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/* If-conversion for vectorizer.

   Copyright (C) 2004, 2005, 2007 Free Software Foundation, Inc.

   Contributed by Devang Patel <dpatel@apple.com>

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/>.  */

/* This pass implements tree level if-conversion transformation of loops.

   Initial goal is to help vectorizer vectorize loops with conditions.

   A short description of if-conversion:

     o Decide if a loop is if-convertible or not.

     o Walk all loop basic blocks in breadth first order (BFS order).

       o Remove conditional statements (at the end of basic block)

         and propagate condition into destination basic blocks'

         predicate list.

       o Replace modify expression with conditional modify expression

         using current basic block's condition.

     o Merge all basic blocks

       o Replace phi nodes with conditional modify expr

       o Merge all basic blocks into header

     Sample transformation:

     INPUT

     -----

     # i_23 = PHI <0(0), i_18(10)>;

     <L0>:;

     j_15 = A[i_23];

     if (j_15 > 41) goto <L1>; else goto <L17>;

     <L17>:;

     goto <bb 3> (<L3>);

     <L1>:;

     # iftmp.2_4 = PHI <0(8), 42(2)>;

     <L3>:;

     A[i_23] = iftmp.2_4;

     i_18 = i_23 + 1;

     if (i_18 <= 15) goto <L19>; else goto <L18>;

     <L19>:;

     goto <bb 1> (<L0>);

     <L18>:;

     OUTPUT

     ------

     # i_23 = PHI <0(0), i_18(10)>;

     <L0>:;

     j_15 = A[i_23];

     <L3>:;

     iftmp.2_4 = j_15 > 41 ? 42 : 0;

     A[i_23] = iftmp.2_4;

     i_18 = i_23 + 1;

     if (i_18 <= 15) goto <L19>; else goto <L18>;

     <L19>:;

     goto <bb 1> (<L0>);

     <L18>:;

*/

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "tree.h"

#include "c-common.h"

#include "flags.h"

#include "timevar.h"

#include "varray.h"

#include "rtl.h"

#include "basic-block.h"

#include "diagnostic.h"

#include "tree-flow.h"

#include "tree-dump.h"

#include "cfgloop.h"

#include "tree-chrec.h"

#include "tree-data-ref.h"

#include "tree-scalar-evolution.h"

#include "tree-pass.h"

#include "target.h"

/* local function prototypes */

static unsigned int main_tree_if_conversion (void);

static tree tree_if_convert_stmt (struct loop *loop, tree, tree,

                                  block_stmt_iterator *);

static void tree_if_convert_cond_expr (struct loop *, tree, tree,

                                       block_stmt_iterator *);

static bool if_convertible_phi_p (struct loop *, basic_block, tree);

static bool if_convertible_modify_expr_p (struct loop *, basic_block, tree);

static bool if_convertible_stmt_p (struct loop *, basic_block, tree);

static bool if_convertible_bb_p (struct loop *, basic_block, basic_block);

static bool if_convertible_loop_p (struct loop *, bool);

static void add_to_predicate_list (basic_block, tree);

static tree add_to_dst_predicate_list (struct loop * loop, edge,

                                       tree, tree,

                                       block_stmt_iterator *);

static void clean_predicate_lists (struct loop *loop);

static basic_block find_phi_replacement_condition (struct loop *loop,

                                                   basic_block, tree *,

                                                   block_stmt_iterator *);

static void replace_phi_with_cond_modify_expr (tree, tree, basic_block,

                                               block_stmt_iterator *);

static void process_phi_nodes (struct loop *);

static void combine_blocks (struct loop *);

static tree ifc_temp_var (tree, tree);

static bool pred_blocks_visited_p (basic_block, bitmap *);

static basic_block * get_loop_body_in_if_conv_order (const struct loop *loop);

static bool bb_with_exit_edge_p (struct loop *, basic_block);

/* List of basic blocks in if-conversion-suitable order.  */

static basic_block *ifc_bbs;

/* Main entry point.

   Apply if-conversion to the LOOP. Return true if successful otherwise return

   false. If false is returned then loop remains unchanged.

