c++: only cache constexpr calls that are constant exprs

[official-gcc.git] / gcc / tree-ssa-loop-ch.cc

/* Loop header copying on trees.
   Copyright (C) 2004-2023 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 "backend.h"
#include "tree.h"
#include "gimple.h"
#include "cfghooks.h"
#include "tree-pass.h"
#include "gimple-ssa.h"
#include "gimple-iterator.h"
#include "tree-cfg.h"
#include "tree-into-ssa.h"
#include "cfgloop.h"
#include "tree-inline.h"
#include "tree-ssa-threadedge.h"
#include "tree-ssa-sccvn.h"
#include "tree-phinodes.h"
#include "ssa-iterators.h"
#include "value-range.h"
#include "gimple-range.h"
#include "gimple-range-path.h"
#include "cfganal.h"

/* Duplicates headers of loops if they are small enough, so that the statements
   in the loop body are always executed when the loop is entered.  This
   increases effectiveness of code motion optimizations, and reduces the need
   for loop preconditioning.  */

/* Given a path through edge E, whose last statement is COND, return
   the range of the solved conditional in R.  */

static void
edge_range_query (irange &r, edge e, gcond *cond, gimple_ranger &ranger)
{
  auto_vec<basic_block> path (2);
  path.safe_push (e->dest);
  path.safe_push (e->src);
  path_range_query query (ranger, path);
  if (!query.range_of_stmt (r, cond))
    r.set_varying (boolean_type_node);
}

/* Return edge that is true in the first iteration of the loop
   and NULL otherwise.  */

static edge
static_loop_exit (class loop *l, gimple_ranger *ranger)
{
  edge e = loop_preheader_edge (l);
  gcond *last = safe_dyn_cast <gcond *> (*gsi_last_bb (e->dest));
  edge ret_e;

  if (!last)
    return NULL;

  edge true_e, false_e;
  extract_true_false_edges_from_block (e->dest, &true_e, &false_e);

  /* If neither edge is the exit edge, this is not a case we'd like to
     special-case.  */
  if (!loop_exit_edge_p (l, true_e) && !loop_exit_edge_p (l, false_e))
    return NULL;

  int_range<1> desired_static_range;
  if (loop_exit_edge_p (l, true_e))
   {
      desired_static_range = range_false ();
      ret_e = true_e;
   }
  else
  {
    desired_static_range = range_true ();
    ret_e = false_e;
  }

  int_range<2> r;
  edge_range_query (r, e, last, *ranger);
  return r == desired_static_range ? ret_e : NULL;
}

/* Return true if OP is invariant.  */

static bool
loop_invariant_op_p (class loop *loop,
                     tree op)
{
  if (is_gimple_min_invariant (op))
    return true;
  if (SSA_NAME_IS_DEFAULT_DEF (op)
      || !flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (op))))
    return true;
  return gimple_uid (SSA_NAME_DEF_STMT (op)) & 2;
}

/* Return true if OP looks like it is derived from IV.  */

static bool
loop_iv_derived_p (class loop *loop,
                    tree op)
{
  /* Always check for invariant first.  */
  gcc_checking_assert (!is_gimple_min_invariant (op)
                       && !SSA_NAME_IS_DEFAULT_DEF (op)
                       && flow_bb_inside_loop_p (loop,
                               gimple_bb (SSA_NAME_DEF_STMT (op))));
  return gimple_uid (SSA_NAME_DEF_STMT (op)) & 1;
}

/* Check whether we should duplicate HEADER of LOOP.  At most *LIMIT
   instructions should be duplicated, limit is decreased by the actual
   amount.  */

static bool
should_duplicate_loop_header_p (basic_block header, class loop *loop,
                                int *limit,
                                hash_set <edge> *invariant_exits)
{
  gimple_stmt_iterator bsi;

  gcc_assert (!header->aux);

  gcc_assert (EDGE_COUNT (header->succs) > 0);
  if (single_succ_p (header))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "  Not duplicating bb %i: it is single succ.\n",
                 header->index);
      return false;
    }

  if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest)
      && flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 1)->dest))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "  Not duplicating bb %i: both successors are in loop.\n",
                 loop->num);
      return false;
    }

