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/* Transformations based on profile information for values.

   Copyright (C) 2003, 2004, 2005 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 2, 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 COPYING.  If not, write to the Free

Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "rtl.h"

#include "expr.h"

#include "hard-reg-set.h"

#include "basic-block.h"

#include "value-prof.h"

#include "output.h"

#include "flags.h"

#include "insn-config.h"

#include "recog.h"

#include "optabs.h"

#include "regs.h"

#include "ggc.h"

#include "tree-flow.h"

#include "tree-flow-inline.h"

#include "diagnostic.h"

#include "coverage.h"

#include "tree.h"

#include "gcov-io.h"

#include "timevar.h"

#include "tree-pass.h"

#include "toplev.h"

static struct value_prof_hooks *value_prof_hooks;

/* This is the vector of histograms.  Created in find_values_to_profile.

   During profile generation, freed by instrument_values.

   During profile use, freed by value_profile_transformations.  */

static histogram_values static_values = NULL;

/* In this file value profile based optimizations are placed.  Currently the

   following optimizations are implemented (for more detailed descriptions

   see comments at value_profile_transformations):

   1) Division/modulo specialization.  Provided that we can determine that the

      operands of the division have some special properties, we may use it to

      produce more effective code.

   2) Speculative prefetching.  If we are able to determine that the difference

      between addresses accessed by a memory reference is usually constant, we

      may add the prefetch instructions.

      FIXME: This transformation was removed together with RTL based value

      profiling.

   Every such optimization should add its requirements for profiled values to

   insn_values_to_profile function.  This function is called from branch_prob

   in profile.c and the requested values are instrumented by it in the first

   compilation with -fprofile-arcs.  The optimization may then read the

   gathered data in the second compilation with -fbranch-probabilities.

   The measured data is pointed to from the histograms

   field of the statement annotation of the instrumented insns.  It is

   kept as a linked list of struct histogram_value_t's, which contain the

   same information as above.  */

static tree tree_divmod_fixed_value (tree, tree, tree, tree,

                                    tree, int, gcov_type, gcov_type);

static tree tree_mod_pow2 (tree, tree, tree, tree, int, gcov_type, gcov_type);

static tree tree_mod_subtract (tree, tree, tree, tree, int, int, int,

                                gcov_type, gcov_type, gcov_type);

static bool tree_divmod_fixed_value_transform (tree);

static bool tree_mod_pow2_value_transform (tree);

static bool tree_mod_subtract_transform (tree);

/* The overall number of invocations of the counter should match execution count

   of basic block.  Report it as error rather than internal error as it might

   mean that user has misused the profile somehow.  */

static bool

check_counter (tree stmt, const char * name, gcov_type all, gcov_type bb_count)

{

  if (all != bb_count)

    {

      location_t * locus;

      locus = (stmt != NULL && EXPR_HAS_LOCATION (stmt)

               ? EXPR_LOCUS (stmt)

               : &DECL_SOURCE_LOCATION (current_function_decl));

      error ("%HCorrupted value profile: %s profiler overall count (%d) does not match BB count (%d)",

             locus, name, (int)all, (int)bb_count);

      return true;

    }

  return false;

}

/* Tree based transformations. */

static bool

tree_value_profile_transformations (void)

{

  basic_block bb;

  block_stmt_iterator bsi;

  bool changed = false;

  FOR_EACH_BB (bb)

    {

      /* Ignore cold areas -- we are enlarging the code.  */

      if (!maybe_hot_bb_p (bb))

        continue;

      for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))

        {

          tree stmt = bsi_stmt (bsi);

          stmt_ann_t ann = get_stmt_ann (stmt);

          histogram_value th = ann->histograms;

          if (!th)

            continue;

          if (dump_file)

            {

              fprintf (dump_file, "Trying transformations on insn ");

              print_generic_stmt (dump_file, stmt, TDF_SLIM);

