tree-cfg.c (execute_build_cfg): Build the loop tree.

[gcc.git] / gcc / cfgloop.c

/* Natural loop discovery code for GNU compiler.
   Copyright (C) 2000-2013 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 "tm.h"
#include "rtl.h"
#include "function.h"
#include "basic-block.h"
#include "cfgloop.h"
#include "diagnostic-core.h"
#include "flags.h"
#include "tree.h"
#include "tree-flow.h"
#include "pointer-set.h"
#include "ggc.h"
#include "dumpfile.h"

static void flow_loops_cfg_dump (FILE *);
\f
/* Dump loop related CFG information.  */

static void
flow_loops_cfg_dump (FILE *file)
{
  basic_block bb;

  if (!file)
    return;

  FOR_EACH_BB (bb)
    {
      edge succ;
      edge_iterator ei;

      fprintf (file, ";; %d succs { ", bb->index);
      FOR_EACH_EDGE (succ, ei, bb->succs)
	fprintf (file, "%d ", succ->dest->index);
      fprintf (file, "}\n");
    }
}

/* Return nonzero if the nodes of LOOP are a subset of OUTER.  */

bool
flow_loop_nested_p (const struct loop *outer, const struct loop *loop)
{
  unsigned odepth = loop_depth (outer);

  return (loop_depth (loop) > odepth
	  && (*loop->superloops)[odepth] == outer);
}

/* Returns the loop such that LOOP is nested DEPTH (indexed from zero)
   loops within LOOP.  */

struct loop *
superloop_at_depth (struct loop *loop, unsigned depth)
{
  unsigned ldepth = loop_depth (loop);

  gcc_assert (depth <= ldepth);

  if (depth == ldepth)
    return loop;

  return (*loop->superloops)[depth];
}

/* Returns the list of the latch edges of LOOP.  */

static vec<edge> 
get_loop_latch_edges (const struct loop *loop)
{
  edge_iterator ei;
  edge e;
  vec<edge> ret = vNULL;

  FOR_EACH_EDGE (e, ei, loop->header->preds)
    {
      if (dominated_by_p (CDI_DOMINATORS, e->src, loop->header))
	ret.safe_push (e);
    }

  return ret;
}

/* Dump the loop information specified by LOOP to the stream FILE
   using auxiliary dump callback function LOOP_DUMP_AUX if non null.  */

void
flow_loop_dump (const struct loop *loop, FILE *file,
		void (*loop_dump_aux) (const struct loop *, FILE *, int),
		int verbose)
{
  basic_block *bbs;
  unsigned i;
  vec<edge> latches;
  edge e;

  if (! loop || ! loop->header)
    return;

  fprintf (file, ";;\n;; Loop %d\n", loop->num);

  fprintf (file, ";;  header %d, ", loop->header->index);
  if (loop->latch)
    fprintf (file, "latch %d\n", loop->latch->index);
  else
    {
      fprintf (file, "multiple latches:");
      latches = get_loop_latch_edges (loop);
      FOR_EACH_VEC_ELT (latches, i, e)
	fprintf (file, " %d", e->src->index);
      latches.release ();
      fprintf (file, "\n");
    }

  fprintf (file, ";;  depth %d, outer %ld\n",
	   loop_depth (loop), (long) (loop_outer (loop)
				      ? loop_outer (loop)->num : -1));

  fprintf (file, ";;  nodes:");
  bbs = get_loop_body (loop);
  for (i = 0; i < loop->num_nodes; i++)
    fprintf (file, " %d", bbs[i]->index);
  free (bbs);
  fprintf (file, "\n");

  if (loop_dump_aux)
    loop_dump_aux (loop, file, verbose);
}

/* Dump the loop information about loops to the stream FILE,
   using auxiliary dump callback function LOOP_DUMP_AUX if non null.  */

void
flow_loops_dump (FILE *file, void (*loop_dump_aux) (const struct loop *, FILE *, int), int verbose)
{
  loop_iterator li;
  struct loop *loop;

  if (!current_loops || ! file)
    return;

  fprintf (file, ";; %d loops found\n", number_of_loops ());

  FOR_EACH_LOOP (li, loop, LI_INCLUDE_ROOT)
    {
      flow_loop_dump (loop, file, loop_dump_aux, verbose);
    }

  if (verbose)
    flow_loops_cfg_dump (file);
}

/* Free data allocated for LOOP.  */

void
flow_loop_free (struct loop *loop)
{
  struct loop_exit *exit, *next;

  vec_free (loop->superloops);

  /* Break the list of the loop exit records.  They will be freed when the
     corresponding edge is rescanned or removed, and this avoids
     accessing the (already released) head of the list stored in the
     loop structure.  */
  for (exit = loop->exits->next; exit != loop->exits; exit = next)
    {
      next = exit->next;
      exit->next = exit;
      exit->prev = exit;
    }

  ggc_free (loop->exits);
  ggc_free (loop);
}

/* Free all the memory allocated for LOOPS.  */

void
flow_loops_free (struct loops *loops)
{
  if (loops->larray)
    {
      unsigned i;
      loop_p loop;

      /* Free the loop descriptors.  */
      FOR_EACH_VEC_SAFE_ELT (loops->larray, i, loop)
	{
	  if (!loop)
	    continue;

	  flow_loop_free (loop);
	}

      vec_free (loops->larray);
    }
}

/* Find the nodes contained within the LOOP with header HEADER.
   Return the number of nodes within the loop.  */

int
flow_loop_nodes_find (basic_block header, struct loop *loop)
{
  vec<basic_block> stack = vNULL;
  int num_nodes = 1;
  edge latch;
  edge_iterator latch_ei;

  header->loop_father = loop;

  FOR_EACH_EDGE (latch, latch_ei, loop->header->preds)
    {
      if (latch->src->loop_father == loop
	  || !dominated_by_p (CDI_DOMINATORS, latch->src, loop->header))
	continue;

      num_nodes++;
      stack.safe_push (latch->src);
      latch->src->loop_father = loop;

      while (!stack.is_empty ())
	{
	  basic_block node;
	  edge e;
	  edge_iterator ei;

	  node = stack.pop ();

