gcc/lto/lto-partition.c

/* LTO partitioning logic routines.
   Copyright (C) 2009-2013 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "toplev.h"
#include "tree.h"
#include "tm.h"
#include "cgraph.h"
#include "lto-streamer.h"
#include "timevar.h"
#include "params.h"
#include "ipa-inline.h"
#include "ipa-utils.h"
#include "lto-partition.h"

/* Classifcation of symbols into classes WRT partitioning.  */
enum symbol_class
{
   /* External declarations are ignored by partitioning algorithms and they are
      added into the boundary later via compute_ltrans_boundary.  */
   SYMBOL_EXTERNAL,
   /* Partitioned symbols are pur into one of partitions.  */
   SYMBOL_PARTITION,
   /* Duplicated symbols (such as comdat or constant pool references) are
      copied into every node needing them via add_symbol_to_partition.  */
   SYMBOL_DUPLICATE
};

vec<ltrans_partition> ltrans_partitions;

static void add_symbol_to_partition (ltrans_partition part, symtab_node node);

/* Classify symbol NODE.  */

enum symbol_class
get_symbol_class (symtab_node node)
{
  /* Inline clones are always duplicated.
     This include external delcarations.   */
  cgraph_node *cnode = dyn_cast <cgraph_node> (node);
  if (cnode && cnode->global.inlined_to)
    return SYMBOL_DUPLICATE;

  /* External declarations are external.  */
  if (DECL_EXTERNAL (node->symbol.decl))
    return SYMBOL_EXTERNAL;

  if (varpool_node *vnode = dyn_cast <varpool_node> (node))
    {
      /* Constant pool references use local symbol names that can not
         be promoted global.  We should never put into a constant pool
         objects that can not be duplicated across partitions.  */
      if (DECL_IN_CONSTANT_POOL (node->symbol.decl))
	return SYMBOL_DUPLICATE;
      gcc_checking_assert (vnode->analyzed);
    }
  /* Functions that are cloned may stay in callgraph even if they are unused.
     Handle them as external; compute_ltrans_boundary take care to make
     proper things to happen (i.e. to make them appear in the boundary but
     with body streamed, so clone can me materialized).  */
  else if (!cgraph (node)->analyzed)
    return SYMBOL_EXTERNAL;

  /* Weakref aliases are always duplicated.  */
  if (lookup_attribute ("weakref", DECL_ATTRIBUTES (node->symbol.decl)))
    return SYMBOL_DUPLICATE;

  /* Comdats are duplicated to every use unless they are keyed.
     Those do not need duplication.  */
  if (DECL_COMDAT (node->symbol.decl)
      && !node->symbol.force_output
      && !symtab_used_from_object_file_p ((symtab_node) node))
    return SYMBOL_DUPLICATE;

  return SYMBOL_PARTITION;
}

/* Create new partition with name NAME.  */

static ltrans_partition
new_partition (const char *name)
{
  ltrans_partition part = XCNEW (struct ltrans_partition_def);
  part->encoder = lto_symtab_encoder_new (false);
  part->name = name;
  part->insns = 0;
  ltrans_partitions.safe_push (part);
  return part;
}

/* Free memory used by ltrans datastructures.  */

void
free_ltrans_partitions (void)
{
  unsigned int idx;
  ltrans_partition part;
  for (idx = 0; ltrans_partitions.iterate (idx, &part); idx++)
    {
      if (part->initializers_visited)
	pointer_set_destroy (part->initializers_visited);
      /* Symtab encoder is freed after streaming.  */
      free (part);
    }
  ltrans_partitions.release ();
}

/* Return true if symbol is already in some partition.  */

static inline bool
symbol_partitioned_p (symtab_node node)
{
  return node->symbol.aux;
}

/* Add references into the partition.  */
static void
add_references_to_partition (ltrans_partition part, symtab_node node)
{
  int i;
  struct ipa_ref *ref;

