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/* CFG cleanup for trees.

   Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010

   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 "toplev.h"

#include "flags.h"

#include "function.h"

#include "expr.h"

#include "ggc.h"

#include "langhooks.h"

#include "diagnostic.h"

#include "tree-flow.h"

#include "timevar.h"

#include "tree-dump.h"

#include "tree-pass.h"

#include "toplev.h"

#include "except.h"

#include "cfgloop.h"

#include "cfglayout.h"

#include "hashtab.h"

#include "tree-ssa-propagate.h"

#include "tree-scalar-evolution.h"

/* The set of blocks in that at least one of the following changes happened:

   -- the statement at the end of the block was changed

   -- the block was newly created

   -- the set of the predecessors of the block changed

   -- the set of the successors of the block changed

   ??? Maybe we could track these changes separately, since they determine

       what cleanups it makes sense to try on the block.  */

bitmap cfgcleanup_altered_bbs;

/* Remove any fallthru edge from EV.  Return true if an edge was removed.  */

static bool

remove_fallthru_edge (VEC(edge,gc) *ev)

{

  edge_iterator ei;

  edge e;

  FOR_EACH_EDGE (e, ei, ev)

    if ((e->flags & EDGE_FALLTHRU) != 0)

      {

        remove_edge_and_dominated_blocks (e);

        return true;

      }

  return false;

}

/* Disconnect an unreachable block in the control expression starting

   at block BB.  */

static bool

cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)

{

  edge taken_edge;

  bool retval = false;

  gimple stmt = gsi_stmt (gsi);

  tree val;

  if (!single_succ_p (bb))

    {

      edge e;

      edge_iterator ei;

      bool warned;

      location_t loc;

      fold_defer_overflow_warnings ();

      loc = gimple_location (stmt);

      switch (gimple_code (stmt))

        {

        case GIMPLE_COND:

          {

            tree lhs = gimple_cond_lhs (stmt);

            tree rhs = gimple_cond_rhs (stmt);

            /* For conditions try harder and lookup single-argument

               PHI nodes.  Only do so from the same basic-block though

               as other basic-blocks may be dead already.  */

            if (TREE_CODE (lhs) == SSA_NAME

                && !name_registered_for_update_p (lhs))

              {

                gimple def_stmt = SSA_NAME_DEF_STMT (lhs);

                if (gimple_code (def_stmt) == GIMPLE_PHI

                    && gimple_phi_num_args (def_stmt) == 1

                    && gimple_bb (def_stmt) == gimple_bb (stmt)

                    && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME

                        || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,

                                                                       0))))

                  lhs = PHI_ARG_DEF (def_stmt, 0);

              }

            if (TREE_CODE (rhs) == SSA_NAME

                && !name_registered_for_update_p (rhs))

              {

                gimple def_stmt = SSA_NAME_DEF_STMT (rhs);

                if (gimple_code (def_stmt) == GIMPLE_PHI

                    && gimple_phi_num_args (def_stmt) == 1

                    && gimple_bb (def_stmt) == gimple_bb (stmt)

                    && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME

                        || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,

                                                                       0))))

                  rhs = PHI_ARG_DEF (def_stmt, 0);

              }

            val = fold_binary_loc (loc, gimple_cond_code (stmt),

                                   boolean_type_node, lhs, rhs);

            break;

          }

        case GIMPLE_SWITCH:

          val = gimple_switch_index (stmt);

          break;

        default:

          val = NULL_TREE;

        }

      taken_edge = find_taken_edge (bb, val);

      if (!taken_edge)

        {

          fold_undefer_and_ignore_overflow_warnings ();

          return false;

        }

      /* Remove all the edges except the one that is always executed.  */

      warned = false;

      for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )

        {

          if (e != taken_edge)

            {

              if (!warned)

                {

                  fold_undefer_overflow_warnings

                    (true, stmt, WARN_STRICT_OVERFLOW_CONDITIONAL);

                  warned = true;

                }

              taken_edge->probability += e->probability;

              taken_edge->count += e->count;

              remove_edge_and_dominated_blocks (e);

              retval = true;

            }

          else

            ei_next (&ei);