	  FOR_EACH_EDGE (e, ei, node->preds)
	    {
	      basic_block ancestor = e->src;

	      if (ancestor->loop_father != loop)
		{
		  ancestor->loop_father = loop;
		  num_nodes++;
		  stack.safe_push (ancestor);
		}
	    }
	}
    }
  stack.release ();

  return num_nodes;
}

/* Records the vector of superloops of the loop LOOP, whose immediate
   superloop is FATHER.  */

static void
establish_preds (struct loop *loop, struct loop *father)
{
  loop_p ploop;
  unsigned depth = loop_depth (father) + 1;
  unsigned i;

  loop->superloops = 0;
  vec_alloc (loop->superloops, depth);
  FOR_EACH_VEC_SAFE_ELT (father->superloops, i, ploop)
    loop->superloops->quick_push (ploop);
  loop->superloops->quick_push (father);

  for (ploop = loop->inner; ploop; ploop = ploop->next)
    establish_preds (ploop, loop);
}

/* Add LOOP to the loop hierarchy tree where FATHER is father of the
   added loop.  If LOOP has some children, take care of that their
   pred field will be initialized correctly.  */

void
flow_loop_tree_node_add (struct loop *father, struct loop *loop)
{
  loop->next = father->inner;
  father->inner = loop;

  establish_preds (loop, father);
}

/* Remove LOOP from the loop hierarchy tree.  */

void
flow_loop_tree_node_remove (struct loop *loop)
{
  struct loop *prev, *father;

  father = loop_outer (loop);

  /* Remove loop from the list of sons.  */
  if (father->inner == loop)
    father->inner = loop->next;
  else
    {
      for (prev = father->inner; prev->next != loop; prev = prev->next)
	continue;
      prev->next = loop->next;
    }

  loop->superloops = NULL;
}

/* Allocates and returns new loop structure.  */

struct loop *
alloc_loop (void)
{
  struct loop *loop = ggc_alloc_cleared_loop ();

  loop->exits = ggc_alloc_cleared_loop_exit ();
  loop->exits->next = loop->exits->prev = loop->exits;
  loop->can_be_parallel = false;

  return loop;
}

/* Initializes loops structure LOOPS, reserving place for NUM_LOOPS loops
   (including the root of the loop tree).  */

static void
init_loops_structure (struct loops *loops, unsigned num_loops)
{
  struct loop *root;

  memset (loops, 0, sizeof *loops);
  vec_alloc (loops->larray, num_loops);

  /* Dummy loop containing whole function.  */
  root = alloc_loop ();
  root->num_nodes = n_basic_blocks;
  root->latch = EXIT_BLOCK_PTR;
  root->header = ENTRY_BLOCK_PTR;
  ENTRY_BLOCK_PTR->loop_father = root;
  EXIT_BLOCK_PTR->loop_father = root;

  loops->larray->quick_push (root);
  loops->tree_root = root;
}

/* Returns whether HEADER is a loop header.  */

bool
bb_loop_header_p (basic_block header)
{
  edge_iterator ei;
  edge e;

  /* If we have an abnormal predecessor, do not consider the
     loop (not worth the problems).  */
  if (bb_has_abnormal_pred (header))
    return false;

  /* Look for back edges where a predecessor is dominated
     by this block.  A natural loop has a single entry
     node (header) that dominates all the nodes in the
     loop.  It also has single back edge to the header
     from a latch node.  */
  FOR_EACH_EDGE (e, ei, header->preds)
    {
      basic_block latch = e->src;
      if (latch != ENTRY_BLOCK_PTR
	  && dominated_by_p (CDI_DOMINATORS, latch, header))
	return true;
    }

  return false;
}

/* Find all the natural loops in the function and save in LOOPS structure and
   recalculate loop_father information in basic block structures.
   If LOOPS is non-NULL then the loop structures for already recorded loops
   will be re-used and their number will not change.  We assume that no
   stale loops exist in LOOPS.
   When LOOPS is NULL it is allocated and re-built from scratch.
   Return the built LOOPS structure.  */

struct loops *
flow_loops_find (struct loops *loops)
{
  bool from_scratch = (loops == NULL);
  int *rc_order;
  int b;
  unsigned i;
  vec<loop_p> larray;

  /* Ensure that the dominators are computed.  */
  calculate_dominance_info (CDI_DOMINATORS);

  if (!loops)
    {
      loops = ggc_alloc_cleared_loops ();
      init_loops_structure (loops, 1);
    }

  /* Ensure that loop exits were released.  */
  gcc_assert (loops->exits == NULL);

  /* Taking care of this degenerate case makes the rest of
     this code simpler.  */
  if (n_basic_blocks == NUM_FIXED_BLOCKS)
    return loops;

  /* The root loop node contains all basic-blocks.  */
  loops->tree_root->num_nodes = n_basic_blocks;

  /* Compute depth first search order of the CFG so that outer
     natural loops will be found before inner natural loops.  */
  rc_order = XNEWVEC (int, n_basic_blocks);
  pre_and_rev_post_order_compute (NULL, rc_order, false);

  /* Gather all loop headers in reverse completion order and allocate
     loop structures for loops that are not already present.  */
  larray.create (loops->larray->length());
  for (b = 0; b < n_basic_blocks - NUM_FIXED_BLOCKS; b++)
    {
      basic_block header = BASIC_BLOCK (rc_order[b]);
      if (bb_loop_header_p (header))
	{
	  struct loop *loop;

	  /* The current active loop tree has valid loop-fathers for
	     header blocks.  */
	  if (!from_scratch
	      && header->loop_father->header == header)
	    {
	      loop = header->loop_father;
	      /* If we found an existing loop remove it from the
		 loop tree.  It is going to be inserted again
		 below.  */
	      flow_loop_tree_node_remove (loop);
	    }
	  else
	    {
	      /* Otherwise allocate a new loop structure for the loop.  */
	      loop = alloc_loop ();
	      /* ???  We could re-use unused loop slots here.  */
	      loop->num = loops->larray->length ();
	      vec_safe_push (loops->larray, loop);
	      loop->header = header;

	      if (!from_scratch
		  && dump_file && (dump_flags & TDF_DETAILS))
		fprintf (dump_file, "flow_loops_find: discovered new "
			 "loop %d with header %d\n",
			 loop->num, header->index);
	    }
	  /* Reset latch, we recompute it below.  */
	  loop->latch = NULL;
	  larray.safe_push (loop);
	}