  /* If this is not the original loop header, we want it to have just
     one predecessor in order to match the && pattern.  */
  if (header != loop->header && !single_pred_p (header))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "  Not duplicating bb %i: it has mutiple predecestors.\n",
                 header->index);
      return false;
    }

  gcond *last = safe_dyn_cast <gcond *> (*gsi_last_bb (header));
  if (!last)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "  Not duplicating bb %i: it does not end by conditional.\n",
                 header->index);
      return false;
    }

  for (gphi_iterator psi = gsi_start_phis (header); !gsi_end_p (psi);
       gsi_next (&psi))
    /* If this is actual loop header PHIs indicate that the SSA_NAME
       may be IV.  Otherwise just give up.  */
    if (header == loop->header)
      {
        gphi *phi = psi.phi ();
        tree res = gimple_phi_result (phi);
        if (INTEGRAL_TYPE_P (TREE_TYPE (res))
            || POINTER_TYPE_P (TREE_TYPE (res)))
          gimple_set_uid (phi, 1 /* IV */);
        else
          gimple_set_uid (phi, 0);
      }
    else
      gimple_set_uid (psi.phi (), 0);

  /* Count number of instructions and punt on calls.
     Populate stmts INV/IV flag to later apply heuristics to the
     kind of conditions we want to copy.  */
  for (bsi = gsi_start_bb (header); !gsi_end_p (bsi); gsi_next (&bsi))
    {
      gimple *last = gsi_stmt (bsi);

      if (gimple_code (last) == GIMPLE_LABEL)
        continue;

      if (is_gimple_debug (last))
        continue;

      if (gimple_code (last) == GIMPLE_CALL
          && (!gimple_inexpensive_call_p (as_a <gcall *> (last))
              /* IFN_LOOP_DIST_ALIAS means that inner loop is distributed
                 at current loop's header.  Don't copy in this case.  */
              || gimple_call_internal_p (last, IFN_LOOP_DIST_ALIAS)))
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file,
                     "  Not duplicating bb %i: it contains call.\n",
                     header->index);
          return false;
        }

      *limit -= estimate_num_insns (last, &eni_size_weights);
      if (*limit < 0)
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file,
                     "  Not duplicating bb %i contains too many insns.\n",
                     header->index);
          return false;
        }

      /* Classify the stmt based on whether its computation is based
         on a IV or whether it is invariant in the loop.  */
      gimple_set_uid (last, 0);
      if (!gimple_vuse (last)
          && gimple_code (last) != GIMPLE_ASM
          && (gimple_code (last) != GIMPLE_CALL
              || gimple_call_flags (last) & ECF_CONST))
        {
          bool inv = true;
          bool iv = true;
          ssa_op_iter i;
          tree op;
          FOR_EACH_SSA_TREE_OPERAND (op, last, i, SSA_OP_USE)
            if (!loop_invariant_op_p (loop, op))
              {
                if (!loop_iv_derived_p (loop, op))
                  {
                    inv = false;
                    iv = false;
                    break;
                  }
                else
                  inv = false;
              }
          gimple_set_uid (last, (iv ? 1 : 0) | (inv ? 2 : 0));
        }
    }

  /* If the condition tests a non-IV loop variant we do not want to rotate
     the loop further.  Unless this is the original loop header.  */
  tree lhs = gimple_cond_lhs (last);
  tree rhs = gimple_cond_rhs (last);
  bool lhs_invariant = loop_invariant_op_p (loop, lhs);
  bool rhs_invariant = loop_invariant_op_p (loop, rhs);
  if (lhs_invariant && rhs_invariant)
    {
      if (invariant_exits)
        {
          edge e;
          edge_iterator ei;
          FOR_EACH_EDGE (e, ei, header->succs)
            if (loop_exit_edge_p (loop, e))
              {
                if (dump_file && (dump_flags & TDF_DETAILS))
                  fprintf (dump_file,
                           "    Will elliminate invariant exit %i->%i\n",
                           e->src->index, e->dest->index);
                invariant_exits->add (e);
              }
        }
      return true;
    }
  /* TODO: This is heuristics that claims that IV based ocnditionals will
     likely be optimized out in duplicated header.  We could use ranger
     query instead to tell this more precisely.  */
  if (header != loop->header
      && ((!lhs_invariant && !loop_iv_derived_p (loop, lhs))
          || (!rhs_invariant && !loop_iv_derived_p (loop, rhs))))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "  Not duplicating bb %i: condition based on non-IV loop"
                 " variant.\n", header->index);
      return false;
    }

  return true;
}

/* Checks whether LOOP is a do-while style loop.  */

static bool
do_while_loop_p (class loop *loop)
{
  gimple *stmt = last_nondebug_stmt (loop->latch);