        }

      if (!warned)

        fold_undefer_and_ignore_overflow_warnings ();

      if (taken_edge->probability > REG_BR_PROB_BASE)

        taken_edge->probability = REG_BR_PROB_BASE;

    }

  else

    taken_edge = single_succ_edge (bb);

  bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);

  gsi_remove (&gsi, true);

  taken_edge->flags = EDGE_FALLTHRU;

  return retval;

}

/* Try to remove superfluous control structures in basic block BB.  Returns

   true if anything changes.  */

static bool

cleanup_control_flow_bb (basic_block bb)

{

  gimple_stmt_iterator gsi;

  bool retval = false;

  gimple stmt;

  /* If the last statement of the block could throw and now cannot,

     we need to prune cfg.  */

  retval |= gimple_purge_dead_eh_edges (bb);

  gsi = gsi_last_bb (bb);

  if (gsi_end_p (gsi))

    return retval;

  stmt = gsi_stmt (gsi);

  if (gimple_code (stmt) == GIMPLE_COND

      || gimple_code (stmt) == GIMPLE_SWITCH)

    retval |= cleanup_control_expr_graph (bb, gsi);

  else if (gimple_code (stmt) == GIMPLE_GOTO

           && TREE_CODE (gimple_goto_dest (stmt)) == ADDR_EXPR

           && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt), 0))

               == LABEL_DECL))

    {

      /* If we had a computed goto which has a compile-time determinable

         destination, then we can eliminate the goto.  */

      edge e;

      tree label;

      edge_iterator ei;

      basic_block target_block;

      /* First look at all the outgoing edges.  Delete any outgoing

         edges which do not go to the right block.  For the one

         edge which goes to the right block, fix up its flags.  */

      label = TREE_OPERAND (gimple_goto_dest (stmt), 0);

      target_block = label_to_block (label);

      for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )

        {

          if (e->dest != target_block)

            remove_edge_and_dominated_blocks (e);

          else

            {

              /* Turn off the EDGE_ABNORMAL flag.  */

              e->flags &= ~EDGE_ABNORMAL;

              /* And set EDGE_FALLTHRU.  */

              e->flags |= EDGE_FALLTHRU;

              ei_next (&ei);

            }

        }

      bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);

      bitmap_set_bit (cfgcleanup_altered_bbs, target_block->index);

      /* Remove the GOTO_EXPR as it is not needed.  The CFG has all the

         relevant information we need.  */

      gsi_remove (&gsi, true);

      retval = true;

    }

  /* Check for indirect calls that have been turned into

     noreturn calls.  */

  else if (is_gimple_call (stmt)

           && gimple_call_noreturn_p (stmt)

           && remove_fallthru_edge (bb->succs))

    retval = true;

  return retval;

}

/* Return true if basic block BB does nothing except pass control

   flow to another block and that we can safely insert a label at

   the start of the successor block.

   As a precondition, we require that BB be not equal to

   ENTRY_BLOCK_PTR.  */

static bool

tree_forwarder_block_p (basic_block bb, bool phi_wanted)

{

  gimple_stmt_iterator gsi;

  location_t locus;

  /* BB must have a single outgoing edge.  */

  if (single_succ_p (bb) != 1

      /* If PHI_WANTED is false, BB must not have any PHI nodes.

         Otherwise, BB must have PHI nodes.  */

      || gimple_seq_empty_p (phi_nodes (bb)) == phi_wanted

      /* BB may not be a predecessor of EXIT_BLOCK_PTR.  */

      || single_succ (bb) == EXIT_BLOCK_PTR

      /* Nor should this be an infinite loop.  */

      || single_succ (bb) == bb

      /* BB may not have an abnormal outgoing edge.  */

      || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))

    return false;

#if ENABLE_CHECKING

  gcc_assert (bb != ENTRY_BLOCK_PTR);

#endif

  locus = single_succ_edge (bb)->goto_locus;

  /* There should not be an edge coming from entry, or an EH edge.  */

  {

    edge_iterator ei;

    edge e;

    FOR_EACH_EDGE (e, ei, bb->preds)

      if (e->src == ENTRY_BLOCK_PTR || (e->flags & EDGE_EH))

        return false;