      /* Make blocks part of the loop root node at start.  */
      header->loop_father = loops->tree_root;
    }

  free (rc_order);

  /* Now iterate over the loops found, insert them into the loop tree
     and assign basic-block ownership.  */
  for (i = 0; i < larray.length (); ++i)
    {
      struct loop *loop = larray[i];
      basic_block header = loop->header;
      edge_iterator ei;
      edge e;

      flow_loop_tree_node_add (header->loop_father, loop);
      loop->num_nodes = flow_loop_nodes_find (loop->header, loop);

      /* Look for the latch for this header block, if it has just a
	 single one.  */
      FOR_EACH_EDGE (e, ei, header->preds)
	{
	  basic_block latch = e->src;

	  if (flow_bb_inside_loop_p (loop, latch))
	    {
	      if (loop->latch != NULL)
		{
		  /* More than one latch edge.  */
		  loop->latch = NULL;
		  break;
		}
	      loop->latch = latch;
	    }
	}
    }

  larray.release();

  return loops;
}

/* Ratio of frequencies of edges so that one of more latch edges is
   considered to belong to inner loop with same header.  */
#define HEAVY_EDGE_RATIO 8

/* Minimum number of samples for that we apply
   find_subloop_latch_edge_by_profile heuristics.  */
#define HEAVY_EDGE_MIN_SAMPLES 10

/* If the profile info is available, finds an edge in LATCHES that much more
   frequent than the remaining edges.  Returns such an edge, or NULL if we do
   not find one.

   We do not use guessed profile here, only the measured one.  The guessed
   profile is usually too flat and unreliable for this (and it is mostly based
   on the loop structure of the program, so it does not make much sense to
   derive the loop structure from it).  */

static edge
find_subloop_latch_edge_by_profile (vec<edge> latches)
{
  unsigned i;
  edge e, me = NULL;
  gcov_type mcount = 0, tcount = 0;

  FOR_EACH_VEC_ELT (latches, i, e)
    {
      if (e->count > mcount)
	{
	  me = e;
	  mcount = e->count;
	}
      tcount += e->count;
    }

  if (tcount < HEAVY_EDGE_MIN_SAMPLES
      || (tcount - mcount) * HEAVY_EDGE_RATIO > tcount)
    return NULL;

  if (dump_file)
    fprintf (dump_file,
	     "Found latch edge %d -> %d using profile information.\n",
	     me->src->index, me->dest->index);
  return me;
}

/* Among LATCHES, guesses a latch edge of LOOP corresponding to subloop, based
   on the structure of induction variables.  Returns this edge, or NULL if we
   do not find any.

   We are quite conservative, and look just for an obvious simple innermost
   loop (which is the case where we would lose the most performance by not
   disambiguating the loop).  More precisely, we look for the following
   situation: The source of the chosen latch edge dominates sources of all
   the other latch edges.  Additionally, the header does not contain a phi node
   such that the argument from the chosen edge is equal to the argument from
   another edge.  */

static edge
find_subloop_latch_edge_by_ivs (struct loop *loop ATTRIBUTE_UNUSED, vec<edge> latches)
{
  edge e, latch = latches[0];
  unsigned i;
  gimple phi;
  gimple_stmt_iterator psi;
  tree lop;
  basic_block bb;

  /* Find the candidate for the latch edge.  */
  for (i = 1; latches.iterate (i, &e); i++)
    if (dominated_by_p (CDI_DOMINATORS, latch->src, e->src))
      latch = e;

  /* Verify that it dominates all the latch edges.  */
  FOR_EACH_VEC_ELT (latches, i, e)
    if (!dominated_by_p (CDI_DOMINATORS, e->src, latch->src))
      return NULL;

  /* Check for a phi node that would deny that this is a latch edge of
     a subloop.  */
  for (psi = gsi_start_phis (loop->header); !gsi_end_p (psi); gsi_next (&psi))
    {
      phi = gsi_stmt (psi);
      lop = PHI_ARG_DEF_FROM_EDGE (phi, latch);

      /* Ignore the values that are not changed inside the subloop.  */
      if (TREE_CODE (lop) != SSA_NAME
	  || SSA_NAME_DEF_STMT (lop) == phi)
	continue;
      bb = gimple_bb (SSA_NAME_DEF_STMT (lop));
      if (!bb || !flow_bb_inside_loop_p (loop, bb))
	continue;

      FOR_EACH_VEC_ELT (latches, i, e)
	if (e != latch
	    && PHI_ARG_DEF_FROM_EDGE (phi, e) == lop)
	  return NULL;
    }

  if (dump_file)
    fprintf (dump_file,
	     "Found latch edge %d -> %d using iv structure.\n",
	     latch->src->index, latch->dest->index);
  return latch;
}

/* If we can determine that one of the several latch edges of LOOP behaves
   as a latch edge of a separate subloop, returns this edge.  Otherwise
   returns NULL.  */

static edge
find_subloop_latch_edge (struct loop *loop)
{
  vec<edge> latches = get_loop_latch_edges (loop);
  edge latch = NULL;

  if (latches.length () > 1)
    {
      latch = find_subloop_latch_edge_by_profile (latches);

      if (!latch
	  /* We consider ivs to guess the latch edge only in SSA.  Perhaps we
	     should use cfghook for this, but it is hard to imagine it would
	     be useful elsewhere.  */
	  && current_ir_type () == IR_GIMPLE)
	latch = find_subloop_latch_edge_by_ivs (loop, latches);
    }

  latches.release ();
  return latch;
}

/* Callback for make_forwarder_block.  Returns true if the edge E is marked
   in the set MFB_REIS_SET.  */

static struct pointer_set_t *mfb_reis_set;
static bool
mfb_redirect_edges_in_set (edge e)
{
  return pointer_set_contains (mfb_reis_set, e);
}

