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/* Optimization of PHI nodes by converting them into straightline code.

   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 "ggc.h"

#include "tree.h"

#include "rtl.h"

#include "flags.h"

#include "tm_p.h"

#include "basic-block.h"

#include "timevar.h"

#include "diagnostic.h"

#include "tree-flow.h"

#include "tree-pass.h"

#include "tree-dump.h"

#include "langhooks.h"

static unsigned int tree_ssa_phiopt (void);

static bool conditional_replacement (basic_block, basic_block,

                                     edge, edge, tree, tree, tree);

static bool value_replacement (basic_block, basic_block,

                               edge, edge, tree, tree, tree);

static bool minmax_replacement (basic_block, basic_block,

                                edge, edge, tree, tree, tree);

static bool abs_replacement (basic_block, basic_block,

                             edge, edge, tree, tree, tree);

static void replace_phi_edge_with_variable (basic_block, edge, tree, tree);

static basic_block *blocks_in_phiopt_order (void);

/* This pass tries to replaces an if-then-else block with an

   assignment.  We have four kinds of transformations.  Some of these

   transformations are also performed by the ifcvt RTL optimizer.

   Conditional Replacement

   -----------------------

   This transformation, implemented in conditional_replacement,

   replaces

     bb0:

      if (cond) goto bb2; else goto bb1;

     bb1:

     bb2:

      x = PHI <0 (bb1), 1 (bb0), ...>;

   with

     bb0:

      x' = cond;

      goto bb2;

     bb2:

      x = PHI <x' (bb0), ...>;

   We remove bb1 as it becomes unreachable.  This occurs often due to

   gimplification of conditionals.

   Value Replacement

   -----------------

   This transformation, implemented in value_replacement, replaces

     bb0:

       if (a != b) goto bb2; else goto bb1;

     bb1:

     bb2:

       x = PHI <a (bb1), b (bb0), ...>;

   with

     bb0:

     bb2:

       x = PHI <b (bb0), ...>;

   This opportunity can sometimes occur as a result of other

   optimizations.

   ABS Replacement

   ---------------

   This transformation, implemented in abs_replacement, replaces

     bb0:

       if (a >= 0) goto bb2; else goto bb1;

     bb1:

       x = -a;

     bb2:

       x = PHI <x (bb1), a (bb0), ...>;

   with

     bb0:

       x' = ABS_EXPR< a >;

     bb2:

       x = PHI <x' (bb0), ...>;

   MIN/MAX Replacement

   -------------------

   This transformation, minmax_replacement replaces

     bb0:

       if (a <= b) goto bb2; else goto bb1;

     bb1:

     bb2:

       x = PHI <b (bb1), a (bb0), ...>;

   with

     bb0:

       x' = MIN_EXPR (a, b)

     bb2:

       x = PHI <x' (bb0), ...>;

   A similar transformation is done for MAX_EXPR.  */

static unsigned int

tree_ssa_phiopt (void)

{

  basic_block bb;

  basic_block *bb_order;

  unsigned n, i;

  bool cfgchanged = false;

  /* Search every basic block for COND_EXPR we may be able to optimize.

     We walk the blocks in order that guarantees that a block with

     a single predecessor is processed before the predecessor.

     This ensures that we collapse inner ifs before visiting the

     outer ones, and also that we do not try to visit a removed

     block.  */

  bb_order = blocks_in_phiopt_order ();

  n = n_basic_blocks - NUM_FIXED_BLOCKS;

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

    {

      tree cond_expr;

      tree phi;

      basic_block bb1, bb2;

      edge e1, e2;

      tree arg0, arg1;

      bb = bb_order[i];

      cond_expr = last_stmt (bb);

      /* Check to see if the last statement is a COND_EXPR.  */

      if (!cond_expr

          || TREE_CODE (cond_expr) != COND_EXPR)

        continue;

      e1 = EDGE_SUCC (bb, 0);

      bb1 = e1->dest;

      e2 = EDGE_SUCC (bb, 1);

      bb2 = e2->dest;

      /* We cannot do the optimization on abnormal edges.  */

      if ((e1->flags & EDGE_ABNORMAL) != 0

          || (e2->flags & EDGE_ABNORMAL) != 0)

       continue;

      /* If either bb1's succ or bb2 or bb2's succ is non NULL.  */

      if (EDGE_COUNT (bb1->succs) == 0

          || bb2 == NULL

          || EDGE_COUNT (bb2->succs) == 0)

        continue;

      /* Find the bb which is the fall through to the other.  */

      if (EDGE_SUCC (bb1, 0)->dest == bb2)

