cost_map == NULL);
 
-         free (sub->iv);
          pre = sub;
          sub = sub->next;
          free (pre);
        }
 
-      free (use->iv);
       BITMAP_FREE (use->related_cands);
       for (j = 0; j < use->n_map_members; j++)
        if (use->cost_map[j].depends_on)
@@ -7227,7 +7222,6 @@ free_loop_data (struct ivopts_data *data)
     {
       struct iv_cand *cand = iv_cand (data, i);
 
-      free (cand->iv);
       if (cand->depends_on)
        BITMAP_FREE (cand->depends_on);
       free (cand);
@@ -7269,6 +7263,7 @@ tree_ssa_iv_optimize_finalize (struct ivopts_data
   delete data->inv_expr_tab;
   data->inv_expr_tab = NULL;
   free_affine_expand_cache (&data->name_expansion_cache);
+  obstack_free (&data->iv_obstack, NULL);
 }
 
 /* Returns true if the loop body BODY includes any function calls.  */