Avoid computing RPO for update_ssa

At some point when domwalk got the ability to use RPO for ordering
dominator children we carefully avoided update_ssa eating the cost
of RPO compute.  Unfortunately some later consolidation of CTORs
lost this again so the following makes this explicit via a special
value to the bb_index_to_rpo argument of domwalk, speeding up
update_ssa again.

	* domwalk.h (dom_walker::dom_walker): Update comment to
	reflect reality and new special argument value for
	bb_index_to_rpo.
	* domwalk.cc (dom_walker::dom_walker): Recognize -1
	bb_index_to_rpo.
	* tree-into-ssa.cc
	(rewrite_update_dom_walker::rewrite_update_dom_walker): Tell
	dom_walker to not use RPO.

1 files changed, 4 insertions, 2 deletions

diff --git a/gcc/domwalk.cc b/gcc/domwalk.cc
index d633088..e36e9eb 100644
--- a/gcc/domwalk.cc
+++ b/gcc/domwalk.cc
@@ -191,7 +191,8 @@ dom_walker::dom_walker (cdi_direction direction,
     m_reachability (reachability),
     m_user_bb_to_rpo (bb_index_to_rpo != NULL),
     m_unreachable_dom (NULL),
-    m_bb_to_rpo (bb_index_to_rpo)
+    m_bb_to_rpo (bb_index_to_rpo == (int *)(uintptr_t)-1
+		 ? NULL : bb_index_to_rpo)
 {
 }
 
@@ -272,7 +273,8 @@ void
 dom_walker::walk (basic_block bb)
 {
   /* Compute the basic-block index to RPO mapping lazily.  */
-  if (!m_bb_to_rpo
+  if (!m_user_bb_to_rpo
+      && !m_bb_to_rpo
       && m_dom_direction == CDI_DOMINATORS)
     {
       int *postorder = XNEWVEC (int, n_basic_blocks_for_fn (cfun));