        ;

      else if (EDGE_SUCC (bb2, 0)->dest == bb1)

        {

          basic_block bb_tmp = bb1;

          edge e_tmp = e1;

          bb1 = bb2;

          bb2 = bb_tmp;

          e1 = e2;

          e2 = e_tmp;

        }

      else

        continue;

      e1 = EDGE_SUCC (bb1, 0);

      /* Make sure that bb1 is just a fall through.  */

      if (!single_succ_p (bb1)

          || (e1->flags & EDGE_FALLTHRU) == 0)

        continue;

      /* Also make sure that bb1 only have one predecessor and that it

         is bb.  */

      if (!single_pred_p (bb1)

          || single_pred (bb1) != bb)

        continue;

      phi = phi_nodes (bb2);

      /* Check to make sure that there is only one PHI node.

         TODO: we could do it with more than one iff the other PHI nodes

         have the same elements for these two edges.  */

      if (!phi || PHI_CHAIN (phi) != NULL)

        continue;

      arg0 = PHI_ARG_DEF_TREE (phi, e1->dest_idx);

      arg1 = PHI_ARG_DEF_TREE (phi, e2->dest_idx);

      /* Something is wrong if we cannot find the arguments in the PHI

         node.  */

      gcc_assert (arg0 != NULL && arg1 != NULL);

      /* Do the replacement of conditional if it can be done.  */

      if (conditional_replacement (bb, bb1, e1, e2, phi, arg0, arg1))

        cfgchanged = true;

      else if (value_replacement (bb, bb1, e1, e2, phi, arg0, arg1))

        cfgchanged = true;

      else if (abs_replacement (bb, bb1, e1, e2, phi, arg0, arg1))

        cfgchanged = true;

      else if (minmax_replacement (bb, bb1, e1, e2, phi, arg0, arg1))

        cfgchanged = true;

    }

  free (bb_order);

  /* If the CFG has changed, we should cleanup the CFG. */

  return cfgchanged ? TODO_cleanup_cfg : 0;

}

/* Returns the list of basic blocks in the function in an order that guarantees

   that if a block X has just a single predecessor Y, then Y is after X in the

   ordering.  */

static basic_block *

blocks_in_phiopt_order (void)

{

  basic_block x, y;

  basic_block *order = XNEWVEC (basic_block, n_basic_blocks);

  unsigned n = n_basic_blocks - NUM_FIXED_BLOCKS;

  unsigned np, i;

  sbitmap visited = sbitmap_alloc (last_basic_block);

#define MARK_VISITED(BB) (SET_BIT (visited, (BB)->index)) 

#define VISITED_P(BB) (TEST_BIT (visited, (BB)->index)) 

  sbitmap_zero (visited);

  MARK_VISITED (ENTRY_BLOCK_PTR);

  FOR_EACH_BB (x)

    {

      if (VISITED_P (x))

        continue;

      /* Walk the predecessors of x as long as they have precisely one

         predecessor and add them to the list, so that they get stored

         after x.  */

      for (y = x, np = 1;

           single_pred_p (y) && !VISITED_P (single_pred (y));

           y = single_pred (y))

        np++;

      for (y = x, i = n - np;

           single_pred_p (y) && !VISITED_P (single_pred (y));

           y = single_pred (y), i++)

        {

          order[i] = y;

          MARK_VISITED (y);

        }

      order[i] = y;

      MARK_VISITED (y);

      gcc_assert (i == n - 1);

      n -= np;

    }

  sbitmap_free (visited);

  gcc_assert (n == 0);

  return order;

#undef MARK_VISITED

#undef VISITED_P

}

/* Return TRUE if block BB has no executable statements, otherwise return

   FALSE.  */

bool

empty_block_p (basic_block bb)

{

  block_stmt_iterator bsi;

  /* BB must have no executable statements.  */

  bsi = bsi_start (bb);

  while (!bsi_end_p (bsi)

          && (TREE_CODE (bsi_stmt (bsi)) == LABEL_EXPR

              || IS_EMPTY_STMT (bsi_stmt (bsi))))

    bsi_next (&bsi);

  if (!bsi_end_p (bsi))

    return false;

  return true;

}

/* Replace PHI node element whose edge is E in block BB with variable NEW.