            }

          /* Transformations:  */

          /* The order of things in this conditional controls which

             transformation is used when more than one is applicable.  */

          /* It is expected that any code added by the transformations

             will be added before the current statement, and that the

             current statement remain valid (although possibly

             modified) upon return.  */

          if (flag_value_profile_transformations

              && (tree_mod_subtract_transform (stmt)

                  || tree_divmod_fixed_value_transform (stmt)

                  || tree_mod_pow2_value_transform (stmt)))

            {

              changed = true;

              /* Original statement may no longer be in the same block. */

              bb = bb_for_stmt (stmt);

            }

          /* Free extra storage from compute_value_histograms.  */

          while (th)

            {

              free (th->hvalue.counters);

              th = th->hvalue.next;

            }

          ann->histograms = 0;

        }

    }

  if (changed)

    {

      counts_to_freqs ();

    }

  return changed;

}

/* Generate code for transformation 1 (with OPERATION, operands OP1

   and OP2, whose value is expected to be VALUE, parent modify-expr STMT and

   probability of taking the optimal path PROB, which is equivalent to COUNT/ALL

   within roundoff error).  This generates the result into a temp and returns

   the temp; it does not replace or alter the original STMT.  */

static tree

tree_divmod_fixed_value (tree stmt, tree operation,

                         tree op1, tree op2, tree value, int prob, gcov_type count,

                         gcov_type all)

{

  tree stmt1, stmt2, stmt3;

  tree tmp1, tmp2, tmpv;

  tree label_decl1 = create_artificial_label ();

  tree label_decl2 = create_artificial_label ();

  tree label_decl3 = create_artificial_label ();

  tree label1, label2, label3;

  tree bb1end, bb2end, bb3end;

  basic_block bb, bb2, bb3, bb4;

  tree optype = TREE_TYPE (operation);

  edge e12, e13, e23, e24, e34;

  block_stmt_iterator bsi;

  bb = bb_for_stmt (stmt);

  bsi = bsi_for_stmt (stmt);

  tmpv = create_tmp_var (optype, "PROF");

  tmp1 = create_tmp_var (optype, "PROF");

  stmt1 = build2 (MODIFY_EXPR, optype, tmpv, fold_convert (optype, value));

  stmt2 = build2 (MODIFY_EXPR, optype, tmp1, op2);

  stmt3 = build3 (COND_EXPR, void_type_node,

            build2 (NE_EXPR, boolean_type_node, tmp1, tmpv),

            build1 (GOTO_EXPR, void_type_node, label_decl2),

            build1 (GOTO_EXPR, void_type_node, label_decl1));

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt2, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt3, BSI_SAME_STMT);

  bb1end = stmt3;

  tmp2 = create_tmp_var (optype, "PROF");

  label1 = build1 (LABEL_EXPR, void_type_node, label_decl1);

  stmt1 = build2 (MODIFY_EXPR, optype, tmp2,

                  build2 (TREE_CODE (operation), optype, op1, tmpv));

  bsi_insert_before (&bsi, label1, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bb2end = stmt1;

  label2 = build1 (LABEL_EXPR, void_type_node, label_decl2);

  stmt1 = build2 (MODIFY_EXPR, optype, tmp2,

                  build2 (TREE_CODE (operation), optype, op1, op2));

  bsi_insert_before (&bsi, label2, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bb3end = stmt1;

  label3 = build1 (LABEL_EXPR, void_type_node, label_decl3);

  bsi_insert_before (&bsi, label3, BSI_SAME_STMT);

  /* Fix CFG. */

  /* Edge e23 connects bb2 to bb3, etc. */

  e12 = split_block (bb, bb1end);

  bb2 = e12->dest;

  bb2->count = count;

  e23 = split_block (bb2, bb2end);

  bb3 = e23->dest;

  bb3->count = all - count;

  e34 = split_block (bb3, bb3end);

  bb4 = e34->dest;

  bb4->count = all;

  e12->flags &= ~EDGE_FALLTHRU;

  e12->flags |= EDGE_FALSE_VALUE;

  e12->probability = prob;

  e12->count = count;

  e13 = make_edge (bb, bb3, EDGE_TRUE_VALUE);

  e13->probability = REG_BR_PROB_BASE - prob;

  e13->count = all - count;

  remove_edge (e23);

  e24 = make_edge (bb2, bb4, EDGE_FALLTHRU);

  e24->probability = REG_BR_PROB_BASE;

  e24->count = count;

  e34->probability = REG_BR_PROB_BASE;

  e34->count = all - count;

  return tmp2;

