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/* Code sinking for trees

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

   Free Software Foundation, Inc.

   Contributed by Daniel Berlin <dan@dberlin.org>

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 "basic-block.h"

#include "gimple-pretty-print.h"

#include "tree-inline.h"

#include "tree-flow.h"

#include "gimple.h"

#include "tree-dump.h"

#include "timevar.h"

#include "fibheap.h"

#include "hashtab.h"

#include "tree-iterator.h"

#include "alloc-pool.h"

#include "tree-pass.h"

#include "flags.h"

#include "bitmap.h"

#include "langhooks.h"

#include "cfgloop.h"

#include "params.h"

/* TODO:

   1. Sinking store only using scalar promotion (IE without moving the RHS):

   *q = p;

   p = p + 1;

   if (something)

     *q = <not p>;

   else

     y = *q;

   should become

   sinktemp = p;

   p = p + 1;

   if (something)

     *q = <not p>;

   else

   {

     *q = sinktemp;

     y = *q

   }

   Store copy propagation will take care of the store elimination above.

   2. Sinking using Partial Dead Code Elimination.  */

static struct

{

  /* The number of statements sunk down the flowgraph by code sinking.  */

  int sunk;

} sink_stats;

/* Given a PHI, and one of its arguments (DEF), find the edge for

   that argument and return it.  If the argument occurs twice in the PHI node,

   we return NULL.  */

static basic_block

find_bb_for_arg (gimple phi, tree def)

{

  size_t i;

  bool foundone = false;

  basic_block result = NULL;

  for (i = 0; i < gimple_phi_num_args (phi); i++)

    if (PHI_ARG_DEF (phi, i) == def)

      {

        if (foundone)

          return NULL;

        foundone = true;

        result = gimple_phi_arg_edge (phi, i)->src;

      }

  return result;

}

/* When the first immediate use is in a statement, then return true if all

   immediate uses in IMM are in the same statement.

   We could also do the case where  the first immediate use is in a phi node,

   and all the other uses are in phis in the same basic block, but this

   requires some expensive checking later (you have to make sure no def/vdef

   in the statement occurs for multiple edges in the various phi nodes it's

   used in, so that you only have one place you can sink it to.  */

static bool

all_immediate_uses_same_place (gimple stmt)

{

  gimple firstuse = NULL;

  ssa_op_iter op_iter;

  imm_use_iterator imm_iter;

  use_operand_p use_p;

  tree var;

  FOR_EACH_SSA_TREE_OPERAND (var, stmt, op_iter, SSA_OP_ALL_DEFS)

    {

      FOR_EACH_IMM_USE_FAST (use_p, imm_iter, var)

        {

          if (is_gimple_debug (USE_STMT (use_p)))

            continue;

          if (firstuse == NULL)

            firstuse = USE_STMT (use_p);

          else

            if (firstuse != USE_STMT (use_p))

              return false;

        }

    }

  return true;

}

/* Some global stores don't necessarily have VDEF's of global variables,

   but we still must avoid moving them around.  */

bool

is_hidden_global_store (gimple stmt)

{

  /* Check virtual definitions.  If we get here, the only virtual

     definitions we should see are those generated by assignment or call

     statements.  */

  if (gimple_vdef (stmt))

    {

      tree lhs;

      gcc_assert (is_gimple_assign (stmt) || is_gimple_call (stmt));

      /* Note that we must not check the individual virtual operands

         here.  In particular, if this is an aliased store, we could

         end up with something like the following (SSA notation

         redacted for brevity):

                foo (int *p, int i)

                {

                  int x;

                  p_1 = (i_2 > 3) ? &x : p;

                  # x_4 = VDEF <x_3>

                  *p_1 = 5;

                  return 2;

                }

         Notice that the store to '*p_1' should be preserved, if we

         were to check the virtual definitions in that store, we would

         not mark it needed.  This is because 'x' is not a global

         variable.