  /* If the latch of the loop is not empty, it is not a do-while loop.  */
  if (stmt
      && gimple_code (stmt) != GIMPLE_LABEL)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Loop %i is not do-while loop: latch is not empty.\n",
                 loop->num);
      return false;
    }

  /* If the latch does not have a single predecessor, it is not a
     do-while loop.  */
  if (!single_pred_p (loop->latch))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Loop %i is not do-while loop: latch has multiple "
                 "predecessors.\n", loop->num);
      return false;
    }

  /* If the latch predecessor doesn't exit the loop, it is not a
     do-while loop.  */
  if (!loop_exits_from_bb_p (loop, single_pred (loop->latch)))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Loop %i is not do-while loop: latch predecessor "
                 "does not exit loop.\n", loop->num);
      return false;
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "Loop %i is do-while loop\n", loop->num);

  return true;
}

/* Update profile after header copying of LOOP.
   REGION is the original (in loop) sequence, REGION_COPY is the
   duplicated header (now outside of loop). N_REGION is number of
   bbs duplicated.
   ELIMINATED_EDGE is edge to be removed from duplicated sequence.
   INVARIANT_EXITS are edges in the loop body to be elimianted
   since they are loop invariants

   So We expect the following:

      // region_copy_start entry will be scaled to entry_count
         if (cond1)         <- this condition will become false
                               and we update probabilities
           goto loop_exit;
         if (cond2)         <- this condition is loop invariant
           goto loop_exit;
         goto loop_header   <- this will be redirected to loop.
       // region_copy_end
     loop:
               <body>
       // region start
     loop_header:
               if (cond1)   <- we need to update probabbility here
                 goto loop_exit;
               if (cond2)   <- and determine scaling factor here.
                               moreover cond2 is now always true
                 goto loop_exit;
               else
                 goto loop;
       // region end

     Adding support for more exits can be done similarly,
     but only consumer so far is tree-ssa-loop-ch and it uses only this
     to handle the common case of peeling headers which have
     conditionals known to be always true upon entry.  */

static void
update_profile_after_ch (class loop *loop,
                         basic_block *region, basic_block *region_copy,
                         unsigned n_region, edge eliminated_edge,
                         hash_set <edge> *invariant_exits,
                         profile_count entry_count)
{
  for (unsigned int i = 0; i < n_region; i++)
    {
      edge exit_e, exit_e_copy, e, e_copy;
      if (EDGE_COUNT (region[i]->succs) == 1)
        {
          region_copy[i]->count = entry_count;
          region[i]->count -= entry_count;
          continue;
        }

      gcc_checking_assert (EDGE_COUNT (region[i]->succs) == 2);
      if (loop_exit_edge_p (loop,
                            EDGE_SUCC (region[i], 0)))
        {
          exit_e = EDGE_SUCC (region[i], 0);
          exit_e_copy = EDGE_SUCC (region_copy[i], 0);
          e = EDGE_SUCC (region[i], 1);
          e_copy = EDGE_SUCC (region_copy[i], 1);
        }
      else
        {
          exit_e = EDGE_SUCC (region[i], 1);
          exit_e_copy = EDGE_SUCC (region_copy[i], 1);
          e = EDGE_SUCC (region[i], 0);
          e_copy = EDGE_SUCC (region_copy[i], 0);
        }
      gcc_assert (i == n_region - 1
                  || (e->dest == region[i + 1]
                      && e_copy->dest == region_copy[i + 1]));
      region_copy[i]->count = entry_count;
      profile_count exit_e_count = exit_e->count ();
      if (eliminated_edge == exit_e)
        {
          /* Update profile and the conditional.
             CFG update is done by caller.  */
          e_copy->probability = profile_probability::always ();
          exit_e_copy->probability = profile_probability::never ();
          gcond *cond_stmt
                  = as_a <gcond *>(*gsi_last_bb (region_copy[i]));
          if (e_copy->flags & EDGE_TRUE_VALUE)
            gimple_cond_make_true (cond_stmt);
          else
            gimple_cond_make_false (cond_stmt);
          update_stmt (cond_stmt);
          /* Header copying is a special case of jump threading, so use
             common code to update loop body exit condition.  */
          update_bb_profile_for_threading (region[i], entry_count, e);
          eliminated_edge = NULL;
        }
      else
        region[i]->count -= region_copy[i]->count;
      if (invariant_exits->contains (exit_e))
        {
          invariant_exits->remove (exit_e);
          /* All exits will happen in exit_e_copy which is out of the
             loop, so increase probability accordingly.
             If the edge is eliminated_edge we already corrected
             profile above.  */
          if (entry_count.nonzero_p () && eliminated_edge != exit_e)
            set_edge_probability_and_rescale_others
                    (exit_e_copy, exit_e_count.probability_in
                                                        (entry_count));
          /* Eliminate in-loop conditional.  */
          e->probability = profile_probability::always ();
          exit_e->probability = profile_probability::never ();
          gcond *cond_stmt = as_a <gcond *>(*gsi_last_bb (region[i]));
          if (e->flags & EDGE_TRUE_VALUE)
            gimple_cond_make_true (cond_stmt);
          else
            gimple_cond_make_false (cond_stmt);
          update_stmt (cond_stmt);
        }
      entry_count = e_copy->count ();
    }
  /* Be sure that we seen all edges we are supposed to update.  */
  gcc_checking_assert (!eliminated_edge
                       && invariant_exits->is_empty ());
}

