tree-optimization/112281 - loop distribution and zero dependence distances

[official-gcc.git] / gcc / tree-loop-distribution.cc

/* Loop distribution.
   Copyright (C) 2006-2023 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

   Loop distribution is the dual of loop fusion.  It separates statements
   of a loop (or loop nest) into multiple loops (or loop nests) with the
   same loop header.  The major goal is to separate statements which may
   be vectorized from those that can't.  This pass implements distribution
   in the following steps:

     1) Seed partitions with specific type statements.  For now we support
        two types seed statements: statement defining variable used outside
        of loop; statement storing to memory.
     2) Build reduced dependence graph (RDG) for loop to be distributed.
        The vertices (RDG:V) model all statements in the loop and the edges
        (RDG:E) model flow and control dependencies between statements.
     3) Apart from RDG, compute data dependencies between memory references.
     4) Starting from seed statement, build up partition by adding depended
        statements according to RDG's dependence information.  Partition is
        classified as parallel type if it can be executed paralleled; or as
        sequential type if it can't.  Parallel type partition is further
        classified as different builtin kinds if it can be implemented as
        builtin function calls.
     5) Build partition dependence graph (PG) based on data dependencies.
        The vertices (PG:V) model all partitions and the edges (PG:E) model
        all data dependencies between every partitions pair.  In general,
        data dependence is either compilation time known or unknown.  In C
        family languages, there exists quite amount compilation time unknown
        dependencies because of possible alias relation of data references.
        We categorize PG's edge to two types: "true" edge that represents
        compilation time known data dependencies; "alias" edge for all other
        data dependencies.
     6) Traverse subgraph of PG as if all "alias" edges don't exist.  Merge
        partitions in each strong connected component (SCC) correspondingly.
        Build new PG for merged partitions.
     7) Traverse PG again and this time with both "true" and "alias" edges
        included.  We try to break SCCs by removing some edges.  Because
        SCCs by "true" edges are all fused in step 6), we can break SCCs
        by removing some "alias" edges.  It's NP-hard to choose optimal
        edge set, fortunately simple approximation is good enough for us
        given the small problem scale.
     8) Collect all data dependencies of the removed "alias" edges.  Create
        runtime alias checks for collected data dependencies.
     9) Version loop under the condition of runtime alias checks.  Given
        loop distribution generally introduces additional overhead, it is
        only useful if vectorization is achieved in distributed loop.  We
        version loop with internal function call IFN_LOOP_DIST_ALIAS.  If
        no distributed loop can be vectorized, we simply remove distributed
        loops and recover to the original one.

   TODO:
     1) We only distribute innermost two-level loop nest now.  We should
        extend it for arbitrary loop nests in the future.
     2) We only fuse partitions in SCC now.  A better fusion algorithm is
        desired to minimize loop overhead, maximize parallelism and maximize
        data reuse.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "tree.h"
#include "gimple.h"
#include "cfghooks.h"
#include "tree-pass.h"
#include "ssa.h"
#include "gimple-pretty-print.h"
#include "fold-const.h"
#include "cfganal.h"
#include "gimple-iterator.h"
#include "gimplify-me.h"
#include "stor-layout.h"
#include "tree-cfg.h"
#include "tree-ssa-loop-manip.h"
#include "tree-ssa-loop-ivopts.h"
#include "tree-ssa-loop.h"
#include "tree-into-ssa.h"
#include "tree-ssa.h"
#include "cfgloop.h"
#include "tree-scalar-evolution.h"
#include "tree-vectorizer.h"
#include "tree-eh.h"
#include "gimple-fold.h"
#include "tree-affine.h"
#include "intl.h"
#include "rtl.h"
#include "memmodel.h"
#include "optabs.h"
#include "tree-ssa-loop-niter.h"


#define MAX_DATAREFS_NUM \
        ((unsigned) param_loop_max_datarefs_for_datadeps)

/* Threshold controlling number of distributed partitions.  Given it may
   be unnecessary if a memory stream cost model is invented in the future,
   we define it as a temporary macro, rather than a parameter.  */
#define NUM_PARTITION_THRESHOLD (4)

/* Hashtable helpers.  */

struct ddr_hasher : nofree_ptr_hash <struct data_dependence_relation>
{
  static inline hashval_t hash (const data_dependence_relation *);
  static inline bool equal (const data_dependence_relation *,
                            const data_dependence_relation *);
};

/* Hash function for data dependence.  */

inline hashval_t
ddr_hasher::hash (const data_dependence_relation *ddr)
{
  inchash::hash h;
  h.add_ptr (DDR_A (ddr));
  h.add_ptr (DDR_B (ddr));
  return h.end ();
}

/* Hash table equality function for data dependence.  */

inline bool
ddr_hasher::equal (const data_dependence_relation *ddr1,
                   const data_dependence_relation *ddr2)
{
  return (DDR_A (ddr1) == DDR_A (ddr2) && DDR_B (ddr1) == DDR_B (ddr2));
}



#define DR_INDEX(dr)      ((uintptr_t) (dr)->aux)

/* A Reduced Dependence Graph (RDG) vertex representing a statement.  */
struct rdg_vertex
{
  /* The statement represented by this vertex.  */
  gimple *stmt;

  /* Vector of data-references in this statement.  */
  vec<data_reference_p> datarefs;

  /* True when the statement contains a write to memory.  */
  bool has_mem_write;

  /* True when the statement contains a read from memory.  */
  bool has_mem_reads;
};

#define RDGV_STMT(V)     ((struct rdg_vertex *) ((V)->data))->stmt
#define RDGV_DATAREFS(V) ((struct rdg_vertex *) ((V)->data))->datarefs
#define RDGV_HAS_MEM_WRITE(V) ((struct rdg_vertex *) ((V)->data))->has_mem_write
#define RDGV_HAS_MEM_READS(V) ((struct rdg_vertex *) ((V)->data))->has_mem_reads
#define RDG_STMT(RDG, I) RDGV_STMT (&(RDG->vertices[I]))
#define RDG_DATAREFS(RDG, I) RDGV_DATAREFS (&(RDG->vertices[I]))
#define RDG_MEM_WRITE_STMT(RDG, I) RDGV_HAS_MEM_WRITE (&(RDG->vertices[I]))
#define RDG_MEM_READS_STMT(RDG, I) RDGV_HAS_MEM_READS (&(RDG->vertices[I]))

/* Data dependence type.  */

enum rdg_dep_type
{
  /* Read After Write (RAW).  */
  flow_dd = 'f',

  /* Control dependence (execute conditional on).  */
  control_dd = 'c'
};

/* Dependence information attached to an edge of the RDG.  */

struct rdg_edge
{
  /* Type of the dependence.  */
  enum rdg_dep_type type;
};

#define RDGE_TYPE(E)        ((struct rdg_edge *) ((E)->data))->type

/* Kind of distributed loop.  */
enum partition_kind {
    PKIND_NORMAL,
    /* Partial memset stands for a paritition can be distributed into a loop
       of memset calls, rather than a single memset call.  It's handled just
       like a normal parition, i.e, distributed as separate loop, no memset
       call is generated.

       Note: This is a hacking fix trying to distribute ZERO-ing stmt in a
       loop nest as deep as possible.  As a result, parloop achieves better
       parallelization by parallelizing deeper loop nest.  This hack should
       be unnecessary and removed once distributed memset can be understood
       and analyzed in data reference analysis.  See PR82604 for more.  */
    PKIND_PARTIAL_MEMSET,
    PKIND_MEMSET, PKIND_MEMCPY, PKIND_MEMMOVE
};

/* Type of distributed loop.  */
enum partition_type {
    /* The distributed loop can be executed parallelly.  */
    PTYPE_PARALLEL = 0,
    /* The distributed loop has to be executed sequentially.  */
    PTYPE_SEQUENTIAL
};

/* Builtin info for loop distribution.  */
struct builtin_info
{
  /* data-references a kind != PKIND_NORMAL partition is about.  */
  data_reference_p dst_dr;
  data_reference_p src_dr;
  /* Base address and size of memory objects operated by the builtin.  Note
     both dest and source memory objects must have the same size.  */
  tree dst_base;
  tree src_base;
  tree size;
  /* Base and offset part of dst_base after stripping constant offset.  This
     is only used in memset builtin distribution for now.  */
  tree dst_base_base;
  unsigned HOST_WIDE_INT dst_base_offset;
};

/* Partition for loop distribution.  */
struct partition
{
  /* Statements of the partition.  */
  bitmap stmts;
  /* True if the partition defines variable which is used outside of loop.  */
  bool reduction_p;
  location_t loc;
  enum partition_kind kind;
  enum partition_type type;
  /* Data references in the partition.  */
  bitmap datarefs;
  /* Information of builtin parition.  */
  struct builtin_info *builtin;
};

/* Partitions are fused because of different reasons.  */
enum fuse_type
{
  FUSE_NON_BUILTIN = 0,
  FUSE_REDUCTION = 1,
  FUSE_SHARE_REF = 2,
  FUSE_SAME_SCC = 3,
  FUSE_FINALIZE = 4
};

/* Description on different fusing reason.  */
static const char *fuse_message[] = {
  "they are non-builtins",
  "they have reductions",
  "they have shared memory refs",
  "they are in the same dependence scc",
  "there is no point to distribute loop"};


/* Dump vertex I in RDG to FILE.  */

static void
dump_rdg_vertex (FILE *file, struct graph *rdg, int i)
{
  struct vertex *v = &(rdg->vertices[i]);
  struct graph_edge *e;

  fprintf (file, "(vertex %d: (%s%s) (in:", i,
           RDG_MEM_WRITE_STMT (rdg, i) ? "w" : "",
           RDG_MEM_READS_STMT (rdg, i) ? "r" : "");

  if (v->pred)
    for (e = v->pred; e; e = e->pred_next)
      fprintf (file, " %d", e->src);

  fprintf (file, ") (out:");

  if (v->succ)
    for (e = v->succ; e; e = e->succ_next)
      fprintf (file, " %d", e->dest);

  fprintf (file, ")\n");
  print_gimple_stmt (file, RDGV_STMT (v), 0, TDF_VOPS|TDF_MEMSYMS);
  fprintf (file, ")\n");
}

