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/* Natural loop analysis code for GNU compiler.

   Copyright (C) 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 "rtl.h"

#include "hard-reg-set.h"

#include "obstack.h"

#include "basic-block.h"

#include "cfgloop.h"

#include "expr.h"

#include "output.h"

#include "graphds.h"

#include "params.h"

struct target_cfgloop default_target_cfgloop;

#if SWITCHABLE_TARGET

struct target_cfgloop *this_target_cfgloop = &default_target_cfgloop;

#endif

/* Checks whether BB is executed exactly once in each LOOP iteration.  */

bool

just_once_each_iteration_p (const struct loop *loop, const_basic_block bb)

{

  /* It must be executed at least once each iteration.  */

  if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb))

    return false;

  /* And just once.  */

  if (bb->loop_father != loop)

    return false;

  /* But this was not enough.  We might have some irreducible loop here.  */

  if (bb->flags & BB_IRREDUCIBLE_LOOP)

    return false;

  return true;

}

/* Marks blocks and edges that are part of non-recognized loops; i.e. we

   throw away all latch edges and mark blocks inside any remaining cycle.

   Everything is a bit complicated due to fact we do not want to do this

   for parts of cycles that only "pass" through some loop -- i.e. for

   each cycle, we want to mark blocks that belong directly to innermost

   loop containing the whole cycle.

   LOOPS is the loop tree.  */

#define LOOP_REPR(LOOP) ((LOOP)->num + last_basic_block)

#define BB_REPR(BB) ((BB)->index + 1)

bool

mark_irreducible_loops (void)

{

  basic_block act;

  struct graph_edge *ge;

  edge e;

  edge_iterator ei;

  int src, dest;

  unsigned depth;

  struct graph *g;

  int num = number_of_loops ();

  struct loop *cloop;

  bool irred_loop_found = false;

  int i;

  gcc_assert (current_loops != NULL);

  /* Reset the flags.  */

  FOR_BB_BETWEEN (act, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb)

    {

      act->flags &= ~BB_IRREDUCIBLE_LOOP;

      FOR_EACH_EDGE (e, ei, act->succs)

        e->flags &= ~EDGE_IRREDUCIBLE_LOOP;

    }

  /* Create the edge lists.  */

  g = new_graph (last_basic_block + num);

  FOR_BB_BETWEEN (act, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb)

    FOR_EACH_EDGE (e, ei, act->succs)

      {

        /* Ignore edges to exit.  */

        if (e->dest == EXIT_BLOCK_PTR)

          continue;

        src = BB_REPR (act);

        dest = BB_REPR (e->dest);

        /* Ignore latch edges.  */

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

            && e->dest->loop_father->latch == act)

          continue;

        /* Edges inside a single loop should be left where they are.  Edges

           to subloop headers should lead to representative of the subloop,

           but from the same place.

           Edges exiting loops should lead from representative

           of the son of nearest common ancestor of the loops in that

           act lays.  */

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

          dest = LOOP_REPR (e->dest->loop_father);

        if (!flow_bb_inside_loop_p (act->loop_father, e->dest))

          {

            depth = 1 + loop_depth (find_common_loop (act->loop_father,

                                                      e->dest->loop_father));

            if (depth == loop_depth (act->loop_father))

              cloop = act->loop_father;

            else

              cloop = VEC_index (loop_p, act->loop_father->superloops, depth);

            src = LOOP_REPR (cloop);

          }

        add_edge (g, src, dest)->data = e;

      }

  /* Find the strongly connected components.  */

  graphds_scc (g, NULL);

  /* Mark the irreducible loops.  */

  for (i = 0; i < g->n_vertices; i++)

    for (ge = g->vertices[i].succ; ge; ge = ge->succ_next)

      {

        edge real = (edge) ge->data;

        /* edge E in graph G is irreducible if it connects two vertices in the

           same scc.  */

        /* All edges should lead from a component with higher number to the

           one with lower one.  */

        gcc_assert (g->vertices[ge->src].component >= g->vertices[ge->dest].component);

        if (g->vertices[ge->src].component != g->vertices[ge->dest].component)

          continue;

        real->flags |= EDGE_IRREDUCIBLE_LOOP;

        irred_loop_found = true;

        if (flow_bb_inside_loop_p (real->src->loop_father, real->dest))

          real->src->flags |= BB_IRREDUCIBLE_LOOP;