         Therefore, we check the base address of the LHS.  If the

         address is a pointer, we check if its name tag or symbol tag is

         a global variable.  Otherwise, we check if the base variable

         is a global.  */

      lhs = gimple_get_lhs (stmt);

      if (REFERENCE_CLASS_P (lhs))

        lhs = get_base_address (lhs);

      if (lhs == NULL_TREE)

        {

          /* If LHS is NULL, it means that we couldn't get the base

             address of the reference.  In which case, we should not

             move this store.  */

          return true;

        }

      else if (DECL_P (lhs))

        {

          /* If the store is to a global symbol, we need to keep it.  */

          if (is_global_var (lhs))

            return true;

        }

      else if (INDIRECT_REF_P (lhs)

               || TREE_CODE (lhs) == MEM_REF

               || TREE_CODE (lhs) == TARGET_MEM_REF)

        return ptr_deref_may_alias_global_p (TREE_OPERAND (lhs, 0));

      else if (CONSTANT_CLASS_P (lhs))

        return true;

      else

        gcc_unreachable ();

    }

  return false;

}

/* Find the nearest common dominator of all of the immediate uses in IMM.  */

static basic_block

nearest_common_dominator_of_uses (gimple stmt, bool *debug_stmts)

{

  bitmap blocks = BITMAP_ALLOC (NULL);

  basic_block commondom;

  unsigned int j;

  bitmap_iterator bi;

  ssa_op_iter op_iter;

  imm_use_iterator imm_iter;

  use_operand_p use_p;

  tree var;

  bitmap_clear (blocks);

  FOR_EACH_SSA_TREE_OPERAND (var, stmt, op_iter, SSA_OP_ALL_DEFS)

    {

      FOR_EACH_IMM_USE_FAST (use_p, imm_iter, var)

        {

          gimple usestmt = USE_STMT (use_p);

          basic_block useblock;

          if (gimple_code (usestmt) == GIMPLE_PHI)

            {

              int idx = PHI_ARG_INDEX_FROM_USE (use_p);

              useblock = gimple_phi_arg_edge (usestmt, idx)->src;

            }

          else if (is_gimple_debug (usestmt))

            {

              *debug_stmts = true;

              continue;

            }

          else

            {

              useblock = gimple_bb (usestmt);

            }

          /* Short circuit. Nothing dominates the entry block.  */

          if (useblock == ENTRY_BLOCK_PTR)

            {

              BITMAP_FREE (blocks);

              return NULL;

            }

          bitmap_set_bit (blocks, useblock->index);

        }

    }

  commondom = BASIC_BLOCK (bitmap_first_set_bit (blocks));

  EXECUTE_IF_SET_IN_BITMAP (blocks, 0, j, bi)

    commondom = nearest_common_dominator (CDI_DOMINATORS, commondom,

                                          BASIC_BLOCK (j));

  BITMAP_FREE (blocks);

  return commondom;

}

/* Given EARLY_BB and LATE_BB, two blocks in a path through the dominator

   tree, return the best basic block between them (inclusive) to place

   statements.

   We want the most control dependent block in the shallowest loop nest.

   If the resulting block is in a shallower loop nest, then use it.  Else

   only use the resulting block if it has significantly lower execution

   frequency than EARLY_BB to avoid gratutious statement movement.  We

   consider statements with VOPS more desirable to move.

