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/* Control flow graph building code for GNU compiler.

   Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,

   1999, 2000, 2001, 2002, 2003, 2004, 2005, 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 "hard-reg-set.h"

#include "basic-block.h"

#include "regs.h"

#include "flags.h"

#include "output.h"

#include "function.h"

#include "except.h"

#include "expr.h"

#include "toplev.h"

#include "timevar.h"

static void make_edges (basic_block, basic_block, int);

static void make_label_edge (sbitmap, basic_block, rtx, int);

static void find_bb_boundaries (basic_block);

static void compute_outgoing_frequencies (basic_block);

/* Return true if insn is something that should be contained inside basic

   block.  */

bool

inside_basic_block_p (const_rtx insn)

{

  switch (GET_CODE (insn))

    {

    case CODE_LABEL:

      /* Avoid creating of basic block for jumptables.  */

      return (NEXT_INSN (insn) == 0

              || !JUMP_P (NEXT_INSN (insn))

              || (GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_VEC

                  && GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_DIFF_VEC));

    case JUMP_INSN:

      return (GET_CODE (PATTERN (insn)) != ADDR_VEC

              && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);

    case CALL_INSN:

    case INSN:

    case DEBUG_INSN:

      return true;

    case BARRIER:

    case NOTE:

      return false;

    default:

      gcc_unreachable ();

    }

}

/* Return true if INSN may cause control flow transfer, so it should be last in

   the basic block.  */

bool

control_flow_insn_p (const_rtx insn)

{

  switch (GET_CODE (insn))

    {

    case NOTE:

    case CODE_LABEL:

    case DEBUG_INSN:

      return false;

    case JUMP_INSN:

      /* Jump insn always causes control transfer except for tablejumps.  */

      return (GET_CODE (PATTERN (insn)) != ADDR_VEC

              && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);

    case CALL_INSN:

      /* Noreturn and sibling call instructions terminate the basic blocks

         (but only if they happen unconditionally).  */

      if ((SIBLING_CALL_P (insn)

           || find_reg_note (insn, REG_NORETURN, 0))

          && GET_CODE (PATTERN (insn)) != COND_EXEC)

        return true;

      /* Call insn may return to the nonlocal goto handler.  */

      if (can_nonlocal_goto (insn))

        return true;

      break;

    case INSN:

      /* Treat trap instructions like noreturn calls (same provision).  */

      if (GET_CODE (PATTERN (insn)) == TRAP_IF

          && XEXP (PATTERN (insn), 0) == const1_rtx)

        return true;

      if (!flag_non_call_exceptions)

        return false;

      break;

    case BARRIER:

      /* It is nonsense to reach barrier when looking for the

         end of basic block, but before dead code is eliminated

         this may happen.  */

      return false;

    default:

      gcc_unreachable ();

    }

  return can_throw_internal (insn);

}

/* Create an edge between two basic blocks.  FLAGS are auxiliary information

   about the edge that is accumulated between calls.  */

/* Create an edge from a basic block to a label.  */

static void

make_label_edge (sbitmap edge_cache, basic_block src, rtx label, int flags)

{

  gcc_assert (LABEL_P (label));

  /* If the label was never emitted, this insn is junk, but avoid a

     crash trying to refer to BLOCK_FOR_INSN (label).  This can happen

     as a result of a syntax error and a diagnostic has already been

     printed.  */

  if (INSN_UID (label) == 0)

    return;

  cached_make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);

}

/* Create the edges generated by INSN in REGION.  */

void

rtl_make_eh_edge (sbitmap edge_cache, basic_block src, rtx insn)

{

  eh_landing_pad lp = get_eh_landing_pad_from_rtx (insn);

  if (lp)

    {

      rtx label = lp->landing_pad;

      /* During initial rtl generation, use the post_landing_pad.  */

      if (label == NULL)

        {

          gcc_assert (lp->post_landing_pad);

          label = label_rtx (lp->post_landing_pad);

        }

      make_label_edge (edge_cache, src, label,

                       EDGE_ABNORMAL | EDGE_EH

                       | (CALL_P (insn) ? EDGE_ABNORMAL_CALL : 0));

    }

}

/* States of basic block as seen by find_many_sub_basic_blocks.  */

enum state {

  /* Basic blocks created via split_block belong to this state.

     make_edges will examine these basic blocks to see if we need to

     create edges going out of them.  */

  BLOCK_NEW = 0,

  /* Basic blocks that do not need examining belong to this state.