      }

  free_graph (g);

  loops_state_set (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS);

  return irred_loop_found;

}

/* Counts number of insns inside LOOP.  */

int

num_loop_insns (const struct loop *loop)

{

  basic_block *bbs, bb;

  unsigned i, ninsns = 0;

  rtx insn;

  bbs = get_loop_body (loop);

  for (i = 0; i < loop->num_nodes; i++)

    {

      bb = bbs[i];

      FOR_BB_INSNS (bb, insn)

        if (NONDEBUG_INSN_P (insn))

          ninsns++;

    }

  free (bbs);

  if (!ninsns)

    ninsns = 1; /* To avoid division by zero.  */

  return ninsns;

}

/* Counts number of insns executed on average per iteration LOOP.  */

int

average_num_loop_insns (const struct loop *loop)

{

  basic_block *bbs, bb;

  unsigned i, binsns, ninsns, ratio;

  rtx insn;

  ninsns = 0;

  bbs = get_loop_body (loop);

  for (i = 0; i < loop->num_nodes; i++)

    {

      bb = bbs[i];

      binsns = 0;

      FOR_BB_INSNS (bb, insn)

        if (NONDEBUG_INSN_P (insn))

          binsns++;

      ratio = loop->header->frequency == 0

              ? BB_FREQ_MAX

              : (bb->frequency * BB_FREQ_MAX) / loop->header->frequency;

      ninsns += binsns * ratio;

    }

  free (bbs);

  ninsns /= BB_FREQ_MAX;

  if (!ninsns)

    ninsns = 1; /* To avoid division by zero.  */

  return ninsns;

}

/* Returns expected number of iterations of LOOP, according to

   measured or guessed profile.  No bounding is done on the

   value.  */

gcov_type

expected_loop_iterations_unbounded (const struct loop *loop)

{

  edge e;

  edge_iterator ei;

  if (loop->latch->count || loop->header->count)

    {

      gcov_type count_in, count_latch, expected;

      count_in = 0;

      count_latch = 0;

      FOR_EACH_EDGE (e, ei, loop->header->preds)

        if (e->src == loop->latch)

          count_latch = e->count;

        else

          count_in += e->count;

      if (count_in == 0)

        expected = count_latch * 2;

      else

        expected = (count_latch + count_in - 1) / count_in;

      return expected;

    }

  else

    {

      int freq_in, freq_latch;

      freq_in = 0;

      freq_latch = 0;

      FOR_EACH_EDGE (e, ei, loop->header->preds)

        if (e->src == loop->latch)

          freq_latch = EDGE_FREQUENCY (e);

        else

          freq_in += EDGE_FREQUENCY (e);

      if (freq_in == 0)

        return freq_latch * 2;

      return (freq_latch + freq_in - 1) / freq_in;

    }

}

/* Returns expected number of LOOP iterations.  The returned value is bounded

   by REG_BR_PROB_BASE.  */

unsigned

expected_loop_iterations (const struct loop *loop)

{

  gcov_type expected = expected_loop_iterations_unbounded (loop);

  return (expected > REG_BR_PROB_BASE ? REG_BR_PROB_BASE : expected);

}

/* Returns the maximum level of nesting of subloops of LOOP.  */

unsigned

get_loop_level (const struct loop *loop)

{

  const struct loop *ploop;

  unsigned mx = 0, l;

  for (ploop = loop->inner; ploop; ploop = ploop->next)

    {

      l = get_loop_level (ploop);

      if (l >= mx)

        mx = l + 1;

    }

  return mx;

}

/* Returns estimate on cost of computing SEQ.  */

static unsigned

seq_cost (const_rtx seq, bool speed)

{

  unsigned cost = 0;

  rtx set;

  for (; seq; seq = NEXT_INSN (seq))