/* Creates a subloop of LOOP with latch edge LATCH.  */

static void
form_subloop (struct loop *loop, edge latch)
{
  edge_iterator ei;
  edge e, new_entry;
  struct loop *new_loop;

  mfb_reis_set = pointer_set_create ();
  FOR_EACH_EDGE (e, ei, loop->header->preds)
    {
      if (e != latch)
	pointer_set_insert (mfb_reis_set, e);
    }
  new_entry = make_forwarder_block (loop->header, mfb_redirect_edges_in_set,
				    NULL);
  pointer_set_destroy (mfb_reis_set);

  loop->header = new_entry->src;

  /* Find the blocks and subloops that belong to the new loop, and add it to
     the appropriate place in the loop tree.  */
  new_loop = alloc_loop ();
  new_loop->header = new_entry->dest;
  new_loop->latch = latch->src;
  add_loop (new_loop, loop);
}

/* Make all the latch edges of LOOP to go to a single forwarder block --
   a new latch of LOOP.  */

static void
merge_latch_edges (struct loop *loop)
{
  vec<edge> latches = get_loop_latch_edges (loop);
  edge latch, e;
  unsigned i;

  gcc_assert (latches.length () > 0);

  if (latches.length () == 1)
    loop->latch = latches[0]->src;
  else
    {
      if (dump_file)
	fprintf (dump_file, "Merged latch edges of loop %d\n", loop->num);

      mfb_reis_set = pointer_set_create ();
      FOR_EACH_VEC_ELT (latches, i, e)
	pointer_set_insert (mfb_reis_set, e);
      latch = make_forwarder_block (loop->header, mfb_redirect_edges_in_set,
				    NULL);
      pointer_set_destroy (mfb_reis_set);

      loop->header = latch->dest;
      loop->latch = latch->src;
    }

  latches.release ();
}

/* LOOP may have several latch edges.  Transform it into (possibly several)
   loops with single latch edge.  */

static void
disambiguate_multiple_latches (struct loop *loop)
{
  edge e;

  /* We eliminate the multiple latches by splitting the header to the forwarder
     block F and the rest R, and redirecting the edges.  There are two cases:

     1) If there is a latch edge E that corresponds to a subloop (we guess
        that based on profile -- if it is taken much more often than the
	remaining edges; and on trees, using the information about induction
	variables of the loops), we redirect E to R, all the remaining edges to
	F, then rescan the loops and try again for the outer loop.
     2) If there is no such edge, we redirect all latch edges to F, and the
        entry edges to R, thus making F the single latch of the loop.  */

  if (dump_file)
    fprintf (dump_file, "Disambiguating loop %d with multiple latches\n",
	     loop->num);

  /* During latch merging, we may need to redirect the entry edges to a new
     block.  This would cause problems if the entry edge was the one from the
     entry block.  To avoid having to handle this case specially, split
     such entry edge.  */
  e = find_edge (ENTRY_BLOCK_PTR, loop->header);
  if (e)
    split_edge (e);

  while (1)
    {
      e = find_subloop_latch_edge (loop);
      if (!e)
	break;

      form_subloop (loop, e);
    }

  merge_latch_edges (loop);
}

/* Split loops with multiple latch edges.  */

void
disambiguate_loops_with_multiple_latches (void)
{
  loop_iterator li;
  struct loop *loop;

  FOR_EACH_LOOP (li, loop, 0)
    {
      if (!loop->latch)
	disambiguate_multiple_latches (loop);
    }
}

/* Return nonzero if basic block BB belongs to LOOP.  */
bool
flow_bb_inside_loop_p (const struct loop *loop, const_basic_block bb)
{
  struct loop *source_loop;

  if (bb == ENTRY_BLOCK_PTR || bb == EXIT_BLOCK_PTR)
    return 0;

  source_loop = bb->loop_father;
  return loop == source_loop || flow_loop_nested_p (loop, source_loop);
}

/* Enumeration predicate for get_loop_body_with_size.  */
static bool
glb_enum_p (const_basic_block bb, const void *glb_loop)
{
  const struct loop *const loop = (const struct loop *) glb_loop;
  return (bb != loop->header
	  && dominated_by_p (CDI_DOMINATORS, bb, loop->header));
}

/* Gets basic blocks of a LOOP.  Header is the 0-th block, rest is in dfs
   order against direction of edges from latch.  Specially, if
   header != latch, latch is the 1-st block.  LOOP cannot be the fake
   loop tree root, and its size must be at most MAX_SIZE.  The blocks
   in the LOOP body are stored to BODY, and the size of the LOOP is
   returned.  */

unsigned
get_loop_body_with_size (const struct loop *loop, basic_block *body,
			 unsigned max_size)
{
  return dfs_enumerate_from (loop->header, 1, glb_enum_p,
			     body, max_size, loop);
}

/* Gets basic blocks of a LOOP.  Header is the 0-th block, rest is in dfs
   order against direction of edges from latch.  Specially, if
   header != latch, latch is the 1-st block.  */

basic_block *
get_loop_body (const struct loop *loop)
{
  basic_block *body, bb;
  unsigned tv = 0;

  gcc_assert (loop->num_nodes);

  body = XNEWVEC (basic_block, loop->num_nodes);

  if (loop->latch == EXIT_BLOCK_PTR)
    {
      /* There may be blocks unreachable from EXIT_BLOCK, hence we need to
	 special-case the fake loop that contains the whole function.  */
      gcc_assert (loop->num_nodes == (unsigned) n_basic_blocks);
      body[tv++] = loop->header;
      body[tv++] = EXIT_BLOCK_PTR;
      FOR_EACH_BB (bb)
	body[tv++] = bb;
    }
  else
    tv = get_loop_body_with_size (loop, body, loop->num_nodes);

  gcc_assert (tv == loop->num_nodes);
  return body;
}

/* Fills dominance descendants inside LOOP of the basic block BB into
   array TOVISIT from index *TV.  */

static void
fill_sons_in_loop (const struct loop *loop, basic_block bb,
		   basic_block *tovisit, int *tv)
{
  basic_block son, postpone = NULL;

  tovisit[(*tv)++] = bb;
  for (son = first_dom_son (CDI_DOMINATORS, bb);
       son;
       son = next_dom_son (CDI_DOMINATORS, son))
    {
      if (!flow_bb_inside_loop_p (loop, son))
	continue;

      if (dominated_by_p (CDI_DOMINATORS, loop->latch, son))
	{
	  postpone = son;
	  continue;
	}
      fill_sons_in_loop (loop, son, tovisit, tv);
    }

  if (postpone)
    fill_sons_in_loop (loop, postpone, tovisit, tv);
}

/* Gets body of a LOOP (that must be different from the outermost loop)
   sorted by dominance relation.  Additionally, if a basic block s dominates
   the latch, then only blocks dominated by s are be after it.  */

basic_block *
get_loop_body_in_dom_order (const struct loop *loop)
{
  basic_block *tovisit;
  int tv;

  gcc_assert (loop->num_nodes);

  tovisit = XNEWVEC (basic_block, loop->num_nodes);

