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/* Loop distribution.

   Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011

   Free Software Foundation, Inc.

   Contributed by Georges-Andre Silber <Georges-Andre.Silber@ensmp.fr>

   and Sebastian Pop <sebastian.pop@amd.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 performs loop distribution: for example, the loop

   |DO I = 2, N

   |    A(I) = B(I) + C

   |    D(I) = A(I-1)*E

   |ENDDO

   is transformed to

   |DOALL I = 2, N

   |   A(I) = B(I) + C

   |ENDDO

   |

   |DOALL I = 2, N

   |   D(I) = A(I-1)*E

   |ENDDO

   This pass uses an RDG, Reduced Dependence Graph built on top of the

   data dependence relations.  The RDG is then topologically sorted to

   obtain a map of information producers/consumers based on which it

   generates the new loops.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tree-flow.h"

#include "cfgloop.h"

#include "tree-chrec.h"

#include "tree-data-ref.h"

#include "tree-scalar-evolution.h"

#include "tree-pass.h"

/* If bit I is not set, it means that this node represents an

   operation that has already been performed, and that should not be

   performed again.  This is the subgraph of remaining important

   computations that is passed to the DFS algorithm for avoiding to

   include several times the same stores in different loops.  */

static bitmap remaining_stmts;

/* A node of the RDG is marked in this bitmap when it has as a

   predecessor a node that writes to memory.  */

static bitmap upstream_mem_writes;

/* Returns true when DEF is an SSA_NAME defined in LOOP and used after

   the LOOP.  */

static bool

ssa_name_has_uses_outside_loop_p (tree def, loop_p loop)

{

  imm_use_iterator imm_iter;

  use_operand_p use_p;

  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, def)

    if (loop != loop_containing_stmt (USE_STMT (use_p)))

      return true;

  return false;

}

/* Returns true when STMT defines a scalar variable used after the

   loop.  */

static bool

stmt_has_scalar_dependences_outside_loop (gimple stmt)

{

  tree name;

  switch (gimple_code (stmt))

    {

    case GIMPLE_CALL:

    case GIMPLE_ASSIGN:

      name = gimple_get_lhs (stmt);

      break;

    case GIMPLE_PHI:

      name = gimple_phi_result (stmt);

      break;

    default:

      return false;

    }

  return (name

          && TREE_CODE (name) == SSA_NAME

          && ssa_name_has_uses_outside_loop_p (name,

                                               loop_containing_stmt (stmt)));

}

/* Update the PHI nodes of NEW_LOOP.  NEW_LOOP is a duplicate of

   ORIG_LOOP.  */

static void

update_phis_for_loop_copy (struct loop *orig_loop, struct loop *new_loop)

{

  tree new_ssa_name;

  gimple_stmt_iterator si_new, si_orig;

  edge orig_loop_latch = loop_latch_edge (orig_loop);

  edge orig_entry_e = loop_preheader_edge (orig_loop);

  edge new_loop_entry_e = loop_preheader_edge (new_loop);

  /* Scan the phis in the headers of the old and new loops

     (they are organized in exactly the same order).  */

  for (si_new = gsi_start_phis (new_loop->header),

       si_orig = gsi_start_phis (orig_loop->header);

       !gsi_end_p (si_new) && !gsi_end_p (si_orig);

       gsi_next (&si_new), gsi_next (&si_orig))

    {

      tree def;

      source_location locus;

      gimple phi_new = gsi_stmt (si_new);

      gimple phi_orig = gsi_stmt (si_orig);

      /* Add the first phi argument for the phi in NEW_LOOP (the one

         associated with the entry of NEW_LOOP)  */

      def = PHI_ARG_DEF_FROM_EDGE (phi_orig, orig_entry_e);

      locus = gimple_phi_arg_location_from_edge (phi_orig, orig_entry_e);

      add_phi_arg (phi_new, def, new_loop_entry_e, locus);

      /* Add the second phi argument for the phi in NEW_LOOP (the one

         associated with the latch of NEW_LOOP)  */

      def = PHI_ARG_DEF_FROM_EDGE (phi_orig, orig_loop_latch);

      locus = gimple_phi_arg_location_from_edge (phi_orig, orig_loop_latch);

      if (TREE_CODE (def) == SSA_NAME)

        {

          new_ssa_name = get_current_def (def);

          if (!new_ssa_name)