   Remove the edge from COND_BLOCK which does not lead to BB (COND_BLOCK

   is known to have two edges, one of which must reach BB).  */

static void

replace_phi_edge_with_variable (basic_block cond_block,

                                edge e, tree phi, tree new)

{

  basic_block bb = bb_for_stmt (phi);

  basic_block block_to_remove;

  block_stmt_iterator bsi;

  /* Change the PHI argument to new.  */

  SET_USE (PHI_ARG_DEF_PTR (phi, e->dest_idx), new);

  /* Remove the empty basic block.  */

  if (EDGE_SUCC (cond_block, 0)->dest == bb)

    {

      EDGE_SUCC (cond_block, 0)->flags |= EDGE_FALLTHRU;

      EDGE_SUCC (cond_block, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);

      EDGE_SUCC (cond_block, 0)->probability = REG_BR_PROB_BASE;

      EDGE_SUCC (cond_block, 0)->count += EDGE_SUCC (cond_block, 1)->count;

      block_to_remove = EDGE_SUCC (cond_block, 1)->dest;

    }

  else

    {

      EDGE_SUCC (cond_block, 1)->flags |= EDGE_FALLTHRU;

      EDGE_SUCC (cond_block, 1)->flags

        &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);

      EDGE_SUCC (cond_block, 1)->probability = REG_BR_PROB_BASE;

      EDGE_SUCC (cond_block, 1)->count += EDGE_SUCC (cond_block, 0)->count;

      block_to_remove = EDGE_SUCC (cond_block, 0)->dest;

    }

  delete_basic_block (block_to_remove);

  /* Eliminate the COND_EXPR at the end of COND_BLOCK.  */

  bsi = bsi_last (cond_block);

  bsi_remove (&bsi, true);

  if (dump_file && (dump_flags & TDF_DETAILS))

    fprintf (dump_file,

              "COND_EXPR in block %d and PHI in block %d converted to straightline code.\n",

              cond_block->index,

              bb->index);

}

/*  The function conditional_replacement does the main work of doing the

    conditional replacement.  Return true if the replacement is done.

    Otherwise return false.

    BB is the basic block where the replacement is going to be done on.  ARG0

    is argument 0 from PHI.  Likewise for ARG1.  */

static bool

conditional_replacement (basic_block cond_bb, basic_block middle_bb,

                         edge e0, edge e1, tree phi,

                         tree arg0, tree arg1)

{

  tree result;

  tree old_result = NULL;

  tree new, cond;

  block_stmt_iterator bsi;

  edge true_edge, false_edge;

  tree new_var = NULL;

  tree new_var1;

  /* The PHI arguments have the constants 0 and 1, then convert

     it to the conditional.  */

  if ((integer_zerop (arg0) && integer_onep (arg1))

      || (integer_zerop (arg1) && integer_onep (arg0)))

    ;

  else

    return false;

  if (!empty_block_p (middle_bb))

    return false;

  /* If the condition is not a naked SSA_NAME and its type does not

     match the type of the result, then we have to create a new

     variable to optimize this case as it would likely create

     non-gimple code when the condition was converted to the

     result's type.  */

  cond = COND_EXPR_COND (last_stmt (cond_bb));

  result = PHI_RESULT (phi);

  if (TREE_CODE (cond) != SSA_NAME

      && !lang_hooks.types_compatible_p (TREE_TYPE (cond), TREE_TYPE (result)))

    {

      tree tmp;

      if (!COMPARISON_CLASS_P (cond))

        return false;

      tmp = create_tmp_var (TREE_TYPE (cond), NULL);

      add_referenced_var (tmp);

      new_var = make_ssa_name (tmp, NULL);

      old_result = cond;

      cond = new_var;

    }

  /* If the condition was a naked SSA_NAME and the type is not the

     same as the type of the result, then convert the type of the

     condition.  */

  if (!lang_hooks.types_compatible_p (TREE_TYPE (cond), TREE_TYPE (result)))

    cond = fold_convert (TREE_TYPE (result), cond);

  /* We need to know which is the true edge and which is the false

     edge so that we know when to invert the condition below.  */

  extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);

  /* Insert our new statement at the end of conditional block before the

     COND_EXPR.  */

  bsi = bsi_last (cond_bb);

  bsi_insert_before (&bsi, build_empty_stmt (), BSI_NEW_STMT);

  if (old_result)

    {

      tree new1;

      new1 = build2 (TREE_CODE (old_result), TREE_TYPE (old_result),

                     TREE_OPERAND (old_result, 0),

                     TREE_OPERAND (old_result, 1));

      new1 = build2 (MODIFY_EXPR, TREE_TYPE (old_result), new_var, new1);

      SSA_NAME_DEF_STMT (new_var) = new1;

      bsi_insert_after (&bsi, new1, BSI_NEW_STMT);

    }

  new_var1 = duplicate_ssa_name (PHI_RESULT (phi), NULL);

  /* At this point we know we have a COND_EXPR with two successors.