   This pass would obviously benefit from PDO as it utilizes block

   frequencies.  It would also benefit from recomputing frequencies

   if profile data is not available since frequencies often get out

   of sync with reality.  */

static basic_block

select_best_block (basic_block early_bb,

                   basic_block late_bb,

                   gimple stmt)

{

  basic_block best_bb = late_bb;

  basic_block temp_bb = late_bb;

  int threshold;

  while (temp_bb != early_bb)

    {

      /* If we've moved into a lower loop nest, then that becomes

         our best block.  */

      if (temp_bb->loop_depth < best_bb->loop_depth)

        best_bb = temp_bb;

      /* Walk up the dominator tree, hopefully we'll find a shallower

         loop nest.  */

      temp_bb = get_immediate_dominator (CDI_DOMINATORS, temp_bb);

    }

  /* If we found a shallower loop nest, then we always consider that

     a win.  This will always give us the most control dependent block

     within that loop nest.  */

  if (best_bb->loop_depth < early_bb->loop_depth)

    return best_bb;

  /* Get the sinking threshold.  If the statement to be moved has memory

     operands, then increase the threshold by 7% as those are even more

     profitable to avoid, clamping at 100%.  */

  threshold = PARAM_VALUE (PARAM_SINK_FREQUENCY_THRESHOLD);

  if (gimple_vuse (stmt) || gimple_vdef (stmt))

    {

      threshold += 7;

      if (threshold > 100)

        threshold = 100;

    }

  /* If BEST_BB is at the same nesting level, then require it to have

     significantly lower execution frequency to avoid gratutious movement.  */

  if (best_bb->loop_depth == early_bb->loop_depth

      && best_bb->frequency < (early_bb->frequency * threshold / 100.0))

    return best_bb;

  /* No better block found, so return EARLY_BB, which happens to be the

     statement's original block.  */

  return early_bb;

}

/* Given a statement (STMT) and the basic block it is currently in (FROMBB),

   determine the location to sink the statement to, if any.

   Returns true if there is such location; in that case, TOGSI points to the

   statement before that STMT should be moved.  */

static bool

statement_sink_location (gimple stmt, basic_block frombb,

                         gimple_stmt_iterator *togsi)

{

  gimple use;

  use_operand_p one_use = NULL_USE_OPERAND_P;

  basic_block sinkbb;

  use_operand_p use_p;

  def_operand_p def_p;

  ssa_op_iter iter;

  imm_use_iterator imm_iter;

  /* We only can sink assignments.  */

  if (!is_gimple_assign (stmt))

    return false;

  /* We only can sink stmts with a single definition.  */

  def_p = single_ssa_def_operand (stmt, SSA_OP_ALL_DEFS);

  if (def_p == NULL_DEF_OPERAND_P)

    return false;

  /* Return if there are no immediate uses of this stmt.  */

  if (has_zero_uses (DEF_FROM_PTR (def_p)))

    return false;

  /* There are a few classes of things we can't or don't move, some because we

     don't have code to handle it, some because it's not profitable and some

     because it's not legal.

     We can't sink things that may be global stores, at least not without

     calculating a lot more information, because we may cause it to no longer

     be seen by an external routine that needs it depending on where it gets

     moved to.

     We don't want to sink loads from memory.

     We can't sink statements that end basic blocks without splitting the

     incoming edge for the sink location to place it there.

     We can't sink statements that have volatile operands.

     We don't want to sink dead code, so anything with 0 immediate uses is not

     sunk.

     Don't sink BLKmode assignments if current function has any local explicit

     register variables, as BLKmode assignments may involve memcpy or memset

     calls or, on some targets, inline expansion thereof that sometimes need

     to use specific hard registers.

  */

  if (stmt_ends_bb_p (stmt)

      || gimple_has_side_effects (stmt)

      || gimple_has_volatile_ops (stmt)

      || (gimple_vuse (stmt) && !gimple_vdef (stmt))

      || (cfun->has_local_explicit_reg_vars

          && TYPE_MODE (TREE_TYPE (gimple_assign_lhs (stmt))) == BLKmode))

    return false;

  if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (DEF_FROM_PTR (def_p)))

    return false;

  FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES)

    {

      tree use = USE_FROM_PTR (use_p);

      if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (use))

        return false;

    }

  use = NULL;

  /* If stmt is a store the one and only use needs to be the VOP

     merging PHI node.  */

  if (gimple_vdef (stmt))