namespace {

/* Common superclass for both header-copying phases.  */
class ch_base : public gimple_opt_pass
{
  protected:
    ch_base (pass_data data, gcc::context *ctxt)
      : gimple_opt_pass (data, ctxt)
    {}

  /* Copies headers of all loops in FUN for which process_loop_p is true.  */
  unsigned int copy_headers (function *fun);

  /* Return true to copy headers of LOOP or false to skip.  */
  virtual bool process_loop_p (class loop *loop) = 0;
};

const pass_data pass_data_ch =
{
  GIMPLE_PASS, /* type */
  "ch", /* name */
  OPTGROUP_LOOP, /* optinfo_flags */
  TV_TREE_CH, /* tv_id */
  ( PROP_cfg | PROP_ssa ), /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  0, /* todo_flags_finish */
};

class pass_ch : public ch_base
{
public:
  pass_ch (gcc::context *ctxt)
    : ch_base (pass_data_ch, ctxt)
  {}

  /* opt_pass methods: */
  bool gate (function *) final override { return flag_tree_ch != 0; }
  
  /* Initialize and finalize loop structures, copying headers inbetween.  */
  unsigned int execute (function *) final override;

  opt_pass * clone () final override { return new pass_ch (m_ctxt); }

protected:
  /* ch_base method: */
  bool process_loop_p (class loop *loop) final override;
}; // class pass_ch

const pass_data pass_data_ch_vect =
{
  GIMPLE_PASS, /* type */
  "ch_vect", /* name */
  OPTGROUP_LOOP, /* optinfo_flags */
  TV_TREE_CH, /* tv_id */
  ( PROP_cfg | PROP_ssa ), /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  0, /* todo_flags_finish */
};

/* This is a more aggressive version of the same pass, designed to run just
   before if-conversion and vectorization, to put more loops into the form
   required for those phases.  */
class pass_ch_vect : public ch_base
{
public:
  pass_ch_vect (gcc::context *ctxt)
    : ch_base (pass_data_ch_vect, ctxt)
  {}

  /* opt_pass methods: */
  bool gate (function *fun) final override
  {
    return flag_tree_ch != 0
           && (flag_tree_loop_vectorize != 0 || fun->has_force_vectorize_loops);
  }
  
  /* Just copy headers, no initialization/finalization of loop structures.  */
  unsigned int execute (function *) final override;

protected:
  /* ch_base method: */
  bool process_loop_p (class loop *loop) final override;
}; // class pass_ch_vect