     One successor is BB, the other successor is an empty block which

     falls through into BB.

     There is a single PHI node at the join point (BB) and its arguments

     are constants (0, 1).

     So, given the condition COND, and the two PHI arguments, we can

     rewrite this PHI into non-branching code:

       dest = (COND) or dest = COND'

     We use the condition as-is if the argument associated with the

     true edge has the value one or the argument associated with the

     false edge as the value zero.  Note that those conditions are not

     the same since only one of the outgoing edges from the COND_EXPR

     will directly reach BB and thus be associated with an argument.  */

  if ((e0 == true_edge && integer_onep (arg0))

      || (e0 == false_edge && integer_zerop (arg0))

      || (e1 == true_edge && integer_onep (arg1))

      || (e1 == false_edge && integer_zerop (arg1)))

    {

      new = build2 (MODIFY_EXPR, TREE_TYPE (new_var1), new_var1, cond);

    }

  else

    {

      tree cond1 = invert_truthvalue (cond);

      cond = cond1;

      /* If what we get back is a conditional expression, there is no

          way that it can be gimple.  */

      if (TREE_CODE (cond) == COND_EXPR)

        {

          release_ssa_name (new_var1);

          return false;

        }

      /* If COND is not something we can expect to be reducible to a GIMPLE

         condition, return early.  */

      if (is_gimple_cast (cond))

        cond1 = TREE_OPERAND (cond, 0);

      if (TREE_CODE (cond1) == TRUTH_NOT_EXPR

          && !is_gimple_val (TREE_OPERAND (cond1, 0)))

        {

          release_ssa_name (new_var1);

          return false;

        }

      /* If what we get back is not gimple try to create it as gimple by

         using a temporary variable.  */

      if (is_gimple_cast (cond)

          && !is_gimple_val (TREE_OPERAND (cond, 0)))

        {

          tree op0, tmp, cond_tmp;

          /* Only "real" casts are OK here, not everything that is

             acceptable to is_gimple_cast.  Make sure we don't do

             anything stupid here.  */

          gcc_assert (TREE_CODE (cond) == NOP_EXPR

                      || TREE_CODE (cond) == CONVERT_EXPR);

          op0 = TREE_OPERAND (cond, 0);

          tmp = create_tmp_var (TREE_TYPE (op0), NULL);

          add_referenced_var (tmp);

          cond_tmp = make_ssa_name (tmp, NULL);

          new = build2 (MODIFY_EXPR, TREE_TYPE (cond_tmp), cond_tmp, op0);

          SSA_NAME_DEF_STMT (cond_tmp) = new;

          bsi_insert_after (&bsi, new, BSI_NEW_STMT);

          cond = fold_convert (TREE_TYPE (result), cond_tmp);

        }

      new = build2 (MODIFY_EXPR, TREE_TYPE (new_var1), new_var1, cond);

    }

  bsi_insert_after (&bsi, new, BSI_NEW_STMT);

  SSA_NAME_DEF_STMT (new_var1) = new;

  replace_phi_edge_with_variable (cond_bb, e1, phi, new_var1);

  /* Note that we optimized this PHI.  */

  return true;

}

/*  The function value_replacement does the main work of doing the value

    replacement.  Return true if the replacement is done.  Otherwise return

    false.

    BB is the basic block where the replacement is going to be done on.  ARG0

    is argument 0 from the PHI.  Likewise for ARG1.  */

static bool

value_replacement (basic_block cond_bb, basic_block middle_bb,

                   edge e0, edge e1, tree phi,

                   tree arg0, tree arg1)

{

  tree cond;

  edge true_edge, false_edge;

  /* If the type says honor signed zeros we cannot do this

     optimization.  */

  if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (arg1))))

    return false;

  if (!empty_block_p (middle_bb))

    return false;

  cond = COND_EXPR_COND (last_stmt (cond_bb));

  /* This transformation is only valid for equality comparisons.  */

  if (TREE_CODE (cond) != NE_EXPR && TREE_CODE (cond) != EQ_EXPR)

    return false;

  /* We need to know which is the true edge and which is the false

      edge so that we know if have abs or negative abs.  */

  extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);

  /* At this point we know we have a COND_EXPR with two successors.

     One successor is BB, the other successor is an empty block which

     falls through into BB.

     The condition for the COND_EXPR is known to be NE_EXPR or EQ_EXPR.

     There is a single PHI node at the join point (BB) with two arguments.