    {

      FOR_EACH_IMM_USE_FAST (use_p, imm_iter, DEF_FROM_PTR (def_p))

        {

          gimple use_stmt = USE_STMT (use_p);

          /* A killing definition is not a use.  */

          if (gimple_assign_single_p (use_stmt)

              && gimple_vdef (use_stmt)

              && operand_equal_p (gimple_assign_lhs (stmt),

                                  gimple_assign_lhs (use_stmt), 0))

            continue;

          if (gimple_code (use_stmt) != GIMPLE_PHI)

            return false;

          if (use

              && use != use_stmt)

            return false;

          use = use_stmt;

        }

      if (!use)

        return false;

    }

  /* If all the immediate uses are not in the same place, find the nearest

     common dominator of all the immediate uses.  For PHI nodes, we have to

     find the nearest common dominator of all of the predecessor blocks, since

     that is where insertion would have to take place.  */

  else if (!all_immediate_uses_same_place (stmt))

    {

      bool debug_stmts = false;

      basic_block commondom = nearest_common_dominator_of_uses (stmt,

                                                                &debug_stmts);

      if (commondom == frombb)

        return false;

      /* Our common dominator has to be dominated by frombb in order to be a

         trivially safe place to put this statement, since it has multiple

         uses.  */

      if (!dominated_by_p (CDI_DOMINATORS, commondom, frombb))

        return false;

      commondom = select_best_block (frombb, commondom, stmt);

      if (commondom == frombb)

        return false;

      *togsi = gsi_after_labels (commondom);

      return true;

    }

  else

    {

      FOR_EACH_IMM_USE_FAST (one_use, imm_iter, DEF_FROM_PTR (def_p))

        {

          if (is_gimple_debug (USE_STMT (one_use)))

            continue;

          break;

        }

      use = USE_STMT (one_use);

      if (gimple_code (use) != GIMPLE_PHI)

        {

          sinkbb = gimple_bb (use);

          sinkbb = select_best_block (frombb, gimple_bb (use), stmt);

          if (sinkbb == frombb)

            return false;

          *togsi = gsi_for_stmt (use);

          return true;

        }

    }

  sinkbb = find_bb_for_arg (use, DEF_FROM_PTR (def_p));

  /* This can happen if there are multiple uses in a PHI.  */

  if (!sinkbb)

    return false;

  sinkbb = select_best_block (frombb, sinkbb, stmt);

  if (!sinkbb || sinkbb == frombb)

    return false;

  /* If the latch block is empty, don't make it non-empty by sinking

     something into it.  */

  if (sinkbb == frombb->loop_father->latch

      && empty_block_p (sinkbb))

    return false;

  *togsi = gsi_after_labels (sinkbb);

  return true;

}

/* Perform code sinking on BB */

static void

sink_code_in_bb (basic_block bb)

{

  basic_block son;

  gimple_stmt_iterator gsi;

  edge_iterator ei;

  edge e;

  bool last = true;

  /* If this block doesn't dominate anything, there can't be any place to sink

     the statements to.  */

  if (first_dom_son (CDI_DOMINATORS, bb) == NULL)

    goto earlyout;

  /* We can't move things across abnormal edges, so don't try.  */

  FOR_EACH_EDGE (e, ei, bb->succs)

    if (e->flags & EDGE_ABNORMAL)

      goto earlyout;

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

    {

      gimple stmt = gsi_stmt (gsi);

      gimple_stmt_iterator togsi;

      if (!statement_sink_location (stmt, bb, &togsi))

        {

          if (!gsi_end_p (gsi))

            gsi_prev (&gsi);

          last = false;

          continue;

        }

      if (dump_file)

        {

          fprintf (dump_file, "Sinking ");

          print_gimple_stmt (dump_file, stmt, 0, TDF_VOPS);

          fprintf (dump_file, " from bb %d to bb %d\n",

                   bb->index, (gsi_bb (togsi))->index);

