--- a/gcc/bitmap.c	Fri Oct 27 22:46:09 2017 +0900
+++ b/gcc/bitmap.c	Thu Oct 25 07:37:49 2018 +0900
@@ -1,5 +1,5 @@
 /* Functions to support general ended bitmaps.
-   Copyright (C) 1997-2017 Free Software Foundation, Inc.
+   Copyright (C) 1997-2018 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -26,6 +26,8 @@
 /* Memory allocation statistics purpose instance.  */
 mem_alloc_description<bitmap_usage> bitmap_mem_desc;
 
+static bitmap_element *bitmap_tree_listify_from (bitmap, bitmap_element *);
+
 /* Register new bitmap.  */
 void
 bitmap_register (bitmap b MEM_STAT_DECL)
@@ -49,22 +51,18 @@
 static GTY((deletable)) bitmap_element *bitmap_ggc_free; /* Freelist of
 							    GC'd elements.  */
 
-static void bitmap_elem_to_freelist (bitmap, bitmap_element *);
-static void bitmap_element_free (bitmap, bitmap_element *);
-static bitmap_element *bitmap_element_allocate (bitmap);
-static int bitmap_element_zerop (const bitmap_element *);
-static void bitmap_element_link (bitmap, bitmap_element *);
-static bitmap_element *bitmap_elt_insert_after (bitmap, bitmap_element *, unsigned int);
-static void bitmap_elt_clear_from (bitmap, bitmap_element *);
-static bitmap_element *bitmap_find_bit (bitmap, unsigned int);
 
-
-/* Add ELEM to the appropriate freelist.  */
+/* Bitmap memory management.  */
+
+/* Add ELT to the appropriate freelist.  */
 static inline void
 bitmap_elem_to_freelist (bitmap head, bitmap_element *elt)
 {
   bitmap_obstack *bit_obstack = head->obstack;
 
+  if (GATHER_STATISTICS)
+    register_overhead (head, -((int)sizeof (bitmap_element)));
+
   elt->next = NULL;
   elt->indx = -1;
   if (bit_obstack)
@@ -79,41 +77,6 @@
     }
 }
 
-/* Free a bitmap element.  Since these are allocated off the
-   bitmap_obstack, "free" actually means "put onto the freelist".  */
-
-static inline void
-bitmap_element_free (bitmap head, bitmap_element *elt)
-{
-  bitmap_element *next = elt->next;
-  bitmap_element *prev = elt->prev;
-
-  if (prev)
-    prev->next = next;
-
-  if (next)
-    next->prev = prev;
-
-  if (head->first == elt)
-    head->first = next;
-
-  /* Since the first thing we try is to insert before current,
-     make current the next entry in preference to the previous.  */
-  if (head->current == elt)
-    {
-      head->current = next != 0 ? next : prev;
-      if (head->current)
-	head->indx = head->current->indx;
-      else
-	head->indx = 0;
-    }
-
-  if (GATHER_STATISTICS)
-    register_overhead (head, -((int)sizeof (bitmap_element)));
-
-  bitmap_elem_to_freelist (head, elt);
-}
-
 /* Allocate a bitmap element.  The bits are cleared, but nothing else is.  */
 
 static inline bitmap_element *
@@ -166,7 +129,8 @@
   return element;
 }
 
-/* Remove ELT and all following elements from bitmap HEAD.  */
+/* Remove ELT and all following elements from bitmap HEAD.
+   Put the released elements in the freelist for HEAD.  */
 
 void
 bitmap_elt_clear_from (bitmap head, bitmap_element *elt)
@@ -174,7 +138,11 @@
   bitmap_element *prev;
   bitmap_obstack *bit_obstack = head->obstack;
 
-  if (!elt) return;
+  if (!elt)
+    return;
+
+  if (head->tree_form)
+    elt = bitmap_tree_listify_from (head, elt);
 