  /* Add all duplicated references to the partition.  */
  for (i = 0; ipa_ref_list_reference_iterate (&node->symbol.ref_list, i, ref); i++)
    if (get_symbol_class (ref->referred) == SYMBOL_DUPLICATE)
      add_symbol_to_partition (part, ref->referred);
    /* References to a readonly variable may be constant foled into its value.
       Recursively look into the initializers of the constant variable and add
       references, too.  */
    else if (is_a <varpool_node> (ref->referred)
	     && const_value_known_p (ref->referred->symbol.decl)
	     && !lto_symtab_encoder_in_partition_p (part->encoder, ref->referred))
      {
	if (!part->initializers_visited)
	  part->initializers_visited = pointer_set_create ();
	if (!pointer_set_insert (part->initializers_visited, ref->referred))
	  add_references_to_partition (part, ref->referred);
      }
}

/* Helper function for add_symbol_to_partition doing the actual dirty work
   of adding NODE to PART.  */

static bool
add_symbol_to_partition_1 (ltrans_partition part, symtab_node node)
{
  enum symbol_class c = get_symbol_class (node);
  int i;
  struct ipa_ref *ref;
  symtab_node node1;

  /* If NODE is already there, we have nothing to do.  */
  if (lto_symtab_encoder_in_partition_p (part->encoder, (symtab_node) node))
    return true;

  /* non-duplicated aliases or tunks of a duplicated symbol needs to be output
     just once.

     Be lax about comdats; they may or may not be duplicated and we may
     end up in need to duplicate keyed comdat because it has unkeyed alias.  */
  if (c == SYMBOL_PARTITION && !DECL_COMDAT (node->symbol.decl)
      && symbol_partitioned_p (node))
    return false;

  /* Be sure that we never try to duplicate partitioned symbol
     or add external symbol.  */
  gcc_assert (c != SYMBOL_EXTERNAL
	      && (c == SYMBOL_DUPLICATE || !symbol_partitioned_p (node)));

  lto_set_symtab_encoder_in_partition (part->encoder, (symtab_node) node);

  if (symbol_partitioned_p (node))
    {
      node->symbol.in_other_partition = 1;
      if (cgraph_dump_file)
        fprintf (cgraph_dump_file, "Symbol node %s now used in multiple partitions\n",
		 symtab_node_name (node));
    }
  node->symbol.aux = (void *)((size_t)node->symbol.aux + 1);

  if (cgraph_node *cnode = dyn_cast <cgraph_node> (node))
    {
      struct cgraph_edge *e;
      part->insns += inline_summary (cnode)->self_size;

      /* Add all inline clones and callees that are duplicated.  */
      for (e = cnode->callees; e; e = e->next_callee)
	if (!e->inline_failed)
	  add_symbol_to_partition_1 (part, (symtab_node) e->callee);
	else if (get_symbol_class ((symtab_node) e->callee) == SYMBOL_DUPLICATE)
	  add_symbol_to_partition (part, (symtab_node) e->callee);

      /* Add all thunks associated with the function.  */
      for (e = cnode->callers; e; e = e->next_caller)
	if (e->caller->thunk.thunk_p)
	  add_symbol_to_partition_1 (part, (symtab_node) e->caller);
    }

  add_references_to_partition (part, node);

  /* Add all aliases associated with the symbol.  */
  for (i = 0; ipa_ref_list_referring_iterate (&node->symbol.ref_list, i, ref); i++)
    if (ref->use == IPA_REF_ALIAS
	&& !lookup_attribute ("weakref",
			      DECL_ATTRIBUTES
				(ref->referring->symbol.decl)))
      add_symbol_to_partition_1 (part, ref->referring);

  /* Ensure that SAME_COMDAT_GROUP lists all allways added in a group.  */
  if (node->symbol.same_comdat_group)
    for (node1 = node->symbol.same_comdat_group;
	 node1 != node; node1 = node1->symbol.same_comdat_group)
      {
	bool added = add_symbol_to_partition_1 (part, node1);
	gcc_assert (added);
      }
  return true;
}

