Remove cycle checking from compute_control_dep_chain

Now that we have DFS_BACK_EDGE marks we can simply avoid walking
those instead of repeatedly looking for a cycle on the current chain.

	* gimple-predicate-analysis.cc (compute_control_dep_chain):
	Remove cycle detection, instead avoid walking backedges.

diff --git a/gcc/gimple-predicate-analysis.cc b/gcc/gimple-predicate-analysis.cc
index 2982268fdfdf0bed4e5617db0e144128fa46aeba..a754ff0a029dd0761e8dad8a8ce8add3fbfd338f 100644 (file)
--- a/gcc/gimple-predicate-analysis.cc
+++ b/gcc/gimple-predicate-analysis.cc
@@ -1035,18 +1035,6 @@ compute_control_dep_chain (basic_block dom_bb, const_basic_block dep_bb,
        fprintf (dump_file, "chain length exceeds 5: %u\n", cur_chain_len);
     }
 
-  for (unsigned i = 0; i < cur_chain_len; i++)
-    {
-      edge e = cur_cd_chain[i];
-      /* Cycle detected.  */
-      if (e->src == dom_bb)
-       {
-         if (dump_file)
-           fprintf (dump_file, "cycle detected\n");
-         return false;
-       }
-    }
-
   if (DEBUG_PREDICATE_ANALYZER && dump_file)
     fprintf (dump_file,
             "%*s%s (dom_bb = %u, dep_bb = %u, cd_chains = { %s }, ...)\n",
@@ -1061,7 +1049,7 @@ compute_control_dep_chain (basic_block dom_bb, const_basic_block dep_bb,
   FOR_EACH_EDGE (e, ei, dom_bb->succs)
     {
       int post_dom_check = 0;
-      if (e->flags & (EDGE_FAKE | EDGE_ABNORMAL))
+      if (e->flags & (EDGE_FAKE | EDGE_ABNORMAL | EDGE_DFS_BACK))
        continue;
 
       basic_block cd_bb = e->dest;
@@ -1110,6 +1098,12 @@ compute_control_dep_chain (basic_block dom_bb, const_basic_block dep_bb,
              break;
            }
 
+         /* The post-dominator walk will reach a backedge only
+            from a forwarder, otherwise it should choose to exit
+            the SCC.  */
+         if (single_succ_p (cd_bb)
+             && single_succ_edge (cd_bb)->flags & EDGE_DFS_BACK)
+           break;
          cd_bb = get_immediate_dominator (CDI_POST_DOMINATORS, cd_bb);
          post_dom_check++;
          if (cd_bb == EXIT_BLOCK_PTR_FOR_FN (cfun)