   if (GATHER_STATISTICS)
     {
@@ -201,7 +169,7 @@
       head->indx = 0;
     }
 
-  /* Put the entire list onto the free list in one operation. */
+  /* Put the entire list onto the freelist in one operation. */
   if (bit_obstack)
     {
       elt->prev = bit_obstack->elements;
@@ -213,14 +181,521 @@
       bitmap_ggc_free = elt;
     }
 }
-
-/* Clear a bitmap by freeing the linked list.  */
+
+/* Linked-list view of bitmaps.
+
+   In this representation, the bitmap elements form a double-linked list
+   with elements sorted by increasing index.  */
+
+/* Link the bitmap element into the current bitmap linked list.  */
+
+static inline void
+bitmap_list_link_element (bitmap head, bitmap_element *element)
+{
+  unsigned int indx = element->indx;
+  bitmap_element *ptr;
+
+  gcc_checking_assert (!head->tree_form);
+
+  /* If this is the first and only element, set it in.  */
+  if (head->first == 0)
+    {
+      element->next = element->prev = 0;
+      head->first = element;
+    }
+
+  /* If this index is less than that of the current element, it goes someplace
+     before the current element.  */
+  else if (indx < head->indx)
+    {
+      for (ptr = head->current;
+	   ptr->prev != 0 && ptr->prev->indx > indx;
+	   ptr = ptr->prev)
+	;
+
+      if (ptr->prev)
+	ptr->prev->next = element;
+      else
+	head->first = element;
+
+      element->prev = ptr->prev;
+      element->next = ptr;
+      ptr->prev = element;
+    }
+
+  /* Otherwise, it must go someplace after the current element.  */
+  else
+    {
+      for (ptr = head->current;
+	   ptr->next != 0 && ptr->next->indx < indx;
+	   ptr = ptr->next)
+	;
+
+      if (ptr->next)
+	ptr->next->prev = element;
+
+      element->next = ptr->next;
+      element->prev = ptr;
+      ptr->next = element;
+    }
+
+  /* Set up so this is the first element searched.  */
+  head->current = element;
+  head->indx = indx;
+}
+
+/* Unlink the bitmap element from the current bitmap linked list,
+   and return it to the freelist.  */
+
+static inline void
+bitmap_list_unlink_element (bitmap head, bitmap_element *element)
+{
+  bitmap_element *next = element->next;
+  bitmap_element *prev = element->prev;
+
+  gcc_checking_assert (!head->tree_form);
+
+  if (prev)
+    prev->next = next;
+
+  if (next)
+    next->prev = prev;
+
+  if (head->first == element)
+    head->first = next;
+
+  /* Since the first thing we try is to insert before current,
+     make current the next entry in preference to the previous.  */
+  if (head->current == element)
+    {
+      head->current = next != 0 ? next : prev;
+      if (head->current)
+	head->indx = head->current->indx;
+      else
+	head->indx = 0;
+    }
+
+  bitmap_elem_to_freelist (head, element);
+}
+
+/* Insert a new uninitialized element into bitmap HEAD after element
+   ELT.  If ELT is NULL, insert the element at the start.  Return the
+   new element.  */
+
+static bitmap_element *
+bitmap_list_insert_element_after (bitmap head,
+				  bitmap_element *elt, unsigned int indx)
+{
+  bitmap_element *node = bitmap_element_allocate (head);
+  node->indx = indx;
+
+  gcc_checking_assert (!head->tree_form);
+
+  if (!elt)
+    {
+      if (!head->current)
+	{
+	  head->current = node;
+	  head->indx = indx;
+	}
+      node->next = head->first;
+      if (node->next)
+	node->next->prev = node;
+      head->first = node;
+      node->prev = NULL;
+    }
+  else
+    {
+      gcc_checking_assert (head->current);
+      node->next = elt->next;
+      if (node->next)
+	node->next->prev = node;
+      elt->next = node;
+      node->prev = elt;
+    }
+  return node;
+}
+
+/* Return the element for INDX, or NULL if the element doesn't exist.
+   Update the `current' field even if we can't find an element that  
+   would hold the bitmap's bit to make eventual allocation
+   faster.  */
+
+static inline bitmap_element *
+bitmap_list_find_element (bitmap head, unsigned int indx)
+{
+  bitmap_element *element;
+
+  if (head->current == NULL
+      || head->indx == indx)
+    return head->current;
+
+  if (head->current == head->first
+      && head->first->next == NULL)
+    return NULL;
+
+  /* Usage can be NULL due to allocated bitmaps for which we do not
+     call initialize function.  */
+  bitmap_usage *usage = NULL;
+  if (GATHER_STATISTICS)
+    usage = bitmap_mem_desc.get_descriptor_for_instance (head);
+
+  /* This bitmap has more than one element, and we're going to look
+     through the elements list.  Count that as a search.  */
+  if (GATHER_STATISTICS && usage)
+    usage->m_nsearches++;
+
+  if (head->indx < indx)
+    /* INDX is beyond head->indx.  Search from head->current
+       forward.  */
+    for (element = head->current;
+	 element->next != 0 && element->indx < indx;
+	 element = element->next)
+      {
+	if (GATHER_STATISTICS && usage)
+	  usage->m_search_iter++;
+      }
+
+  else if (head->indx / 2 < indx)
+    /* INDX is less than head->indx and closer to head->indx than to
+       0.  Search from head->current backward.  */
+    for (element = head->current;
+	 element->prev != 0 && element->indx > indx;
+	 element = element->prev)
+      {
+	if (GATHER_STATISTICS && usage)
+	  usage->m_search_iter++;
+      }
+
+  else
+    /* INDX is less than head->indx and closer to 0 than to
+       head->indx.  Search from head->first forward.  */
+    for (element = head->first;
+	 element->next != 0 && element->indx < indx;
+	 element = element->next)
+      {
+	if (GATHER_STATISTICS && usage)
+	  usage->m_search_iter++;
+      }
+
+  /* `element' is the nearest to the one we want.  If it's not the one we
+     want, the one we want doesn't exist.  */
+  gcc_checking_assert (element != NULL);
+  head->current = element;
+  head->indx = element->indx;
+  if (element->indx != indx)
+    element = 0;
+  return element;
+}
+
+
+/* Splay-tree view of bitmaps.
+
+   This is an almost one-to-one the implementatin of the simple top-down
+   splay tree in Sleator and Tarjan's "Self-adjusting Binary Search Trees".
+   It is probably not the most efficient form of splay trees, but it should
+   be good enough to experiment with this idea of bitmaps-as-trees.
+   
+   For all functions below, the variable or function argument "t" is a node
+   in the tree, and "e" is a temporary or new node in the tree.  The rest
+   is sufficiently straigh-forward (and very well explained in the paper)
+   that comment would only clutter things.  */
+
+static inline void