/* If symbol NODE is really part of other symbol's definition (i.e. it is
   internal label, thunk, alias or so), return the outer symbol. 
   When add_symbol_to_partition_1 is called on the outer symbol it must
   eventually add NODE, too.  */
static symtab_node
contained_in_symbol (symtab_node node)
{
  /* Weakrefs are never contained in anything.  */
  if (lookup_attribute ("weakref",
			DECL_ATTRIBUTES (node->symbol.decl)))
    return node;
  if (cgraph_node *cnode = dyn_cast <cgraph_node> (node))
    {
      cnode = cgraph_function_node (cnode, NULL);
      if (cnode->global.inlined_to)
	cnode = cnode->global.inlined_to;
      return (symtab_node) cnode;
    }
  else if (varpool_node *vnode = dyn_cast <varpool_node> (node))
    return (symtab_node) varpool_variable_node (vnode, NULL);
  return node;
}

/* Add symbol NODE to partition.  When definition of NODE is part
   of other symbol definition, add the other symbol, too.  */

static void
add_symbol_to_partition (ltrans_partition part, symtab_node node)
{
  symtab_node node1;

  /* Verify that we do not try to duplicate something that can not be.  */
  gcc_checking_assert (get_symbol_class (node) == SYMBOL_DUPLICATE
		       || !symbol_partitioned_p (node));

  while ((node1 = contained_in_symbol (node)) != node)
    node = node1;

  /* If we have duplicated symbol contained in something we can not duplicate,
     we are very badly screwed.  The other way is possible, so we do not
     assert this in add_symbol_to_partition_1. 

     Be lax about comdats; they may or may not be duplicated and we may
     end up in need to duplicate keyed comdat because it has unkeyed alias.  */
  gcc_assert (get_symbol_class (node) == SYMBOL_DUPLICATE
	      || DECL_COMDAT (node->symbol.decl)
	      || !symbol_partitioned_p (node));
  add_symbol_to_partition_1 (part, node);
}

/* Undo all additions until number of cgraph nodes in PARITION is N_CGRAPH_NODES
   and number of varpool nodes is N_VARPOOL_NODES.  */

static void
undo_partition (ltrans_partition partition, unsigned int n_nodes)
{
  while (lto_symtab_encoder_size (partition->encoder) > (int)n_nodes)
    {
      symtab_node node = lto_symtab_encoder_deref (partition->encoder,
						   n_nodes);

      /* After UNDO we no longer know what was visited.  */
      if (partition->initializers_visited)
	pointer_set_destroy (partition->initializers_visited);
      partition->initializers_visited = NULL;

      if (cgraph_node *cnode = dyn_cast <cgraph_node> (node))
        partition->insns -= inline_summary (cnode)->self_size;
      lto_symtab_encoder_delete_node (partition->encoder, node);
      node->symbol.aux = (void *)((size_t)node->symbol.aux - 1);
    }
}

/* Group cgrah nodes by input files.  This is used mainly for testing
   right now.  */

void
lto_1_to_1_map (void)
{
  symtab_node node;
  struct lto_file_decl_data *file_data;
  struct pointer_map_t *pmap;
  ltrans_partition partition;
  void **slot;
  int npartitions = 0;

  pmap = pointer_map_create ();

  FOR_EACH_SYMBOL (node)
    {
      if (get_symbol_class (node) != SYMBOL_PARTITION
	  || symbol_partitioned_p (node))
	continue;

      file_data = node->symbol.lto_file_data;

      if (file_data)
	{
          slot = pointer_map_contains (pmap, file_data);
          if (slot)
	    partition = (ltrans_partition) *slot;
	  else
	    {
	      partition = new_partition (file_data->file_name);
	      slot = pointer_map_insert (pmap, file_data);
	      *slot = partition;
	      npartitions++;
	    }
	}
      else if (!file_data && ltrans_partitions.length ())
	partition = ltrans_partitions[0];
      else
	{
	  partition = new_partition ("");
	  slot = pointer_map_insert (pmap, NULL);
	  *slot = partition;
	  npartitions++;
	}

      add_symbol_to_partition (partition, (symtab_node) node);
    }

  /* If the cgraph is empty, create one cgraph node set so that there is still
     an output file for any variables that need to be exported in a DSO.  */
  if (!npartitions)
    new_partition ("empty");

  pointer_map_destroy (pmap);

}

/* Maximal partitioning.  Put every new symbol into new partition if possible.  */

void
lto_max_map (void)
{
  symtab_node node;
  ltrans_partition partition;
  int npartitions = 0;