/* Call dump_rdg_vertex on stderr.  */

DEBUG_FUNCTION void
debug_rdg_vertex (struct graph *rdg, int i)
{
  dump_rdg_vertex (stderr, rdg, i);
}

/* Dump the reduced dependence graph RDG to FILE.  */

static void
dump_rdg (FILE *file, struct graph *rdg)
{
  fprintf (file, "(rdg\n");
  for (int i = 0; i < rdg->n_vertices; i++)
    dump_rdg_vertex (file, rdg, i);
  fprintf (file, ")\n");
}

/* Call dump_rdg on stderr.  */

DEBUG_FUNCTION void
debug_rdg (struct graph *rdg)
{
  dump_rdg (stderr, rdg);
}

static void
dot_rdg_1 (FILE *file, struct graph *rdg)
{
  int i;
  pretty_printer buffer;
  pp_needs_newline (&buffer) = false;
  buffer.buffer->stream = file;

  fprintf (file, "digraph RDG {\n");

  for (i = 0; i < rdg->n_vertices; i++)
    {
      struct vertex *v = &(rdg->vertices[i]);
      struct graph_edge *e;

      fprintf (file, "%d [label=\"[%d] ", i, i);
      pp_gimple_stmt_1 (&buffer, RDGV_STMT (v), 0, TDF_SLIM);
      pp_flush (&buffer);
      fprintf (file, "\"]\n");

      /* Highlight reads from memory.  */
      if (RDG_MEM_READS_STMT (rdg, i))
       fprintf (file, "%d [style=filled, fillcolor=green]\n", i);

      /* Highlight stores to memory.  */
      if (RDG_MEM_WRITE_STMT (rdg, i))
       fprintf (file, "%d [style=filled, fillcolor=red]\n", i);

      if (v->succ)
       for (e = v->succ; e; e = e->succ_next)
         switch (RDGE_TYPE (e))
           {
           case flow_dd:
             /* These are the most common dependences: don't print these. */
             fprintf (file, "%d -> %d \n", i, e->dest);
             break;

           case control_dd:
             fprintf (file, "%d -> %d [label=control] \n", i, e->dest);
             break;

           default:
             gcc_unreachable ();
           }
    }

  fprintf (file, "}\n\n");
}

/* Display the Reduced Dependence Graph using dotty.  */

DEBUG_FUNCTION void
dot_rdg (struct graph *rdg)
{
  /* When debugging, you may want to enable the following code.  */
#ifdef HAVE_POPEN
  FILE *file = popen ("dot -Tx11", "w");
  if (!file)
    return;
  dot_rdg_1 (file, rdg);
  fflush (file);
  close (fileno (file));
  pclose (file);
#else
  dot_rdg_1 (stderr, rdg);
#endif
}

/* Returns the index of STMT in RDG.  */

static int
rdg_vertex_for_stmt (struct graph *rdg ATTRIBUTE_UNUSED, gimple *stmt)
{
  int index = gimple_uid (stmt);
  gcc_checking_assert (index == -1 || RDG_STMT (rdg, index) == stmt);
  return index;
}

/* Creates dependence edges in RDG for all the uses of DEF.  IDEF is
   the index of DEF in RDG.  */

static void
create_rdg_edges_for_scalar (struct graph *rdg, tree def, int idef)
{
  use_operand_p imm_use_p;
  imm_use_iterator iterator;

  FOR_EACH_IMM_USE_FAST (imm_use_p, iterator, def)
    {
      struct graph_edge *e;
      int use = rdg_vertex_for_stmt (rdg, USE_STMT (imm_use_p));

      if (use < 0)
        continue;

      e = add_edge (rdg, idef, use);
      e->data = XNEW (struct rdg_edge);
      RDGE_TYPE (e) = flow_dd;
    }
}

/* Creates an edge for the control dependences of BB to the vertex V.  */

static void
create_edge_for_control_dependence (struct graph *rdg, basic_block bb,
                                    int v, control_dependences *cd)
{
  bitmap_iterator bi;
  unsigned edge_n;
  EXECUTE_IF_SET_IN_BITMAP (cd->get_edges_dependent_on (bb->index),
                            0, edge_n, bi)
    {
      basic_block cond_bb = cd->get_edge_src (edge_n);
      gimple *stmt = *gsi_last_bb (cond_bb);
      if (stmt && is_ctrl_stmt (stmt))
        {
          struct graph_edge *e;
          int c = rdg_vertex_for_stmt (rdg, stmt);
          if (c < 0)
            continue;

          e = add_edge (rdg, c, v);
          e->data = XNEW (struct rdg_edge);
          RDGE_TYPE (e) = control_dd;
        }
    }
}

/* Creates the edges of the reduced dependence graph RDG.  */

static void
create_rdg_flow_edges (struct graph *rdg)
{
  int i;
  def_operand_p def_p;
  ssa_op_iter iter;

  for (i = 0; i < rdg->n_vertices; i++)
    FOR_EACH_PHI_OR_STMT_DEF (def_p, RDG_STMT (rdg, i),
                              iter, SSA_OP_DEF)
      create_rdg_edges_for_scalar (rdg, DEF_FROM_PTR (def_p), i);
}

/* Creates the edges of the reduced dependence graph RDG.  */

static void
create_rdg_cd_edges (struct graph *rdg, control_dependences *cd, loop_p loop)
{
  int i;

  for (i = 0; i < rdg->n_vertices; i++)
    {
      gimple *stmt = RDG_STMT (rdg, i);
      if (gimple_code (stmt) == GIMPLE_PHI)
        {
          edge_iterator ei;
          edge e;
          FOR_EACH_EDGE (e, ei, gimple_bb (stmt)->preds)
            if (flow_bb_inside_loop_p (loop, e->src))
              create_edge_for_control_dependence (rdg, e->src, i, cd);
        }
      else
        create_edge_for_control_dependence (rdg, gimple_bb (stmt), i, cd);
    }
}


class loop_distribution
{
  private:
  /* The loop (nest) to be distributed.  */
  vec<loop_p> loop_nest;

  /* Vector of data references in the loop to be distributed.  */
  vec<data_reference_p> datarefs_vec;

  /* If there is nonaddressable data reference in above vector.  */
  bool has_nonaddressable_dataref_p;

  /* Store index of data reference in aux field.  */

  /* Hash table for data dependence relation in the loop to be distributed.  */
  hash_table<ddr_hasher> *ddrs_table;

  /* Array mapping basic block's index to its topological order.  */
  int *bb_top_order_index;
  /* And size of the array.  */
  int bb_top_order_index_size;

  /* Build the vertices of the reduced dependence graph RDG.  Return false
     if that failed.  */
  bool create_rdg_vertices (struct graph *rdg, const vec<gimple *> &stmts,
                            loop_p loop);

  /* Initialize STMTS with all the statements of LOOP.  We use topological
     order to discover all statements.  The order is important because
     generate_loops_for_partition is using the same traversal for identifying
     statements in loop copies.  */
  void stmts_from_loop (class loop *loop, vec<gimple *> *stmts);


  /* Build the Reduced Dependence Graph (RDG) with one vertex per statement of
     LOOP, and one edge per flow dependence or control dependence from control
     dependence CD.  During visiting each statement, data references are also
     collected and recorded in global data DATAREFS_VEC.  */
  struct graph * build_rdg (class loop *loop, control_dependences *cd);

/* Merge PARTITION into the partition DEST.  RDG is the reduced dependence
   graph and we update type for result partition if it is non-NULL.  */
  void partition_merge_into (struct graph *rdg,
                             partition *dest, partition *partition,
                             enum fuse_type ft);


  /* Return data dependence relation for data references A and B.  The two
     data references must be in lexicographic order wrto reduced dependence
     graph RDG.  We firstly try to find ddr from global ddr hash table.  If
     it doesn't exist, compute the ddr and cache it.  */
  data_dependence_relation * get_data_dependence (struct graph *rdg,
                                                  data_reference_p a,
                                                  data_reference_p b);


  /* In reduced dependence graph RDG for loop distribution, return true if
     dependence between references DR1 and DR2 leads to a dependence cycle
     and such dependence cycle can't be resolved by runtime alias check.  */
  bool data_dep_in_cycle_p (struct graph *rdg, data_reference_p dr1,
                            data_reference_p dr2);


  /* Given reduced dependence graph RDG, PARTITION1 and PARTITION2, update
     PARTITION1's type after merging PARTITION2 into PARTITION1.  */
  void update_type_for_merge (struct graph *rdg,
                              partition *partition1, partition *partition2);


  /* Returns a partition with all the statements needed for computing
     the vertex V of the RDG, also including the loop exit conditions.  */
  partition *build_rdg_partition_for_vertex (struct graph *rdg, int v);

  /* Given data references DST_DR and SRC_DR in loop nest LOOP and RDG, classify
     if it forms builtin memcpy or memmove call.  */
  void classify_builtin_ldst (loop_p loop, struct graph *rdg, partition *partition,
                              data_reference_p dst_dr, data_reference_p src_dr);

  /* Classifies the builtin kind we can generate for PARTITION of RDG and LOOP.
     For the moment we detect memset, memcpy and memmove patterns.  Bitmap
     STMT_IN_ALL_PARTITIONS contains statements belonging to all partitions.
     Returns true if there is a reduction in all partitions and we
     possibly did not mark PARTITION as having one for this reason.  */

  bool
  classify_partition (loop_p loop,
                      struct graph *rdg, partition *partition,
                      bitmap stmt_in_all_partitions);