+bitmap_tree_link_left (bitmap_element * &t, bitmap_element * &l)
+{
+  l->next = t;
+  l = t;
+  t = t->next;
+}
+
+static inline void
+bitmap_tree_link_right (bitmap_element * &t, bitmap_element * &r)
+{
+  r->prev = t;
+  r = t;
+  t = t->prev;
+}
+
+static inline void
+bitmap_tree_rotate_left (bitmap_element * &t)
+{
+  bitmap_element *e = t->next;
+  t->next = t->next->prev;
+  e->prev = t;
+  t = e;
+}
+
+static inline void
+bitmap_tree_rotate_right (bitmap_element * &t)
+{
+  bitmap_element *e = t->prev;
+  t->prev = t->prev->next;
+  e->next = t;
+  t = e;
+}
+
+static bitmap_element *
+bitmap_tree_splay (bitmap head, bitmap_element *t, unsigned int indx)
+{
+  bitmap_element N, *l, *r;
+
+  if (t == NULL)
+    return NULL;
+
+  bitmap_usage *usage = NULL;
+  if (GATHER_STATISTICS)
+    usage = bitmap_mem_desc.get_descriptor_for_instance (head);
+
+  N.prev = N.next = NULL;
+  l = r = &N;
+
+  while (indx != t->indx)
+    {
+      if (GATHER_STATISTICS && usage)
+	usage->m_search_iter++;
+
+      if (indx < t->indx)
+	{
+	  if (t->prev != NULL && indx < t->prev->indx)
+	    bitmap_tree_rotate_right (t);
+	  if (t->prev == NULL)
+	    break;
+	  bitmap_tree_link_right (t, r);
+	}
+      else if (indx > t->indx)
+	{
+	  if (t->next != NULL && indx > t->next->indx)
+	    bitmap_tree_rotate_left (t);
+	  if (t->next == NULL)
+	    break;
+	  bitmap_tree_link_left (t, l);
+	}
+    }
+
+  l->next = t->prev;
+  r->prev = t->next;
+  t->prev = N.next;
+  t->next = N.prev;
+  return t;
+}
+
+/* Link bitmap element E into the current bitmap splay tree.  */
+
+static inline void
+bitmap_tree_link_element (bitmap head, bitmap_element *e)
+{
+  if (head->first == NULL)
+    e->prev = e->next = NULL;
+  else
+    {
+      bitmap_element *t = bitmap_tree_splay (head, head->first, e->indx);
+      if (e->indx < t->indx)
+	{
+	  e->prev = t->prev;
+	  e->next = t;
+	  t->prev = NULL;
+	}
+      else if (e->indx > t->indx)
+	{
+	  e->next = t->next;
+	  e->prev = t;
+	  t->next = NULL;
+	}
+      else
+	gcc_unreachable ();
+    }
+  head->first = e;
+  head->current = e;
+  head->indx = e->indx;
+}
+
+/* Unlink bitmap element E from the current bitmap splay tree,
+   and return it to the freelist.  */
+
+static void
+bitmap_tree_unlink_element (bitmap head, bitmap_element *e)
+{
+  bitmap_element *t = bitmap_tree_splay (head, head->first, e->indx);
+
+  gcc_checking_assert (t == e);
+
+  if (e->prev == NULL)
+    t = e->next;
+  else
+    {
+      t = bitmap_tree_splay (head, e->prev, e->indx);
+      t->next = e->next;
+    }
+  head->first = t;
+  head->current = t;
+  head->indx = (t != NULL) ? t->indx : 0;
+
+  bitmap_elem_to_freelist (head, e);
+}
+
+/* Return the element for INDX, or NULL if the element doesn't exist.  */
+
+static inline bitmap_element *
+bitmap_tree_find_element (bitmap head, unsigned int indx)
+{
+  if (head->current == NULL
+      || head->indx == indx)
+    return head->current;
+
+  /* Usage can be NULL due to allocated bitmaps for which we do not
+     call initialize function.  */
+  bitmap_usage *usage = NULL;
+  if (GATHER_STATISTICS)
+    usage = bitmap_mem_desc.get_descriptor_for_instance (head);
+
+  /* This bitmap has more than one element, and we're going to look
+     through the elements list.  Count that as a search.  */
+  if (GATHER_STATISTICS && usage)
+    usage->m_nsearches++;
+
+  bitmap_element *element = bitmap_tree_splay (head, head->first, indx);
+  gcc_checking_assert (element != NULL);
+  head->first = element;
+  head->current = element;
+  head->indx = element->indx;
+  if (element->indx != indx)
+    element = 0;
+  return element;
+}
+
+/* Converting bitmap views from linked-list to tree and vice versa.  */
+
+/* Splice element E and all elements with a larger index from
+   bitmap HEAD, convert the spliced elements to the linked-list
+   view, and return the head of the list (which should be E again),  */
+
+static bitmap_element *
+bitmap_tree_listify_from (bitmap head, bitmap_element *e)
+{
+  bitmap_element *t, *erb;
+
+  /* Detach the right branch from E (all elements with indx > E->indx),
+     and splay E to the root.  */
+  erb = e->next;
+  e->next = NULL;
+  t = bitmap_tree_splay (head, head->first, e->indx);
+  gcc_checking_assert (t == e);
+
+  /* Because E has no right branch, and we rotated it to the root,
+     the left branch is the new root.  */
+  t = e->prev;
+  head->first = t;
+  head->current = t;
+  head->indx = (t != NULL) ? t->indx : 0;
+
+  /* Detach the tree from E, and re-attach the right branch of E.  */
+  e->prev = NULL;
+  e->next = erb;
+
+  /* The tree is now valid again.  Now we need to "un-tree" E.
+     It is imperative that a non-recursive implementation is used
+     for this, because splay trees have a worst case depth of O(N)
+     for a tree with N nodes.  A recursive implementation could
+     result in a stack overflow for a sufficiently large, unbalanced
+     bitmap tree.  */
+
+  auto_vec<bitmap_element *, 32> stack;
+  auto_vec<bitmap_element *, 32> sorted_elements;
+  bitmap_element *n = e;
+
+  while (true)
+    {
+      while (n != NULL)
+	{
+	  stack.safe_push (n);
+	  n = n->prev;
+	}
+
+      if (stack.is_empty ())
+	break;
+
+      n = stack.pop ();
+      sorted_elements.safe_push (n);
+      n = n->next;
+    }
+
+  gcc_assert (sorted_elements[0] == e);
+
+  bitmap_element *prev = NULL;
+  unsigned ix;
+  FOR_EACH_VEC_ELT (sorted_elements, ix, n)
+    {
+      if (prev != NULL)
+        prev->next = n;
+      n->prev = prev;
+      n->next = NULL;
+      prev = n;
+    }
+
+  return e;
+}
+
+/* Convert bitmap HEAD from splay-tree view to linked-list view.  */
+
+void
+bitmap_list_view (bitmap head)
+{
+  bitmap_element *ptr;
+
+  gcc_assert (head->tree_form);
+
+  ptr = head->first;
+  if (ptr)
+    {
+      while (ptr->prev)
+	bitmap_tree_rotate_right (ptr);
+      head->first = ptr;
+      head->first = bitmap_tree_listify_from (head, ptr);
+    }
+
+  head->tree_form = false;
+}
+
+/* Convert bitmap HEAD from linked-list view to splay-tree view.
+   This is simply a matter of dropping the prev or next pointers
+   and setting the tree_form flag.  The tree will balance itself
+   if and when it is used.  */
+
+void
+bitmap_tree_view (bitmap head)
+{
+  bitmap_element *ptr;
+
+  gcc_assert (! head->tree_form);
+
+  ptr = head->first;
+  while (ptr)
+    {
+      ptr->prev = NULL;
+      ptr = ptr->next;
+    }
+
+  head->tree_form = true;
+}
+
+/* Clear a bitmap by freeing all its elements.  */
 