   FOR_VECTORIZER is a boolean flag. It indicates whether if-conversion is used

   for vectorizer or not. If it is used for vectorizer, additional checks are

   used. (Vectorization checks are not yet implemented).  */

static bool

tree_if_conversion (struct loop *loop, bool for_vectorizer)

{

  basic_block bb;

  block_stmt_iterator itr;

  unsigned int i;

  ifc_bbs = NULL;

  /* if-conversion is not appropriate for all loops. First, check if loop  is

     if-convertible or not.  */

  if (!if_convertible_loop_p (loop, for_vectorizer))

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file,"-------------------------\n");

      if (ifc_bbs)

        {

          free (ifc_bbs);

          ifc_bbs = NULL;

        }

      free_dominance_info (CDI_POST_DOMINATORS);

      return false;

    }

  /* Do actual work now.  */

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

    {

      tree cond;

      bb = ifc_bbs [i];

      /* Update condition using predicate list.  */

      cond = bb->aux;

      /* Process all statements in this basic block.

         Remove conditional expression, if any, and annotate

         destination basic block(s) appropriately.  */

      for (itr = bsi_start (bb); !bsi_end_p (itr); /* empty */)

        {

          tree t = bsi_stmt (itr);

          cond = tree_if_convert_stmt (loop, t, cond, &itr);

          if (!bsi_end_p (itr))

            bsi_next (&itr);

        }

      /* If current bb has only one successor, then consider it as an

         unconditional goto.  */

      if (single_succ_p (bb))

        {

          basic_block bb_n = single_succ (bb);

          if (cond != NULL_TREE)

            add_to_predicate_list (bb_n, cond);

        }

    }

  /* Now, all statements are if-converted and basic blocks are

     annotated appropriately. Combine all basic block into one huge

     basic block.  */

  combine_blocks (loop);

  /* clean up */

  clean_predicate_lists (loop);

  free (ifc_bbs);

  ifc_bbs = NULL;

  return true;

}

/* if-convert stmt T which is part of LOOP.

   If T is a MODIFY_EXPR than it is converted into conditional modify

   expression using COND.  For conditional expressions, add condition in the

   destination basic block's predicate list and remove conditional

   expression itself. BSI is the iterator used to traverse statements of

   loop. It is used here when it is required to delete current statement.  */

static tree

tree_if_convert_stmt (struct loop *  loop, tree t, tree cond,

                      block_stmt_iterator *bsi)

{

  if (dump_file && (dump_flags & TDF_DETAILS))

    {

      fprintf (dump_file, "------if-convert stmt\n");

      print_generic_stmt (dump_file, t, TDF_SLIM);

      print_generic_stmt (dump_file, cond, TDF_SLIM);

    }

  switch (TREE_CODE (t))

    {

      /* Labels are harmless here.  */

    case LABEL_EXPR:

      break;

    case MODIFY_EXPR:

      /* This modify_expr is killing previous value of LHS. Appropriate value will

         be selected by PHI node based on condition. It is possible that before

         this transformation, PHI nodes was selecting default value and now it will

         use this new value. This is OK because it does not change validity the

         program.  */

      break;

    case COND_EXPR:

      /* Update destination blocks' predicate list and remove this

         condition expression.  */

      tree_if_convert_cond_expr (loop, t, cond, bsi);

      cond = NULL_TREE;

      break;

    default:

      gcc_unreachable ();

    }

  return cond;

}

/* STMT is COND_EXPR. Update two destination's predicate list.

   Remove COND_EXPR, if it is not the loop exit condition. Otherwise

   update loop exit condition appropriately.  BSI is the iterator

   used to traverse statement list. STMT is part of loop LOOP.  */

static void

tree_if_convert_cond_expr (struct loop *loop, tree stmt, tree cond,

                           block_stmt_iterator *bsi)

{

  tree c, c2;

  edge true_edge, false_edge;

  gcc_assert (TREE_CODE (stmt) == COND_EXPR);

  c = COND_EXPR_COND (stmt);

  extract_true_false_edges_from_block (bb_for_stmt (stmt),

                                       &true_edge, &false_edge);

  /* Add new condition into destination's predicate list.  */

  /* If 'c' is true then TRUE_EDGE is taken.  */

  add_to_dst_predicate_list (loop, true_edge, cond,

                             unshare_expr (c), bsi);

  /* If 'c' is false then FALSE_EDGE is taken.  */

  c2 = invert_truthvalue (unshare_expr (c));

  add_to_dst_predicate_list (loop, false_edge, cond, c2, bsi);

  /* Now this conditional statement is redundant. Remove it.

