--- a/gcc/domwalk.c	Thu Oct 25 07:37:49 2018 +0900
+++ b/gcc/domwalk.c	Thu Feb 13 11:34:05 2020 +0900
@@ -1,5 +1,5 @@
 /* Generic dominator tree walker
-   Copyright (C) 2003-2018 Free Software Foundation, Inc.
+   Copyright (C) 2003-2020 Free Software Foundation, Inc.
    Contributed by Diego Novillo <dnovillo@redhat.com>
 
 This file is part of GCC.
@@ -128,14 +128,12 @@
     which is currently an abstraction over walking tree statements.  Thus
     the dominator walker is currently only useful for trees.  */
 
-/* Reverse postorder index of each basic block.  */
-static int *bb_postorder;
-
 static int
-cmp_bb_postorder (const void *a, const void *b)
+cmp_bb_postorder (const void *a, const void *b, void *data)
 {
   basic_block bb1 = *(const basic_block *)(a);
   basic_block bb2 = *(const basic_block *)(b);
+  int *bb_postorder = (int *)data;
   /* Place higher completion number first (pop off lower number first).  */
   return bb_postorder[bb2->index] - bb_postorder[bb1->index];
 }
@@ -144,7 +142,7 @@
    i.e. by descending number in BB_POSTORDER array.  */
 
 static void
-sort_bbs_postorder (basic_block *bbs, int n)
+sort_bbs_postorder (basic_block *bbs, int n, int *bb_postorder)
 {
   if (__builtin_expect (n == 2, true))
     {
@@ -166,7 +164,7 @@
       bbs[0] = bb0, bbs[1] = bb1, bbs[2] = bb2;
     }
   else
-    qsort (bbs, n, sizeof *bbs, cmp_bb_postorder);
+    gcc_sort_r (bbs, n, sizeof *bbs, cmp_bb_postorder, bb_postorder);
 }
 
 /* Set EDGE_EXECUTABLE on every edge within FN's CFG.  */
@@ -190,69 +188,11 @@
 			enum reachability reachability,
 			int *bb_index_to_rpo)
   : m_dom_direction (direction),
-    m_skip_unreachable_blocks (reachability != ALL_BLOCKS),
-    m_user_bb_to_rpo (true),
+    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)
 {
-  /* Set up edge flags if need be.  */
-  switch (reachability)
-    {
-    default:
-      gcc_unreachable ();
-    case ALL_BLOCKS:
-      /* No need to touch edge flags.  */
-      break;
-
-    case REACHABLE_BLOCKS:
-      set_all_edges_as_executable (cfun);
-      break;
-
-    case REACHABLE_BLOCKS_PRESERVING_FLAGS:
-      /* Preserve the edge flags.  */
-      break;
-    }
-}
-
-/* Constructor for a dom walker.  */
-
-dom_walker::dom_walker (cdi_direction direction,
-			enum reachability reachability)
-  : m_dom_direction (direction),
-    m_skip_unreachable_blocks (reachability != ALL_BLOCKS),
-    m_user_bb_to_rpo (false),
-    m_unreachable_dom (NULL),
-    m_bb_to_rpo (NULL)
-{
-  /* Compute the basic-block index to RPO mapping.  */
-  if (direction == CDI_DOMINATORS)
-    {
-      int *postorder = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
-      int postorder_num = pre_and_rev_post_order_compute (NULL, postorder,
-							  true);
-      m_bb_to_rpo = XNEWVEC (int, last_basic_block_for_fn (cfun));
-      for (int i = 0; i < postorder_num; ++i)
-	m_bb_to_rpo[postorder[i]] = i;
-      free (postorder);
-    }
-
-  /* Set up edge flags if need be.  */
-  switch (reachability)
-    {
-    default:
-      gcc_unreachable ();
-    case ALL_BLOCKS:
-      /* No need to touch edge flags.  */
-      break;
-
-    case REACHABLE_BLOCKS:
-      set_all_edges_as_executable (cfun);
-      break;
-
-    case REACHABLE_BLOCKS_PRESERVING_FLAGS:
-      /* Preserve the edge flags.  */
-      break;
-    }
 }
 
 /* Destructor.  */
@@ -270,7 +210,7 @@
 {
   /* If we're not skipping unreachable blocks, then assume everything
      is reachable.  */
-  if (!m_skip_unreachable_blocks)
+  if (m_reachability == ALL_BLOCKS)
     return true;
 
   /* If any of the predecessor edges that do not come from blocks dominated
@@ -331,11 +271,27 @@
 void
 dom_walker::walk (basic_block bb)
 {
+  /* Compute the basic-block index to RPO mapping lazily.  */
+  if (!m_bb_to_rpo
+      && m_dom_direction == CDI_DOMINATORS)
+    {
+      int *postorder = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
+      int postorder_num = pre_and_rev_post_order_compute (NULL, postorder,
+							  true);
+      m_bb_to_rpo = XNEWVEC (int, last_basic_block_for_fn (cfun));
+      for (int i = 0; i < postorder_num; ++i)
+	m_bb_to_rpo[postorder[i]] = i;
+      free (postorder);
+    }
+
+  /* Set up edge flags if need be.  */
+  if (m_reachability == REACHABLE_BLOCKS)
+    set_all_edges_as_executable (cfun);
+
   basic_block dest;
   basic_block *worklist = XNEWVEC (basic_block,
 				   n_basic_blocks_for_fn (cfun) * 2);
   int sp = 0;
-  bb_postorder = m_bb_to_rpo;
 
   while (true)
     {
@@ -380,7 +336,8 @@
 	      if (sp - saved_sp > 1
 		  && m_dom_direction == CDI_DOMINATORS
 		  && m_bb_to_rpo)
-		sort_bbs_postorder (&worklist[saved_sp], sp - saved_sp);
+		sort_bbs_postorder (&worklist[saved_sp], sp - saved_sp,
+				    m_bb_to_rpo);
 	    }
 	}
       /* NULL is used to mark pop operations in the recursion stack.  */
@@ -401,6 +358,5 @@
       else
 	break;
     }
-  bb_postorder = NULL;
   free (worklist);
 }