            /* This only happens if there are no definitions inside the

               loop.  Use the the invariant in the new loop as is.  */

            new_ssa_name = def;

        }

      else

        /* Could be an integer.  */

        new_ssa_name = def;

      add_phi_arg (phi_new, new_ssa_name, loop_latch_edge (new_loop), locus);

    }

}

/* Return a copy of LOOP placed before LOOP.  */

static struct loop *

copy_loop_before (struct loop *loop)

{

  struct loop *res;

  edge preheader = loop_preheader_edge (loop);

  if (!single_exit (loop))

    return NULL;

  initialize_original_copy_tables ();

  res = slpeel_tree_duplicate_loop_to_edge_cfg (loop, preheader);

  free_original_copy_tables ();

  if (!res)

    return NULL;

  update_phis_for_loop_copy (loop, res);

  rename_variables_in_loop (res);

  return res;

}

/* Creates an empty basic block after LOOP.  */

static void

create_bb_after_loop (struct loop *loop)

{

  edge exit = single_exit (loop);

  if (!exit)

    return;

  split_edge (exit);

}

/* Generate code for PARTITION from the code in LOOP.  The loop is

   copied when COPY_P is true.  All the statements not flagged in the

   PARTITION bitmap are removed from the loop or from its copy.  The

   statements are indexed in sequence inside a basic block, and the

   basic blocks of a loop are taken in dom order.  Returns true when

   the code gen succeeded. */

static bool

generate_loops_for_partition (struct loop *loop, bitmap partition, bool copy_p)

{

  unsigned i, x;

  gimple_stmt_iterator bsi;

  basic_block *bbs;

  if (copy_p)

    {

      loop = copy_loop_before (loop);

      create_preheader (loop, CP_SIMPLE_PREHEADERS);

      create_bb_after_loop (loop);

    }

  if (loop == NULL)

    return false;

  /* Remove stmts not in the PARTITION bitmap.  The order in which we

     visit the phi nodes and the statements is exactly as in

     stmts_from_loop.  */

  bbs = get_loop_body_in_dom_order (loop);

  if (MAY_HAVE_DEBUG_STMTS)

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

      {

        basic_block bb = bbs[i];

        for (bsi = gsi_start_phis (bb); !gsi_end_p (bsi); gsi_next (&bsi))

          if (!bitmap_bit_p (partition, x++))

            reset_debug_uses (gsi_stmt (bsi));

        for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi))

          {

            gimple stmt = gsi_stmt (bsi);

            if (gimple_code (stmt) != GIMPLE_LABEL

                && !is_gimple_debug (stmt)

                && !bitmap_bit_p (partition, x++))

              reset_debug_uses (stmt);

          }

      }

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

    {

      basic_block bb = bbs[i];

      for (bsi = gsi_start_phis (bb); !gsi_end_p (bsi);)

        if (!bitmap_bit_p (partition, x++))

          {

            gimple phi = gsi_stmt (bsi);

            if (!is_gimple_reg (gimple_phi_result (phi)))

              mark_virtual_phi_result_for_renaming (phi);

            remove_phi_node (&bsi, true);

          }

        else

          gsi_next (&bsi);

      for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi);)

        {

          gimple stmt = gsi_stmt (bsi);

          if (gimple_code (stmt) != GIMPLE_LABEL

              && !is_gimple_debug (stmt)

              && !bitmap_bit_p (partition, x++))

            {

              unlink_stmt_vdef (stmt);

              gsi_remove (&bsi, true);

              release_defs (stmt);

            }

          else

            gsi_next (&bsi);

        }

    }

  free (bbs);

  return true;

}

/* Build the size argument for a memset call.  */

static inline tree

build_size_arg_loc (location_t loc, tree nb_iter, tree op,

                    gimple_seq *stmt_list)

{

  gimple_seq stmts;

  tree x = fold_build2_loc (loc, MULT_EXPR, size_type_node,

                            fold_convert_loc (loc, size_type_node, nb_iter),

                            fold_convert_loc (loc, size_type_node,

                                              TYPE_SIZE_UNIT (TREE_TYPE (op))));

  x = force_gimple_operand (x, &stmts, true, NULL);

  gimple_seq_add_seq (stmt_list, stmts);

  return x;