 void
 bitmap_clear (bitmap head)
 {
-  if (head->first)
-    bitmap_elt_clear_from (head, head->first);
+  if (head->first == NULL)
+    return;
+  if (head->tree_form)
+    {
+      bitmap_element *e, *t;
+      for (e = head->first; e->prev; e = e->prev)
+	/* Loop to find the element with the smallest index.  */ ;
+      t = bitmap_tree_splay (head, head->first, e->indx);
+      gcc_checking_assert (t == e);
+      head->first = t;
+    }
+  bitmap_elt_clear_from (head, head->first);
 }
 
 /* Initialize a bitmap obstack.  If BIT_OBSTACK is NULL, initialize
@@ -344,96 +819,6 @@
 #endif
 }
 
-/* Link the bitmap element into the current bitmap linked list.  */
-
-static inline void
-bitmap_element_link (bitmap head, bitmap_element *element)
-{
-  unsigned int indx = element->indx;
-  bitmap_element *ptr;
-
-  /* If this is the first and only element, set it in.  */
-  if (head->first == 0)
-    {
-      element->next = element->prev = 0;
-      head->first = element;
-    }
-
-  /* If this index is less than that of the current element, it goes someplace
-     before the current element.  */
-  else if (indx < head->indx)
-    {
-      for (ptr = head->current;
-	   ptr->prev != 0 && ptr->prev->indx > indx;
-	   ptr = ptr->prev)
-	;
-
-      if (ptr->prev)
-	ptr->prev->next = element;
-      else
-	head->first = element;
-
-      element->prev = ptr->prev;
-      element->next = ptr;
-      ptr->prev = element;
-    }
-
-  /* Otherwise, it must go someplace after the current element.  */
-  else
-    {
-      for (ptr = head->current;
-	   ptr->next != 0 && ptr->next->indx < indx;
-	   ptr = ptr->next)
-	;
-
-      if (ptr->next)
-	ptr->next->prev = element;
-
-      element->next = ptr->next;
-      element->prev = ptr;
-      ptr->next = element;
-    }
-
-  /* Set up so this is the first element searched.  */
-  head->current = element;
-  head->indx = indx;
-}
-
-/* Insert a new uninitialized element into bitmap HEAD after element
-   ELT.  If ELT is NULL, insert the element at the start.  Return the
-   new element.  */
-
-static bitmap_element *
-bitmap_elt_insert_after (bitmap head, bitmap_element *elt, unsigned int indx)
-{
-  bitmap_element *node = bitmap_element_allocate (head);
-  node->indx = indx;
-
-  if (!elt)
-    {
-      if (!head->current)
-	{
-	  head->current = node;
-	  head->indx = indx;
-	}
-      node->next = head->first;
-      if (node->next)
-	node->next->prev = node;
-      head->first = node;
-      node->prev = NULL;
-    }
-  else
-    {
-      gcc_checking_assert (head->current);
-      node->next = elt->next;
-      if (node->next)
-	node->next->prev = node;
-      elt->next = node;
-      node->prev = elt;
-    }
-  return node;
-}
-
 /* Copy a bitmap to another bitmap.  */
 
 void
@@ -442,6 +827,8 @@
   const bitmap_element *from_ptr;
   bitmap_element *to_ptr = 0;
 
+  gcc_checking_assert (!to->tree_form && !from->tree_form);
+
   bitmap_clear (to);
 
   /* Copy elements in forward direction one at a time.  */
@@ -452,8 +839,9 @@
       to_elt->indx = from_ptr->indx;
       memcpy (to_elt->bits, from_ptr->bits, sizeof (to_elt->bits));
 
-      /* Here we have a special case of bitmap_element_link, for the case
-	 where we know the links are being entered in sequence.  */
+      /* Here we have a special case of bitmap_list_link_element,
+         for the case where we know the links are being entered
+	 in sequence.  */
       if (to_ptr == 0)
 	{
 	  to->first = to->current = to_elt;
@@ -492,85 +880,18 @@
     }
 }
 
-/* Find a bitmap element that would hold a bitmap's bit.
-   Update the `current' field even if we can't find an element that
-   would hold the bitmap's bit to make eventual allocation
-   faster.  */
-
-static inline bitmap_element *
-bitmap_find_bit (bitmap head, unsigned int bit)
-{
-  bitmap_element *element;
-  unsigned int indx = bit / BITMAP_ELEMENT_ALL_BITS;
-
-  if (head->current == NULL
-      || head->indx == indx)
-    return head->current;
-  if (head->current == head->first
-      && head->first->next == NULL)
-    return NULL;
-
-  /* Usage can be NULL due to allocated bitmaps for which we do not
-     call initialize function.  */
-  bitmap_usage *usage = NULL;
-  if (GATHER_STATISTICS)
-    usage = bitmap_mem_desc.get_descriptor_for_instance (head);
-
-  /* This bitmap has more than one element, and we're going to look
-     through the elements list.  Count that as a search.  */
-  if (GATHER_STATISTICS && usage)
-    usage->m_nsearches++;
-
-  if (head->indx < indx)
-    /* INDX is beyond head->indx.  Search from head->current
-       forward.  */
-    for (element = head->current;
-	 element->next != 0 && element->indx < indx;
-	 element = element->next)
-      {
-	if (GATHER_STATISTICS && usage)
-	  usage->m_search_iter++;
-      }
-
-  else if (head->indx / 2 < indx)
-    /* INDX is less than head->indx and closer to head->indx than to
-       0.  Search from head->current backward.  */
-    for (element = head->current;
-	 element->prev != 0 && element->indx > indx;
-	 element = element->prev)
-      {
-	if (GATHER_STATISTICS && usage)
-	  usage->m_search_iter++;
-      }
-
-  else
-    /* INDX is less than head->indx and closer to 0 than to
-       head->indx.  Search from head->first forward.  */
-    for (element = head->first;
-	 element->next != 0 && element->indx < indx;
-	 element = element->next)
-      if (GATHER_STATISTICS && usage)
-	{
-	  usage->m_search_iter++;
-	}
-
-  /* `element' is the nearest to the one we want.  If it's not the one we
-     want, the one we want doesn't exist.  */
-  head->current = element;
-  head->indx = element->indx;
-  if (element->indx != indx)
-    element = 0;
-
-  return element;
-}
-
 /* Clear a single bit in a bitmap.  Return true if the bit changed.  */
 