      /* If goto_locus of any of the edges differs, prevent removing

         the forwarder block for -O0.  */

      else if (optimize == 0 && e->goto_locus != locus)

        return false;

  }

  /* Now walk through the statements backward.  We can ignore labels,

     anything else means this is not a forwarder block.  */

  for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))

    {

      gimple stmt = gsi_stmt (gsi);

      switch (gimple_code (stmt))

        {

        case GIMPLE_LABEL:

          if (DECL_NONLOCAL (gimple_label_label (stmt)))

            return false;

          if (optimize == 0 && gimple_location (stmt) != locus)

            return false;

          break;

          /* ??? For now, hope there's a corresponding debug

             assignment at the destination.  */

        case GIMPLE_DEBUG:

          break;

        default:

          return false;

        }

    }

  if (current_loops)

    {

      basic_block dest;

      /* Protect loop latches, headers and preheaders.  */

      if (bb->loop_father->header == bb)

        return false;

      dest = EDGE_SUCC (bb, 0)->dest;

      if (dest->loop_father->header == dest)

        return false;

    }

  return true;

}

/* Return true if BB has at least one abnormal incoming edge.  */

static inline bool

has_abnormal_incoming_edge_p (basic_block bb)

{

  edge e;

  edge_iterator ei;

  FOR_EACH_EDGE (e, ei, bb->preds)

    if (e->flags & EDGE_ABNORMAL)

      return true;

  return false;

}

/* If all the PHI nodes in DEST have alternatives for E1 and E2 and

   those alternatives are equal in each of the PHI nodes, then return

   true, else return false.  */

static bool

phi_alternatives_equal (basic_block dest, edge e1, edge e2)

{

  int n1 = e1->dest_idx;

  int n2 = e2->dest_idx;

  gimple_stmt_iterator gsi;

  for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))

    {

      gimple phi = gsi_stmt (gsi);

      tree val1 = gimple_phi_arg_def (phi, n1);

      tree val2 = gimple_phi_arg_def (phi, n2);

      gcc_assert (val1 != NULL_TREE);

      gcc_assert (val2 != NULL_TREE);

      if (!operand_equal_for_phi_arg_p (val1, val2))

        return false;

    }

  return true;

}

/* Removes forwarder block BB.  Returns false if this failed.  */

static bool

remove_forwarder_block (basic_block bb)

{

  edge succ = single_succ_edge (bb), e, s;

  basic_block dest = succ->dest;

  gimple label;

  edge_iterator ei;

  gimple_stmt_iterator gsi, gsi_to;

  bool can_move_debug_stmts;

  /* We check for infinite loops already in tree_forwarder_block_p.

     However it may happen that the infinite loop is created

     afterwards due to removal of forwarders.  */

  if (dest == bb)

    return false;

  /* If the destination block consists of a nonlocal label or is a

     EH landing pad, do not merge it.  */

  label = first_stmt (dest);

  if (label

      && gimple_code (label) == GIMPLE_LABEL

      && (DECL_NONLOCAL (gimple_label_label (label))

          || EH_LANDING_PAD_NR (gimple_label_label (label)) != 0))

    return false;

  /* If there is an abnormal edge to basic block BB, but not into

     dest, problems might occur during removal of the phi node at out

     of ssa due to overlapping live ranges of registers.

     If there is an abnormal edge in DEST, the problems would occur

     anyway since cleanup_dead_labels would then merge the labels for

     two different eh regions, and rest of exception handling code

     does not like it.

     So if there is an abnormal edge to BB, proceed only if there is

     no abnormal edge to DEST and there are no phi nodes in DEST.  */

  if (has_abnormal_incoming_edge_p (bb)

      && (has_abnormal_incoming_edge_p (dest)

          || !gimple_seq_empty_p (phi_nodes (dest))))

    return false;

  /* If there are phi nodes in DEST, and some of the blocks that are

     predecessors of BB are also predecessors of DEST, check that the

     phi node arguments match.  */

  if (!gimple_seq_empty_p (phi_nodes (dest)))

    {

      FOR_EACH_EDGE (e, ei, bb->preds)