}

/* Generate a call to memset.  Return true when the operation succeeded.  */

static void

generate_memset_zero (gimple stmt, tree op0, tree nb_iter,

                      gimple_stmt_iterator bsi)

{

  tree addr_base, nb_bytes;

  bool res = false;

  gimple_seq stmt_list = NULL, stmts;

  gimple fn_call;

  tree mem, fn;

  struct data_reference *dr = XCNEW (struct data_reference);

  location_t loc = gimple_location (stmt);

  DR_STMT (dr) = stmt;

  DR_REF (dr) = op0;

  res = dr_analyze_innermost (dr, loop_containing_stmt (stmt));

  gcc_assert (res && stride_of_unit_type_p (DR_STEP (dr), TREE_TYPE (op0)));

  nb_bytes = build_size_arg_loc (loc, nb_iter, op0, &stmt_list);

  addr_base = size_binop_loc (loc, PLUS_EXPR, DR_OFFSET (dr), DR_INIT (dr));

  addr_base = fold_convert_loc (loc, sizetype, addr_base);

  /* Test for a negative stride, iterating over every element.  */

  if (tree_int_cst_sgn (DR_STEP (dr)) == -1)

    {

      addr_base = size_binop_loc (loc, MINUS_EXPR, addr_base,

                                  fold_convert_loc (loc, sizetype, nb_bytes));

      addr_base = size_binop_loc (loc, PLUS_EXPR, addr_base,

                                  TYPE_SIZE_UNIT (TREE_TYPE (op0)));

    }

  addr_base = fold_build_pointer_plus_loc (loc,

                                           DR_BASE_ADDRESS (dr), addr_base);

  mem = force_gimple_operand (addr_base, &stmts, true, NULL);

  gimple_seq_add_seq (&stmt_list, stmts);

  fn = build_fold_addr_expr (builtin_decl_implicit (BUILT_IN_MEMSET));

  fn_call = gimple_build_call (fn, 3, mem, integer_zero_node, nb_bytes);

  gimple_seq_add_stmt (&stmt_list, fn_call);

  gsi_insert_seq_after (&bsi, stmt_list, GSI_CONTINUE_LINKING);

  if (dump_file && (dump_flags & TDF_DETAILS))

    fprintf (dump_file, "generated memset zero\n");

  free_data_ref (dr);

}

/* Tries to generate a builtin function for the instructions of LOOP

   pointed to by the bits set in PARTITION.  Returns true when the

   operation succeeded.  */

static bool

generate_builtin (struct loop *loop, bitmap partition, bool copy_p)

{

  bool res = false;

  unsigned i, x = 0;

  basic_block *bbs;

  gimple write = NULL;

  gimple_stmt_iterator bsi;

  tree nb_iter = number_of_exit_cond_executions (loop);

  if (!nb_iter || nb_iter == chrec_dont_know)

    return false;

  bbs = get_loop_body_in_dom_order (loop);

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

    {

      basic_block bb = bbs[i];

      for (bsi = gsi_start_phis (bb); !gsi_end_p (bsi); gsi_next (&bsi))

        x++;

      for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi))

        {

          gimple stmt = gsi_stmt (bsi);

          if (gimple_code (stmt) == GIMPLE_LABEL

              || is_gimple_debug (stmt))

            continue;

          if (!bitmap_bit_p (partition, x++))

            continue;

          /* If the stmt has uses outside of the loop fail.  */

          if (stmt_has_scalar_dependences_outside_loop (stmt))

            goto end;

          if (is_gimple_assign (stmt)

              && !is_gimple_reg (gimple_assign_lhs (stmt)))

            {

              /* Don't generate the builtins when there are more than

                 one memory write.  */

              if (write != NULL)

                goto end;

              write = stmt;

              if (bb == loop->latch)

                nb_iter = number_of_latch_executions (loop);

            }

        }

    }

  if (!stmt_with_adjacent_zero_store_dr_p (write))

    goto end;

  /* The new statements will be placed before LOOP.  */

  bsi = gsi_last_bb (loop_preheader_edge (loop)->src);

  generate_memset_zero (write, gimple_assign_lhs (write), nb_iter, bsi);

  res = true;

  /* If this is the last partition for which we generate code, we have

     to destroy the loop.  */

  if (!copy_p)