 bool
 bitmap_clear_bit (bitmap head, int bit)
 {
-  bitmap_element *const ptr = bitmap_find_bit (head, bit);
-
+  unsigned int indx = bit / BITMAP_ELEMENT_ALL_BITS;
+  bitmap_element *ptr;
+
+  if (!head->tree_form)
+    ptr = bitmap_list_find_element (head, indx);
+  else
+    ptr = bitmap_tree_find_element (head, indx);
   if (ptr != 0)
     {
       unsigned bit_num  = bit % BITMAP_WORD_BITS;
@@ -583,7 +904,12 @@
 	  /* If we cleared the entire word, free up the element.  */
 	  if (!ptr->bits[word_num]
 	      && bitmap_element_zerop (ptr))
-	    bitmap_element_free (head, ptr);
+	    {
+	      if (!head->tree_form)
+		bitmap_list_unlink_element (head, ptr);
+	      else
+		bitmap_tree_unlink_element (head, ptr);
+	    }
 	}
 
       return res;
@@ -597,26 +923,32 @@
 bool
 bitmap_set_bit (bitmap head, int bit)
 {
-  bitmap_element *ptr = bitmap_find_bit (head, bit);
+  unsigned indx = bit / BITMAP_ELEMENT_ALL_BITS;
+  bitmap_element *ptr;
+  if (!head->tree_form)
+    ptr = bitmap_list_find_element (head, indx);
+  else
+    ptr = bitmap_tree_find_element (head, indx);
   unsigned word_num = bit / BITMAP_WORD_BITS % BITMAP_ELEMENT_WORDS;
   unsigned bit_num  = bit % BITMAP_WORD_BITS;
   BITMAP_WORD bit_val = ((BITMAP_WORD) 1) << bit_num;
 
-  if (ptr == 0)
-    {
-      ptr = bitmap_element_allocate (head);
-      ptr->indx = bit / BITMAP_ELEMENT_ALL_BITS;
-      ptr->bits[word_num] = bit_val;
-      bitmap_element_link (head, ptr);
-      return true;
-    }
-  else
+  if (ptr != 0)
     {
       bool res = (ptr->bits[word_num] & bit_val) == 0;
       if (res)
 	ptr->bits[word_num] |= bit_val;
       return res;
     }
+
+  ptr = bitmap_element_allocate (head);
+  ptr->indx = bit / BITMAP_ELEMENT_ALL_BITS;
+  ptr->bits[word_num] = bit_val;
+  if (!head->tree_form)
+    bitmap_list_link_element (head, ptr);
+  else
+    bitmap_tree_link_element (head, ptr);
+  return true;
 }
 
 /* Return whether a bit is set within a bitmap.  */
@@ -624,11 +956,15 @@
 int
 bitmap_bit_p (bitmap head, int bit)
 {
+  unsigned int indx = bit / BITMAP_ELEMENT_ALL_BITS;
   bitmap_element *ptr;
   unsigned bit_num;
   unsigned word_num;
 
-  ptr = bitmap_find_bit (head, bit);
+  if (!head->tree_form)
+    ptr = bitmap_list_find_element (head, indx);
+  else
+    ptr = bitmap_tree_find_element (head, indx);
   if (ptr == 0)
     return 0;
 
@@ -692,6 +1028,7 @@
   unsigned long count = 0;
   const bitmap_element *elt;
 
+  gcc_checking_assert (!a->tree_form);
   for (elt = a->first; elt; elt = elt->next)
     count += bitmap_count_bits_in_word (elt->bits);
 
@@ -748,9 +1085,11 @@
     return false;
 
   elt = a->first;
+
   /* As there are no completely empty bitmap elements, a second one
      means we have more than one bit set.  */
-  if (elt->next != NULL)
+  if (elt->next != NULL
+      && (!a->tree_form || elt->prev != NULL))
     return false;
 
   for (ix = 0; ix != BITMAP_ELEMENT_WORDS; ix++)
@@ -782,6 +1121,11 @@
   unsigned ix;
 
   gcc_checking_assert (elt);
+
+  if (a->tree_form)
+    while (elt->prev)
+      elt = elt->prev;
+
   bit_no = elt->indx * BITMAP_ELEMENT_ALL_BITS;
   for (ix = 0; ix != BITMAP_ELEMENT_WORDS; ix++)
     {
@@ -827,14 +1171,20 @@
 unsigned
 bitmap_last_set_bit (const_bitmap a)
 {
-  const bitmap_element *elt = a->current ? a->current : a->first;
+  const bitmap_element *elt;
   unsigned bit_no;
   BITMAP_WORD word;
   int ix;
 
+  if (a->tree_form)
+    elt = a->first;
+  else
+    elt = a->current ? a->current : a->first;
   gcc_checking_assert (elt);
+
   while (elt->next)
     elt = elt->next;
+
   bit_no = elt->indx * BITMAP_ELEMENT_ALL_BITS;
   for (ix = BITMAP_ELEMENT_WORDS - 1; ix >= 0; ix--)
     {
@@ -876,6 +1226,7 @@
   const bitmap_element *b_elt = b->first;
   bitmap_element *dst_prev = NULL;
 
+  gcc_checking_assert (!dst->tree_form && !a->tree_form && !b->tree_form);
   gcc_assert (dst != a && dst != b);
 
   if (a == b)
@@ -897,7 +1248,8 @@
 	  BITMAP_WORD ior = 0;
 
 	  if (!dst_elt)
-	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
+	    dst_elt = bitmap_list_insert_element_after (dst, dst_prev,
+							a_elt->indx);
 	  else
 	    dst_elt->indx = a_elt->indx;
 	  for (ix = 0; ix < BITMAP_ELEMENT_WORDS; ix++)
@@ -934,6 +1286,8 @@
   bitmap_element *next;
   bool changed = false;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
+
   if (a == b)
     return false;
 