  FOR_EACH_SYMBOL (node)
    {
      if (get_symbol_class (node) != SYMBOL_PARTITION
	  || symbol_partitioned_p (node))
	continue;
      partition = new_partition (symtab_node_asm_name (node));
      add_symbol_to_partition (partition, (symtab_node) node);
      npartitions++;
    }
  if (!npartitions)
    new_partition ("empty");
}

/* Helper function for qsort; sort nodes by order.  */
static int
node_cmp (const void *pa, const void *pb)
{
  const struct cgraph_node *a = *(const struct cgraph_node * const *) pa;
  const struct cgraph_node *b = *(const struct cgraph_node * const *) pb;
  return b->symbol.order - a->symbol.order;
}

/* Helper function for qsort; sort nodes by order.  */
static int
varpool_node_cmp (const void *pa, const void *pb)
{
  const struct varpool_node *a = *(const struct varpool_node * const *) pa;
  const struct varpool_node *b = *(const struct varpool_node * const *) pb;
  return b->symbol.order - a->symbol.order;
}

/* Group cgraph nodes into equally-sized partitions.

   The partitioning algorithm is simple: nodes are taken in predefined order.
   The order corresponds to the order we want functions to have in the final
   output.  In the future this will be given by function reordering pass, but
   at the moment we use the topological order, which is a good approximation.

   The goal is to partition this linear order into intervals (partitions) so
   that all the partitions have approximately the same size and the number of
   callgraph or IPA reference edges crossing boundaries is minimal.

   This is a lot faster (O(n) in size of callgraph) than algorithms doing
   priority-based graph clustering that are generally O(n^2) and, since
   WHOPR is designed to make things go well across partitions, it leads
   to good results.

   We compute the expected size of a partition as:

     max (total_size / lto_partitions, min_partition_size)

   We use dynamic expected size of partition so small programs are partitioned
   into enough partitions to allow use of multiple CPUs, while large programs
   are not partitioned too much.  Creating too many partitions significantly
   increases the streaming overhead.

   In the future, we would like to bound the maximal size of partitions so as
   to prevent the LTRANS stage from consuming too much memory.  At the moment,
   however, the WPA stage is the most memory intensive for large benchmarks,
   since too many types and declarations are read into memory.

   The function implements a simple greedy algorithm.  Nodes are being added
   to the current partition until after 3/4 of the expected partition size is
   reached.  Past this threshold, we keep track of boundary size (number of
   edges going to other partitions) and continue adding functions until after
   the current partition has grown to twice the expected partition size.  Then
   the process is undone to the point where the minimal ratio of boundary size
   and in-partition calls was reached.  */

void
lto_balanced_map (void)
{
  int n_nodes = 0;
  int n_varpool_nodes = 0, varpool_pos = 0;
  struct cgraph_node **postorder =
    XCNEWVEC (struct cgraph_node *, cgraph_n_nodes);
  struct cgraph_node **order = XNEWVEC (struct cgraph_node *, cgraph_max_uid);
  struct varpool_node **varpool_order = NULL;
  int i, postorder_len;
  struct cgraph_node *node;
  int total_size = 0, best_total_size = 0;
  int partition_size;
  ltrans_partition partition;
  int last_visited_node = 0;
  struct varpool_node *vnode;
  int cost = 0, internal = 0;
  int best_n_nodes = 0, best_i = 0, best_cost =
    INT_MAX, best_internal = 0;
  int npartitions;
  int current_order = -1;

  FOR_EACH_VARIABLE (vnode)
    gcc_assert (!vnode->symbol.aux);
  /* Until we have better ordering facility, use toplogical order.
     Include only nodes we will partition and compute estimate of program
     size.  Note that since nodes that are not partitioned might be put into
     multiple partitions, this is just an estimate of real size.  This is why
     we keep partition_size updated after every partition is finalized.  */
  postorder_len = ipa_reverse_postorder (postorder);
    
  for (i = 0; i < postorder_len; i++)
    {
      node = postorder[i];
      if (get_symbol_class ((symtab_node) node) == SYMBOL_PARTITION)
	{
	  order[n_nodes++] = node;
          total_size += inline_summary (node)->size;
	}
    }
  free (postorder);

  if (!flag_toplevel_reorder)
    {
      qsort (order, n_nodes, sizeof (struct cgraph_node *), node_cmp);