     But, do not remove exit condition! Update exit condition

     using new condition.  */

  if (!bb_with_exit_edge_p (loop, bb_for_stmt (stmt)))

    {

      bsi_remove (bsi, true);

      cond = NULL_TREE;

    }

  return;

}

/* Return true, iff PHI is if-convertible. PHI is part of loop LOOP

   and it belongs to basic block BB.

   PHI is not if-convertible

   - if it has more than 2 arguments.

   - Virtual PHI is immediately used in another PHI node.  */

static bool

if_convertible_phi_p (struct loop *loop, basic_block bb, tree phi)

{

  if (dump_file && (dump_flags & TDF_DETAILS))

    {

      fprintf (dump_file, "-------------------------\n");

      print_generic_stmt (dump_file, phi, TDF_SLIM);

    }

  if (bb != loop->header && PHI_NUM_ARGS (phi) != 2)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "More than two phi node args.\n");

      return false;

    }

  if (!is_gimple_reg (SSA_NAME_VAR (PHI_RESULT (phi))))

    {

      imm_use_iterator imm_iter;

      use_operand_p use_p;

      FOR_EACH_IMM_USE_FAST (use_p, imm_iter, PHI_RESULT (phi))

        {

          if (TREE_CODE (USE_STMT (use_p)) == PHI_NODE)

            {

              if (dump_file && (dump_flags & TDF_DETAILS))

                fprintf (dump_file, "Difficult to handle this virtual phi.\n");

              return false;

            }

        }

    }

  return true;

}

/* Return true, if M_EXPR is if-convertible.

   MODIFY_EXPR is not if-convertible if,

   - It is not movable.

   - It could trap.

   - LHS is not var decl.

  MODIFY_EXPR is part of block BB, which is inside loop LOOP.

*/

static bool

if_convertible_modify_expr_p (struct loop *loop, basic_block bb, tree m_expr)

{

  if (dump_file && (dump_flags & TDF_DETAILS))

    {

      fprintf (dump_file, "-------------------------\n");

      print_generic_stmt (dump_file, m_expr, TDF_SLIM);

    }

  /* Be conservative and do not handle immovable expressions.  */

  if (movement_possibility (m_expr) == MOVE_IMPOSSIBLE)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "stmt is movable. Don't take risk\n");

      return false;

    }

  /* See if it needs speculative loading or not.  */

  if (bb != loop->header

      && tree_could_trap_p (TREE_OPERAND (m_expr, 1)))

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "tree could trap...\n");

      return false;

    }

  if (TREE_CODE (TREE_OPERAND (m_expr, 1)) == CALL_EXPR)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "CALL_EXPR \n");

      return false;

    }

  if (TREE_CODE (TREE_OPERAND (m_expr, 0)) != SSA_NAME

      && bb != loop->header

      && !bb_with_exit_edge_p (loop, bb))

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        {

          fprintf (dump_file, "LHS is not var\n");

          print_generic_stmt (dump_file, m_expr, TDF_SLIM);

        }

      return false;

    }

  return true;

}

/* Return true, iff STMT is if-convertible.

   Statement is if-convertible if,

   - It is if-convertible MODIFY_EXPR

   - IT is LABEL_EXPR or COND_EXPR.

   STMT is inside block BB, which is inside loop LOOP.  */

static bool

if_convertible_stmt_p (struct loop *loop, basic_block bb, tree stmt)

{

  switch (TREE_CODE (stmt))

    {

    case LABEL_EXPR:

      break;

    case MODIFY_EXPR:

      if (!if_convertible_modify_expr_p (loop, bb, stmt))

        return false;

      break;

    case COND_EXPR:

      break;

    default:

      /* Don't know what to do with 'em so don't do anything.  */

      if (dump_file && (dump_flags & TDF_DETAILS))

        {

          fprintf (dump_file, "don't know what to do\n");

          print_generic_stmt (dump_file, stmt, TDF_SLIM);

        }

      return false;

      break;

    }

  return true;

}

/* Return true, iff BB is if-convertible.

   Note: This routine does _not_ check basic block statements and phis.

   Basic block is not if-convertible if,

   - Basic block is non-empty and it is after exit block (in BFS order).

   - Basic block is after exit block but before latch.

   - Basic block edge(s) is not normal.

   EXIT_BB_SEEN is true if basic block with exit edge is already seen.