@@ -942,7 +1296,7 @@
       if (a_elt->indx < b_elt->indx)
 	{
 	  next = a_elt->next;
-	  bitmap_element_free (a, a_elt);
+	  bitmap_list_unlink_element (a, a_elt);
 	  a_elt = next;
 	  changed = true;
 	}
@@ -964,7 +1318,7 @@
 	    }
 	  next = a_elt->next;
 	  if (!ior)
-	    bitmap_element_free (a, a_elt);
+	    bitmap_list_unlink_element (a, a_elt);
 	  a_elt = next;
 	  b_elt = b_elt->next;
 	}
@@ -1006,7 +1360,8 @@
     {
       changed = true;
       if (!dst_elt)
-	dst_elt = bitmap_elt_insert_after (dst, dst_prev, src_elt->indx);
+	dst_elt = bitmap_list_insert_element_after (dst, dst_prev,
+						    src_elt->indx);
       else
 	dst_elt->indx = src_elt->indx;
       memcpy (dst_elt->bits, src_elt->bits, sizeof (dst_elt->bits));
@@ -1028,6 +1383,7 @@
   bitmap_element **dst_prev_pnext = &dst->first;
   bool changed = false;
 
+  gcc_checking_assert (!dst->tree_form && !a->tree_form && !b->tree_form);
   gcc_assert (dst != a && dst != b);
 
   if (a == b)
@@ -1076,7 +1432,8 @@
 	      bool new_element;
 	      if (!dst_elt || dst_elt->indx > a_elt->indx)
 		{
-		  dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
+		  dst_elt = bitmap_list_insert_element_after (dst, dst_prev,
+							      a_elt->indx);
 		  new_element = true;
 		}
 	      else
@@ -1098,7 +1455,7 @@
 	      else
 	        {
 	          changed |= !new_element;
-		  bitmap_element_free (dst, dst_elt);
+		  bitmap_list_unlink_element (dst, dst_elt);
 		  dst_elt = *dst_prev_pnext;
 		}
 	    }
@@ -1139,6 +1496,8 @@
   bitmap_element *next;
   BITMAP_WORD changed = 0;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
+
   if (a == b)
     {
       if (bitmap_empty_p (a))
@@ -1173,7 +1532,7 @@
 	    }
 	  next = a_elt->next;
 	  if (!ior)
-	    bitmap_element_free (a, a_elt);
+	    bitmap_list_unlink_element (a, a_elt);
 	  a_elt = next;
 	  b_elt = b_elt->next;
 	}
@@ -1191,6 +1550,8 @@
   bitmap_element *elt, *elt_prev;
   unsigned int i;
 
+  gcc_checking_assert (!head->tree_form);
+
   if (!count)
     return;
 
@@ -1203,9 +1564,9 @@
   first_index = start / BITMAP_ELEMENT_ALL_BITS;
   end_bit_plus1 = start + count;
   last_index = (end_bit_plus1 - 1) / BITMAP_ELEMENT_ALL_BITS;
-  elt = bitmap_find_bit (head, start);
-
-  /* If bitmap_find_bit returns zero, the current is the closest block
+  elt = bitmap_list_find_element (head, first_index);
+
+  /* If bitmap_list_find_element returns zero, the current is the closest block
      to the result.  Otherwise, just use bitmap_element_allocate to
      ensure ELT is set; in the loop below, ELT == NULL means "insert
      at the end of the bitmap".  */
@@ -1213,7 +1574,7 @@
     {
       elt = bitmap_element_allocate (head);
       elt->indx = first_index;
-      bitmap_element_link (head, elt);
+      bitmap_list_link_element (head, elt);
     }
 
   gcc_checking_assert (elt->indx == first_index);
@@ -1230,7 +1591,7 @@
       unsigned int ix;
 
       if (!elt || elt->indx != i)
-	elt = bitmap_elt_insert_after (head, elt_prev, i);
+	elt = bitmap_list_insert_element_after (head, elt_prev, i);
 
       if (elt_start_bit <= start)
 	{
@@ -1296,6 +1657,8 @@
   unsigned int first_index, end_bit_plus1, last_index;
   bitmap_element *elt;
 
+  gcc_checking_assert (!head->tree_form);
+
   if (!count)
     return;
 
@@ -1308,9 +1671,9 @@
   first_index = start / BITMAP_ELEMENT_ALL_BITS;
   end_bit_plus1 = start + count;
   last_index = (end_bit_plus1 - 1) / BITMAP_ELEMENT_ALL_BITS;
-  elt = bitmap_find_bit (head, start);
-
-  /* If bitmap_find_bit returns zero, the current is the closest block
+  elt = bitmap_list_find_element (head, first_index);
+
+  /* If bitmap_list_find_element returns zero, the current is the closest block
      to the result.  If the current is less than first index, find the
      next one.  Otherwise, just set elt to be current.  */
   if (!elt)
@@ -1339,7 +1702,7 @@
 
       if (elt_start_bit >= start && elt_end_bit_plus1 <= end_bit_plus1)
 	/* Get rid of the entire elt and go to the next one.  */
-	bitmap_element_free (head, elt);
+	bitmap_list_unlink_element (head, elt);
       else
 	{
 	  /* Going to have to knock out some bits in this elt.  */
@@ -1409,7 +1772,7 @@
 	      }
 	  /* Check to see if there are any bits left.  */
 	  if (clear)
-	    bitmap_element_free (head, elt);
+	    bitmap_list_unlink_element (head, elt);
 	}
       elt = next_elt;
     }
@@ -1431,6 +1794,7 @@
   bitmap_element *a_prev = NULL;
   bitmap_element *next;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
   gcc_assert (a != b);
 