     These blocks will be left intact.  In particular, make_edges will

     not create edges going out of these basic blocks.  */

  BLOCK_ORIGINAL,

  /* Basic blocks that may need splitting (due to a label appearing in

     the middle, etc) belong to this state.  After splitting them,

     make_edges will create edges going out of them as needed.  */

  BLOCK_TO_SPLIT

};

#define STATE(BB) (enum state) ((size_t) (BB)->aux)

#define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))

/* Used internally by purge_dead_tablejump_edges, ORed into state.  */

#define BLOCK_USED_BY_TABLEJUMP         32

#define FULL_STATE(BB) ((size_t) (BB)->aux)

/* Identify the edges going out of basic blocks between MIN and MAX,

   inclusive, that have their states set to BLOCK_NEW or

   BLOCK_TO_SPLIT.

   UPDATE_P should be nonzero if we are updating CFG and zero if we

   are building CFG from scratch.  */

static void

make_edges (basic_block min, basic_block max, int update_p)

{

  basic_block bb;

  sbitmap edge_cache = NULL;

  /* Heavy use of computed goto in machine-generated code can lead to

     nearly fully-connected CFGs.  In that case we spend a significant

     amount of time searching the edge lists for duplicates.  */

  if (forced_labels || cfun->cfg->max_jumptable_ents > 100)

    edge_cache = sbitmap_alloc (last_basic_block);

  /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block

     is always the entry.  */

  if (min == ENTRY_BLOCK_PTR->next_bb)

    make_edge (ENTRY_BLOCK_PTR, min, EDGE_FALLTHRU);

  FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)

    {

      rtx insn, x;

      enum rtx_code code;

      edge e;

      edge_iterator ei;

      if (STATE (bb) == BLOCK_ORIGINAL)

        continue;

      /* If we have an edge cache, cache edges going out of BB.  */

      if (edge_cache)

        {

          sbitmap_zero (edge_cache);

          if (update_p)

            {

              FOR_EACH_EDGE (e, ei, bb->succs)

                if (e->dest != EXIT_BLOCK_PTR)

                  SET_BIT (edge_cache, e->dest->index);

            }

        }

      if (LABEL_P (BB_HEAD (bb))

          && LABEL_ALT_ENTRY_P (BB_HEAD (bb)))

        cached_make_edge (NULL, ENTRY_BLOCK_PTR, bb, 0);

      /* Examine the last instruction of the block, and discover the

         ways we can leave the block.  */

      insn = BB_END (bb);

      code = GET_CODE (insn);

      /* A branch.  */

      if (code == JUMP_INSN)

        {

          rtx tmp;

          /* Recognize a non-local goto as a branch outside the

             current function.  */

          if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))

            ;

          /* Recognize a tablejump and do the right thing.  */

          else if (tablejump_p (insn, NULL, &tmp))

            {

              rtvec vec;

              int j;

              if (GET_CODE (PATTERN (tmp)) == ADDR_VEC)

                vec = XVEC (PATTERN (tmp), 0);

              else

                vec = XVEC (PATTERN (tmp), 1);

              for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)

                make_label_edge (edge_cache, bb,

                                 XEXP (RTVEC_ELT (vec, j), 0), 0);

              /* Some targets (eg, ARM) emit a conditional jump that also

                 contains the out-of-range target.  Scan for these and

                 add an edge if necessary.  */

              if ((tmp = single_set (insn)) != NULL

                  && SET_DEST (tmp) == pc_rtx

                  && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE

                  && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)

                make_label_edge (edge_cache, bb,

                                 XEXP (XEXP (SET_SRC (tmp), 2), 0), 0);

            }

          /* If this is a computed jump, then mark it as reaching

             everything on the forced_labels list.  */

          else if (computed_jump_p (insn))

            {

              for (x = forced_labels; x; x = XEXP (x, 1))

                make_label_edge (edge_cache, bb, XEXP (x, 0), EDGE_ABNORMAL);

            }

          /* Returns create an exit out.  */

          else if (returnjump_p (insn))

            cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, 0);

          /* Recognize asm goto and do the right thing.  */

          else if ((tmp = extract_asm_operands (PATTERN (insn))) != NULL)

            {

              int i, n = ASM_OPERANDS_LABEL_LENGTH (tmp);

              for (i = 0; i < n; ++i)

                make_label_edge (edge_cache, bb,

                                 XEXP (ASM_OPERANDS_LABEL (tmp, i), 0), 0);

            }

          /* Otherwise, we have a plain conditional or unconditional jump.  */

          else

            {

              gcc_assert (JUMP_LABEL (insn));

              make_label_edge (edge_cache, bb, JUMP_LABEL (insn), 0);

            }

        }

      /* If this is a sibling call insn, then this is in effect a combined call

         and return, and so we need an edge to the exit block.  No need to

         worry about EH edges, since we wouldn't have created the sibling call

         in the first place.  */

      if (code == CALL_INSN && SIBLING_CALL_P (insn))

        cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR,

                          EDGE_SIBCALL | EDGE_ABNORMAL);

      /* If this is a CALL_INSN, then mark it as reaching the active EH

         handler for this CALL_INSN.  If we're handling non-call

         exceptions then any insn can reach any of the active handlers.