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  tv = 0;
  fill_sons_in_loop (loop, loop->header, tovisit, &tv);

  gcc_assert (tv == (int) loop->num_nodes);

  return tovisit;
}

/* Gets body of a LOOP sorted via provided BB_COMPARATOR.  */

basic_block *
get_loop_body_in_custom_order (const struct loop *loop,
			       int (*bb_comparator) (const void *, const void *))
{
  basic_block *bbs = get_loop_body (loop);

  qsort (bbs, loop->num_nodes, sizeof (basic_block), bb_comparator);

  return bbs;
}

/* Get body of a LOOP in breadth first sort order.  */

basic_block *
get_loop_body_in_bfs_order (const struct loop *loop)
{
  basic_block *blocks;
  basic_block bb;
  bitmap visited;
  unsigned int i = 0;
  unsigned int vc = 1;

  gcc_assert (loop->num_nodes);
  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  blocks = XNEWVEC (basic_block, loop->num_nodes);
  visited = BITMAP_ALLOC (NULL);

  bb = loop->header;
  while (i < loop->num_nodes)
    {
      edge e;
      edge_iterator ei;

      if (bitmap_set_bit (visited, bb->index))
	/* This basic block is now visited */
	blocks[i++] = bb;

      FOR_EACH_EDGE (e, ei, bb->succs)
	{
	  if (flow_bb_inside_loop_p (loop, e->dest))
	    {
	      if (bitmap_set_bit (visited, e->dest->index))
		blocks[i++] = e->dest;
	    }
	}

      gcc_assert (i >= vc);

      bb = blocks[vc++];
    }

  BITMAP_FREE (visited);
  return blocks;
}

/* Hash function for struct loop_exit.  */

static hashval_t
loop_exit_hash (const void *ex)
{
  const struct loop_exit *const exit = (const struct loop_exit *) ex;

  return htab_hash_pointer (exit->e);
}

/* Equality function for struct loop_exit.  Compares with edge.  */

static int
loop_exit_eq (const void *ex, const void *e)
{
  const struct loop_exit *const exit = (const struct loop_exit *) ex;

  return exit->e == e;
}

/* Frees the list of loop exit descriptions EX.  */

static void
loop_exit_free (void *ex)
{
  struct loop_exit *exit = (struct loop_exit *) ex, *next;

  for (; exit; exit = next)
    {
      next = exit->next_e;

      exit->next->prev = exit->prev;
      exit->prev->next = exit->next;

      ggc_free (exit);
    }
}

/* Returns the list of records for E as an exit of a loop.  */

static struct loop_exit *
get_exit_descriptions (edge e)
{
  return (struct loop_exit *) htab_find_with_hash (current_loops->exits, e,
			                           htab_hash_pointer (e));
}

/* Updates the lists of loop exits in that E appears.
   If REMOVED is true, E is being removed, and we
   just remove it from the lists of exits.
   If NEW_EDGE is true and E is not a loop exit, we
   do not try to remove it from loop exit lists.  */

void
rescan_loop_exit (edge e, bool new_edge, bool removed)
{
  void **slot;
  struct loop_exit *exits = NULL, *exit;
  struct loop *aloop, *cloop;

  if (!loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    return;

  if (!removed
      && e->src->loop_father != NULL
      && e->dest->loop_father != NULL
      && !flow_bb_inside_loop_p (e->src->loop_father, e->dest))
    {
      cloop = find_common_loop (e->src->loop_father, e->dest->loop_father);
      for (aloop = e->src->loop_father;
	   aloop != cloop;
	   aloop = loop_outer (aloop))
	{
	  exit = ggc_alloc_loop_exit ();
	  exit->e = e;

	  exit->next = aloop->exits->next;
	  exit->prev = aloop->exits;
	  exit->next->prev = exit;
	  exit->prev->next = exit;

	  exit->next_e = exits;
	  exits = exit;
	}
    }

  if (!exits && new_edge)
    return;

  slot = htab_find_slot_with_hash (current_loops->exits, e,
				   htab_hash_pointer (e),
				   exits ? INSERT : NO_INSERT);
  if (!slot)
    return;

  if (exits)
    {
      if (*slot)
	loop_exit_free (*slot);
      *slot = exits;
    }
  else
    htab_clear_slot (current_loops->exits, slot);
}

/* For each loop, record list of exit edges, and start maintaining these
   lists.  */

void
record_loop_exits (void)
{
  basic_block bb;
  edge_iterator ei;
  edge e;

  if (!current_loops)
    return;

  if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    return;
  loops_state_set (LOOPS_HAVE_RECORDED_EXITS);

  gcc_assert (current_loops->exits == NULL);
  current_loops->exits = htab_create_ggc (2 * number_of_loops (),
					  loop_exit_hash, loop_exit_eq,
					  loop_exit_free);

  FOR_EACH_BB (bb)
    {
      FOR_EACH_EDGE (e, ei, bb->succs)
	{
	  rescan_loop_exit (e, true, false);
	}
    }
}