  /* Returns true when PARTITION1 and PARTITION2 access the same memory
     object in RDG.  */
  bool share_memory_accesses (struct graph *rdg,
                              partition *partition1, partition *partition2);

  /* For each seed statement in STARTING_STMTS, this function builds
     partition for it by adding depended statements according to RDG.
     All partitions are recorded in PARTITIONS.  */
  void rdg_build_partitions (struct graph *rdg,
                             vec<gimple *> starting_stmts,
                             vec<partition *> *partitions);

  /* Compute partition dependence created by the data references in DRS1
     and DRS2, modify and return DIR according to that.  IF ALIAS_DDR is
     not NULL, we record dependence introduced by possible alias between
     two data references in ALIAS_DDRS; otherwise, we simply ignore such
     dependence as if it doesn't exist at all.  */
  int pg_add_dependence_edges (struct graph *rdg, int dir, bitmap drs1,
                               bitmap drs2, vec<ddr_p> *alias_ddrs);


  /* Build and return partition dependence graph for PARTITIONS.  RDG is
     reduced dependence graph for the loop to be distributed.  If IGNORE_ALIAS_P
     is true, data dependence caused by possible alias between references
     is ignored, as if it doesn't exist at all; otherwise all depdendences
     are considered.  */
  struct graph *build_partition_graph (struct graph *rdg,
                                       vec<struct partition *> *partitions,
                                       bool ignore_alias_p);

  /* Given reduced dependence graph RDG merge strong connected components
     of PARTITIONS.  If IGNORE_ALIAS_P is true, data dependence caused by
     possible alias between references is ignored, as if it doesn't exist
     at all; otherwise all depdendences are considered.  */
  void merge_dep_scc_partitions (struct graph *rdg, vec<struct partition *>
                                 *partitions, bool ignore_alias_p);

/* This is the main function breaking strong conected components in
   PARTITIONS giving reduced depdendence graph RDG.  Store data dependence
   relations for runtime alias check in ALIAS_DDRS.  */
  void break_alias_scc_partitions (struct graph *rdg, vec<struct partition *>
                                   *partitions, vec<ddr_p> *alias_ddrs);


  /* Fuse PARTITIONS of LOOP if necessary before finalizing distribution.
     ALIAS_DDRS contains ddrs which need runtime alias check.  */
  void finalize_partitions (class loop *loop, vec<struct partition *>
                            *partitions, vec<ddr_p> *alias_ddrs);

  /* Distributes the code from LOOP in such a way that producer statements
     are placed before consumer statements.  Tries to separate only the
     statements from STMTS into separate loops.  Returns the number of
     distributed loops.  Set NB_CALLS to number of generated builtin calls.
     Set *DESTROY_P to whether LOOP needs to be destroyed.  */
  int distribute_loop (class loop *loop, const vec<gimple *> &stmts,
                       control_dependences *cd, int *nb_calls, bool *destroy_p,
                       bool only_patterns_p);

  /* Transform loops which mimic the effects of builtins rawmemchr or strlen and
     replace them accordingly.  */
  bool transform_reduction_loop (loop_p loop);

  /* Compute topological order for basic blocks.  Topological order is
     needed because data dependence is computed for data references in
     lexicographical order.  */
  void bb_top_order_init (void);

  void bb_top_order_destroy (void);

  public:

  /* Getter for bb_top_order.  */

  inline int get_bb_top_order_index_size (void)
    {
      return bb_top_order_index_size;
    }

  inline int get_bb_top_order_index (int i)
    {
      return bb_top_order_index[i];
    }

  unsigned int execute (function *fun);
};


/* If X has a smaller topological sort number than Y, returns -1;
   if greater, returns 1.  */
static int
bb_top_order_cmp_r (const void *x, const void *y, void *loop)
{
  loop_distribution *_loop =
    (loop_distribution *) loop;

  basic_block bb1 = *(const basic_block *) x;
  basic_block bb2 = *(const basic_block *) y;

  int bb_top_order_index_size = _loop->get_bb_top_order_index_size ();

  gcc_assert (bb1->index < bb_top_order_index_size
              && bb2->index < bb_top_order_index_size);
  gcc_assert (bb1 == bb2
              || _loop->get_bb_top_order_index(bb1->index)
                 != _loop->get_bb_top_order_index(bb2->index));

  return (_loop->get_bb_top_order_index(bb1->index) - 
          _loop->get_bb_top_order_index(bb2->index));
}

bool
loop_distribution::create_rdg_vertices (struct graph *rdg,
                                        const vec<gimple *> &stmts,
                                        loop_p loop)
{
  int i;
  gimple *stmt;

  FOR_EACH_VEC_ELT (stmts, i, stmt)
    {
      struct vertex *v = &(rdg->vertices[i]);

      /* Record statement to vertex mapping.  */
      gimple_set_uid (stmt, i);

      v->data = XNEW (struct rdg_vertex);
      RDGV_STMT (v) = stmt;
      RDGV_DATAREFS (v).create (0);
      RDGV_HAS_MEM_WRITE (v) = false;
      RDGV_HAS_MEM_READS (v) = false;
      if (gimple_code (stmt) == GIMPLE_PHI)
        continue;

      unsigned drp = datarefs_vec.length ();
      if (!find_data_references_in_stmt (loop, stmt, &datarefs_vec))
        return false;
      for (unsigned j = drp; j < datarefs_vec.length (); ++j)
        {
          data_reference_p dr = datarefs_vec[j];
          if (DR_IS_READ (dr))
            RDGV_HAS_MEM_READS (v) = true;
          else
            RDGV_HAS_MEM_WRITE (v) = true;
          RDGV_DATAREFS (v).safe_push (dr);
          has_nonaddressable_dataref_p |= may_be_nonaddressable_p (dr->ref);
        }
    }
  return true;
}

void
loop_distribution::stmts_from_loop (class loop *loop, vec<gimple *> *stmts)
{
  unsigned int i;
  basic_block *bbs = get_loop_body_in_custom_order (loop, this, bb_top_order_cmp_r);

  for (i = 0; i < loop->num_nodes; i++)
    {
      basic_block bb = bbs[i];

      for (gphi_iterator bsi = gsi_start_phis (bb); !gsi_end_p (bsi);
           gsi_next (&bsi))
        if (!virtual_operand_p (gimple_phi_result (bsi.phi ())))
          stmts->safe_push (bsi.phi ());

      for (gimple_stmt_iterator 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))
            stmts->safe_push (stmt);
        }
    }

  free (bbs);
}

/* Free the reduced dependence graph RDG.  */

static void
free_rdg (struct graph *rdg)
{
  int i;

  for (i = 0; i < rdg->n_vertices; i++)
    {
      struct vertex *v = &(rdg->vertices[i]);
      struct graph_edge *e;

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

      if (v->data)
        {
          gimple_set_uid (RDGV_STMT (v), -1);
          (RDGV_DATAREFS (v)).release ();
          free (v->data);
        }
    }

  free_graph (rdg);
}

struct graph *
loop_distribution::build_rdg (class loop *loop, control_dependences *cd)
{
  struct graph *rdg;

  /* Create the RDG vertices from the stmts of the loop nest.  */
  auto_vec<gimple *, 10> stmts;
  stmts_from_loop (loop, &stmts);
  rdg = new_graph (stmts.length ());
  if (!create_rdg_vertices (rdg, stmts, loop))
    {
      free_rdg (rdg);
      return NULL;
    }
  stmts.release ();

  create_rdg_flow_edges (rdg);
  if (cd)
    create_rdg_cd_edges (rdg, cd, loop);

  return rdg;
}


/* Allocate and initialize a partition from BITMAP.  */

static partition *
partition_alloc (void)
{
  partition *partition = XCNEW (struct partition);
  partition->stmts = BITMAP_ALLOC (NULL);
  partition->reduction_p = false;
  partition->loc = UNKNOWN_LOCATION;
  partition->kind = PKIND_NORMAL;
  partition->type = PTYPE_PARALLEL;
  partition->datarefs = BITMAP_ALLOC (NULL);
  return partition;
}

/* Free PARTITION.  */

static void
partition_free (partition *partition)
{
  BITMAP_FREE (partition->stmts);
  BITMAP_FREE (partition->datarefs);
  if (partition->builtin)
    free (partition->builtin);

  free (partition);
}

/* Returns true if the partition can be generated as a builtin.  */

static bool
partition_builtin_p (partition *partition)
{
  return partition->kind > PKIND_PARTIAL_MEMSET;
}

/* Returns true if the partition contains a reduction.  */

static bool
partition_reduction_p (partition *partition)
{
  return partition->reduction_p;
}

void
loop_distribution::partition_merge_into (struct graph *rdg,
                      partition *dest, partition *partition, enum fuse_type ft)
{
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "Fuse partitions because %s:\n", fuse_message[ft]);
      fprintf (dump_file, "  Part 1: ");
      dump_bitmap (dump_file, dest->stmts);
      fprintf (dump_file, "  Part 2: ");
      dump_bitmap (dump_file, partition->stmts);
    }

  dest->kind = PKIND_NORMAL;
  if (dest->type == PTYPE_PARALLEL)
    dest->type = partition->type;

  bitmap_ior_into (dest->stmts, partition->stmts);
  if (partition_reduction_p (partition))
    dest->reduction_p = true;