   if (bitmap_empty_p (a))
@@ -1451,13 +1815,13 @@
 	  /* A is before B.  Remove A */
 	  next = a_elt->next;
 	  a_prev = a_elt->prev;
-	  bitmap_element_free (a, a_elt);
+	  bitmap_list_unlink_element (a, a_elt);
 	  a_elt = next;
 	}
       else if (!a_elt || b_elt->indx < a_elt->indx)
 	{
 	  /* B is before A.  Copy B. */
-	  next = bitmap_elt_insert_after (a, a_prev, b_elt->indx);
+	  next = bitmap_list_insert_element_after (a, a_prev, b_elt->indx);
 	  memcpy (next->bits, b_elt->bits, sizeof (next->bits));
 	  a_prev = next;
 	  b_elt = b_elt->next;
@@ -1478,7 +1842,7 @@
 	    }
 	  next = a_elt->next;
 	  if (!ior)
-	    bitmap_element_free (a, a_elt);
+	    bitmap_list_unlink_element (a, a_elt);
 	  else
 	    a_prev = a_elt;
 	  a_elt = next;
@@ -1523,7 +1887,8 @@
 	{
 	  changed = true;
 	  if (!dst_elt)
-	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
+	    dst_elt = bitmap_list_insert_element_after (dst, dst_prev,
+							a_elt->indx);
 	  else
 	    dst_elt->indx = a_elt->indx;
 	  for (ix = 0; ix < BITMAP_ELEMENT_WORDS; ix++)
@@ -1562,6 +1927,7 @@
   bitmap_element **dst_prev_pnext = &dst->first;
   bool changed = false;
 
+  gcc_checking_assert (!dst->tree_form && !a->tree_form && !b->tree_form);
   gcc_assert (dst != a && dst != b);
 
   while (a_elt || b_elt)
@@ -1610,6 +1976,7 @@
   bitmap_element **a_prev_pnext = &a->first;
   bool changed = false;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
   if (a == b)
     return false;
 
@@ -1648,7 +2015,9 @@
   const bitmap_element *b_elt = b->first;
   bitmap_element *dst_prev = NULL;
 
+  gcc_checking_assert (!dst->tree_form && !a->tree_form && !b->tree_form);
   gcc_assert (dst != a && dst != b);
+
   if (a == b)
     {
       bitmap_clear (dst);
@@ -1664,7 +2033,8 @@
 	  BITMAP_WORD ior = 0;
 
 	  if (!dst_elt)
-	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
+	    dst_elt = bitmap_list_insert_element_after (dst, dst_prev,
+							a_elt->indx);
 	  else
 	    dst_elt->indx = a_elt->indx;
 	  for (ix = 0; ix < BITMAP_ELEMENT_WORDS; ix++)
@@ -1699,7 +2069,8 @@
 	    }
 
 	  if (!dst_elt)
-	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, src->indx);
+	    dst_elt = bitmap_list_insert_element_after (dst, dst_prev,
+							src->indx);
 	  else
 	    dst_elt->indx = src->indx;
 	  memcpy (dst_elt->bits, src->bits, sizeof (dst_elt->bits));
@@ -1724,6 +2095,8 @@
   const bitmap_element *b_elt = b->first;
   bitmap_element *a_prev = NULL;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
+
   if (a == b)
     {
       bitmap_clear (a);
@@ -1735,7 +2108,8 @@
       if (!a_elt || b_elt->indx < a_elt->indx)
 	{
 	  /* Copy b_elt.  */
-	  bitmap_element *dst = bitmap_elt_insert_after (a, a_prev, b_elt->indx);
+	  bitmap_element *dst = bitmap_list_insert_element_after (a, a_prev,
+								  b_elt->indx);
 	  memcpy (dst->bits, b_elt->bits, sizeof (dst->bits));
 	  a_prev = dst;
 	  b_elt = b_elt->next;
@@ -1763,7 +2137,7 @@
 	  if (ior)
 	    a_prev = a_elt;
 	  else
-	    bitmap_element_free (a, a_elt);
+	    bitmap_list_unlink_element (a, a_elt);
 	  a_elt = next;
 	}
     }
@@ -1783,6 +2157,8 @@
   const bitmap_element *b_elt;
   unsigned ix;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
+
   for (a_elt = a->first, b_elt = b->first;
        a_elt && b_elt;
        a_elt = a_elt->next, b_elt = b_elt->next)
@@ -1805,6 +2181,8 @@
   const bitmap_element *b_elt;
   unsigned ix;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
+
   for (a_elt = a->first, b_elt = b->first;
        a_elt && b_elt;)
     {
@@ -1832,6 +2210,9 @@
   const bitmap_element *a_elt;
   const bitmap_element *b_elt;
   unsigned ix;
+
+  gcc_checking_assert (!a->tree_form && !b->tree_form);
+
   for (a_elt = a->first, b_elt = b->first;
        a_elt && b_elt;)
     {
@@ -1866,6 +2247,8 @@
   bitmap_element *dst_prev = NULL;
   bitmap_element **dst_prev_pnext = &dst->first;
 
+  gcc_checking_assert (!dst->tree_form && !a->tree_form && !b->tree_form
+		       && !kill->tree_form);
   gcc_assert (dst != a && dst != b && dst != kill);
 
   /* Special cases.  We don't bother checking for bitmap_equal_p (b, kill).  */
@@ -1958,16 +2341,18 @@
   return changed;
 }
 
-/* A |= (FROM1 & ~FROM2).  Return true if A changes.  */
+/* A |= (B & ~C).  Return true if A changes.  */
 
 bool
-bitmap_ior_and_compl_into (bitmap a, const_bitmap from1, const_bitmap from2)
+bitmap_ior_and_compl_into (bitmap a, const_bitmap b, const_bitmap c)
 {
   bitmap_head tmp;
   bool changed;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form && !c->tree_form);
+
   bitmap_initialize (&tmp, &bitmap_default_obstack);
-  bitmap_and_compl (&tmp, from1, from2);
+  bitmap_and_compl (&tmp, b, c);
   changed = bitmap_ior_into (a, &tmp);
   bitmap_clear (&tmp);
 
@@ -1988,6 +2373,8 @@
   bool changed = false;
   unsigned ix;
 