/* For all loops, copy the condition at the end of the loop body in front
   of the loop.  This is beneficial since it increases efficiency of
   code motion optimizations.  It also saves one jump on entry to the loop.  */

unsigned int
ch_base::copy_headers (function *fun)
{
  basic_block header;
  edge exit, nonexit, entry;
  basic_block *bbs, *copied_bbs;
  unsigned n_bbs;
  unsigned bbs_size;
  bool changed = false;

  if (number_of_loops (fun) <= 1)
    return 0;

  bbs = XNEWVEC (basic_block, n_basic_blocks_for_fn (fun));
  copied_bbs = XNEWVEC (basic_block, n_basic_blocks_for_fn (fun));
  bbs_size = n_basic_blocks_for_fn (fun);

  struct candidate {class loop *loop; edge static_exit;};
  auto_vec<struct candidate> candidates;
  auto_vec<std::pair<edge, loop_p> > copied;
  auto_vec<class loop *> loops_to_unloop;
  auto_vec<int> loops_to_unloop_nunroll;

  mark_dfs_back_edges ();
  gimple_ranger *ranger = new gimple_ranger;
  for (auto loop : loops_list (cfun, 0))
    {
      int initial_limit = param_max_loop_header_insns;
      int remaining_limit = initial_limit;
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Analyzing loop %i\n", loop->num);

      header = loop->header;
      if (!get_max_loop_iterations_int (loop))
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file, "Loop %d never loops.\n", loop->num);
          scale_loop_profile (loop, profile_probability::always (), 0);
          loops_to_unloop.safe_push (loop);
          loops_to_unloop_nunroll.safe_push (0);
          continue;
        }

      /* If the loop is already a do-while style one (either because it was
         written as such, or because jump threading transformed it into one),
         we might be in fact peeling the first iteration of the loop.  This
         in general is not a good idea.  Also avoid touching infinite loops.  */
      if (!loop_has_exit_edges (loop)
          || !process_loop_p (loop))
        continue;

      edge static_exit = static_loop_exit (loop, ranger);

      /* Avoid loop header copying when optimizing for size unless we can
         determine that the loop condition is static in the first
         iteration.  */
      if (optimize_loop_for_size_p (loop)
          && !loop->force_vectorize
          && !static_exit)
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file,
                     "  Not duplicating bb %i: optimizing for size.\n",
                     header->index);
          continue;
        }

      if (should_duplicate_loop_header_p (header, loop, &remaining_limit, NULL))
        candidates.safe_push ({loop, static_exit});
    }
  /* Do not use ranger after we change the IL and not have updated SSA.  */
  delete ranger;

  for (auto candidate : candidates)
    {
      class loop *loop = candidate.loop;
      int initial_limit = param_max_loop_header_insns;
      int remaining_limit = initial_limit;
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Copying headers of loop %i\n", loop->num);

      header = loop->header;

      /* Iterate the header copying up to limit; this takes care of the cases
         like while (a && b) {...}, where we want to have both of the conditions
         copied.  TODO -- handle while (a || b) - like cases, by not requiring
         the header to have just a single successor and copying up to
         postdominator.  */

      nonexit = NULL;
      n_bbs = 0;
      int nexits = 0;
      profile_count exit_count = profile_count::zero ();
      profile_count entry_count = profile_count::zero ();
      edge e;
      edge_iterator ei;
      hash_set <edge> invariant_exits;
      FOR_EACH_EDGE (e, ei, loop->header->preds)
        if (e->src != loop->latch)
          entry_count += e->count ();
      while (should_duplicate_loop_header_p (header, loop, &remaining_limit,
                                             &invariant_exits))
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file, "    Will duplicate bb %i\n", header->index);

          /* Find a successor of header that is inside a loop; i.e. the new
             header after the condition is copied.  */
          if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest))
            {
              nonexit = EDGE_SUCC (header, 0);
              exit = EDGE_SUCC (header, 1);
            }
          else
            {
              nonexit = EDGE_SUCC (header, 1);
              exit = EDGE_SUCC (header, 0);
            }
          exit_count += exit->count ();
          nexits++;
          bbs[n_bbs++] = header;
          gcc_assert (bbs_size > n_bbs);
          header = nonexit->dest;
        }

      if (!nonexit)
        continue;

      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          fprintf (dump_file,
                   "Duplicating header of the loop %d up to edge %d->%d,"
                   " %i insns.\n",
                   loop->num, exit->src->index, exit->dest->index,
                   initial_limit - remaining_limit);
          if (candidate.static_exit)
            fprintf (dump_file,
                     "  Will eliminate peeled conditional in bb %d.\n",
                     candidate.static_exit->src->index);
        }