}

/* Do transform 1) on INSN if applicable.  */

static bool

tree_divmod_fixed_value_transform (tree stmt)

{

  stmt_ann_t ann = get_stmt_ann (stmt);

  histogram_value histogram;

  enum tree_code code;

  gcov_type val, count, all;

  tree modify, op, op1, op2, result, value, tree_val;

  int prob;

  modify = stmt;

  if (TREE_CODE (stmt) == RETURN_EXPR

      && TREE_OPERAND (stmt, 0)

      && TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR)

    modify = TREE_OPERAND (stmt, 0);

  if (TREE_CODE (modify) != MODIFY_EXPR)

    return false;

  op = TREE_OPERAND (modify, 1);

  if (!INTEGRAL_TYPE_P (TREE_TYPE (op)))

    return false;

  code = TREE_CODE (op);

  if (code != TRUNC_DIV_EXPR && code != TRUNC_MOD_EXPR)

    return false;

  op1 = TREE_OPERAND (op, 0);

  op2 = TREE_OPERAND (op, 1);

  if (!ann->histograms)

    return false;

  for (histogram = ann->histograms; histogram; histogram = histogram->hvalue.next)

    if (histogram->type == HIST_TYPE_SINGLE_VALUE)

      break;

  if (!histogram)

    return false;

  value = histogram->hvalue.value;

  val = histogram->hvalue.counters[0];

  count = histogram->hvalue.counters[1];

  all = histogram->hvalue.counters[2];

  /* We require that count is at least half of all; this means

     that for the transformation to fire the value must be constant

     at least 50% of time (and 75% gives the guarantee of usage).  */

  if (simple_cst_equal (op2, value) != 1 || 2 * count < all)

    return false;

  if (check_counter (stmt, "value", all, bb_for_stmt (stmt)->count))

    return false;

  /* Compute probability of taking the optimal path.  */

  prob = (count * REG_BR_PROB_BASE + all / 2) / all;

  tree_val = build_int_cst_wide (get_gcov_type (),

                                 (unsigned HOST_WIDE_INT) val,

                                 val >> (HOST_BITS_PER_WIDE_INT - 1) >> 1);

  result = tree_divmod_fixed_value (stmt, op, op1, op2, tree_val, prob, count, all);

  if (dump_file)

    {

      fprintf (dump_file, "Div/mod by constant ");

      print_generic_expr (dump_file, value, TDF_SLIM);

      fprintf (dump_file, "=");

      print_generic_expr (dump_file, tree_val, TDF_SLIM);

      fprintf (dump_file, " transformation on insn ");

      print_generic_stmt (dump_file, stmt, TDF_SLIM);

    }

  TREE_OPERAND (modify, 1) = result;

  return true;

}

/* Generate code for transformation 2 (with OPERATION, operands OP1

   and OP2, parent modify-expr STMT and probability of taking the optimal

   path PROB, which is equivalent to COUNT/ALL within roundoff error).

   This generates the result into a temp and returns

   the temp; it does not replace or alter the original STMT.  */

static tree

tree_mod_pow2 (tree stmt, tree operation, tree op1, tree op2, int prob,

               gcov_type count, gcov_type all)