     We now need to verify that the two arguments in the PHI node match

     the two arguments to the equality comparison.  */

  if ((operand_equal_for_phi_arg_p (arg0, TREE_OPERAND (cond, 0))

       && operand_equal_for_phi_arg_p (arg1, TREE_OPERAND (cond, 1)))

      || (operand_equal_for_phi_arg_p (arg1, TREE_OPERAND (cond, 0))

          && operand_equal_for_phi_arg_p (arg0, TREE_OPERAND (cond, 1))))

    {

      edge e;

      tree arg;

      /* For NE_EXPR, we want to build an assignment result = arg where

         arg is the PHI argument associated with the true edge.  For

         EQ_EXPR we want the PHI argument associated with the false edge.  */

      e = (TREE_CODE (cond) == NE_EXPR ? true_edge : false_edge);

      /* Unfortunately, E may not reach BB (it may instead have gone to

         OTHER_BLOCK).  If that is the case, then we want the single outgoing

         edge from OTHER_BLOCK which reaches BB and represents the desired

         path from COND_BLOCK.  */

      if (e->dest == middle_bb)

        e = single_succ_edge (e->dest);

      /* Now we know the incoming edge to BB that has the argument for the

         RHS of our new assignment statement.  */

      if (e0 == e)

        arg = arg0;

      else

        arg = arg1;

      replace_phi_edge_with_variable (cond_bb, e1, phi, arg);

      /* Note that we optimized this PHI.  */

      return true;

    }

  return false;

}

/*  The function minmax_replacement does the main work of doing the minmax

    replacement.  Return true if the replacement is done.  Otherwise return

    false.

    BB is the basic block where the replacement is going to be done on.  ARG0

    is argument 0 from the PHI.  Likewise for ARG1.  */

static bool

minmax_replacement (basic_block cond_bb, basic_block middle_bb,

                    edge e0, edge e1, tree phi,

                    tree arg0, tree arg1)

{

  tree result, type;

  tree cond, new;

  edge true_edge, false_edge;

  enum tree_code cmp, minmax, ass_code;

  tree smaller, larger, arg_true, arg_false;

  block_stmt_iterator bsi, bsi_from;

  type = TREE_TYPE (PHI_RESULT (phi));

  /* The optimization may be unsafe due to NaNs.  */

  if (HONOR_NANS (TYPE_MODE (type)))

    return false;

  cond = COND_EXPR_COND (last_stmt (cond_bb));

  cmp = TREE_CODE (cond);

  result = PHI_RESULT (phi);

  /* This transformation is only valid for order comparisons.  Record which

     operand is smaller/larger if the result of the comparison is true.  */

  if (cmp == LT_EXPR || cmp == LE_EXPR)

    {

      smaller = TREE_OPERAND (cond, 0);

      larger = TREE_OPERAND (cond, 1);

    }

  else if (cmp == GT_EXPR || cmp == GE_EXPR)

    {

      smaller = TREE_OPERAND (cond, 1);

      larger = TREE_OPERAND (cond, 0);

    }

  else

    return false;

  /* We need to know which is the true edge and which is the false

      edge so that we know if have abs or negative abs.  */

  extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);

  /* Forward the edges over the middle basic block.  */

  if (true_edge->dest == middle_bb)

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

  if (false_edge->dest == middle_bb)

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

  if (true_edge == e0)

    {

      gcc_assert (false_edge == e1);

      arg_true = arg0;

      arg_false = arg1;

    }

  else

    {

      gcc_assert (false_edge == e0);

      gcc_assert (true_edge == e1);

      arg_true = arg1;

      arg_false = arg0;

    }

  if (empty_block_p (middle_bb))

    {

      if (operand_equal_for_phi_arg_p (arg_true, smaller)

          && operand_equal_for_phi_arg_p (arg_false, larger))

        {

          /* Case

             if (smaller < larger)

             rslt = smaller;

             else

             rslt = larger;  */

          minmax = MIN_EXPR;

        }

      else if (operand_equal_for_phi_arg_p (arg_false, smaller)

               && operand_equal_for_phi_arg_p (arg_true, larger))

        minmax = MAX_EXPR;

      else

        return false;

    }

  else

    {

      /* Recognize the following case, assuming d <= u:

         if (a <= u)

           b = MAX (a, d);

         x = PHI <b, u>

         This is equivalent to

         b = MAX (a, d);

         x = MIN (b, u);  */

      tree assign = last_and_only_stmt (middle_bb);

      tree lhs, rhs, op0, op1, bound;

      if (!assign

          || TREE_CODE (assign) != MODIFY_EXPR)

        return false;

      lhs = TREE_OPERAND (assign, 0);

      rhs = TREE_OPERAND (assign, 1);