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/* Loop header copying on trees.

   Copyright (C) 2004, 2005, 2006, 2007, 2008 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 "tree.h"

#include "rtl.h"

#include "tm_p.h"

#include "hard-reg-set.h"

#include "basic-block.h"

#include "output.h"

#include "diagnostic.h"

#include "tree-flow.h"

#include "tree-dump.h"

#include "tree-pass.h"

#include "timevar.h"

#include "cfgloop.h"

#include "tree-inline.h"

#include "flags.h"

#include "tree-inline.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.  */

/* 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, struct loop *loop,

                                int *limit)

{

  gimple_stmt_iterator bsi;

  gimple last;

  /* Do not copy one block more than once (we do not really want to do

     loop peeling here).  */

  if (header->aux)

    return false;

  /* Loop header copying usually increases size of the code.  This used not to

     be true, since quite often it is possible to verify that the condition is

     satisfied in the first iteration and therefore to eliminate it.  Jump

     threading handles these cases now.  */

  if (optimize_loop_for_size_p (loop))

    return false;

  gcc_assert (EDGE_COUNT (header->succs) > 0);

  if (single_succ_p (header))

    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))

    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))

    return false;

  last = last_stmt (header);

  if (gimple_code (last) != GIMPLE_COND)

    return false;

  /* Approximately copy the conditions that used to be used in jump.c --

     at most 20 insns and no calls.  */

  for (bsi = gsi_start_bb (header); !gsi_end_p (bsi); gsi_next (&bsi))

    {

      last = gsi_stmt (bsi);

      if (gimple_code (last) == GIMPLE_LABEL)

        continue;

      if (is_gimple_debug (last))

        continue;

      if (is_gimple_call (last))

        return false;

      *limit -= estimate_num_insns (last, &eni_size_weights);

      if (*limit < 0)

        return false;

    }

  return true;

}

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

static bool

do_while_loop_p (struct loop *loop)

{

  gimple stmt = last_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)

    return false;

  /* If the header contains just a condition, it is not a do-while loop.  */

  stmt = last_and_only_stmt (loop->header);

  if (stmt

      && gimple_code (stmt) == GIMPLE_COND)

    return false;

  return true;

}

/* 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.  */

static unsigned int

copy_loop_headers (void)

{

  loop_iterator li;

  struct loop *loop;

  basic_block header;

  edge exit, entry;

  basic_block *bbs, *copied_bbs;

  unsigned n_bbs;

  unsigned bbs_size;

  loop_optimizer_init (LOOPS_HAVE_PREHEADERS

                       | LOOPS_HAVE_SIMPLE_LATCHES);

  if (number_of_loops () <= 1)

    {

      loop_optimizer_finalize ();

      return 0;

    }

#ifdef ENABLE_CHECKING

  verify_loop_structure ();

#endif

  bbs = XNEWVEC (basic_block, n_basic_blocks);

  copied_bbs = XNEWVEC (basic_block, n_basic_blocks);

  bbs_size = n_basic_blocks;

  FOR_EACH_LOOP (li, loop, 0)

    {

      /* Copy at most 20 insns.  */

      int limit = 20;

      header = loop->header;

      /* 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.  */

      if (do_while_loop_p (loop))

        continue;

      /* 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.  */

      exit = NULL;

      n_bbs = 0;

      while (should_duplicate_loop_header_p (header, loop, &limit))

        {

          /* 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))

            exit = EDGE_SUCC (header, 0);

          else

            exit = EDGE_SUCC (header, 1);

          bbs[n_bbs++] = header;

          gcc_assert (bbs_size > n_bbs);

          header = exit->dest;

        }

      if (!exit)

        continue;

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file,

                 "Duplicating header of the loop %d up to edge %d->%d.\n",

                 loop->num, exit->src->index, exit->dest->index);

      /* Ensure that the header will have just the latch as a predecessor

         inside the loop.  */

      if (!single_pred_p (exit->dest))

        exit = single_pred_edge (split_edge (exit));

      entry = loop_preheader_edge (loop);

      if (!gimple_duplicate_sese_region (entry, exit, bbs, n_bbs, copied_bbs))

        {

          fprintf (dump_file, "Duplication failed.\n");

          continue;

        }

      /* 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)

                    gimple_set_no_warning (stmt, true);

                  else if (is_gimple_assign (stmt))

                    {

                      enum tree_code rhs_code = gimple_assign_rhs_code (stmt);

                      if (TREE_CODE_CLASS (rhs_code) == tcc_comparison)

                        gimple_set_no_warning (stmt, true);

                    }

                }

            }

        }

      /* Ensure that the latch and the preheader is simple (we know that they

         are not now, since there was the loop exit condition.  */

      split_edge (loop_preheader_edge (loop));

      split_edge (loop_latch_edge (loop));

    }

  free (bbs);

  free (copied_bbs);

  loop_optimizer_finalize ();

  return 0;

}

static bool

gate_ch (void)

{

  return flag_tree_ch != 0;

}

struct gimple_opt_pass pass_ch =

{

 {

  GIMPLE_PASS,

  "ch",                                 /* name */

  gate_ch,                              /* gate */

  copy_loop_headers,                    /* execute */

  NULL,                                 /* sub */

  NULL,                                 /* next */

  0,                                     /* static_pass_number */

  TV_TREE_CH,                           /* tv_id */

  PROP_cfg | PROP_ssa,                  /* properties_required */

  0,                                     /* properties_provided */

  0,                                     /* properties_destroyed */

  0,                                     /* todo_flags_start */

  TODO_cleanup_cfg | TODO_dump_func

  | TODO_verify_ssa                     /* todo_flags_finish */

 }

};