{

  tree stmt1, stmt2, stmt3, stmt4;

  tree tmp1, tmp2, tmp3;

  tree label_decl1 = create_artificial_label ();

  tree label_decl2 = create_artificial_label ();

  tree label_decl3 = create_artificial_label ();

  tree label1, label2, label3;

  tree bb1end, bb2end, bb3end;

  basic_block bb, bb2, bb3, bb4;

  tree optype = TREE_TYPE (operation);

  edge e12, e13, e23, e24, e34;

  block_stmt_iterator bsi;

  tree result = create_tmp_var (optype, "PROF");

  bb = bb_for_stmt (stmt);

  bsi = bsi_for_stmt (stmt);

  tmp1 = create_tmp_var (optype, "PROF");

  tmp2 = create_tmp_var (optype, "PROF");

  tmp3 = create_tmp_var (optype, "PROF");

  stmt1 = build2 (MODIFY_EXPR, optype, tmp1, fold_convert (optype, op2));

  stmt2 = build2 (MODIFY_EXPR, optype, tmp2,

                    build2 (PLUS_EXPR, optype, op2, integer_minus_one_node));

  stmt3 = build2 (MODIFY_EXPR, optype, tmp3,

                    build2 (BIT_AND_EXPR, optype, tmp2, tmp1));

  stmt4 = build3 (COND_EXPR, void_type_node,

            build2 (NE_EXPR, boolean_type_node, tmp3, integer_zero_node),

            build1 (GOTO_EXPR, void_type_node, label_decl2),

            build1 (GOTO_EXPR, void_type_node, label_decl1));

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt2, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt3, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt4, BSI_SAME_STMT);

  bb1end = stmt4;

  /* tmp2 == op2-1 inherited from previous block */

  label1 = build1 (LABEL_EXPR, void_type_node, label_decl1);

  stmt1 = build2 (MODIFY_EXPR, optype, result,

                  build2 (BIT_AND_EXPR, optype, op1, tmp2));

  bsi_insert_before (&bsi, label1, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bb2end = stmt1;

  label2 = build1 (LABEL_EXPR, void_type_node, label_decl2);

  stmt1 = build2 (MODIFY_EXPR, optype, result,

                  build2 (TREE_CODE (operation), optype, op1, op2));

  bsi_insert_before (&bsi, label2, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bb3end = stmt1;

  label3 = build1 (LABEL_EXPR, void_type_node, label_decl3);

  bsi_insert_before (&bsi, label3, BSI_SAME_STMT);

  /* Fix CFG. */

  /* Edge e23 connects bb2 to bb3, etc. */

  e12 = split_block (bb, bb1end);

  bb2 = e12->dest;

  bb2->count = count;

  e23 = split_block (bb2, bb2end);

  bb3 = e23->dest;

  bb3->count = all - count;

  e34 = split_block (bb3, bb3end);

  bb4 = e34->dest;

  bb4->count = all;

  e12->flags &= ~EDGE_FALLTHRU;

  e12->flags |= EDGE_FALSE_VALUE;

  e12->probability = prob;

  e12->count = count;

  e13 = make_edge (bb, bb3, EDGE_TRUE_VALUE);

  e13->probability = REG_BR_PROB_BASE - prob;

  e13->count = all - count;

  remove_edge (e23);

  e24 = make_edge (bb2, bb4, EDGE_FALLTHRU);

  e24->probability = REG_BR_PROB_BASE;

  e24->count = count;

  e34->probability = REG_BR_PROB_BASE;

  e34->count = all - count;

  return result;

}

/* Do transform 2) on INSN if applicable.  */

static bool

tree_mod_pow2_value_transform (tree stmt)

{

  stmt_ann_t ann = get_stmt_ann (stmt);

  histogram_value histogram;

  enum tree_code code;

  gcov_type count, wrong_values, all;

  tree modify, op, op1, op2, result, value;

  int prob;

  modify = stmt;

  if (TREE_CODE (stmt) == RETURN_EXPR

      && TREE_OPERAND (stmt, 0)

      && TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR)

    modify = TREE_OPERAND (stmt, 0);

  if (TREE_CODE (modify) != MODIFY_EXPR)

    return false;

  op = TREE_OPERAND (modify, 1);

  if (!INTEGRAL_TYPE_P (TREE_TYPE (op)))

    return false;

  code = TREE_CODE (op);

  if (code != TRUNC_MOD_EXPR || !TYPE_UNSIGNED (TREE_TYPE (op)))

    return false;

  op1 = TREE_OPERAND (op, 0);

  op2 = TREE_OPERAND (op, 1);

  if (!ann->histograms)

    return false;

  for (histogram = ann->histograms; histogram; histogram = histogram->hvalue.next)

    if (histogram->type == HIST_TYPE_POW2)

      break;

  if (!histogram)

    return false;

  value = histogram->hvalue.value;

  wrong_values = histogram->hvalue.counters[0];

  count = histogram->hvalue.counters[1];

  /* We require that we hit a power of 2 at least half of all evaluations.  */

  if (simple_cst_equal (op2, value) != 1 || count < wrong_values)

    return false;

  if (dump_file)

    {

      fprintf (dump_file, "Mod power of 2 transformation on insn ");

      print_generic_stmt (dump_file, stmt, TDF_SLIM);

    }

  /* Compute probability of taking the optimal path.  */

  all = count + wrong_values;

  if (check_counter (stmt, "pow2", all, bb_for_stmt (stmt)->count))

    return false;

  prob = (count * REG_BR_PROB_BASE + all / 2) / all;

  result = tree_mod_pow2 (stmt, op, op1, op2, prob, count, all);

  TREE_OPERAND (modify, 1) = result;

  return true;

}

/* Generate code for transformations 3 and 4 (with OPERATION, operands OP1

   and OP2, parent modify-expr STMT, and NCOUNTS the number of cases to

   support.  Currently only NCOUNTS==0 or 1 is supported and this is

   built into this interface.  The probabilities of taking the optimal

   paths are PROB1 and PROB2, which are equivalent to COUNT1/ALL and

   COUNT2/ALL respectively within roundoff error).  This generates the

   result into a temp and returns the temp; it does not replace or alter

   the original STMT.  */

/* FIXME: Generalize the interface to handle NCOUNTS > 1.  */

static tree

tree_mod_subtract (tree stmt, tree operation, tree op1, tree op2,

                    int prob1, int prob2, int ncounts,

                    gcov_type count1, gcov_type count2, gcov_type all)

{

  tree stmt1, stmt2, stmt3;

  tree tmp1;

  tree label_decl1 = create_artificial_label ();

  tree label_decl2 = create_artificial_label ();

  tree label_decl3 = create_artificial_label ();

  tree label1, label2, label3;

  tree bb1end, bb2end = NULL_TREE, bb3end;

  basic_block bb, bb2, bb3, bb4;

  tree optype = TREE_TYPE (operation);

  edge e12, e23 = 0, e24, e34, e14;

  block_stmt_iterator bsi;

  tree result = create_tmp_var (optype, "PROF");

  bb = bb_for_stmt (stmt);

  bsi = bsi_for_stmt (stmt);

  tmp1 = create_tmp_var (optype, "PROF");

  stmt1 = build2 (MODIFY_EXPR, optype, result, op1);

  stmt2 = build2 (MODIFY_EXPR, optype, tmp1, op2);

  stmt3 = build3 (COND_EXPR, void_type_node,

            build2 (LT_EXPR, boolean_type_node, result, tmp1),

            build1 (GOTO_EXPR, void_type_node, label_decl3),

            build1 (GOTO_EXPR, void_type_node,

                    ncounts ? label_decl1 : label_decl2));

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt2, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt3, BSI_SAME_STMT);

  bb1end = stmt3;

  if (ncounts)  /* Assumed to be 0 or 1 */

    {

      label1 = build1 (LABEL_EXPR, void_type_node, label_decl1);

      stmt1 = build2 (MODIFY_EXPR, optype, result,

                      build2 (MINUS_EXPR, optype, result, tmp1));

      stmt2 = build3 (COND_EXPR, void_type_node,

                build2 (LT_EXPR, boolean_type_node, result, tmp1),

                build1 (GOTO_EXPR, void_type_node, label_decl3),

                build1 (GOTO_EXPR, void_type_node, label_decl2));

      bsi_insert_before (&bsi, label1, BSI_SAME_STMT);

      bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

      bsi_insert_before (&bsi, stmt2, BSI_SAME_STMT);

      bb2end = stmt2;