         Also mark the CALL_INSN as reaching any nonlocal goto handler.  */

      else if (code == CALL_INSN || flag_non_call_exceptions)

        {

          /* Add any appropriate EH edges.  */

          rtl_make_eh_edge (edge_cache, bb, insn);

          if (code == CALL_INSN && nonlocal_goto_handler_labels)

            {

              /* ??? This could be made smarter: in some cases it's possible

                 to tell that certain calls will not do a nonlocal goto.

                 For example, if the nested functions that do the nonlocal

                 gotos do not have their addresses taken, then only calls to

                 those functions or to other nested functions that use them

                 could possibly do nonlocal gotos.  */

              if (can_nonlocal_goto (insn))

                for (x = nonlocal_goto_handler_labels; x; x = XEXP (x, 1))

                  make_label_edge (edge_cache, bb, XEXP (x, 0),

                                   EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);

            }

        }

      /* Find out if we can drop through to the next block.  */

      insn = NEXT_INSN (insn);

      e = find_edge (bb, EXIT_BLOCK_PTR);

      if (e && e->flags & EDGE_FALLTHRU)

        insn = NULL;

      while (insn

             && NOTE_P (insn)

             && NOTE_KIND (insn) != NOTE_INSN_BASIC_BLOCK)

        insn = NEXT_INSN (insn);

      if (!insn)

        cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, EDGE_FALLTHRU);

      else if (bb->next_bb != EXIT_BLOCK_PTR)

        {

          if (insn == BB_HEAD (bb->next_bb))

            cached_make_edge (edge_cache, bb, bb->next_bb, EDGE_FALLTHRU);

        }

    }

  if (edge_cache)

    sbitmap_vector_free (edge_cache);

}

static void

mark_tablejump_edge (rtx label)

{

  basic_block bb;

  gcc_assert (LABEL_P (label));

  /* See comment in make_label_edge.  */

  if (INSN_UID (label) == 0)

    return;

  bb = BLOCK_FOR_INSN (label);

  SET_STATE (bb, FULL_STATE (bb) | BLOCK_USED_BY_TABLEJUMP);

}

static void

purge_dead_tablejump_edges (basic_block bb, rtx table)

{

  rtx insn = BB_END (bb), tmp;

  rtvec vec;

  int j;

  edge_iterator ei;

  edge e;

  if (GET_CODE (PATTERN (table)) == ADDR_VEC)

    vec = XVEC (PATTERN (table), 0);

  else

    vec = XVEC (PATTERN (table), 1);

  for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)

    mark_tablejump_edge (XEXP (RTVEC_ELT (vec, j), 0));

  /* Some targets (eg, ARM) emit a conditional jump that also

     contains the out-of-range target.  Scan for these and

     add an edge if necessary.  */

  if ((tmp = single_set (insn)) != NULL

       && SET_DEST (tmp) == pc_rtx

       && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE

       && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)

    mark_tablejump_edge (XEXP (XEXP (SET_SRC (tmp), 2), 0));

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

    {

      if (FULL_STATE (e->dest) & BLOCK_USED_BY_TABLEJUMP)

        SET_STATE (e->dest, FULL_STATE (e->dest)

                            & ~(size_t) BLOCK_USED_BY_TABLEJUMP);

      else if (!(e->flags & (EDGE_ABNORMAL | EDGE_EH)))

        {

          remove_edge (e);

          continue;

        }

      ei_next (&ei);

    }

}

/* Scan basic block BB for possible BB boundaries inside the block

   and create new basic blocks in the progress.  */

static void

find_bb_boundaries (basic_block bb)

{

  basic_block orig_bb = bb;

  rtx insn = BB_HEAD (bb);

  rtx end = BB_END (bb), x;

  rtx table;

  rtx flow_transfer_insn = NULL_RTX;

  edge fallthru = NULL;

  if (insn == BB_END (bb))

    return;

  if (LABEL_P (insn))

    insn = NEXT_INSN (insn);

  /* Scan insn chain and try to find new basic block boundaries.  */

  while (1)

    {

      enum rtx_code code = GET_CODE (insn);

      /* In case we've previously seen an insn that effects a control

         flow transfer, split the block.  */

      if ((flow_transfer_insn || code == CODE_LABEL)

          && inside_basic_block_p (insn))

        {

          fallthru = split_block (bb, PREV_INSN (insn));

          if (flow_transfer_insn)

            {

              BB_END (bb) = flow_transfer_insn;

              /* Clean up the bb field for the insns between the blocks.  */

              for (x = NEXT_INSN (flow_transfer_insn);

                   x != BB_HEAD (fallthru->dest);

                   x = NEXT_INSN (x))

                if (!BARRIER_P (x))

                  set_block_for_insn (x, NULL);