/* Dumps information about the exit in *SLOT to FILE.
   Callback for htab_traverse.  */

static int
dump_recorded_exit (void **slot, void *file)
{
  struct loop_exit *exit = (struct loop_exit *) *slot;
  unsigned n = 0;
  edge e = exit->e;

  for (; exit != NULL; exit = exit->next_e)
    n++;

  fprintf ((FILE*) file, "Edge %d->%d exits %u loops\n",
	   e->src->index, e->dest->index, n);

  return 1;
}

/* Dumps the recorded exits of loops to FILE.  */

extern void dump_recorded_exits (FILE *);
void
dump_recorded_exits (FILE *file)
{
  if (!current_loops->exits)
    return;
  htab_traverse (current_loops->exits, dump_recorded_exit, file);
}

/* Releases lists of loop exits.  */

void
release_recorded_exits (void)
{
  gcc_assert (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS));
  htab_delete (current_loops->exits);
  current_loops->exits = NULL;
  loops_state_clear (LOOPS_HAVE_RECORDED_EXITS);
}

/* Returns the list of the exit edges of a LOOP.  */

vec<edge> 
get_loop_exit_edges (const struct loop *loop)
{
  vec<edge> edges = vNULL;
  edge e;
  unsigned i;
  basic_block *body;
  edge_iterator ei;
  struct loop_exit *exit;

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  /* If we maintain the lists of exits, use them.  Otherwise we must
     scan the body of the loop.  */
  if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    {
      for (exit = loop->exits->next; exit->e; exit = exit->next)
	edges.safe_push (exit->e);
    }
  else
    {
      body = get_loop_body (loop);
      for (i = 0; i < loop->num_nodes; i++)
	FOR_EACH_EDGE (e, ei, body[i]->succs)
	  {
	    if (!flow_bb_inside_loop_p (loop, e->dest))
	      edges.safe_push (e);
	  }
      free (body);
    }

  return edges;
}

/* Counts the number of conditional branches inside LOOP.  */

unsigned
num_loop_branches (const struct loop *loop)
{
  unsigned i, n;
  basic_block * body;

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  body = get_loop_body (loop);
  n = 0;
  for (i = 0; i < loop->num_nodes; i++)
    if (EDGE_COUNT (body[i]->succs) >= 2)
      n++;
  free (body);

  return n;
}

/* Adds basic block BB to LOOP.  */
void
add_bb_to_loop (basic_block bb, struct loop *loop)
{
  unsigned i;
  loop_p ploop;
  edge_iterator ei;
  edge e;

  gcc_assert (bb->loop_father == NULL);
  bb->loop_father = loop;
  loop->num_nodes++;
  FOR_EACH_VEC_SAFE_ELT (loop->superloops, i, ploop)
    ploop->num_nodes++;

  FOR_EACH_EDGE (e, ei, bb->succs)
    {
      rescan_loop_exit (e, true, false);
    }
  FOR_EACH_EDGE (e, ei, bb->preds)
    {
      rescan_loop_exit (e, true, false);
    }
}

/* Remove basic block BB from loops.  */
void
remove_bb_from_loops (basic_block bb)
{
  unsigned i;
  struct loop *loop = bb->loop_father;
  loop_p ploop;
  edge_iterator ei;
  edge e;

  gcc_assert (loop != NULL);
  loop->num_nodes--;
  FOR_EACH_VEC_SAFE_ELT (loop->superloops, i, ploop)
    ploop->num_nodes--;
  bb->loop_father = NULL;

  FOR_EACH_EDGE (e, ei, bb->succs)
    {
      rescan_loop_exit (e, false, true);
    }
  FOR_EACH_EDGE (e, ei, bb->preds)
    {
      rescan_loop_exit (e, false, true);
    }
}

/* Finds nearest common ancestor in loop tree for given loops.  */
struct loop *
find_common_loop (struct loop *loop_s, struct loop *loop_d)
{
  unsigned sdepth, ddepth;

  if (!loop_s) return loop_d;
  if (!loop_d) return loop_s;

  sdepth = loop_depth (loop_s);
  ddepth = loop_depth (loop_d);

  if (sdepth < ddepth)
    loop_d = (*loop_d->superloops)[sdepth];
  else if (sdepth > ddepth)
    loop_s = (*loop_s->superloops)[ddepth];

  while (loop_s != loop_d)
    {
      loop_s = loop_outer (loop_s);
      loop_d = loop_outer (loop_d);
    }
  return loop_s;
}

/* Removes LOOP from structures and frees its data.  */

void
delete_loop (struct loop *loop)
{
  /* Remove the loop from structure.  */
  flow_loop_tree_node_remove (loop);

  /* Remove loop from loops array.  */
  (*current_loops->larray)[loop->num] = NULL;

  /* Free loop data.  */
  flow_loop_free (loop);
}

/* Cancels the LOOP; it must be innermost one.  */

static void
cancel_loop (struct loop *loop)
{
  basic_block *bbs;
  unsigned i;
  struct loop *outer = loop_outer (loop);

  gcc_assert (!loop->inner);

  /* Move blocks up one level (they should be removed as soon as possible).  */
  bbs = get_loop_body (loop);
  for (i = 0; i < loop->num_nodes; i++)
    bbs[i]->loop_father = outer;

  free (bbs);
  delete_loop (loop);
}

/* Cancels LOOP and all its subloops.  */
void
cancel_loop_tree (struct loop *loop)
{
  while (loop->inner)
    cancel_loop_tree (loop->inner);
  cancel_loop (loop);
}

/* Checks that information about loops is correct
     -- sizes of loops are all right
     -- results of get_loop_body really belong to the loop
     -- loop header have just single entry edge and single latch edge
     -- loop latches have only single successor that is header of their loop
     -- irreducible loops are correctly marked
     -- the cached loop depth and loop father of each bb is correct
  */
DEBUG_FUNCTION void
verify_loop_structure (void)
{
  unsigned *sizes, i, j;
  sbitmap irreds;
  basic_block bb, *bbs;
  struct loop *loop;
  int err = 0;
  edge e;
  unsigned num = number_of_loops ();
  loop_iterator li;
  struct loop_exit *exit, *mexit;
  bool dom_available = dom_info_available_p (CDI_DOMINATORS);
  sbitmap visited;

  if (loops_state_satisfies_p (LOOPS_NEED_FIXUP))
    {
      error ("loop verification on loop tree that needs fixup");
      err = 1;
    }