    {

      unsigned nbbs = loop->num_nodes;

      edge exit = single_exit (loop);

      basic_block src = loop_preheader_edge (loop)->src, dest = exit->dest;

      redirect_edge_pred (exit, src);

      exit->flags &= ~(EDGE_TRUE_VALUE|EDGE_FALSE_VALUE);

      exit->flags |= EDGE_FALLTHRU;

      cancel_loop_tree (loop);

      rescan_loop_exit (exit, false, true);

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

        delete_basic_block (bbs[i]);

      set_immediate_dominator (CDI_DOMINATORS, dest,

                               recompute_dominator (CDI_DOMINATORS, dest));

    }

 end:

  free (bbs);

  return res;

}

/* Generates code for PARTITION.  For simple loops, this function can

   generate a built-in.  */

static bool

generate_code_for_partition (struct loop *loop, bitmap partition, bool copy_p)

{

  if (generate_builtin (loop, partition, copy_p))

    return true;

  return generate_loops_for_partition (loop, partition, copy_p);

}

/* Returns true if the node V of RDG cannot be recomputed.  */

static bool

rdg_cannot_recompute_vertex_p (struct graph *rdg, int v)

{

  if (RDG_MEM_WRITE_STMT (rdg, v))

    return true;

  return false;

}

/* Returns true when the vertex V has already been generated in the

   current partition (V is in PROCESSED), or when V belongs to another

   partition and cannot be recomputed (V is not in REMAINING_STMTS).  */

static inline bool

already_processed_vertex_p (bitmap processed, int v)

{

  return (bitmap_bit_p (processed, v)

          || !bitmap_bit_p (remaining_stmts, v));

}

/* Returns NULL when there is no anti-dependence among the successors

   of vertex V, otherwise returns the edge with the anti-dep.  */

static struct graph_edge *

has_anti_dependence (struct vertex *v)

{

  struct graph_edge *e;

  if (v->succ)

    for (e = v->succ; e; e = e->succ_next)

      if (RDGE_TYPE (e) == anti_dd)

        return e;

  return NULL;

}

/* Returns true when V has an anti-dependence edge among its successors.  */

static bool

predecessor_has_mem_write (struct graph *rdg, struct vertex *v)

{

  struct graph_edge *e;

  if (v->pred)

    for (e = v->pred; e; e = e->pred_next)

      if (bitmap_bit_p (upstream_mem_writes, e->src)

          /* Don't consider flow channels: a write to memory followed

             by a read from memory.  These channels allow the split of

             the RDG in different partitions.  */

          && !RDG_MEM_WRITE_STMT (rdg, e->src))

        return true;

  return false;

}

/* Initializes the upstream_mem_writes bitmap following the

   information from RDG.  */

static void

mark_nodes_having_upstream_mem_writes (struct graph *rdg)

{

  int v, x;

  bitmap seen = BITMAP_ALLOC (NULL);

  for (v = rdg->n_vertices - 1; v >= 0; v--)

    if (!bitmap_bit_p (seen, v))

      {

        unsigned i;

        VEC (int, heap) *nodes = VEC_alloc (int, heap, 3);

        graphds_dfs (rdg, &v, 1, &nodes, false, NULL);

        FOR_EACH_VEC_ELT (int, nodes, i, x)

          {

            if (!bitmap_set_bit (seen, x))

              continue;

            if (RDG_MEM_WRITE_STMT (rdg, x)

                || predecessor_has_mem_write (rdg, &(rdg->vertices[x]))

                /* In anti dependences the read should occur before

                   the write, this is why both the read and the write

                   should be placed in the same partition.  */

                || has_anti_dependence (&(rdg->vertices[x])))

              {

                bitmap_set_bit (upstream_mem_writes, x);

              }

          }

        VEC_free (int, heap, nodes);

      }

}

/* Returns true when vertex u has a memory write node as a predecessor

   in RDG.  */

static bool

has_upstream_mem_writes (int u)

{

  return bitmap_bit_p (upstream_mem_writes, u);

}

static void rdg_flag_vertex_and_dependent (struct graph *, int, bitmap, bitmap,

                                           bitmap, bool *);

/* Flag the uses of U stopping following the information from

   upstream_mem_writes.  */

static void

rdg_flag_uses (struct graph *rdg, int u, bitmap partition, bitmap loops,

               bitmap processed, bool *part_has_writes)