      FOR_EACH_VARIABLE (vnode)
	if (get_symbol_class ((symtab_node) vnode) == SYMBOL_PARTITION)
	  n_varpool_nodes++;
      varpool_order = XNEWVEC (struct varpool_node *, n_varpool_nodes);

      n_varpool_nodes = 0;
      FOR_EACH_VARIABLE (vnode)
	if (get_symbol_class ((symtab_node) vnode) == SYMBOL_PARTITION)
	  varpool_order[n_varpool_nodes++] = vnode;
      qsort (varpool_order, n_varpool_nodes, sizeof (struct varpool_node *),
	     varpool_node_cmp);
    }

  /* Compute partition size and create the first partition.  */
  partition_size = total_size / PARAM_VALUE (PARAM_LTO_PARTITIONS);
  if (partition_size < PARAM_VALUE (MIN_PARTITION_SIZE))
    partition_size = PARAM_VALUE (MIN_PARTITION_SIZE);
  npartitions = 1;
  partition = new_partition ("");
  if (cgraph_dump_file)
    fprintf (cgraph_dump_file, "Total unit size: %i, partition size: %i\n",
	     total_size, partition_size);

  for (i = 0; i < n_nodes; i++)
    {
      if (symbol_partitioned_p ((symtab_node) order[i]))
	continue;

      current_order = order[i]->symbol.order;

      if (!flag_toplevel_reorder)
	while (varpool_pos < n_varpool_nodes
	       && varpool_order[varpool_pos]->symbol.order < current_order)
	  {
	    if (!symbol_partitioned_p ((symtab_node) varpool_order[varpool_pos]))
	      add_symbol_to_partition (partition, (symtab_node) varpool_order[varpool_pos]);
	    varpool_pos++;
	  }

      add_symbol_to_partition (partition, (symtab_node) order[i]);
      total_size -= inline_summary (order[i])->size;
	  

      /* Once we added a new node to the partition, we also want to add
         all referenced variables unless they was already added into some
         earlier partition.
	 add_symbol_to_partition adds possibly multiple nodes and
	 variables that are needed to satisfy needs of ORDER[i].
         We remember last visited cgraph and varpool node from last iteration
         of outer loop that allows us to process every new addition. 

	 At the same time we compute size of the boundary into COST.  Every
         callgraph or IPA reference edge leaving the partition contributes into
         COST.  Every edge inside partition was earlier computed as one leaving
	 it and thus we need to subtract it from COST.  */
      while (last_visited_node < lto_symtab_encoder_size (partition->encoder))
	{
	  struct ipa_ref_list *refs;
	  int j;
	  struct ipa_ref *ref;
	  symtab_node snode = lto_symtab_encoder_deref (partition->encoder,
							last_visited_node);

	  if (cgraph_node *node = dyn_cast <cgraph_node> (snode))
	    {
	      struct cgraph_edge *edge;

	      refs = &node->symbol.ref_list;

	      last_visited_node++;

	      gcc_assert (node->analyzed);

	      /* Compute boundary cost of callgraph edges.  */
	      for (edge = node->callees; edge; edge = edge->next_callee)
		if (edge->callee->analyzed)
		  {
		    int edge_cost = edge->frequency;
		    int index;

		    if (!edge_cost)
		      edge_cost = 1;
		    gcc_assert (edge_cost > 0);
		    index = lto_symtab_encoder_lookup (partition->encoder,
						       (symtab_node)edge->callee);
		    if (index != LCC_NOT_FOUND
		        && index < last_visited_node - 1)
		      cost -= edge_cost, internal += edge_cost;
		    else
		      cost += edge_cost;
		  }
	      for (edge = node->callers; edge; edge = edge->next_caller)
		{
		  int edge_cost = edge->frequency;
		  int index;

		  gcc_assert (edge->caller->analyzed);
		  if (!edge_cost)
		    edge_cost = 1;
		  gcc_assert (edge_cost > 0);
		  index = lto_symtab_encoder_lookup (partition->encoder,
						     (symtab_node)edge->caller);
		  if (index != LCC_NOT_FOUND
		      && index < last_visited_node - 1)
		    cost -= edge_cost;
		  else
		    cost += edge_cost;
		}
	    }
	  else
	    {
	      refs = &snode->symbol.ref_list;
	      last_visited_node++;
	    }