  /* We need up-to-date dominators, compute or verify them.  */
  if (!dom_available)
    calculate_dominance_info (CDI_DOMINATORS);
  else
    verify_dominators (CDI_DOMINATORS);

  /* Check the headers.  */
  FOR_EACH_BB (bb)
    if (bb_loop_header_p (bb))
      {
	if (bb->loop_father->header == NULL)
	  {
	    error ("loop with header %d marked for removal", bb->index);
	    err = 1;
	  }
	else if (bb->loop_father->header != bb)
	  {
	    error ("loop with header %d not in loop tree", bb->index);
	    err = 1;
	  }
      }
    else if (bb->loop_father->header == bb)
      {
	error ("non-loop with header %d not marked for removal", bb->index);
	err = 1;
      }

  /* Check the recorded loop father and sizes of loops.  */
  visited = sbitmap_alloc (last_basic_block);
  bitmap_clear (visited);
  bbs = XNEWVEC (basic_block, n_basic_blocks);
  FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
    {
      unsigned n;

      if (loop->header == NULL)
	{
	  error ("removed loop %d in loop tree", loop->num);
	  err = 1;
	  continue;
	}

      n = get_loop_body_with_size (loop, bbs, n_basic_blocks);
      if (loop->num_nodes != n)
	{
	  error ("size of loop %d should be %d, not %d",
		 loop->num, n, loop->num_nodes);
	  err = 1;
	}

      for (j = 0; j < n; j++)
	{
	  bb = bbs[j];

	  if (!flow_bb_inside_loop_p (loop, bb))
	    {
	      error ("bb %d does not belong to loop %d",
		     bb->index, loop->num);
	      err = 1;
	    }

	  /* Ignore this block if it is in an inner loop.  */
	  if (bitmap_bit_p (visited, bb->index))
	    continue;
	  bitmap_set_bit (visited, bb->index);

	  if (bb->loop_father != loop)
	    {
	      error ("bb %d has father loop %d, should be loop %d",
		     bb->index, bb->loop_father->num, loop->num);
	      err = 1;
	    }
	}
    }
  free (bbs);
  sbitmap_free (visited);

  /* Check headers and latches.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      i = loop->num;
      if (loop->header == NULL)
	continue;
      if (!bb_loop_header_p (loop->header))
	{
	  error ("loop %d%'s header is not a loop header", i);
	  err = 1;
	}
      if (loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS)
	  && EDGE_COUNT (loop->header->preds) != 2)
	{
	  error ("loop %d%'s header does not have exactly 2 entries", i);
	  err = 1;
	}
      if (loop->latch)
	{
	  if (!find_edge (loop->latch, loop->header))
	    {
	      error ("loop %d%'s latch does not have an edge to its header", i);
	      err = 1;
	    }
	  if (!dominated_by_p (CDI_DOMINATORS, loop->latch, loop->header))
	    {
	      error ("loop %d%'s latch is not dominated by its header", i);
	      err = 1;
	    }
	}
      if (loops_state_satisfies_p (LOOPS_HAVE_SIMPLE_LATCHES))
	{
	  if (!single_succ_p (loop->latch))
	    {
	      error ("loop %d%'s latch does not have exactly 1 successor", i);
	      err = 1;
	    }
	  if (single_succ (loop->latch) != loop->header)
	    {
	      error ("loop %d%'s latch does not have header as successor", i);
	      err = 1;
	    }
	  if (loop->latch->loop_father != loop)
	    {
	      error ("loop %d%'s latch does not belong directly to it", i);
	      err = 1;
	    }
	}
      if (loop->header->loop_father != loop)
	{
	  error ("loop %d%'s header does not belong directly to it", i);
	  err = 1;
	}
      if (loops_state_satisfies_p (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS)
	  && (loop_latch_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP))
	{
	  error ("loop %d%'s latch is marked as part of irreducible region", i);
	  err = 1;
	}
    }

  /* Check irreducible loops.  */
  if (loops_state_satisfies_p (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS))
    {
      /* Record old info.  */
      irreds = sbitmap_alloc (last_basic_block);
      FOR_EACH_BB (bb)
	{
	  edge_iterator ei;
	  if (bb->flags & BB_IRREDUCIBLE_LOOP)
	    bitmap_set_bit (irreds, bb->index);
	  else
	    bitmap_clear_bit (irreds, bb->index);
	  FOR_EACH_EDGE (e, ei, bb->succs)
	    if (e->flags & EDGE_IRREDUCIBLE_LOOP)
	      e->flags |= EDGE_ALL_FLAGS + 1;
	}

      /* Recount it.  */
      mark_irreducible_loops ();

      /* Compare.  */
      FOR_EACH_BB (bb)
	{
	  edge_iterator ei;

	  if ((bb->flags & BB_IRREDUCIBLE_LOOP)
	      && !bitmap_bit_p (irreds, bb->index))
	    {
	      error ("basic block %d should be marked irreducible", bb->index);
	      err = 1;
	    }
	  else if (!(bb->flags & BB_IRREDUCIBLE_LOOP)
	      && bitmap_bit_p (irreds, bb->index))
	    {
	      error ("basic block %d should not be marked irreducible", bb->index);
	      err = 1;
	    }
	  FOR_EACH_EDGE (e, ei, bb->succs)
	    {
	      if ((e->flags & EDGE_IRREDUCIBLE_LOOP)
		  && !(e->flags & (EDGE_ALL_FLAGS + 1)))
		{
		  error ("edge from %d to %d should be marked irreducible",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	      else if (!(e->flags & EDGE_IRREDUCIBLE_LOOP)
		       && (e->flags & (EDGE_ALL_FLAGS + 1)))
		{
		  error ("edge from %d to %d should not be marked irreducible",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	      e->flags &= ~(EDGE_ALL_FLAGS + 1);
	    }
	}
      free (irreds);
    }

