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/* Loop unswitching.

   Copyright (C) 2004, 2005, 2007 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 "timevar.h"

#include "cfgloop.h"

#include "domwalk.h"

#include "params.h"

#include "tree-pass.h"

/* This file implements the loop unswitching, i.e. transformation of loops like

   while (A)

     {

       if (inv)

         B;

       X;

       if (!inv)

         C;

     }

   where inv is the loop invariant, into

   if (inv)

     {

       while (A)

         {

           B;

           X;

         }

     }

   else

     {

       while (A)

         {

           X;

           C;

         }

     }

   Inv is considered invariant iff the values it compares are both invariant;

   tree-ssa-loop-im.c ensures that all the suitable conditions are in this

   shape.  */

static struct loop *tree_unswitch_loop (struct loops *, struct loop *, basic_block,

                                   tree);

static bool tree_unswitch_single_loop (struct loops *, struct loop *, int);

static tree tree_may_unswitch_on (basic_block, struct loop *);

/* Main entry point.  Perform loop unswitching on all suitable LOOPS.  */

unsigned int

tree_ssa_unswitch_loops (struct loops *loops)

{

  int i, num;

  struct loop *loop;

  bool changed = false;

  /* Go through inner loops (only original ones).  */

  num = loops->num;

  for (i = 1; i < num; i++)

    {

      /* Removed loop?  */

      loop = loops->parray[i];

      if (!loop)

        continue;

      if (loop->inner)

        continue;

      changed |= tree_unswitch_single_loop (loops, loop, 0);

    }

  if (changed)

    return TODO_cleanup_cfg;

  return 0;

}

/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its

   basic blocks (for what it means see comments below).  */

static tree

tree_may_unswitch_on (basic_block bb, struct loop *loop)

{

  tree stmt, def, cond, use;

  basic_block def_bb;

  ssa_op_iter iter;

  /* BB must end in a simple conditional jump.  */

  stmt = last_stmt (bb);

  if (!stmt || TREE_CODE (stmt) != COND_EXPR)

    return NULL_TREE;

  /* Condition must be invariant.  */

  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)

    {

      def = SSA_NAME_DEF_STMT (use);

      def_bb = bb_for_stmt (def);

      if (def_bb

          && flow_bb_inside_loop_p (loop, def_bb))

        return NULL_TREE;

    }

  cond = COND_EXPR_COND (stmt);

  /* To keep the things simple, we do not directly remove the conditions,

     but just replace tests with 0/1.  Prevent the infinite loop where we

     would unswitch again on such a condition.  */

  if (integer_zerop (cond) || integer_nonzerop (cond))

    return NULL_TREE;

  return cond;

}

/* Simplifies COND using checks in front of the entry of the LOOP.  Just very

   simplish (sufficient to prevent us from duplicating loop in unswitching

   unnecessarily).  */

static tree

simplify_using_entry_checks (struct loop *loop, tree cond)

{

  edge e = loop_preheader_edge (loop);

  tree stmt;

  while (1)

    {

      stmt = last_stmt (e->src);

      if (stmt

          && TREE_CODE (stmt) == COND_EXPR

          && operand_equal_p (COND_EXPR_COND (stmt), cond, 0))

        return (e->flags & EDGE_TRUE_VALUE

                ? boolean_true_node

                : boolean_false_node);

      if (!single_pred_p (e->src))

        return cond;

      e = single_pred_edge (e->src);

      if (e->src == ENTRY_BLOCK_PTR)

        return cond;

    }

}

/* Unswitch single LOOP.  NUM is number of unswitchings done; we do not allow

   it to grow too much, it is too easy to create example on that the code would

   grow exponentially.  */

static bool

tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num)

{

  basic_block *bbs;

  struct loop *nloop;

  unsigned i;

  tree cond = NULL_TREE, stmt;

  bool changed = false;

  /* Do not unswitch too much.  */

  if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL))

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, ";; Not unswitching anymore, hit max level\n");

      return false;

    }

  /* Only unswitch innermost loops.  */

  if (loop->inner)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, ";; Not unswitching, not innermost loop\n");

      return false;

    }

  /* The loop should not be too large, to limit code growth.  */

  if (tree_num_loop_insns (loop)

      > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, ";; Not unswitching, loop too big\n");

      return false;

    }

  i = 0;

  bbs = get_loop_body (loop);

  while (1)

    {

      /* Find a bb to unswitch on.  */

      for (; i < loop->num_nodes; i++)

        if ((cond = tree_may_unswitch_on (bbs[i], loop)))

          break;

      if (i == loop->num_nodes)

        {

          free (bbs);

          return changed;

        }

      cond = simplify_using_entry_checks (loop, cond);

      stmt = last_stmt (bbs[i]);

      if (integer_nonzerop (cond))

        {

          /* Remove false path.  */

          COND_EXPR_COND (stmt) = boolean_true_node;

          changed = true;

        }

      else if (integer_zerop (cond))

        {

          /* Remove true path.  */

          COND_EXPR_COND (stmt) = boolean_false_node;

          changed = true;

        }

      else

        break;

      update_stmt (stmt);

      i++;

    }

  if (dump_file && (dump_flags & TDF_DETAILS))

    fprintf (dump_file, ";; Unswitching loop\n");

  initialize_original_copy_tables ();

  /* Unswitch the loop on this condition.  */

  nloop = tree_unswitch_loop (loops, loop, bbs[i], cond);

  if (!nloop)

    {

      free_original_copy_tables ();

      free (bbs);

      return changed;

    }

  /* Update the SSA form after unswitching.  */

  update_ssa (TODO_update_ssa);

  free_original_copy_tables ();

  /* Invoke itself on modified loops.  */

  tree_unswitch_single_loop (loops, nloop, num + 1);

  tree_unswitch_single_loop (loops, loop, num + 1);

  free (bbs);

  return true;

}

/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON.  We only support

   unswitching of innermost loops.  COND is the condition determining which

   loop is entered -- the new loop is entered if COND is true.  Returns NULL

   if impossible, new loop otherwise.  */

static struct loop *

tree_unswitch_loop (struct loops *loops, struct loop *loop,

                    basic_block unswitch_on, tree cond)

{

  basic_block condition_bb;

  /* Some sanity checking.  */

  gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));

  gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);

  gcc_assert (loop->inner == NULL);

  return loop_version (loops, loop, unshare_expr (cond),

                       &condition_bb, false);

}