  /* Further check if any data dependence prevents us from executing the
     new partition parallelly.  */
  if (dest->type == PTYPE_PARALLEL && rdg != NULL)
    update_type_for_merge (rdg, dest, partition);

  bitmap_ior_into (dest->datarefs, partition->datarefs);
}


/* 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 (is_gimple_debug (USE_STMT (use_p)))
        continue;

      basic_block use_bb = gimple_bb (USE_STMT (use_p));
      if (!flow_bb_inside_loop_p (loop, use_bb))
        return true;
    }

  return false;
}

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

static bool
stmt_has_scalar_dependences_outside_loop (loop_p loop, gimple *stmt)
{
  def_operand_p def_p;
  ssa_op_iter op_iter;

  if (gimple_code (stmt) == GIMPLE_PHI)
    return ssa_name_has_uses_outside_loop_p (gimple_phi_result (stmt), loop);

  FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, op_iter, SSA_OP_DEF)
    if (ssa_name_has_uses_outside_loop_p (DEF_FROM_PTR (def_p), loop))
      return true;

  return false;
}

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

static class loop *
copy_loop_before (class loop *loop, bool redirect_lc_phi_defs)
{
  class loop *res;
  edge preheader = loop_preheader_edge (loop);

  initialize_original_copy_tables ();
  res = slpeel_tree_duplicate_loop_to_edge_cfg (loop, single_exit (loop), NULL,
                                                NULL, preheader, NULL, false);
  gcc_assert (res != NULL);

  /* When a not last partition is supposed to keep the LC PHIs computed
     adjust their definitions.  */
  if (redirect_lc_phi_defs)
    {
      edge exit = single_exit (loop);
      for (gphi_iterator si = gsi_start_phis (exit->dest); !gsi_end_p (si);
           gsi_next (&si))
        {
          gphi *phi = si.phi ();
          if (virtual_operand_p (gimple_phi_result (phi)))
            continue;
          use_operand_p use_p = PHI_ARG_DEF_PTR_FROM_EDGE (phi, exit);
          tree new_def = get_current_def (USE_FROM_PTR (use_p));
          SET_USE (use_p, new_def);
        }
    }

  free_original_copy_tables ();
  delete_update_ssa ();

  return res;
}

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

static void
create_bb_after_loop (class 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.  */

static void
generate_loops_for_partition (class loop *loop, partition *partition,
                              bool copy_p, bool keep_lc_phis_p)
{
  unsigned i;
  basic_block *bbs;

  if (copy_p)
    {
      int orig_loop_num = loop->orig_loop_num;
      loop = copy_loop_before (loop, keep_lc_phis_p);
      gcc_assert (loop != NULL);
      loop->orig_loop_num = orig_loop_num;
      create_preheader (loop, CP_SIMPLE_PREHEADERS);
      create_bb_after_loop (loop);
    }
  else
    {
      /* Origin number is set to the new versioned loop's num.  */
      gcc_assert (loop->orig_loop_num != loop->num);
    }

  /* Remove stmts not in the PARTITION bitmap.  */
  bbs = get_loop_body_in_dom_order (loop);

  if (MAY_HAVE_DEBUG_BIND_STMTS)
    for (i = 0; i < loop->num_nodes; i++)
      {
        basic_block bb = bbs[i];

        for (gphi_iterator bsi = gsi_start_phis (bb); !gsi_end_p (bsi);
             gsi_next (&bsi))
          {
            gphi *phi = bsi.phi ();
            if (!virtual_operand_p (gimple_phi_result (phi))
                && !bitmap_bit_p (partition->stmts, gimple_uid (phi)))
              reset_debug_uses (phi);
          }

        for (gimple_stmt_iterator 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->stmts, gimple_uid (stmt)))
              reset_debug_uses (stmt);
          }
      }

  for (i = 0; i < loop->num_nodes; i++)
    {
      basic_block bb = bbs[i];
      edge inner_exit = NULL;

      if (loop != bb->loop_father)
        inner_exit = single_exit (bb->loop_father);

      for (gphi_iterator bsi = gsi_start_phis (bb); !gsi_end_p (bsi);)
        {
          gphi *phi = bsi.phi ();
          if (!virtual_operand_p (gimple_phi_result (phi))
              && !bitmap_bit_p (partition->stmts, gimple_uid (phi)))
            remove_phi_node (&bsi, true);
          else
            gsi_next (&bsi);
        }

      for (gimple_stmt_iterator 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->stmts, gimple_uid (stmt)))
            {
              /* In distribution of loop nest, if bb is inner loop's exit_bb,
                 we choose its exit edge/path in order to avoid generating
                 infinite loop.  For all other cases, we choose an arbitrary
                 path through the empty CFG part that this unnecessary
                 control stmt controls.  */
              if (gcond *cond_stmt = dyn_cast <gcond *> (stmt))
                {
                  if (inner_exit && inner_exit->flags & EDGE_TRUE_VALUE)
                    gimple_cond_make_true (cond_stmt);
                  else
                    gimple_cond_make_false (cond_stmt);
                  update_stmt (stmt);
                }
              else if (gimple_code (stmt) == GIMPLE_SWITCH)
                {
                  gswitch *switch_stmt = as_a <gswitch *> (stmt);
                  gimple_switch_set_index
                      (switch_stmt, CASE_LOW (gimple_switch_label (switch_stmt, 1)));
                  update_stmt (stmt);
                }
              else
                {
                  unlink_stmt_vdef (stmt);
                  gsi_remove (&bsi, true);
                  release_defs (stmt);
                  continue;
                }
            }
          gsi_next (&bsi);
        }
    }

  free (bbs);
}

/* If VAL memory representation contains the same value in all bytes,
   return that value, otherwise return -1.
   E.g. for 0x24242424 return 0x24, for IEEE double
   747708026454360457216.0 return 0x44, etc.  */

static int
const_with_all_bytes_same (tree val)
{
  unsigned char buf[64];
  int i, len;

  if (integer_zerop (val)
      || (TREE_CODE (val) == CONSTRUCTOR
          && !TREE_CLOBBER_P (val)
          && CONSTRUCTOR_NELTS (val) == 0))
    return 0;

  if (real_zerop (val))
    {
      /* Only return 0 for +0.0, not for -0.0, which doesn't have
         an all bytes same memory representation.  Don't transform
         -0.0 stores into +0.0 even for !HONOR_SIGNED_ZEROS.  */
      switch (TREE_CODE (val))
        {
        case REAL_CST:
          if (!real_isneg (TREE_REAL_CST_PTR (val)))
            return 0;
          break;
        case COMPLEX_CST:
          if (!const_with_all_bytes_same (TREE_REALPART (val))
              && !const_with_all_bytes_same (TREE_IMAGPART (val)))
            return 0;
          break;
        case VECTOR_CST:
          {
            unsigned int count = vector_cst_encoded_nelts (val);
            unsigned int j;
            for (j = 0; j < count; ++j)
              if (const_with_all_bytes_same (VECTOR_CST_ENCODED_ELT (val, j)))
                break;
            if (j == count)
              return 0;
            break;
          }
        default:
          break;
        }
    }

  if (CHAR_BIT != 8 || BITS_PER_UNIT != 8)
    return -1;

  len = native_encode_expr (val, buf, sizeof (buf));
  if (len == 0)
    return -1;
  for (i = 1; i < len; i++)
    if (buf[i] != buf[0])
      return -1;
  return buf[0];
}

/* Generate a call to memset for PARTITION in LOOP.  */

static void
generate_memset_builtin (class loop *loop, partition *partition)
{
  gimple_stmt_iterator gsi;
  tree mem, fn, nb_bytes;
  tree val;
  struct builtin_info *builtin = partition->builtin;
  gimple *fn_call;

  /* The new statements will be placed before LOOP.  */
  gsi = gsi_last_bb (loop_preheader_edge (loop)->src);

  nb_bytes = rewrite_to_non_trapping_overflow (builtin->size);
  nb_bytes = force_gimple_operand_gsi (&gsi, nb_bytes, true, NULL_TREE,
                                       false, GSI_CONTINUE_LINKING);
  mem = rewrite_to_non_trapping_overflow (builtin->dst_base);
  mem = force_gimple_operand_gsi (&gsi, mem, true, NULL_TREE,
                                  false, GSI_CONTINUE_LINKING);

  /* This exactly matches the pattern recognition in classify_partition.  */
  val = gimple_assign_rhs1 (DR_STMT (builtin->dst_dr));
  /* Handle constants like 0x15151515 and similarly
     floating point constants etc. where all bytes are the same.  */
  int bytev = const_with_all_bytes_same (val);
  if (bytev != -1)
    val = build_int_cst (integer_type_node, bytev);
  else if (TREE_CODE (val) == INTEGER_CST)
    val = fold_convert (integer_type_node, val);
  else if (!useless_type_conversion_p (integer_type_node, TREE_TYPE (val)))
    {
      tree tem = make_ssa_name (integer_type_node);
      gimple *cstmt = gimple_build_assign (tem, NOP_EXPR, val);
      gsi_insert_after (&gsi, cstmt, GSI_CONTINUE_LINKING);
      val = tem;
    }

  fn = build_fold_addr_expr (builtin_decl_implicit (BUILT_IN_MEMSET));
  fn_call = gimple_build_call (fn, 3, mem, val, nb_bytes);
  gimple_set_location (fn_call, partition->loc);
  gsi_insert_after (&gsi, fn_call, GSI_CONTINUE_LINKING);
  fold_stmt (&gsi);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "generated memset");
      if (bytev == 0)
        fprintf (dump_file, " zero\n");
      else
        fprintf (dump_file, "\n");
    }
}

/* Generate a call to memcpy for PARTITION in LOOP.  */

static void
generate_memcpy_builtin (class loop *loop, partition *partition)
{
  gimple_stmt_iterator gsi;
  gimple *fn_call;
  tree dest, src, fn, nb_bytes;
  enum built_in_function kind;
  struct builtin_info *builtin = partition->builtin;