  /* Check the recorded loop exits.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      if (!loop->exits || loop->exits->e != NULL)
	{
	  error ("corrupted head of the exits list of loop %d",
		 loop->num);
	  err = 1;
	}
      else
	{
	  /* Check that the list forms a cycle, and all elements except
	     for the head are nonnull.  */
	  for (mexit = loop->exits, exit = mexit->next, i = 0;
	       exit->e && exit != mexit;
	       exit = exit->next)
	    {
	      if (i++ & 1)
		mexit = mexit->next;
	    }

	  if (exit != loop->exits)
	    {
	      error ("corrupted exits list of loop %d", loop->num);
	      err = 1;
	    }
	}

      if (!loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
	{
	  if (loop->exits->next != loop->exits)
	    {
	      error ("nonempty exits list of loop %d, but exits are not recorded",
		     loop->num);
	      err = 1;
	    }
	}
    }

  if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    {
      unsigned n_exits = 0, eloops;

      sizes = XCNEWVEC (unsigned, num);
      memset (sizes, 0, sizeof (unsigned) * num);
      FOR_EACH_BB (bb)
	{
	  edge_iterator ei;
	  if (bb->loop_father == current_loops->tree_root)
	    continue;
	  FOR_EACH_EDGE (e, ei, bb->succs)
	    {
	      if (flow_bb_inside_loop_p (bb->loop_father, e->dest))
		continue;

	      n_exits++;
	      exit = get_exit_descriptions (e);
	      if (!exit)
		{
		  error ("exit %d->%d not recorded",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	      eloops = 0;
	      for (; exit; exit = exit->next_e)
		eloops++;

	      for (loop = bb->loop_father;
		   loop != e->dest->loop_father
		   /* When a loop exit is also an entry edge which
		      can happen when avoiding CFG manipulations
		      then the last loop exited is the outer loop
		      of the loop entered.  */
		   && loop != loop_outer (e->dest->loop_father);
		   loop = loop_outer (loop))
		{
		  eloops--;
		  sizes[loop->num]++;
		}

	      if (eloops != 0)
		{
		  error ("wrong list of exited loops for edge  %d->%d",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	    }
	}

      if (n_exits != htab_elements (current_loops->exits))
	{
	  error ("too many loop exits recorded");
	  err = 1;
	}

      FOR_EACH_LOOP (li, loop, 0)
	{
	  eloops = 0;
	  for (exit = loop->exits->next; exit->e; exit = exit->next)
	    eloops++;
	  if (eloops != sizes[loop->num])
	    {
	      error ("%d exits recorded for loop %d (having %d exits)",
		     eloops, loop->num, sizes[loop->num]);
	      err = 1;
	    }
	}

      free (sizes);
    }

  gcc_assert (!err);

  if (!dom_available)
    free_dominance_info (CDI_DOMINATORS);
}

/* Returns latch edge of LOOP.  */
edge
loop_latch_edge (const struct loop *loop)
{
  return find_edge (loop->latch, loop->header);
}

/* Returns preheader edge of LOOP.  */
edge
loop_preheader_edge (const struct loop *loop)
{
  edge e;
  edge_iterator ei;

  gcc_assert (loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS));

  FOR_EACH_EDGE (e, ei, loop->header->preds)
    if (e->src != loop->latch)
      break;

  return e;
}

/* Returns true if E is an exit of LOOP.  */

bool
loop_exit_edge_p (const struct loop *loop, const_edge e)
{
  return (flow_bb_inside_loop_p (loop, e->src)
	  && !flow_bb_inside_loop_p (loop, e->dest));
}

/* Returns the single exit edge of LOOP, or NULL if LOOP has either no exit
   or more than one exit.  If loops do not have the exits recorded, NULL
   is returned always.  */

edge
single_exit (const struct loop *loop)
{
  struct loop_exit *exit = loop->exits->next;

  if (!loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    return NULL;

  if (exit->e && exit->next == loop->exits)
    return exit->e;
  else
    return NULL;
}

/* Returns true when BB has an incoming edge exiting LOOP.  */

bool
loop_exits_to_bb_p (struct loop *loop, basic_block bb)
{
  edge e;
  edge_iterator ei;

  FOR_EACH_EDGE (e, ei, bb->preds)
    if (loop_exit_edge_p (loop, e))
      return true;

  return false;
}

/* Returns true when BB has an outgoing edge exiting LOOP.  */

bool
loop_exits_from_bb_p (struct loop *loop, basic_block bb)
{
  edge e;
  edge_iterator ei;

  FOR_EACH_EDGE (e, ei, bb->succs)
    if (loop_exit_edge_p (loop, e))
      return true;

  return false;
}

/* Return location corresponding to the loop control condition if possible.  */

location_t
get_loop_location (struct loop *loop)
{
  rtx insn = NULL;
  struct niter_desc *desc = NULL;
  edge exit;

  /* For a for or while loop, we would like to return the location
     of the for or while statement, if possible.  To do this, look
     for the branch guarding the loop back-edge.  */

  /* If this is a simple loop with an in_edge, then the loop control
     branch is typically at the end of its source.  */
  desc = get_simple_loop_desc (loop);
  if (desc->in_edge)
    {
      FOR_BB_INSNS_REVERSE (desc->in_edge->src, insn)
        {
          if (INSN_P (insn) && INSN_HAS_LOCATION (insn))
            return INSN_LOCATION (insn);
        }
    }
  /* If loop has a single exit, then the loop control branch
     must be at the end of its source.  */
  if ((exit = single_exit (loop)))
    {
      FOR_BB_INSNS_REVERSE (exit->src, insn)
        {
          if (INSN_P (insn) && INSN_HAS_LOCATION (insn))
            return INSN_LOCATION (insn);
        }
    }
  /* Next check the latch, to see if it is non-empty.  */
  FOR_BB_INSNS_REVERSE (loop->latch, insn)
    {
      if (INSN_P (insn) && INSN_HAS_LOCATION (insn))
        return INSN_LOCATION (insn);
    }
  /* Finally, if none of the above identifies the loop control branch,
     return the first location in the loop header.  */
  FOR_BB_INSNS (loop->header, insn)
    {
      if (INSN_P (insn) && INSN_HAS_LOCATION (insn))
        return INSN_LOCATION (insn);
    }
  /* If all else fails, simply return the current function location.  */
  return DECL_SOURCE_LOCATION (current_function_decl);
}