        }

      /* Update virtual operands of statements in the path we

         do not sink to.  */

      if (gimple_vdef (stmt))

        {

          imm_use_iterator iter;

          use_operand_p use_p;

          gimple vuse_stmt;

          FOR_EACH_IMM_USE_STMT (vuse_stmt, iter, gimple_vdef (stmt))

            if (gimple_code (vuse_stmt) != GIMPLE_PHI)

              FOR_EACH_IMM_USE_ON_STMT (use_p, iter)

                SET_USE (use_p, gimple_vuse (stmt));

        }

      /* If this is the end of the basic block, we need to insert at the end

         of the basic block.  */

      if (gsi_end_p (togsi))

        gsi_move_to_bb_end (&gsi, gsi_bb (togsi));

      else

        gsi_move_before (&gsi, &togsi);

      sink_stats.sunk++;

      /* If we've just removed the last statement of the BB, the

         gsi_end_p() test below would fail, but gsi_prev() would have

         succeeded, and we want it to succeed.  So we keep track of

         whether we're at the last statement and pick up the new last

         statement.  */

      if (last)

        {

          gsi = gsi_last_bb (bb);

          continue;

        }

      last = false;

      if (!gsi_end_p (gsi))

        gsi_prev (&gsi);

    }

 earlyout:

  for (son = first_dom_son (CDI_POST_DOMINATORS, bb);

       son;

       son = next_dom_son (CDI_POST_DOMINATORS, son))

    {

      sink_code_in_bb (son);

    }

}

/* Perform code sinking.

   This moves code down the flowgraph when we know it would be

   profitable to do so, or it wouldn't increase the number of

   executions of the statement.

   IE given

   a_1 = b + c;

   if (<something>)

   {

   }

   else

   {

     foo (&b, &c);

     a_5 = b + c;

   }

   a_6 = PHI (a_5, a_1);

   USE a_6.

   we'll transform this into:

   if (<something>)

   {

      a_1 = b + c;

   }

   else

   {

      foo (&b, &c);

      a_5 = b + c;

   }

   a_6 = PHI (a_5, a_1);

   USE a_6.

   Note that this reduces the number of computations of a = b + c to 1

   when we take the else edge, instead of 2.

*/

static void

execute_sink_code (void)

{

  loop_optimizer_init (LOOPS_NORMAL);

  connect_infinite_loops_to_exit ();

  memset (&sink_stats, 0, sizeof (sink_stats));

  calculate_dominance_info (CDI_DOMINATORS);

  calculate_dominance_info (CDI_POST_DOMINATORS);

  sink_code_in_bb (EXIT_BLOCK_PTR);

  statistics_counter_event (cfun, "Sunk statements", sink_stats.sunk);

  free_dominance_info (CDI_POST_DOMINATORS);

  remove_fake_exit_edges ();

  loop_optimizer_finalize ();

}

/* Gate and execute functions for PRE.  */

static unsigned int

do_sink (void)

{

  execute_sink_code ();

  return 0;

}

static bool

gate_sink (void)

{

  return flag_tree_sink != 0;

}

struct gimple_opt_pass pass_sink_code =

{

 {

  GIMPLE_PASS,

  "sink",                               /* name */

  gate_sink,                            /* gate */

  do_sink,                              /* execute */

  NULL,                                 /* sub */

  NULL,                                 /* next */

  0,                                     /* static_pass_number */

  TV_TREE_SINK,                         /* tv_id */

  PROP_no_crit_edges | PROP_cfg

    | PROP_ssa,                         /* properties_required */

  0,                                     /* properties_provided */

  0,                                     /* properties_destroyed */

  0,                                     /* todo_flags_start */

  TODO_update_ssa

    | TODO_verify_ssa

    | TODO_verify_flow

    | TODO_ggc_collect                  /* todo_flags_finish */

 }

};