      /* Ensure that the header will have just the latch as a predecessor
         inside the loop.  */
      if (!single_pred_p (nonexit->dest))
        {
          header = split_edge (nonexit);
          exit = single_pred_edge (header);
        }

      entry = loop_preheader_edge (loop);

      propagate_threaded_block_debug_into (exit->dest, entry->dest);
      if (!gimple_duplicate_seme_region (entry, exit, bbs, n_bbs, copied_bbs,
                                         true))
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file, "Duplication failed.\n");
          continue;
        }
      if (loop->header->count.initialized_p ())
        update_profile_after_ch (loop, bbs, copied_bbs, n_bbs,
                                 candidate.static_exit, &invariant_exits,
                                 entry_count);
      copied.safe_push (std::make_pair (entry, loop));

      /* If the loop has the form "for (i = j; i < j + 10; i++)" then
         this copying can introduce a case where we rely on undefined
         signed overflow to eliminate the preheader condition, because
         we assume that "j < j + 10" is true.  We don't want to warn
         about that case for -Wstrict-overflow, because in general we
         don't warn about overflow involving loops.  Prevent the
         warning by setting the no_warning flag in the condition.  */
      if (warn_strict_overflow > 0)
        {
          unsigned int i;

          for (i = 0; i < n_bbs; ++i)
            {
              gimple_stmt_iterator bsi;

              for (bsi = gsi_start_bb (copied_bbs[i]);
                   !gsi_end_p (bsi);
                   gsi_next (&bsi))
                {
                  gimple *stmt = gsi_stmt (bsi);
                  if (gimple_code (stmt) == GIMPLE_COND)
                    {
                      tree lhs = gimple_cond_lhs (stmt);
                      if (gimple_cond_code (stmt) != EQ_EXPR
                          && gimple_cond_code (stmt) != NE_EXPR
                          && INTEGRAL_TYPE_P (TREE_TYPE (lhs))
                          && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (lhs)))
                        suppress_warning (stmt, OPT_Wstrict_overflow_);
                    }
                  else if (is_gimple_assign (stmt))
                    {
                      enum tree_code rhs_code = gimple_assign_rhs_code (stmt);
                      tree rhs1 = gimple_assign_rhs1 (stmt);
                      if (TREE_CODE_CLASS (rhs_code) == tcc_comparison
                          && rhs_code != EQ_EXPR
                          && rhs_code != NE_EXPR
                          && INTEGRAL_TYPE_P (TREE_TYPE (rhs1))
                          && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (rhs1)))
                        suppress_warning (stmt, OPT_Wstrict_overflow_);
                    }
                }
            }
        }

      /* Update header of the loop.  */
      loop->header = header;
      /* Find correct latch.  We only duplicate chain of conditionals so
         there should be precisely two edges to the new header.  One entry
         edge and one to latch.  */
      FOR_EACH_EDGE (e, ei, loop->header->preds)
        if (header != e->src)
          {
            loop->latch = e->src;
            break;
          }
      /* Ensure that the latch is simple.  */
      if (!single_succ_p (loop_latch_edge (loop)->src))
        split_edge (loop_latch_edge (loop));

      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          if (do_while_loop_p (loop))
            fprintf (dump_file, "Loop %d is now do-while loop.\n", loop->num);
          else
            fprintf (dump_file, "Loop %d is still not do-while loop.\n",
                     loop->num);
          fprintf (dump_file, "Exit count: ");
          exit_count.dump (dump_file);
          fprintf (dump_file, "\nEntry count: ");
          entry_count.dump (dump_file);
          fprintf (dump_file, "\n");
        }