	  /* Compute boundary cost of IPA REF edges and at the same time look into
	     variables referenced from current partition and try to add them.  */
	  for (j = 0; ipa_ref_list_reference_iterate (refs, j, ref); j++)
	    if (is_a <varpool_node> (ref->referred))
	      {
		int index;

		vnode = ipa_ref_varpool_node (ref);
		if (!vnode->finalized)
		  continue;
		if (!symbol_partitioned_p ((symtab_node) vnode) && flag_toplevel_reorder
		    && get_symbol_class ((symtab_node) vnode) == SYMBOL_PARTITION)
		  add_symbol_to_partition (partition, (symtab_node) vnode);
		index = lto_symtab_encoder_lookup (partition->encoder,
						   (symtab_node)vnode);
		if (index != LCC_NOT_FOUND
		    && index < last_visited_node - 1)
		  cost--, internal++;
		else
		  cost++;
	      }
	    else
	      {
		int index;

		node = ipa_ref_node (ref);
		if (!node->analyzed)
		  continue;
		index = lto_symtab_encoder_lookup (partition->encoder,
						   (symtab_node)node);
		if (index != LCC_NOT_FOUND
		    && index < last_visited_node - 1)
		  cost--, internal++;
		else
		  cost++;
	      }
	  for (j = 0; ipa_ref_list_referring_iterate (refs, j, ref); j++)
	    if (is_a <varpool_node> (ref->referring))
	      {
		int index;

		vnode = ipa_ref_referring_varpool_node (ref);
		gcc_assert (vnode->finalized);
		if (!symbol_partitioned_p ((symtab_node) vnode) && flag_toplevel_reorder
		    && get_symbol_class ((symtab_node) vnode) == SYMBOL_PARTITION)
		  add_symbol_to_partition (partition, (symtab_node) vnode);
		index = lto_symtab_encoder_lookup (partition->encoder,
						   (symtab_node)vnode);
		if (index != LCC_NOT_FOUND
		    && index < last_visited_node - 1)
		  cost--;
		else
		  cost++;
	      }
	    else
	      {
		int index;

		node = ipa_ref_referring_node (ref);
		gcc_assert (node->analyzed);
		index = lto_symtab_encoder_lookup (partition->encoder,
						   (symtab_node)node);
		if (index != LCC_NOT_FOUND
		    && index < last_visited_node - 1)
		  cost--;
		else
		  cost++;
	      }
	}

      /* If the partition is large enough, start looking for smallest boundary cost.  */
      if (partition->insns < partition_size * 3 / 4
	  || best_cost == INT_MAX
	  || ((!cost 
	       || (best_internal * (HOST_WIDE_INT) cost
		   > (internal * (HOST_WIDE_INT)best_cost)))
  	      && partition->insns < partition_size * 5 / 4))
	{
	  best_cost = cost;
	  best_internal = internal;
	  best_i = i;
	  best_n_nodes = lto_symtab_encoder_size (partition->encoder);
	  best_total_size = total_size;
	}
      if (cgraph_dump_file)
	fprintf (cgraph_dump_file, "Step %i: added %s/%i, size %i, cost %i/%i best %i/%i, step %i\n", i,
		 cgraph_node_name (order[i]), order[i]->uid, partition->insns, cost, internal,
		 best_cost, best_internal, best_i);
      /* Partition is too large, unwind into step when best cost was reached and
	 start new partition.  */
      if (partition->insns > 2 * partition_size)
	{
	  if (best_i != i)
	    {
	      if (cgraph_dump_file)
		fprintf (cgraph_dump_file, "Unwinding %i insertions to step %i\n",
			 i - best_i, best_i);
	      undo_partition (partition, best_n_nodes);
	    }
	  i = best_i;
 	  /* When we are finished, avoid creating empty partition.  */
	  while (i < n_nodes - 1 && symbol_partitioned_p ((symtab_node) order[i + 1]))
	    i++;
	  if (i == n_nodes - 1)
	    break;
	  partition = new_partition ("");
	  last_visited_node = 0;
	  total_size = best_total_size;
	  cost = 0;

	  if (cgraph_dump_file)
	    fprintf (cgraph_dump_file, "New partition\n");
	  best_n_nodes = 0;
	  best_cost = INT_MAX;