            }

          bb = fallthru->dest;

          remove_edge (fallthru);

          flow_transfer_insn = NULL_RTX;

          if (code == CODE_LABEL && LABEL_ALT_ENTRY_P (insn))

            make_edge (ENTRY_BLOCK_PTR, bb, 0);

        }

      else if (code == BARRIER)

        {

          /* __builtin_unreachable () may cause a barrier to be emitted in

             the middle of a BB.  We need to split it in the same manner as

             if the barrier were preceded by a control_flow_insn_p insn.  */

          if (!flow_transfer_insn)

            flow_transfer_insn = prev_nonnote_insn_bb (insn);

        }

      if (control_flow_insn_p (insn))

        flow_transfer_insn = insn;

      if (insn == end)

        break;

      insn = NEXT_INSN (insn);

    }

  /* In case expander replaced normal insn by sequence terminating by

     return and barrier, or possibly other sequence not behaving like

     ordinary jump, we need to take care and move basic block boundary.  */

  if (flow_transfer_insn)

    {

      BB_END (bb) = flow_transfer_insn;

      /* Clean up the bb field for the insns that do not belong to BB.  */

      x = flow_transfer_insn;

      while (x != end)

        {

          x = NEXT_INSN (x);

          if (!BARRIER_P (x))

            set_block_for_insn (x, NULL);

        }

    }

  /* We've possibly replaced the conditional jump by conditional jump

     followed by cleanup at fallthru edge, so the outgoing edges may

     be dead.  */

  purge_dead_edges (bb);

  /* purge_dead_edges doesn't handle tablejump's, but if we have split the

     basic block, we might need to kill some edges.  */

  if (bb != orig_bb && tablejump_p (BB_END (bb), NULL, &table))

    purge_dead_tablejump_edges (bb, table);

}

/*  Assume that frequency of basic block B is known.  Compute frequencies

    and probabilities of outgoing edges.  */

static void

compute_outgoing_frequencies (basic_block b)

{

  edge e, f;

  edge_iterator ei;

  if (EDGE_COUNT (b->succs) == 2)

    {

      rtx note = find_reg_note (BB_END (b), REG_BR_PROB, NULL);

      int probability;

      if (note)

        {

          probability = INTVAL (XEXP (note, 0));

          e = BRANCH_EDGE (b);

          e->probability = probability;

          e->count = ((b->count * probability + REG_BR_PROB_BASE / 2)

                      / REG_BR_PROB_BASE);

          f = FALLTHRU_EDGE (b);

          f->probability = REG_BR_PROB_BASE - probability;

          f->count = b->count - e->count;

          return;

        }

    }

  if (single_succ_p (b))

    {

      e = single_succ_edge (b);

      e->probability = REG_BR_PROB_BASE;

      e->count = b->count;

      return;

    }

  guess_outgoing_edge_probabilities (b);

  if (b->count)

    FOR_EACH_EDGE (e, ei, b->succs)

      e->count = ((b->count * e->probability + REG_BR_PROB_BASE / 2)

                  / REG_BR_PROB_BASE);

}

/* Assume that some pass has inserted labels or control flow

   instructions within a basic block.  Split basic blocks as needed

   and create edges.  */

void

find_many_sub_basic_blocks (sbitmap blocks)

{

  basic_block bb, min, max;

  FOR_EACH_BB (bb)

    SET_STATE (bb,

               TEST_BIT (blocks, bb->index) ? BLOCK_TO_SPLIT : BLOCK_ORIGINAL);

  FOR_EACH_BB (bb)

    if (STATE (bb) == BLOCK_TO_SPLIT)

      find_bb_boundaries (bb);

  FOR_EACH_BB (bb)

    if (STATE (bb) != BLOCK_ORIGINAL)

      break;

  min = max = bb;

  for (; bb != EXIT_BLOCK_PTR; bb = bb->next_bb)

    if (STATE (bb) != BLOCK_ORIGINAL)

      max = bb;

  /* Now re-scan and wire in all edges.  This expect simple (conditional)

     jumps at the end of each new basic blocks.  */

  make_edges (min, max, 1);

  /* Update branch probabilities.  Expect only (un)conditional jumps

     to be created with only the forward edges.  */

  if (profile_status != PROFILE_ABSENT)

    FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)

      {

        edge e;

        edge_iterator ei;

        if (STATE (bb) == BLOCK_ORIGINAL)

          continue;

        if (STATE (bb) == BLOCK_NEW)

          {

            bb->count = 0;

            bb->frequency = 0;

            FOR_EACH_EDGE (e, ei, bb->preds)

              {

                bb->count += e->count;

                bb->frequency += EDGE_FREQUENCY (e);

              }

          }

        compute_outgoing_frequencies (bb);

      }

  FOR_EACH_BB (bb)

    SET_STATE (bb, 0);

}