  /* The new statements will be placed before LOOP.  */
  gsi = gsi_last_bb (loop_preheader_edge (loop)->src);

  nb_bytes = rewrite_to_non_trapping_overflow (builtin->size);
  nb_bytes = force_gimple_operand_gsi (&gsi, nb_bytes, true, NULL_TREE,
                                       false, GSI_CONTINUE_LINKING);
  dest = rewrite_to_non_trapping_overflow (builtin->dst_base);
  src = rewrite_to_non_trapping_overflow (builtin->src_base);
  if (partition->kind == PKIND_MEMCPY
      || ! ptr_derefs_may_alias_p (dest, src))
    kind = BUILT_IN_MEMCPY;
  else
    kind = BUILT_IN_MEMMOVE;
  /* Try harder if we're copying a constant size.  */
  if (kind == BUILT_IN_MEMMOVE && poly_int_tree_p (nb_bytes))
    {
      aff_tree asrc, adest;
      tree_to_aff_combination (src, ptr_type_node, &asrc);
      tree_to_aff_combination (dest, ptr_type_node, &adest);
      aff_combination_scale (&adest, -1);
      aff_combination_add (&asrc, &adest);
      if (aff_comb_cannot_overlap_p (&asrc, wi::to_poly_widest (nb_bytes),
                                     wi::to_poly_widest (nb_bytes)))
        kind = BUILT_IN_MEMCPY;
    }

  dest = force_gimple_operand_gsi (&gsi, dest, true, NULL_TREE,
                                   false, GSI_CONTINUE_LINKING);
  src = force_gimple_operand_gsi (&gsi, src, true, NULL_TREE,
                                  false, GSI_CONTINUE_LINKING);
  fn = build_fold_addr_expr (builtin_decl_implicit (kind));
  fn_call = gimple_build_call (fn, 3, dest, src, nb_bytes);
  gimple_set_location (fn_call, partition->loc);
  gsi_insert_after (&gsi, fn_call, GSI_CONTINUE_LINKING);
  fold_stmt (&gsi);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      if (kind == BUILT_IN_MEMCPY)
        fprintf (dump_file, "generated memcpy\n");
      else
        fprintf (dump_file, "generated memmove\n");
    }
}

/* Remove and destroy the loop LOOP.  */

static void
destroy_loop (class loop *loop)
{
  unsigned nbbs = loop->num_nodes;
  edge exit = single_exit (loop);
  basic_block src = loop_preheader_edge (loop)->src, dest = exit->dest;
  basic_block *bbs;
  unsigned i;

  bbs = get_loop_body_in_dom_order (loop);

  gimple_stmt_iterator dst_gsi = gsi_after_labels (exit->dest);
  bool safe_p = single_pred_p (exit->dest);
  for (unsigned i = 0; i < nbbs; ++i)
    {
      /* We have made sure to not leave any dangling uses of SSA
         names defined in the loop.  With the exception of virtuals.
         Make sure we replace all uses of virtual defs that will remain
         outside of the loop with the bare symbol as delete_basic_block
         will release them.  */
      for (gphi_iterator gsi = gsi_start_phis (bbs[i]); !gsi_end_p (gsi);
           gsi_next (&gsi))
        {
          gphi *phi = gsi.phi ();
          if (virtual_operand_p (gimple_phi_result (phi)))
            mark_virtual_phi_result_for_renaming (phi);
        }
      for (gimple_stmt_iterator gsi = gsi_start_bb (bbs[i]); !gsi_end_p (gsi);)
        {
          gimple *stmt = gsi_stmt (gsi);
          tree vdef = gimple_vdef (stmt);
          if (vdef && TREE_CODE (vdef) == SSA_NAME)
            mark_virtual_operand_for_renaming (vdef);
          /* Also move and eventually reset debug stmts.  We can leave
             constant values in place in case the stmt dominates the exit.
             ???  Non-constant values from the last iteration can be
             replaced with final values if we can compute them.  */
          if (gimple_debug_bind_p (stmt))
            {
              tree val = gimple_debug_bind_get_value (stmt);
              gsi_move_before (&gsi, &dst_gsi);
              if (val
                  && (!safe_p
                      || !is_gimple_min_invariant (val)
                      || !dominated_by_p (CDI_DOMINATORS, exit->src, bbs[i])))
                {
                  gimple_debug_bind_reset_value (stmt);
                  update_stmt (stmt);
                }
            }
          else
            gsi_next (&gsi);
        }
    }

  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);

  i = nbbs;
  do
    {
      --i;
      delete_basic_block (bbs[i]);
    }
  while (i != 0);

  free (bbs);

  set_immediate_dominator (CDI_DOMINATORS, dest,
                           recompute_dominator (CDI_DOMINATORS, dest));
}

/* Generates code for PARTITION.  Return whether LOOP needs to be destroyed.  */

static bool 
generate_code_for_partition (class loop *loop,
                             partition *partition, bool copy_p,
                             bool keep_lc_phis_p)
{
  switch (partition->kind)
    {
    case PKIND_NORMAL:
    case PKIND_PARTIAL_MEMSET:
      /* Reductions all have to be in the last partition.  */
      gcc_assert (!partition_reduction_p (partition)
                  || !copy_p);
      generate_loops_for_partition (loop, partition, copy_p,
                                    keep_lc_phis_p);
      return false;

    case PKIND_MEMSET:
      generate_memset_builtin (loop, partition);
      break;

    case PKIND_MEMCPY:
    case PKIND_MEMMOVE:
      generate_memcpy_builtin (loop, partition);
      break;

    default:
      gcc_unreachable ();
    }

  /* Common tail for partitions we turn into a call.  If this was the last
     partition for which we generate code, we have to destroy the loop.  */
  if (!copy_p)
    return true;
  return false;
}

data_dependence_relation *
loop_distribution::get_data_dependence (struct graph *rdg, data_reference_p a,
                                        data_reference_p b)
{
  struct data_dependence_relation ent, **slot;
  struct data_dependence_relation *ddr;

  gcc_assert (DR_IS_WRITE (a) || DR_IS_WRITE (b));
  gcc_assert (rdg_vertex_for_stmt (rdg, DR_STMT (a))
              <= rdg_vertex_for_stmt (rdg, DR_STMT (b)));
  ent.a = a;
  ent.b = b;
  slot = ddrs_table->find_slot (&ent, INSERT);
  if (*slot == NULL)
    {
      ddr = initialize_data_dependence_relation (a, b, loop_nest);
      compute_affine_dependence (ddr, loop_nest[0]);
      *slot = ddr;
    }

  return *slot;
}

bool
loop_distribution::data_dep_in_cycle_p (struct graph *rdg,
                                        data_reference_p dr1,
                                        data_reference_p dr2)
{
  struct data_dependence_relation *ddr;

  /* Re-shuffle data-refs to be in topological order.  */
  if (rdg_vertex_for_stmt (rdg, DR_STMT (dr1))
      > rdg_vertex_for_stmt (rdg, DR_STMT (dr2)))
    std::swap (dr1, dr2);

  ddr = get_data_dependence (rdg, dr1, dr2);

  /* In case of no data dependence.  */
  if (DDR_ARE_DEPENDENT (ddr) == chrec_known)
    return false;
  /* For unknown data dependence or known data dependence which can't be
     expressed in classic distance vector, we check if it can be resolved
     by runtime alias check.  If yes, we still consider data dependence
     as won't introduce data dependence cycle.  */
  else if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know
           || DDR_NUM_DIST_VECTS (ddr) == 0)
    return !runtime_alias_check_p (ddr, NULL, true);
  else if (DDR_NUM_DIST_VECTS (ddr) > 1)
    return true;
  else if (DDR_REVERSED_P (ddr)
           || lambda_vector_zerop (DDR_DIST_VECT (ddr, 0), 1))
    return false;

  return true;
}

void
loop_distribution::update_type_for_merge (struct graph *rdg,
                                           partition *partition1,
                                           partition *partition2)
{
  unsigned i, j;
  bitmap_iterator bi, bj;
  data_reference_p dr1, dr2;

  EXECUTE_IF_SET_IN_BITMAP (partition1->datarefs, 0, i, bi)
    {
      unsigned start = (partition1 == partition2) ? i + 1 : 0;

      dr1 = datarefs_vec[i];
      EXECUTE_IF_SET_IN_BITMAP (partition2->datarefs, start, j, bj)
        {
          dr2 = datarefs_vec[j];
          if (DR_IS_READ (dr1) && DR_IS_READ (dr2))
            continue;

          /* Partition can only be executed sequentially if there is any
             data dependence cycle.  */
          if (data_dep_in_cycle_p (rdg, dr1, dr2))
            {
              partition1->type = PTYPE_SEQUENTIAL;
              return;
            }
        }
    }
}

partition *
loop_distribution::build_rdg_partition_for_vertex (struct graph *rdg, int v)
{
  partition *partition = partition_alloc ();
  auto_vec<int, 3> nodes;
  unsigned i, j;
  int x;
  data_reference_p dr;

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

  FOR_EACH_VEC_ELT (nodes, i, x)
    {
      bitmap_set_bit (partition->stmts, x);

      for (j = 0; RDG_DATAREFS (rdg, x).iterate (j, &dr); ++j)
        {
          unsigned idx = (unsigned) DR_INDEX (dr);
          gcc_assert (idx < datarefs_vec.length ());

          /* Partition can only be executed sequentially if there is any
             unknown data reference.  */
          if (!DR_BASE_ADDRESS (dr) || !DR_OFFSET (dr)
              || !DR_INIT (dr) || !DR_STEP (dr))
            partition->type = PTYPE_SEQUENTIAL;

          bitmap_set_bit (partition->datarefs, idx);
        }
    }

  if (partition->type == PTYPE_SEQUENTIAL)
    return partition;