    }

  /* Fallback case. */

  label2 = build1 (LABEL_EXPR, void_type_node, label_decl2);

  stmt1 = build2 (MODIFY_EXPR, optype, result,

                    build2 (TREE_CODE (operation), optype, result, tmp1));

  bsi_insert_before (&bsi, label2, BSI_SAME_STMT);

  bsi_insert_before (&bsi, stmt1, BSI_SAME_STMT);

  bb3end = stmt1;

  label3 = build1 (LABEL_EXPR, void_type_node, label_decl3);

  bsi_insert_before (&bsi, label3, BSI_SAME_STMT);

  /* Fix CFG. */

  /* Edge e23 connects bb2 to bb3, etc. */

  /* However block 3 is optional; if it is not there, references

     to 3 really refer to block 2. */

  e12 = split_block (bb, bb1end);

  bb2 = e12->dest;

  bb2->count = all - count1;

  if (ncounts)  /* Assumed to be 0 or 1.  */

    {

      e23 = split_block (bb2, bb2end);

      bb3 = e23->dest;

      bb3->count = all - count1 - count2;

    }

  e34 = split_block (ncounts ? bb3 : bb2, bb3end);

  bb4 = e34->dest;

  bb4->count = all;

  e12->flags &= ~EDGE_FALLTHRU;

  e12->flags |= EDGE_FALSE_VALUE;

  e12->probability = REG_BR_PROB_BASE - prob1;

  e12->count = all - count1;

  e14 = make_edge (bb, bb4, EDGE_TRUE_VALUE);

  e14->probability = prob1;

  e14->count = count1;

  if (ncounts)  /* Assumed to be 0 or 1.  */

    {

      e23->flags &= ~EDGE_FALLTHRU;

      e23->flags |= EDGE_FALSE_VALUE;

      e23->count = all - count1 - count2;

      e23->probability = REG_BR_PROB_BASE - prob2;

      e24 = make_edge (bb2, bb4, EDGE_TRUE_VALUE);

      e24->probability = prob2;

      e24->count = count2;

    }

  e34->probability = REG_BR_PROB_BASE;

  e34->count = all - count1 - count2;

  return result;

}

/* Do transforms 3) and 4) on INSN if applicable.  */

static bool

tree_mod_subtract_transform (tree stmt)

{

  stmt_ann_t ann = get_stmt_ann (stmt);

  histogram_value histogram;

  enum tree_code code;

  gcov_type count, wrong_values, all;

  tree modify, op, op1, op2, result, value;

  int prob1, prob2;

  unsigned int i;

  modify = stmt;

  if (TREE_CODE (stmt) == RETURN_EXPR

      && TREE_OPERAND (stmt, 0)

      && TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR)

    modify = TREE_OPERAND (stmt, 0);

  if (TREE_CODE (modify) != MODIFY_EXPR)

    return false;

  op = TREE_OPERAND (modify, 1);

  if (!INTEGRAL_TYPE_P (TREE_TYPE (op)))

    return false;

  code = TREE_CODE (op);

  if (code != TRUNC_MOD_EXPR || !TYPE_UNSIGNED (TREE_TYPE (op)))

    return false;

  op1 = TREE_OPERAND (op, 0);

  op2 = TREE_OPERAND (op, 1);

  if (!ann->histograms)

    return false;

  for (histogram = ann->histograms; histogram; histogram = histogram->hvalue.next)

    if (histogram->type == HIST_TYPE_INTERVAL)

      break;

  if (!histogram)

    return false;

  value = histogram->hvalue.value;

  all = 0;

  wrong_values = 0;

  for (i = 0; i < histogram->hdata.intvl.steps; i++)

    all += histogram->hvalue.counters[i];

  wrong_values += histogram->hvalue.counters[i];

  wrong_values += histogram->hvalue.counters[i+1];

  all += wrong_values;

  /* Compute probability of taking the optimal path.  */