      /* We possibly decreased number of itrations by 1.  */
      auto_vec<edge> exits = get_loop_exit_edges (loop);
      bool precise = (nexits == (int) exits.length ());
      /* Check that loop may not terminate in other way than via
         basic blocks we duplicated.  */
      if (precise)
        {
          basic_block *bbs = get_loop_body (loop);
          for (unsigned i = 0; i < loop->num_nodes && precise; ++i)
           {
             basic_block bb = bbs[i];
             bool found_exit = false;
             FOR_EACH_EDGE (e, ei, bb->succs)
              if (!flow_bb_inside_loop_p (loop, e->dest))
                {
                  found_exit = true;
                  break;
                }
             /* If BB has exit, it was duplicated.  */
             if (found_exit)
               continue;
             /* Give up on irreducible loops.  */
             if (bb->flags & BB_IRREDUCIBLE_LOOP)
               {
                 precise = false;
                 break;
               }
             /* Check that inner loops are finite.  */
             for (class loop *l = bb->loop_father; l != loop && precise;
                  l = loop_outer (l))
               if (!l->finite_p)
                 {
                   precise = false;
                   break;
                 }
             /* Verify that there is no statement that may be terminate
                execution in a way not visible to CFG.  */
             for (gimple_stmt_iterator bsi = gsi_start_bb (bb);
                  !gsi_end_p (bsi); gsi_next (&bsi))
               if (stmt_can_terminate_bb_p (gsi_stmt (bsi)))
                 precise = false;
           }
          free (bbs);
        }
      if (precise
          && get_max_loop_iterations_int (loop) == 1)
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file, "Loop %d no longer loops.\n", loop->num);
          scale_loop_profile (loop, profile_probability::always (), 0);
          loops_to_unloop.safe_push (loop);
          loops_to_unloop_nunroll.safe_push (0);
        }
      else if (precise)
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file,
                     "Peeled all exits:"
                     " decreased number of iterations of loop %d by 1.\n",
                     loop->num);
          adjust_loop_info_after_peeling (loop, 1, true);
        }
      else if (exit_count >= entry_count.apply_scale (9, 10))
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file,
                     "Peeled likely exits: likely decreased number "
                     "of iterations of loop %d by 1.\n", loop->num);
          adjust_loop_info_after_peeling (loop, 1, false);
        }
      else if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Not decreased number"
                 " of iterations of loop %d; likely exits remains.\n",
                 loop->num);

      changed = true;
    }

  if (changed)
    {
      update_ssa (TODO_update_ssa);
      /* After updating SSA form perform CSE on the loop header
         copies.  This is esp. required for the pass before
         vectorization since nothing cleans up copied exit tests
         that can now be simplified.  CSE from the entry of the
         region we copied till all loop exit blocks but not
         entering the loop itself.  */
      for (unsigned i = 0; i < copied.length (); ++i)
        {
          edge entry = copied[i].first;
          loop_p loop = copied[i].second;
          auto_vec<edge> exit_edges = get_loop_exit_edges (loop);
          bitmap exit_bbs = BITMAP_ALLOC (NULL);
          for (unsigned j = 0; j < exit_edges.length (); ++j)
            bitmap_set_bit (exit_bbs, exit_edges[j]->dest->index);
          bitmap_set_bit (exit_bbs, loop->header->index);
          do_rpo_vn (cfun, entry, exit_bbs);
          BITMAP_FREE (exit_bbs);
        }
    }
  if (!loops_to_unloop.is_empty ())
    {
      bool irred_invalidated;
      unloop_loops (loops_to_unloop, loops_to_unloop_nunroll, NULL, &irred_invalidated);
      changed = true;
    }
  free (bbs);
  free (copied_bbs);

  return changed ? TODO_cleanup_cfg : 0;
}

/* Initialize the loop structures we need, and finalize after.  */

unsigned int
pass_ch::execute (function *fun)
{
  loop_optimizer_init (LOOPS_HAVE_PREHEADERS
                       | LOOPS_HAVE_SIMPLE_LATCHES
                       | LOOPS_HAVE_RECORDED_EXITS);

  unsigned int res = copy_headers (fun);

  loop_optimizer_finalize ();
  return res;
}

/* Assume an earlier phase has already initialized all the loop structures that
   we need here (and perhaps others too), and that these will be finalized by
   a later phase.  */
   
unsigned int
pass_ch_vect::execute (function *fun)
{
  return copy_headers (fun);
}

/* Apply header copying according to a very simple test of do-while shape.  */

bool
pass_ch::process_loop_p (class loop *loop)
{
  return !do_while_loop_p (loop);
}

/* Apply header-copying to loops where we might enable vectorization.  */

bool
pass_ch_vect::process_loop_p (class loop *loop)
{
  if (!flag_tree_loop_vectorize && !loop->force_vectorize)
    return false;

  if (loop->dont_vectorize)
    return false;

  /* The vectorizer won't handle anything with multiple exits, so skip.  */
  edge exit = single_exit (loop);
  if (!exit)
    return false;

  if (!do_while_loop_p (loop))
    return true;

  return false;
}

} // anon namespace

gimple_opt_pass *
make_pass_ch_vect (gcc::context *ctxt)
{
  return new pass_ch_vect (ctxt);
}

gimple_opt_pass *
make_pass_ch (gcc::context *ctxt)
{
  return new pass_ch (ctxt);
}