  /* Further check if any data dependence prevents us from executing the
     partition parallelly.  */
  update_type_for_merge (rdg, partition, partition);

  return partition;
}

/* Given PARTITION of LOOP and RDG, record single load/store data references
   for builtin partition in SRC_DR/DST_DR, return false if there is no such
   data references.  */

static bool
find_single_drs (class loop *loop, struct graph *rdg, const bitmap &partition_stmts,
                 data_reference_p *dst_dr, data_reference_p *src_dr)
{
  unsigned i;
  data_reference_p single_ld = NULL, single_st = NULL;
  bitmap_iterator bi;

  EXECUTE_IF_SET_IN_BITMAP (partition_stmts, 0, i, bi)
    {
      gimple *stmt = RDG_STMT (rdg, i);
      data_reference_p dr;

      if (gimple_code (stmt) == GIMPLE_PHI)
        continue;

      /* Any scalar stmts are ok.  */
      if (!gimple_vuse (stmt))
        continue;

      /* Otherwise just regular loads/stores.  */
      if (!gimple_assign_single_p (stmt))
        return false;

      /* But exactly one store and/or load.  */
      for (unsigned j = 0; RDG_DATAREFS (rdg, i).iterate (j, &dr); ++j)
        {
          tree type = TREE_TYPE (DR_REF (dr));

          /* The memset, memcpy and memmove library calls are only
             able to deal with generic address space.  */
          if (!ADDR_SPACE_GENERIC_P (TYPE_ADDR_SPACE (type)))
            return false;

          if (DR_IS_READ (dr))
            {
              if (single_ld != NULL)
                return false;
              single_ld = dr;
            }
          else
            {
              if (single_st != NULL)
                return false;
              single_st = dr;
            }
        }
    }

  if (!single_ld && !single_st)
    return false;

  basic_block bb_ld = NULL;
  basic_block bb_st = NULL;
  edge exit = single_exit (loop);

  if (single_ld)
    {
      /* Bail out if this is a bitfield memory reference.  */
      if (TREE_CODE (DR_REF (single_ld)) == COMPONENT_REF
          && DECL_BIT_FIELD (TREE_OPERAND (DR_REF (single_ld), 1)))
        return false;

      /* Data reference must be executed exactly once per iteration of each
         loop in the loop nest.  We only need to check dominance information
         against the outermost one in a perfect loop nest because a bb can't
         dominate outermost loop's latch without dominating inner loop's.  */
      bb_ld = gimple_bb (DR_STMT (single_ld));
      if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb_ld))
        return false;

      /* The data reference must also be executed before possibly exiting
         the loop as otherwise we'd for example unconditionally execute
         memset (ptr, 0, n) which even with n == 0 implies ptr is non-NULL.  */
      if (bb_ld != loop->header
          && (!exit
              || !dominated_by_p (CDI_DOMINATORS, exit->src, bb_ld)))
        return false;
    }

  if (single_st)
    {
      /* Bail out if this is a bitfield memory reference.  */
      if (TREE_CODE (DR_REF (single_st)) == COMPONENT_REF
          && DECL_BIT_FIELD (TREE_OPERAND (DR_REF (single_st), 1)))
        return false;

      /* Data reference must be executed exactly once per iteration.
         Same as single_ld, we only need to check against the outermost
         loop.  */
      bb_st = gimple_bb (DR_STMT (single_st));
      if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb_st))
        return false;

      /* And before exiting the loop.  */
      if (bb_st != loop->header
          && (!exit
              || !dominated_by_p (CDI_DOMINATORS, exit->src, bb_st)))
        return false;
    }

  if (single_ld && single_st)
    {
      /* Load and store must be in the same loop nest.  */
      if (bb_st->loop_father != bb_ld->loop_father)
        return false;

      edge e = single_exit (bb_st->loop_father);
      bool dom_ld = dominated_by_p (CDI_DOMINATORS, e->src, bb_ld);
      bool dom_st = dominated_by_p (CDI_DOMINATORS, e->src, bb_st);
      if (dom_ld != dom_st)
        return false;
    }

  *src_dr = single_ld;
  *dst_dr = single_st;
  return true;
}

/* Given data reference DR in LOOP_NEST, this function checks the enclosing
   loops from inner to outer to see if loop's step equals to access size at
   each level of loop.  Return 2 if we can prove this at all level loops;
   record access base and size in BASE and SIZE; save loop's step at each
   level of loop in STEPS if it is not null.  For example:

     int arr[100][100][100];
     for (i = 0; i < 100; i++)       ;steps[2] = 40000
       for (j = 100; j > 0; j--)     ;steps[1] = -400
         for (k = 0; k < 100; k++)   ;steps[0] = 4
           arr[i][j - 1][k] = 0;     ;base = &arr, size = 4000000

   Return 1 if we can prove the equality at the innermost loop, but not all
   level loops.  In this case, no information is recorded.

   Return 0 if no equality can be proven at any level loops.  */

static int
compute_access_range (loop_p loop_nest, data_reference_p dr, tree *base,
                      tree *size, vec<tree> *steps = NULL)
{
  location_t loc = gimple_location (DR_STMT (dr));
  basic_block bb = gimple_bb (DR_STMT (dr));
  class loop *loop = bb->loop_father;
  tree ref = DR_REF (dr);
  tree access_base = build_fold_addr_expr (ref);
  tree access_size = TYPE_SIZE_UNIT (TREE_TYPE (ref));
  int res = 0;

  do {
      tree scev_fn = analyze_scalar_evolution (loop, access_base);
      if (TREE_CODE (scev_fn) != POLYNOMIAL_CHREC)
        return res;

      access_base = CHREC_LEFT (scev_fn);
      if (tree_contains_chrecs (access_base, NULL))
        return res;

      tree scev_step = CHREC_RIGHT (scev_fn);
      /* Only support constant steps.  */
      if (TREE_CODE (scev_step) != INTEGER_CST)
        return res;

      enum ev_direction access_dir = scev_direction (scev_fn);
      if (access_dir == EV_DIR_UNKNOWN)
        return res;

      if (steps != NULL)
        steps->safe_push (scev_step);

      scev_step = fold_convert_loc (loc, sizetype, scev_step);
      /* Compute absolute value of scev step.  */
      if (access_dir == EV_DIR_DECREASES)
        scev_step = fold_build1_loc (loc, NEGATE_EXPR, sizetype, scev_step);

      /* At each level of loop, scev step must equal to access size.  In other
         words, DR must access consecutive memory between loop iterations.  */
      if (!operand_equal_p (scev_step, access_size, 0))
        return res;

      /* Access stride can be computed for data reference at least for the
         innermost loop.  */
      res = 1;

      /* Compute DR's execution times in loop.  */
      tree niters = number_of_latch_executions (loop);
      niters = fold_convert_loc (loc, sizetype, niters);
      if (dominated_by_p (CDI_DOMINATORS, single_exit (loop)->src, bb))
        niters = size_binop_loc (loc, PLUS_EXPR, niters, size_one_node);

      /* Compute DR's overall access size in loop.  */
      access_size = fold_build2_loc (loc, MULT_EXPR, sizetype,
                                     niters, scev_step);
      /* Adjust base address in case of negative step.  */
      if (access_dir == EV_DIR_DECREASES)
        {
          tree adj = fold_build2_loc (loc, MINUS_EXPR, sizetype,
                                      scev_step, access_size);
          access_base = fold_build_pointer_plus_loc (loc, access_base, adj);
        }
  } while (loop != loop_nest && (loop = loop_outer (loop)) != NULL);

  *base = access_base;
  *size = access_size;
  /* Access stride can be computed for data reference at each level loop.  */
  return 2;
}

/* Allocate and return builtin struct.  Record information like DST_DR,
   SRC_DR, DST_BASE, SRC_BASE and SIZE in the allocated struct.  */

static struct builtin_info *
alloc_builtin (data_reference_p dst_dr, data_reference_p src_dr,
               tree dst_base, tree src_base, tree size)
{
  struct builtin_info *builtin = XNEW (struct builtin_info);
  builtin->dst_dr = dst_dr;
  builtin->src_dr = src_dr;
  builtin->dst_base = dst_base;
  builtin->src_base = src_base;
  builtin->size = size;
  return builtin;
}

/* Given data reference DR in loop nest LOOP, classify if it forms builtin
   memset call.  */

static void
classify_builtin_st (loop_p loop, partition *partition, data_reference_p dr)
{
  gimple *stmt = DR_STMT (dr);
  tree base, size, rhs = gimple_assign_rhs1 (stmt);

  if (const_with_all_bytes_same (rhs) == -1
      && (!INTEGRAL_TYPE_P (TREE_TYPE (rhs))
          || (TYPE_MODE (TREE_TYPE (rhs))
              != TYPE_MODE (unsigned_char_type_node))))
    return;

  if (TREE_CODE (rhs) == SSA_NAME
      && !SSA_NAME_IS_DEFAULT_DEF (rhs)
      && flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (rhs))))
    return;

  int res = compute_access_range (loop, dr, &base, &size);
  if (res == 0)
    return;
  if (res == 1)
    {
      partition->kind = PKIND_PARTIAL_MEMSET;
      return;
    }

  tree base_offset;
  tree base_base;
  split_constant_offset (base, &base_base, &base_offset);
  if (!cst_and_fits_in_hwi (base_offset))
    return;
  unsigned HOST_WIDE_INT const_base_offset = int_cst_value (base_offset);

  struct builtin_info *builtin;
  builtin = alloc_builtin (dr, NULL, base, NULL_TREE, size);
  builtin->dst_base_base = base_base;
  builtin->dst_base_offset = const_base_offset;
  partition->builtin = builtin;
  partition->kind = PKIND_MEMSET;
}