+  gcc_checking_assert (!a->tree_form && !b->tree_form && !c->tree_form);
+
   if (b == c)
     return bitmap_ior_into (a, b);
   if (bitmap_empty_p (b) || bitmap_empty_p (c))
@@ -2054,6 +2441,7 @@
 }
 
 /* Compute hash of bitmap (for purposes of hashing).  */
+
 hashval_t
 bitmap_hash (const_bitmap head)
 {
@@ -2061,6 +2449,8 @@
   BITMAP_WORD hash = 0;
   int ix;
 
+  gcc_checking_assert (!head->tree_form);
+
   for (ptr = head->first; ptr; ptr = ptr->next)
     {
       hash ^= ptr->indx;
@@ -2071,6 +2461,61 @@
 }
 
 
+/* Function to obtain a vector of bitmap elements in bit order from
+   HEAD in tree view.  */
+
+static void
+bitmap_tree_to_vec (vec<bitmap_element *> &elts, const_bitmap head)
+{
+  gcc_checking_assert (head->tree_form);
+  auto_vec<bitmap_element *, 32> stack;
+  bitmap_element *e = head->first;
+  while (true)
+    {
+      while (e != NULL)
+	{
+	  stack.safe_push (e);
+	  e = e->prev;
+	}
+      if (stack.is_empty ())
+	break;
+
+      e = stack.pop ();
+      elts.safe_push (e);
+      e = e->next;
+    }
+}
+
+/* Debugging function to print out the contents of a bitmap element.  */
+
+DEBUG_FUNCTION void
+debug_bitmap_elt_file (FILE *file, const bitmap_element *ptr)
+{
+  unsigned int i, j, col = 26;
+
+  fprintf (file, "\t" HOST_PTR_PRINTF " next = " HOST_PTR_PRINTF
+	   " prev = " HOST_PTR_PRINTF " indx = %u\n\t\tbits = {",
+	   (const void*) ptr, (const void*) ptr->next,
+	   (const void*) ptr->prev, ptr->indx);
+
+  for (i = 0; i < BITMAP_ELEMENT_WORDS; i++)
+    for (j = 0; j < BITMAP_WORD_BITS; j++)
+      if ((ptr->bits[i] >> j) & 1)
+	{
+	  if (col > 70)
+	    {
+	      fprintf (file, "\n\t\t\t");
+	      col = 24;
+	    }
+
+	  fprintf (file, " %u", (ptr->indx * BITMAP_ELEMENT_ALL_BITS
+				 + i * BITMAP_WORD_BITS + j));
+	  col += 4;
+	}
+
+  fprintf (file, " }\n");
+}
+
 /* Debugging function to print out the contents of a bitmap.  */
 
 DEBUG_FUNCTION void
@@ -2082,32 +2527,16 @@
 	   " current = " HOST_PTR_PRINTF " indx = %u\n",
 	   (void *) head->first, (void *) head->current, head->indx);
 
-  for (ptr = head->first; ptr; ptr = ptr->next)
+  if (head->tree_form)
     {
-      unsigned int i, j, col = 26;
-
-      fprintf (file, "\t" HOST_PTR_PRINTF " next = " HOST_PTR_PRINTF
-	       " prev = " HOST_PTR_PRINTF " indx = %u\n\t\tbits = {",
-	       (const void*) ptr, (const void*) ptr->next,
-	       (const void*) ptr->prev, ptr->indx);
-
-      for (i = 0; i < BITMAP_ELEMENT_WORDS; i++)
-	for (j = 0; j < BITMAP_WORD_BITS; j++)
-	  if ((ptr->bits[i] >> j) & 1)
-	    {
-	      if (col > 70)
-		{
-		  fprintf (file, "\n\t\t\t");
-		  col = 24;
-		}
-
-	      fprintf (file, " %u", (ptr->indx * BITMAP_ELEMENT_ALL_BITS
-				     + i * BITMAP_WORD_BITS + j));
-	      col += 4;
-	    }
-
-      fprintf (file, " }\n");
+      auto_vec<bitmap_element *, 32> elts;
+      bitmap_tree_to_vec (elts, head);
+      for (unsigned i = 0; i < elts.length (); ++i)
+	debug_bitmap_elt_file (file, elts[i]);
     }
+  else
+    for (ptr = head->first; ptr; ptr = ptr->next)
+      debug_bitmap_elt_file (file, ptr);
 }
 
 /* Function to be called from the debugger to print the contents
@@ -2128,13 +2557,34 @@
 {
   const char *comma = "";
   unsigned i;
-  bitmap_iterator bi;
 
   fputs (prefix, file);
-  EXECUTE_IF_SET_IN_BITMAP (head, 0, i, bi)
+  if (head->tree_form)
     {
-      fprintf (file, "%s%d", comma, i);
-      comma = ", ";
+      auto_vec<bitmap_element *, 32> elts;
+      bitmap_tree_to_vec (elts, head);
+      for (i = 0; i < elts.length (); ++i)
+	for (unsigned ix = 0; ix != BITMAP_ELEMENT_WORDS; ++ix)
+	  {
+	    BITMAP_WORD word = elts[i]->bits[ix];
+	    for (unsigned bit = 0; bit != BITMAP_WORD_BITS; ++bit)
+	      if (word & ((BITMAP_WORD)1 << bit))
+		{
+		  fprintf (file, "%s%d", comma,
+			   (bit + BITMAP_WORD_BITS * ix
+			    + elts[i]->indx * BITMAP_ELEMENT_ALL_BITS));
+		  comma = ", ";
+		}
+	  }
+    }
+  else
+    {
+      bitmap_iterator bi;
+      EXECUTE_IF_SET_IN_BITMAP (head, 0, i, bi)
+	{
+	  fprintf (file, "%s%d", comma, i);
+	  comma = ", ";
+	}
     }
   fputs (suffix, file);
 }
@@ -2164,6 +2614,12 @@
     fprintf (stderr, "<nil>\n");
 }
 
+void
+bitmap_head::dump ()
+{
+  debug (this);
+}
+
 #if CHECKING_P
 
 namespace selftest {