        {

          s = find_edge (e->src, dest);

          if (!s)

            continue;

          if (!phi_alternatives_equal (dest, succ, s))

            return false;

        }

    }

  can_move_debug_stmts = single_pred_p (dest);

  /* Redirect the edges.  */

  for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )

    {

      bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);

      if (e->flags & EDGE_ABNORMAL)

        {

          /* If there is an abnormal edge, redirect it anyway, and

             move the labels to the new block to make it legal.  */

          s = redirect_edge_succ_nodup (e, dest);

        }

      else

        s = redirect_edge_and_branch (e, dest);

      if (s == e)

        {

          /* Create arguments for the phi nodes, since the edge was not

             here before.  */

          for (gsi = gsi_start_phis (dest);

               !gsi_end_p (gsi);

               gsi_next (&gsi))

            {

              gimple phi = gsi_stmt (gsi);

              source_location l = gimple_phi_arg_location_from_edge (phi, succ);

              add_phi_arg (phi, gimple_phi_arg_def (phi, succ->dest_idx), s, l);

            }

        }

    }

  /* Move nonlocal labels and computed goto targets as well as user

     defined labels and labels with an EH landing pad number to the

     new block, so that the redirection of the abnormal edges works,

     jump targets end up in a sane place and debug information for

     labels is retained.  */

  gsi_to = gsi_start_bb (dest);

  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); )

    {

      tree decl;

      label = gsi_stmt (gsi);

      if (is_gimple_debug (label))

        break;

      decl = gimple_label_label (label);

      if (EH_LANDING_PAD_NR (decl) != 0

          || DECL_NONLOCAL (decl)

          || FORCED_LABEL (decl)

          || !DECL_ARTIFICIAL (decl))

        {

          gsi_remove (&gsi, false);

          gsi_insert_before (&gsi_to, label, GSI_SAME_STMT);

        }

      else

        gsi_next (&gsi);

    }

  /* Move debug statements if the destination has just a single

     predecessor.  */

  if (can_move_debug_stmts)

    {

      gsi_to = gsi_after_labels (dest);

      for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); )

        {

          gimple debug = gsi_stmt (gsi);

          if (!is_gimple_debug (debug))

            break;

          gsi_remove (&gsi, false);

          gsi_insert_before (&gsi_to, debug, GSI_SAME_STMT);

        }

    }

  bitmap_set_bit (cfgcleanup_altered_bbs, dest->index);

  /* Update the dominators.  */

  if (dom_info_available_p (CDI_DOMINATORS))

    {

      basic_block dom, dombb, domdest;

      dombb = get_immediate_dominator (CDI_DOMINATORS, bb);

      domdest = get_immediate_dominator (CDI_DOMINATORS, dest);

      if (domdest == bb)

        {

          /* Shortcut to avoid calling (relatively expensive)

             nearest_common_dominator unless necessary.  */

          dom = dombb;

        }

      else

        dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);

      set_immediate_dominator (CDI_DOMINATORS, dest, dom);

    }

  /* And kill the forwarder block.  */

  delete_basic_block (bb);

  return true;

}

/* Split basic blocks on calls in the middle of a basic block that are now

   known not to return, and remove the unreachable code.  */

static bool

split_bbs_on_noreturn_calls (void)

{

  bool changed = false;

  gimple stmt;

  basic_block bb;

  /* Detect cases where a mid-block call is now known not to return.  */

  if (cfun->gimple_df)

    while (VEC_length (gimple, MODIFIED_NORETURN_CALLS (cfun)))

      {

        stmt = VEC_pop (gimple, MODIFIED_NORETURN_CALLS (cfun));

        bb = gimple_bb (stmt);

        /* BB might be deleted at this point, so verify first

           BB is present in the cfg.  */

        if (bb == NULL

            || bb->index < NUM_FIXED_BLOCKS

            || bb->index >= n_basic_blocks

            || BASIC_BLOCK (bb->index) != bb

            || last_stmt (bb) == stmt

            || !gimple_call_noreturn_p (stmt))

          continue;

        changed = true;

        split_block (bb, stmt);

        remove_fallthru_edge (bb->succs);

      }

  return changed;