/* Given data references DST_DR and SRC_DR in loop nest LOOP and RDG, classify
   if it forms builtin memcpy or memmove call.  */

void
loop_distribution::classify_builtin_ldst (loop_p loop, struct graph *rdg,
                                          partition *partition,
                                          data_reference_p dst_dr,
                                          data_reference_p src_dr)
{
  tree base, size, src_base, src_size;
  auto_vec<tree> dst_steps, src_steps;

  /* Compute access range of both load and store.  */
  int res = compute_access_range (loop, dst_dr, &base, &size, &dst_steps);
  if (res != 2)
    return;
  res = compute_access_range (loop, src_dr, &src_base, &src_size, &src_steps);
  if (res != 2)
    return;

  /* They must have the same access size.  */
  if (!operand_equal_p (size, src_size, 0))
    return;

  /* They must have the same storage order.  */
  if (reverse_storage_order_for_component_p (DR_REF (dst_dr))
      != reverse_storage_order_for_component_p (DR_REF (src_dr)))
    return;

  /* Load and store in loop nest must access memory in the same way, i.e,
     their must have the same steps in each loop of the nest.  */
  if (dst_steps.length () != src_steps.length ())
    return;
  for (unsigned i = 0; i < dst_steps.length (); ++i)
    if (!operand_equal_p (dst_steps[i], src_steps[i], 0))
      return;

  /* Now check that if there is a dependence.  */
  ddr_p ddr = get_data_dependence (rdg, src_dr, dst_dr);

  /* Classify as memmove if no dependence between load and store.  */
  if (DDR_ARE_DEPENDENT (ddr) == chrec_known)
    {
      partition->builtin = alloc_builtin (dst_dr, src_dr, base, src_base, size);
      partition->kind = PKIND_MEMMOVE;
      return;
    }

  /* Can't do memmove in case of unknown dependence or dependence without
     classical distance vector.  */
  if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know
      || DDR_NUM_DIST_VECTS (ddr) == 0)
    return;

  unsigned i;
  lambda_vector dist_v;
  int num_lev = (DDR_LOOP_NEST (ddr)).length ();
  FOR_EACH_VEC_ELT (DDR_DIST_VECTS (ddr), i, dist_v)
    {
      unsigned dep_lev = dependence_level (dist_v, num_lev);
      /* Can't do memmove if load depends on store.  */
      if (dep_lev > 0 && dist_v[dep_lev - 1] > 0 && !DDR_REVERSED_P (ddr))
        return;
    }

  partition->builtin = alloc_builtin (dst_dr, src_dr, base, src_base, size);
  partition->kind = PKIND_MEMMOVE;
  return;
}

bool
loop_distribution::classify_partition (loop_p loop,
                                       struct graph *rdg, partition *partition,
                                       bitmap stmt_in_all_partitions)
{
  bitmap_iterator bi;
  unsigned i;
  data_reference_p single_ld = NULL, single_st = NULL;
  bool volatiles_p = false, has_reduction = false;

  EXECUTE_IF_SET_IN_BITMAP (partition->stmts, 0, i, bi)
    {
      gimple *stmt = RDG_STMT (rdg, i);

      if (gimple_has_volatile_ops (stmt))
        volatiles_p = true;

      /* If the stmt is not included by all partitions and there is uses
         outside of the loop, then mark the partition as reduction.  */
      if (stmt_has_scalar_dependences_outside_loop (loop, stmt))
        {
          /* Due to limitation in the transform phase we have to fuse all
             reduction partitions.  As a result, this could cancel valid
             loop distribution especially for loop that induction variable
             is used outside of loop.  To workaround this issue, we skip
             marking partition as reudction if the reduction stmt belongs
             to all partitions.  In such case, reduction will be computed
             correctly no matter how partitions are fused/distributed.  */
          if (!bitmap_bit_p (stmt_in_all_partitions, i))
            partition->reduction_p = true;
          else
            has_reduction = true;
        }
    }

  /* Simple workaround to prevent classifying the partition as builtin
     if it contains any use outside of loop.  For the case where all
     partitions have the reduction this simple workaround is delayed
     to only affect the last partition.  */
  if (partition->reduction_p)
     return has_reduction;

  /* Perform general partition disqualification for builtins.  */
  if (volatiles_p
      || !flag_tree_loop_distribute_patterns)
    return has_reduction;

  /* Find single load/store data references for builtin partition.  */
  if (!find_single_drs (loop, rdg, partition->stmts, &single_st, &single_ld)
      || !single_st)
    return has_reduction;

  if (single_ld && single_st)
    {
      gimple *store = DR_STMT (single_st), *load = DR_STMT (single_ld);
      /* Direct aggregate copy or via an SSA name temporary.  */
      if (load != store
          && gimple_assign_lhs (load) != gimple_assign_rhs1 (store))
        return has_reduction;
    }

  partition->loc = gimple_location (DR_STMT (single_st));

  /* Classify the builtin kind.  */
  if (single_ld == NULL)
    classify_builtin_st (loop, partition, single_st);
  else
    classify_builtin_ldst (loop, rdg, partition, single_st, single_ld);
  return has_reduction;
}

bool
loop_distribution::share_memory_accesses (struct graph *rdg,
                       partition *partition1, partition *partition2)
{
  unsigned i, j;
  bitmap_iterator bi, bj;
  data_reference_p dr1, dr2;

  /* First check whether in the intersection of the two partitions are
     any loads or stores.  Common loads are the situation that happens
     most often.  */
  EXECUTE_IF_AND_IN_BITMAP (partition1->stmts, partition2->stmts, 0, i, bi)
    if (RDG_MEM_WRITE_STMT (rdg, i)
        || RDG_MEM_READS_STMT (rdg, i))
      return true;

  /* Then check whether the two partitions access the same memory object.  */
  EXECUTE_IF_SET_IN_BITMAP (partition1->datarefs, 0, i, bi)
    {
      dr1 = datarefs_vec[i];

      if (!DR_BASE_ADDRESS (dr1)
          || !DR_OFFSET (dr1) || !DR_INIT (dr1) || !DR_STEP (dr1))
        continue;

      EXECUTE_IF_SET_IN_BITMAP (partition2->datarefs, 0, j, bj)
        {
          dr2 = datarefs_vec[j];

          if (!DR_BASE_ADDRESS (dr2)
              || !DR_OFFSET (dr2) || !DR_INIT (dr2) || !DR_STEP (dr2))
            continue;

          if (operand_equal_p (DR_BASE_ADDRESS (dr1), DR_BASE_ADDRESS (dr2), 0)
              && operand_equal_p (DR_OFFSET (dr1), DR_OFFSET (dr2), 0)
              && operand_equal_p (DR_INIT (dr1), DR_INIT (dr2), 0)
              && operand_equal_p (DR_STEP (dr1), DR_STEP (dr2), 0))
            return true;
        }
    }

  return false;
}

/* For each seed statement in STARTING_STMTS, this function builds
   partition for it by adding depended statements according to RDG.
   All partitions are recorded in PARTITIONS.  */

void
loop_distribution::rdg_build_partitions (struct graph *rdg,
                                         vec<gimple *> starting_stmts,
                                         vec<partition *> *partitions)
{
  auto_bitmap processed;
  int i;
  gimple *stmt;

  FOR_EACH_VEC_ELT (starting_stmts, i, stmt)
    {
      int v = rdg_vertex_for_stmt (rdg, stmt);

      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "ldist asked to generate code for vertex %d\n", v);

      /* If the vertex is already contained in another partition so
         is the partition rooted at it.  */
      if (bitmap_bit_p (processed, v))
        continue;

      partition *partition = build_rdg_partition_for_vertex (rdg, v);
      bitmap_ior_into (processed, partition->stmts);

      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          fprintf (dump_file, "ldist creates useful %s partition:\n",
                   partition->type == PTYPE_PARALLEL ? "parallel" : "sequent");
          bitmap_print (dump_file, partition->stmts, "  ", "\n");
        }

      partitions->safe_push (partition);
    }

  /* All vertices should have been assigned to at least one partition now,
     other than vertices belonging to dead code.  */
}

/* Dump to FILE the PARTITIONS.  */

static void
dump_rdg_partitions (FILE *file, const vec<partition *> &partitions)
{
  int i;
  partition *partition;

  FOR_EACH_VEC_ELT (partitions, i, partition)
    debug_bitmap_file (file, partition->stmts);
}

/* Debug PARTITIONS.  */
extern void debug_rdg_partitions (const vec<partition *> &);

DEBUG_FUNCTION void
debug_rdg_partitions (const vec<partition *> &partitions)
{
  dump_rdg_partitions (stderr, partitions);
}

/* Returns the number of read and write operations in the RDG.  */

static int
number_of_rw_in_rdg (struct graph *rdg)
{
  int i, res = 0;

  for (i = 0; i < rdg->n_vertices; i++)
    {
      if (RDG_MEM_WRITE_STMT (rdg, i))
        ++res;

      if (RDG_MEM_READS_STMT (rdg, i))
        ++res;
    }

  return res;
}

/* Returns the number of read and write operations in a PARTITION of
   the RDG.  */

static int
number_of_rw_in_partition (struct graph *rdg, partition *partition)
{
  int res = 0;
  unsigned i;
  bitmap_iterator ii;

  EXECUTE_IF_SET_IN_BITMAP (partition->stmts, 0, i, ii)
    {
      if (RDG_MEM_WRITE_STMT (rdg, i))
        ++res;

      if (RDG_MEM_READS_STMT (rdg, i))
        ++res;
    }

  return res;
}

/* Returns true when one of the PARTITIONS contains all the read or
   write operations of RDG.  */

static bool
partition_contains_all_rw (struct graph *rdg,
                           const vec<partition *> &partitions)
{
  int i;
  partition *partition;
  int nrw = number_of_rw_in_rdg (rdg);