   BB is inside loop LOOP.  */

static bool

if_convertible_bb_p (struct loop *loop, basic_block bb, basic_block exit_bb)

{

  edge e;

  edge_iterator ei;

  if (dump_file && (dump_flags & TDF_DETAILS))

    fprintf (dump_file, "----------[%d]-------------\n", bb->index);

  if (exit_bb)

    {

      if (bb != loop->latch)

        {

          if (dump_file && (dump_flags & TDF_DETAILS))

            fprintf (dump_file, "basic block after exit bb but before latch\n");

          return false;

        }

      else if (!empty_block_p (bb))

        {

          if (dump_file && (dump_flags & TDF_DETAILS))

            fprintf (dump_file, "non empty basic block after exit bb\n");

          return false;

        }

      else if (bb == loop->latch

               && bb != exit_bb

               && !dominated_by_p (CDI_DOMINATORS, bb, exit_bb))

          {

            if (dump_file && (dump_flags & TDF_DETAILS))

              fprintf (dump_file, "latch is not dominated by exit_block\n");

            return false;

          }

    }

  /* Be less adventurous and handle only normal edges.  */

  FOR_EACH_EDGE (e, ei, bb->succs)

    if (e->flags &

        (EDGE_ABNORMAL_CALL | EDGE_EH | EDGE_ABNORMAL | EDGE_IRREDUCIBLE_LOOP))

      {

        if (dump_file && (dump_flags & TDF_DETAILS))

          fprintf (dump_file,"Difficult to handle edges\n");

        return false;

      }

  return true;

}

/* Return true, iff LOOP is if-convertible.

   LOOP is if-convertible if,

   - It is innermost.

   - It has two or more basic blocks.

   - It has only one exit.

   - Loop header is not the exit edge.

   - If its basic blocks and phi nodes are if convertible. See above for

     more info.

   FOR_VECTORIZER enables vectorizer specific checks. For example, support

   for vector conditions, data dependency checks etc.. (Not implemented yet).  */

static bool

if_convertible_loop_p (struct loop *loop, bool for_vectorizer ATTRIBUTE_UNUSED)

{

  tree phi;

  basic_block bb;

  block_stmt_iterator itr;

  unsigned int i;

  edge e;

  edge_iterator ei;

  basic_block exit_bb = NULL;

  /* Handle only inner most loop.  */

  if (!loop || loop->inner)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "not inner most loop\n");

      return false;

    }

  /* If only one block, no need for if-conversion.  */

  if (loop->num_nodes <= 2)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "less than 2 basic blocks\n");

      return false;

    }

  /* More than one loop exit is too much to handle.  */

  if (!loop->single_exit)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "multiple exits\n");

      return false;

    }

  /* ??? Check target's vector conditional operation support for vectorizer.  */

  /* If one of the loop header's edge is exit edge then do not apply

     if-conversion.  */

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

    {

      if (loop_exit_edge_p (loop, e))

        return false;

    }

  calculate_dominance_info (CDI_DOMINATORS);

  calculate_dominance_info (CDI_POST_DOMINATORS);

  /* Allow statements that can be handled during if-conversion.  */

  ifc_bbs = get_loop_body_in_if_conv_order (loop);

  if (!ifc_bbs)

    {

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file,"Irreducible loop\n");

      free_dominance_info (CDI_POST_DOMINATORS);

      return false;

    }

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

    {

      bb = ifc_bbs[i];

      if (!if_convertible_bb_p (loop, bb, exit_bb))

        return false;

      /* Check statements.  */

      for (itr = bsi_start (bb); !bsi_end_p (itr); bsi_next (&itr))

        if (!if_convertible_stmt_p (loop, bb, bsi_stmt (itr)))

          return false;

      /* ??? Check data dependency for vectorizer.  */

      /* What about phi nodes ? */

      phi = phi_nodes (bb);

      /* Clear aux field of incoming edges to a bb with a phi node.  */

      if (phi)

        FOR_EACH_EDGE (e, ei, bb->preds)

          e->aux = NULL;

      /* Check statements.  */

      for (; phi; phi = PHI_CHAIN (phi))

        if (!if_convertible_phi_p (loop, bb, phi))

          return false;

      if (bb_with_exit_edge_p (loop, bb))

        exit_bb = bb;

    }

  /* OK. Did not find any potential issues so go ahead in if-convert

     this loop. Now there is no looking back.  */

  if (dump_file)

    fprintf (dump_file,"Applying if-conversion\n");

  free_dominance_info (CDI_POST_DOMINATORS);

  return true;