	  /* Since the size of partitions is just approximate, update the size after
	     we finished current one.  */
	  if (npartitions < PARAM_VALUE (PARAM_LTO_PARTITIONS))
	    partition_size = total_size
	      / (PARAM_VALUE (PARAM_LTO_PARTITIONS) - npartitions);
	  else
	    partition_size = INT_MAX;

	  if (partition_size < PARAM_VALUE (MIN_PARTITION_SIZE))
	    partition_size = PARAM_VALUE (MIN_PARTITION_SIZE);
	  npartitions ++;
	}
    }

  /* Varables that are not reachable from the code go into last partition.  */
  if (flag_toplevel_reorder)
    {
      FOR_EACH_VARIABLE (vnode)
        if (get_symbol_class ((symtab_node) vnode) == SYMBOL_PARTITION
	    && !symbol_partitioned_p ((symtab_node) vnode))
	  add_symbol_to_partition (partition, (symtab_node) vnode);
    }
  else
    {
      while (varpool_pos < n_varpool_nodes)
	{
	  if (!symbol_partitioned_p ((symtab_node) varpool_order[varpool_pos]))
	    add_symbol_to_partition (partition, (symtab_node) varpool_order[varpool_pos]);
	  varpool_pos++;
	}
      free (varpool_order);
    }
  free (order);
}

/* Promote variable VNODE to be static.  */

static void
promote_symbol (symtab_node node)
{
  /* We already promoted ... */
  if (DECL_VISIBILITY (node->symbol.decl) == VISIBILITY_HIDDEN
      && DECL_VISIBILITY_SPECIFIED (node->symbol.decl)
      && TREE_PUBLIC (node->symbol.decl))
    return;

  gcc_checking_assert (!TREE_PUBLIC (node->symbol.decl)
		       && !DECL_EXTERNAL (node->symbol.decl));
  TREE_PUBLIC (node->symbol.decl) = 1;
  DECL_VISIBILITY (node->symbol.decl) = VISIBILITY_HIDDEN;
  DECL_VISIBILITY_SPECIFIED (node->symbol.decl) = true;
  if (cgraph_dump_file)
    fprintf (cgraph_dump_file,
	    "Promoting as hidden: %s\n", symtab_node_name (node));
}


/* Find out all static decls that need to be promoted to global because
   of cross file sharing.  This function must be run in the WPA mode after
   all inlinees are added.  */

void
lto_promote_cross_file_statics (void)
{
  unsigned i, n_sets;

  gcc_assert (flag_wpa);

  /* First compute boundaries.  */
  n_sets = ltrans_partitions.length ();
  for (i = 0; i < n_sets; i++)
    {
      ltrans_partition part
	= ltrans_partitions[i];
      part->encoder = compute_ltrans_boundary (part->encoder);
    }

  /* Look at boundaries and promote symbols as needed.  */
  for (i = 0; i < n_sets; i++)
    {
      lto_symtab_encoder_iterator lsei;
      lto_symtab_encoder_t encoder;
      ltrans_partition part
	= ltrans_partitions[i];

      encoder = part->encoder;
      for (lsei = lsei_start (encoder); !lsei_end_p (lsei);
	   lsei_next (&lsei))
        {
          symtab_node node = lsei_node (lsei);

	  /* No need to promote if symbol already is externally visible ... */
	  if (node->symbol.externally_visible
 	      /* ... or if it is part of current partition ... */
	      || lto_symtab_encoder_in_partition_p (encoder, node)
	      /* ... or if we do not partition it. This mean that it will
		 appear in every partition refernecing it.  */
	      || get_symbol_class ((symtab_node) node) != SYMBOL_PARTITION)
	    continue;

          promote_symbol (node);
        }
    }
}