{

  use_operand_p use_p;

  struct vertex *x = &(rdg->vertices[u]);

  gimple stmt = RDGV_STMT (x);

  struct graph_edge *anti_dep = has_anti_dependence (x);

  /* Keep in the same partition the destination of an antidependence,

     because this is a store to the exact same location.  Putting this

     in another partition is bad for cache locality.  */

  if (anti_dep)

    {

      int v = anti_dep->dest;

      if (!already_processed_vertex_p (processed, v))

        rdg_flag_vertex_and_dependent (rdg, v, partition, loops,

                                       processed, part_has_writes);

    }

  if (gimple_code (stmt) != GIMPLE_PHI)

    {

      if ((use_p = gimple_vuse_op (stmt)) != NULL_USE_OPERAND_P)

        {

          tree use = USE_FROM_PTR (use_p);

          if (TREE_CODE (use) == SSA_NAME)

            {

              gimple def_stmt = SSA_NAME_DEF_STMT (use);

              int v = rdg_vertex_for_stmt (rdg, def_stmt);

              if (v >= 0

                  && !already_processed_vertex_p (processed, v))

                rdg_flag_vertex_and_dependent (rdg, v, partition, loops,

                                               processed, part_has_writes);

            }

        }

    }

  if (is_gimple_assign (stmt) && has_upstream_mem_writes (u))

    {

      tree op0 = gimple_assign_lhs (stmt);

      /* Scalar channels don't have enough space for transmitting data

         between tasks, unless we add more storage by privatizing.  */

      if (is_gimple_reg (op0))

        {

          use_operand_p use_p;

          imm_use_iterator iter;

          FOR_EACH_IMM_USE_FAST (use_p, iter, op0)

            {

              int v = rdg_vertex_for_stmt (rdg, USE_STMT (use_p));

              if (!already_processed_vertex_p (processed, v))

                rdg_flag_vertex_and_dependent (rdg, v, partition, loops,

                                               processed, part_has_writes);

            }

        }

    }

}

/* Flag V from RDG as part of PARTITION, and also flag its loop number

   in LOOPS.  */

static void

rdg_flag_vertex (struct graph *rdg, int v, bitmap partition, bitmap loops,

                 bool *part_has_writes)

{

  struct loop *loop;

  if (!bitmap_set_bit (partition, v))

    return;

  loop = loop_containing_stmt (RDG_STMT (rdg, v));

  bitmap_set_bit (loops, loop->num);

  if (rdg_cannot_recompute_vertex_p (rdg, v))

    {

      *part_has_writes = true;

      bitmap_clear_bit (remaining_stmts, v);

    }

}

/* Flag in the bitmap PARTITION the vertex V and all its predecessors.

   Also flag their loop number in LOOPS.  */

static void

rdg_flag_vertex_and_dependent (struct graph *rdg, int v, bitmap partition,

                               bitmap loops, bitmap processed,

                               bool *part_has_writes)

{

  unsigned i;

  VEC (int, heap) *nodes = VEC_alloc (int, heap, 3);

  int x;

  bitmap_set_bit (processed, v);

  rdg_flag_uses (rdg, v, partition, loops, processed, part_has_writes);

  graphds_dfs (rdg, &v, 1, &nodes, false, remaining_stmts);

  rdg_flag_vertex (rdg, v, partition, loops, part_has_writes);

  FOR_EACH_VEC_ELT (int, nodes, i, x)

    if (!already_processed_vertex_p (processed, x))

      rdg_flag_vertex_and_dependent (rdg, x, partition, loops, processed,

                                     part_has_writes);

  VEC_free (int, heap, nodes);

}

/* Initialize CONDS with all the condition statements from the basic

   blocks of LOOP.  */

static void

collect_condition_stmts (struct loop *loop, VEC (gimple, heap) **conds)

{

  unsigned i;

  edge e;

  VEC (edge, heap) *exits = get_loop_exit_edges (loop);

  FOR_EACH_VEC_ELT (edge, exits, i, e)

    {

      gimple cond = last_stmt (e->src);

      if (cond)

        VEC_safe_push (gimple, heap, *conds, cond);

    }

  VEC_free (edge, heap, exits);

}

/* Add to PARTITION all the exit condition statements for LOOPS

   together with all their dependent statements determined from

   RDG.  */