}

/* If GIMPLE_OMP_RETURN in basic block BB is unreachable, remove it.  */

static bool

cleanup_omp_return (basic_block bb)

{

  gimple stmt = last_stmt (bb);

  basic_block control_bb;

  if (stmt == NULL

      || gimple_code (stmt) != GIMPLE_OMP_RETURN

      || !single_pred_p (bb))

    return false;

  control_bb = single_pred (bb);

  stmt = last_stmt (control_bb);

  if (stmt == NULL || gimple_code (stmt) != GIMPLE_OMP_SECTIONS_SWITCH)

    return false;

  /* The block with the control statement normally has two entry edges -- one

     from entry, one from continue.  If continue is removed, return is

     unreachable, so we remove it here as well.  */

  if (EDGE_COUNT (control_bb->preds) == 2)

    return false;

  gcc_assert (EDGE_COUNT (control_bb->preds) == 1);

  remove_edge_and_dominated_blocks (single_pred_edge (bb));

  return true;

}

/* Tries to cleanup cfg in basic block BB.  Returns true if anything

   changes.  */

static bool

cleanup_tree_cfg_bb (basic_block bb)

{

  bool retval = false;

  if (cleanup_omp_return (bb))

    return true;

  retval = cleanup_control_flow_bb (bb);

  if (tree_forwarder_block_p (bb, false)

      && remove_forwarder_block (bb))

    return true;

  /* Merging the blocks may create new opportunities for folding

     conditional branches (due to the elimination of single-valued PHI

     nodes).  */

  if (single_succ_p (bb)

      && can_merge_blocks_p (bb, single_succ (bb)))

    {

      merge_blocks (bb, single_succ (bb));

      return true;

    }

  return retval;

}

/* Iterate the cfg cleanups, while anything changes.  */

static bool

cleanup_tree_cfg_1 (void)

{

  bool retval = false;

  basic_block bb;

  unsigned i, n;

  retval |= split_bbs_on_noreturn_calls ();

  /* Prepare the worklists of altered blocks.  */

  cfgcleanup_altered_bbs = BITMAP_ALLOC (NULL);

  /* During forwarder block cleanup, we may redirect edges out of

     SWITCH_EXPRs, which can get expensive.  So we want to enable

     recording of edge to CASE_LABEL_EXPR.  */

  start_recording_case_labels ();

  /* Start by iterating over all basic blocks.  We cannot use FOR_EACH_BB,

     since the basic blocks may get removed.  */

  n = last_basic_block;

  for (i = NUM_FIXED_BLOCKS; i < n; i++)

    {

      bb = BASIC_BLOCK (i);

      if (bb)

        retval |= cleanup_tree_cfg_bb (bb);

    }

  /* Now process the altered blocks, as long as any are available.  */

  while (!bitmap_empty_p (cfgcleanup_altered_bbs))

    {

      i = bitmap_first_set_bit (cfgcleanup_altered_bbs);

      bitmap_clear_bit (cfgcleanup_altered_bbs, i);

      if (i < NUM_FIXED_BLOCKS)

        continue;

      bb = BASIC_BLOCK (i);

      if (!bb)

        continue;

      retval |= cleanup_tree_cfg_bb (bb);

      /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn

         calls.  */

      retval |= split_bbs_on_noreturn_calls ();

    }

  end_recording_case_labels ();

  BITMAP_FREE (cfgcleanup_altered_bbs);

  return retval;

}

/* Remove unreachable blocks and other miscellaneous clean up work.

   Return true if the flowgraph was modified, false otherwise.  */

static bool

cleanup_tree_cfg_noloop (void)

{

  bool changed;

  timevar_push (TV_TREE_CLEANUP_CFG);

  /* Iterate until there are no more cleanups left to do.  If any

     iteration changed the flowgraph, set CHANGED to true.

     If dominance information is available, there cannot be any unreachable

     blocks.  */

  if (!dom_info_available_p (CDI_DOMINATORS))

    {

      changed = delete_unreachable_blocks ();

      calculate_dominance_info (CDI_DOMINATORS);

    }

  else

    {

#ifdef ENABLE_CHECKING

      verify_dominators (CDI_DOMINATORS);

#endif

      changed = false;

    }