}

/* Add condition COND into predicate list of basic block BB.  */

static void

add_to_predicate_list (basic_block bb, tree new_cond)

{

  tree cond = bb->aux;

  if (cond)

    cond = fold_build2 (TRUTH_OR_EXPR, boolean_type_node,

                        unshare_expr (cond), new_cond);

  else

    cond = new_cond;

  bb->aux = cond;

}

/* Add condition COND into BB's predicate list.  PREV_COND is

   existing condition.  */

static tree

add_to_dst_predicate_list (struct loop * loop, edge e,

                           tree prev_cond, tree cond,

                           block_stmt_iterator *bsi)

{

  tree new_cond = NULL_TREE;

  if (!flow_bb_inside_loop_p (loop, e->dest))

    return NULL_TREE;

  if (prev_cond == boolean_true_node || !prev_cond)

    new_cond = unshare_expr (cond);

  else

    {

      tree tmp;

      tree tmp_stmt = NULL_TREE;

      tree tmp_stmts1 = NULL_TREE;

      tree tmp_stmts2 = NULL_TREE;

      prev_cond = force_gimple_operand (unshare_expr (prev_cond),

                                        &tmp_stmts1, true, NULL);

      if (tmp_stmts1)

        bsi_insert_before (bsi, tmp_stmts1, BSI_SAME_STMT);

      cond = force_gimple_operand (unshare_expr (cond),

                                   &tmp_stmts2, true, NULL);

      if (tmp_stmts2)

        bsi_insert_before (bsi, tmp_stmts2, BSI_SAME_STMT);

      /* Add the condition to aux field of the edge.  In case edge

         destination is a PHI node, this condition will be ANDed with

         block predicate to construct complete condition.  */

      e->aux = cond;

      /* new_cond == prev_cond AND cond */

      tmp = build2 (TRUTH_AND_EXPR, boolean_type_node,

                    unshare_expr (prev_cond), cond);

      tmp_stmt = ifc_temp_var (boolean_type_node, tmp);

      bsi_insert_before (bsi, tmp_stmt, BSI_SAME_STMT);

      new_cond = TREE_OPERAND (tmp_stmt, 0);

    }

  add_to_predicate_list (e->dest, new_cond);

  return new_cond;

}

/* During if-conversion aux field from basic block structure is used to hold

   predicate list. Clean each basic block's predicate list for the given LOOP.

   Also clean aux field of succesor edges, used to hold true and false

   condition from conditional expression.  */

static void

clean_predicate_lists (struct loop *loop)

{

  basic_block *bb;

  unsigned int i;

  edge e;

  edge_iterator ei;

  bb = get_loop_body (loop);

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

    {

      bb[i]->aux = NULL;

      FOR_EACH_EDGE (e, ei, bb[i]->succs)

        e->aux = NULL;

    }

  free (bb);

}

/* Basic block BB has two predecessors. Using predecessor's aux field, set

   appropriate condition COND for the PHI node replacement. Return true block

   whose phi arguments are selected when cond is true.  */

static basic_block

find_phi_replacement_condition (struct loop *loop,

                                basic_block bb, tree *cond,

                                block_stmt_iterator *bsi)

{

  edge first_edge, second_edge;

  tree tmp_cond, new_stmts;

  gcc_assert (EDGE_COUNT (bb->preds) == 2);

  first_edge = EDGE_PRED (bb, 0);

  second_edge = EDGE_PRED (bb, 1);

  /* Use condition based on following criteria:

     1)

       S1: x = !c ? a : b;

       S2: x = c ? b : a;

       S2 is preferred over S1. Make 'b' first_bb and use its condition.

     2) Do not make loop header first_bb.

     3)

       S1: x = !(c == d)? a : b;

       S21: t1 = c == d;

       S22: x = t1 ? b : a;

       S3: x = (c == d) ? b : a;

       S3 is preferred over S1 and S2*, Make 'b' first_bb and use

       its condition.

     4) If  pred B is dominated by pred A then use pred B's condition.

        See PR23115.  */

  /* Select condition that is not TRUTH_NOT_EXPR.  */

  tmp_cond = (first_edge->src)->aux;

  if (TREE_CODE (tmp_cond) == TRUTH_NOT_EXPR)

    {

      edge tmp_edge;

      tmp_edge = first_edge;

      first_edge = second_edge;

      second_edge = tmp_edge;