Delay edge removal in forwprop

SSA forwprop has switch simplification code that calls remove edge
and as side-effect releases dominator info.  For a followup we want
to retain that so the following delays removing edges until the end
of the pass.  As usual we have to deal with parts of the edge
vanishing due to EH/abnormal pruning so record edges as basic-block
index pairs and remove them only when they are still there.

	* tree-ssa-forwprop.cc (simplify_gimple_switch_label_vec):
	Delay removing edges and releasing dominator info, instead
	record into edges_to_remove vector.
	(simplify_gimple_switch): Pass through vector of to remove
	edges.
	(pass_forwprop::execute): Likewise.  Remove queued edges.

1 files changed, 25 insertions, 9 deletions

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 9595555..e7342b4 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -972,7 +972,8 @@ forward_propagate_addr_expr (tree name, tree rhs, bool parent_single_use_p)
    have values outside the range of the new type.  */
 
 static void
-simplify_gimple_switch_label_vec (gswitch *stmt, tree index_type)
+simplify_gimple_switch_label_vec (gswitch *stmt, tree index_type,
+				  vec<std::pair<int, int> > &edges_to_remove)
 {
   unsigned int branch_num = gimple_switch_num_labels (stmt);
   auto_vec<tree> labels (branch_num);
@@ -1026,11 +1027,8 @@ simplify_gimple_switch_label_vec (gswitch *stmt, tree index_type)
       for (ei = ei_start (gimple_bb (stmt)->succs); (e = ei_safe_edge (ei)); )
 	{
 	  if (! bitmap_bit_p (target_blocks, e->dest->index))
-	    {
-	      remove_edge (e);
-	      cfg_changed = true;
-	      free_dominance_info (CDI_DOMINATORS);
-	    }
+	    edges_to_remove.safe_push (std::make_pair (e->src->index,
+						       e->dest->index));
 	  else
 	    ei_next (&ei);
 	} 
@@ -1042,7 +1040,8 @@ simplify_gimple_switch_label_vec (gswitch *stmt, tree index_type)
    the condition which we may be able to optimize better.  */
 
 static bool
-simplify_gimple_switch (gswitch *stmt)
+simplify_gimple_switch (gswitch *stmt,
+			vec<std::pair<int, int> > &edges_to_remove)
 {
   /* The optimization that we really care about is removing unnecessary
      casts.  That will let us do much better in propagating the inferred
@@ -1078,7 +1077,8 @@ simplify_gimple_switch (gswitch *stmt)
 		  && (!max || int_fits_type_p (max, ti)))
 		{
 		  gimple_switch_set_index (stmt, def);
-		  simplify_gimple_switch_label_vec (stmt, ti);
+		  simplify_gimple_switch_label_vec (stmt, ti,
+						    edges_to_remove);
 		  update_stmt (stmt);
 		  return true;
 		}
@@ -3518,6 +3518,7 @@ pass_forwprop::execute (function *fun)
     |= EDGE_EXECUTABLE;
   auto_vec<gimple *, 4> to_fixup;
   auto_vec<gimple *, 32> to_remove;
+  auto_vec<std::pair<int, int>, 10> edges_to_remove;
   auto_bitmap simple_dce_worklist;
   auto_bitmap need_ab_cleanup;
   to_purge = BITMAP_ALLOC (NULL);
@@ -4024,7 +4025,8 @@ pass_forwprop::execute (function *fun)
 		  }
 
 		case GIMPLE_SWITCH:
-		  changed = simplify_gimple_switch (as_a <gswitch *> (stmt));
+		  changed = simplify_gimple_switch (as_a <gswitch *> (stmt),
+						    edges_to_remove);
 		  break;
 
 		case GIMPLE_COND:
@@ -4173,6 +4175,20 @@ pass_forwprop::execute (function *fun)
   cfg_changed |= gimple_purge_all_dead_abnormal_call_edges (need_ab_cleanup);
   BITMAP_FREE (to_purge);
 
+  /* Remove edges queued from switch stmt simplification.  */
+  for (auto ep : edges_to_remove)
+    {
+      basic_block src = BASIC_BLOCK_FOR_FN (fun, ep.first);
+      basic_block dest = BASIC_BLOCK_FOR_FN (fun, ep.second);
+      edge e;
+      if (src && dest && (e = find_edge (src, dest)))
+	{
+	  free_dominance_info (CDI_DOMINATORS);
+	  remove_edge (e);
+	  cfg_changed = true;
+	}
+    }
+
   if (get_range_query (fun) != get_global_range_query ())
     disable_ranger (fun);