    {

      set = single_set (seq);

      if (set)

        cost += set_rtx_cost (set, speed);

      else

        cost++;

    }

  return cost;

}

/* Initialize the constants for computing set costs.  */

void

init_set_costs (void)

{

  int speed;

  rtx seq;

  rtx reg1 = gen_raw_REG (SImode, FIRST_PSEUDO_REGISTER);

  rtx reg2 = gen_raw_REG (SImode, FIRST_PSEUDO_REGISTER + 1);

  rtx addr = gen_raw_REG (Pmode, FIRST_PSEUDO_REGISTER + 2);

  rtx mem = validize_mem (gen_rtx_MEM (SImode, addr));

  unsigned i;

  target_avail_regs = 0;

  target_clobbered_regs = 0;

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

    if (TEST_HARD_REG_BIT (reg_class_contents[GENERAL_REGS], i)

        && !fixed_regs[i])

      {

        target_avail_regs++;

        if (call_used_regs[i])

          target_clobbered_regs++;

      }

  target_res_regs = 3;

  for (speed = 0; speed < 2; speed++)

     {

      crtl->maybe_hot_insn_p = speed;

      /* Set up the costs for using extra registers:

         1) If not many free registers remain, we should prefer having an

            additional move to decreasing the number of available registers.

            (TARGET_REG_COST).

         2) If no registers are available, we need to spill, which may require

            storing the old value to memory and loading it back

            (TARGET_SPILL_COST).  */

      start_sequence ();

      emit_move_insn (reg1, reg2);

      seq = get_insns ();

      end_sequence ();

      target_reg_cost [speed] = seq_cost (seq, speed);

      start_sequence ();

      emit_move_insn (mem, reg1);

      emit_move_insn (reg2, mem);

      seq = get_insns ();

      end_sequence ();

      target_spill_cost [speed] = seq_cost (seq, speed);

    }

  default_rtl_profile ();

}

/* Estimates cost of increased register pressure caused by making N_NEW new

   registers live around the loop.  N_OLD is the number of registers live

   around the loop.  If CALL_P is true, also take into account that

   call-used registers may be clobbered in the loop body, reducing the

   number of available registers before we spill.  */

unsigned

estimate_reg_pressure_cost (unsigned n_new, unsigned n_old, bool speed,

                            bool call_p)

{

  unsigned cost;

  unsigned regs_needed = n_new + n_old;

  unsigned available_regs = target_avail_regs;

  /* If there is a call in the loop body, the call-clobbered registers

     are not available for loop invariants.  */

  if (call_p)

    available_regs = available_regs - target_clobbered_regs;

  /* If we have enough registers, we should use them and not restrict

     the transformations unnecessarily.  */

  if (regs_needed + target_res_regs <= available_regs)

    return 0;

  if (regs_needed <= available_regs)

    /* If we are close to running out of registers, try to preserve

       them.  */

    cost = target_reg_cost [speed] * n_new;

  else

    /* If we run out of registers, it is very expensive to add another

       one.  */

    cost = target_spill_cost [speed] * n_new;

  if (optimize && (flag_ira_region == IRA_REGION_ALL

                   || flag_ira_region == IRA_REGION_MIXED)

      && number_of_loops () <= (unsigned) IRA_MAX_LOOPS_NUM)

    /* IRA regional allocation deals with high register pressure

       better.  So decrease the cost (to do more accurate the cost

       calculation for IRA, we need to know how many registers lives

       through the loop transparently).  */

    cost /= 2;

  return cost;

}

/* Sets EDGE_LOOP_EXIT flag for all loop exits.  */

void

mark_loop_exit_edges (void)

{

  basic_block bb;

  edge e;

  if (number_of_loops () <= 1)

    return;

  FOR_EACH_BB (bb)

    {

      edge_iterator ei;

      FOR_EACH_EDGE (e, ei, bb->succs)

        {

          if (loop_outer (bb->loop_father)

              && loop_exit_edge_p (bb->loop_father, e))

            e->flags |= EDGE_LOOP_EXIT;

          else

            e->flags &= ~EDGE_LOOP_EXIT;

        }

    }

}