  FOR_EACH_VEC_ELT (partitions, i, partition)
    if (nrw == number_of_rw_in_partition (rdg, partition))
      return true;

  return false;
}

int
loop_distribution::pg_add_dependence_edges (struct graph *rdg, int dir,
                         bitmap drs1, bitmap drs2, vec<ddr_p> *alias_ddrs)
{
  unsigned i, j;
  bitmap_iterator bi, bj;
  data_reference_p dr1, dr2, saved_dr1;

  /* dependence direction - 0 is no dependence, -1 is back,
     1 is forth, 2 is both (we can stop then, merging will occur).  */
  EXECUTE_IF_SET_IN_BITMAP (drs1, 0, i, bi)
    {
      dr1 = datarefs_vec[i];

      EXECUTE_IF_SET_IN_BITMAP (drs2, 0, j, bj)
        {
          int res, this_dir = 1;
          ddr_p ddr;

          dr2 = datarefs_vec[j];

          /* Skip all <read, read> data dependence.  */
          if (DR_IS_READ (dr1) && DR_IS_READ (dr2))
            continue;

          saved_dr1 = dr1;
          /* Re-shuffle data-refs to be in topological order.  */
          if (rdg_vertex_for_stmt (rdg, DR_STMT (dr1))
              > rdg_vertex_for_stmt (rdg, DR_STMT (dr2)))
            {
              std::swap (dr1, dr2);
              this_dir = -this_dir;
            }
          ddr = get_data_dependence (rdg, dr1, dr2);
          if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know)
            {
              this_dir = 0;
              res = data_ref_compare_tree (DR_BASE_ADDRESS (dr1),
                                           DR_BASE_ADDRESS (dr2));
              /* Be conservative.  If data references are not well analyzed,
                 or the two data references have the same base address and
                 offset, add dependence and consider it alias to each other.
                 In other words, the dependence cannot be resolved by
                 runtime alias check.  */
              if (!DR_BASE_ADDRESS (dr1) || !DR_BASE_ADDRESS (dr2)
                  || !DR_OFFSET (dr1) || !DR_OFFSET (dr2)
                  || !DR_INIT (dr1) || !DR_INIT (dr2)
                  || !DR_STEP (dr1) || !tree_fits_uhwi_p (DR_STEP (dr1))
                  || !DR_STEP (dr2) || !tree_fits_uhwi_p (DR_STEP (dr2))
                  || res == 0)
                this_dir = 2;
              /* Data dependence could be resolved by runtime alias check,
                 record it in ALIAS_DDRS.  */
              else if (alias_ddrs != NULL)
                alias_ddrs->safe_push (ddr);
              /* Or simply ignore it.  */
            }
          else if (DDR_ARE_DEPENDENT (ddr) == NULL_TREE)
            {
              if (DDR_REVERSED_P (ddr))
                this_dir = -this_dir;

              /* Known dependences can still be unordered througout the
                 iteration space, see gcc.dg/tree-ssa/ldist-16.c and
                 gcc.dg/tree-ssa/pr94969.c.  */
              if (DDR_NUM_DIST_VECTS (ddr) != 1)
                this_dir = 2;
              /* If the dependence distance is zero in the innermost
                 loop preserve stmt order.  */
              else if (DDR_DIST_VECT (ddr, 0)
                         [DDR_LOOP_NEST (ddr).length () - 1] == 0)
                ;
              /* Else as the distance vector is lexicographic positive swap
                 the dependence direction.  */
              else
                this_dir = -this_dir;
            }
          else
            this_dir = 0;
          if (this_dir == 2)
            return 2;
          else if (dir == 0)
            dir = this_dir;
          else if (this_dir != 0 && dir != this_dir)
            return 2;
          /* Shuffle "back" dr1.  */
          dr1 = saved_dr1;
        }
    }
  return dir;
}

/* Compare postorder number of the partition graph vertices V1 and V2.  */

static int
pgcmp (const void *v1_, const void *v2_)
{
  const vertex *v1 = (const vertex *)v1_;
  const vertex *v2 = (const vertex *)v2_;
  return v2->post - v1->post;
}

/* Data attached to vertices of partition dependence graph.  */
struct pg_vdata
{
  /* ID of the corresponding partition.  */
  int id;
  /* The partition.  */
  struct partition *partition;
};

/* Data attached to edges of partition dependence graph.  */
struct pg_edata
{
  /* If the dependence edge can be resolved by runtime alias check,
     this vector contains data dependence relations for runtime alias
     check.  On the other hand, if the dependence edge is introduced
     because of compilation time known data dependence, this vector
     contains nothing.  */
  vec<ddr_p> alias_ddrs;
};

/* Callback data for traversing edges in graph.  */
struct pg_edge_callback_data
{
  /* Bitmap contains strong connected components should be merged.  */
  bitmap sccs_to_merge;
  /* Array constains component information for all vertices.  */
  int *vertices_component;
  /* Vector to record all data dependence relations which are needed
     to break strong connected components by runtime alias checks.  */
  vec<ddr_p> *alias_ddrs;
};

/* Initialize vertice's data for partition dependence graph PG with
   PARTITIONS.  */

static void
init_partition_graph_vertices (struct graph *pg,
                               vec<struct partition *> *partitions)
{
  int i;
  partition *partition;
  struct pg_vdata *data;

  for (i = 0; partitions->iterate (i, &partition); ++i)
    {
      data = new pg_vdata;
      pg->vertices[i].data = data;
      data->id = i;
      data->partition = partition;
    }
}

/* Add edge <I, J> to partition dependence graph PG.  Attach vector of data
   dependence relations to the EDGE if DDRS isn't NULL.  */

static void
add_partition_graph_edge (struct graph *pg, int i, int j, vec<ddr_p> *ddrs)
{
  struct graph_edge *e = add_edge (pg, i, j);

  /* If the edge is attached with data dependence relations, it means this
     dependence edge can be resolved by runtime alias checks.  */
  if (ddrs != NULL)
    {
      struct pg_edata *data = new pg_edata;

      gcc_assert (ddrs->length () > 0);
      e->data = data;
      data->alias_ddrs = vNULL;
      data->alias_ddrs.safe_splice (*ddrs);
    }
}

/* Callback function for graph travesal algorithm.  It returns true
   if edge E should skipped when traversing the graph.  */

static bool
pg_skip_alias_edge (struct graph_edge *e)
{
  struct pg_edata *data = (struct pg_edata *)e->data;
  return (data != NULL && data->alias_ddrs.length () > 0);
}

/* Callback function freeing data attached to edge E of graph.  */

static void
free_partition_graph_edata_cb (struct graph *, struct graph_edge *e, void *)
{
  if (e->data != NULL)
    {
      struct pg_edata *data = (struct pg_edata *)e->data;
      data->alias_ddrs.release ();
      delete data;
    }
}

/* Free data attached to vertice of partition dependence graph PG.  */

static void
free_partition_graph_vdata (struct graph *pg)
{
  int i;
  struct pg_vdata *data;

  for (i = 0; i < pg->n_vertices; ++i)
    {
      data = (struct pg_vdata *)pg->vertices[i].data;
      delete data;
    }
}

/* Build and return partition dependence graph for PARTITIONS.  RDG is
   reduced dependence graph for the loop to be distributed.  If IGNORE_ALIAS_P
   is true, data dependence caused by possible alias between references
   is ignored, as if it doesn't exist at all; otherwise all depdendences
   are considered.  */

struct graph *
loop_distribution::build_partition_graph (struct graph *rdg,
                                          vec<struct partition *> *partitions,
                                          bool ignore_alias_p)
{
  int i, j;
  struct partition *partition1, *partition2;
  graph *pg = new_graph (partitions->length ());
  auto_vec<ddr_p> alias_ddrs, *alias_ddrs_p;

  alias_ddrs_p = ignore_alias_p ? NULL : &alias_ddrs;

  init_partition_graph_vertices (pg, partitions);

  for (i = 0; partitions->iterate (i, &partition1); ++i)
    {
      for (j = i + 1; partitions->iterate (j, &partition2); ++j)
        {
          /* dependence direction - 0 is no dependence, -1 is back,
             1 is forth, 2 is both (we can stop then, merging will occur).  */
          int dir = 0;

          /* If the first partition has reduction, add back edge; if the
             second partition has reduction, add forth edge.  This makes
             sure that reduction partition will be sorted as the last one.  */
          if (partition_reduction_p (partition1))
            dir = -1;
          else if (partition_reduction_p (partition2))
            dir = 1;

          /* Cleanup the temporary vector.  */
          alias_ddrs.truncate (0);

          dir = pg_add_dependence_edges (rdg, dir, partition1->datarefs,
                                         partition2->datarefs, alias_ddrs_p);

          /* Add edge to partition graph if there exists dependence.  There
             are two types of edges.  One type edge is caused by compilation
             time known dependence, this type cannot be resolved by runtime
             alias check.  The other type can be resolved by runtime alias
             check.  */
          if (dir == 1 || dir == 2
              || alias_ddrs.length () > 0)
            {
              /* Attach data dependence relations to edge that can be resolved
                 by runtime alias check.  */
              bool alias_edge_p = (dir != 1 && dir != 2);
              add_partition_graph_edge (pg, i, j,
                                        (alias_edge_p) ? &alias_ddrs : NULL);
            }
          if (dir == -1 || dir == 2
              || alias_ddrs.length () > 0)
            {
              /* Attach data dependence relations to edge that can be resolved
                 by runtime alias check.  */
              bool alias_edge_p = (dir != -1 && dir != 2);
              add_partition_graph_edge (pg, j, i,
                                        (alias_edge_p) ? &alias_ddrs : NULL);
            }
        }
    }
  return pg;
}

/* Sort partitions in PG in descending post order and store them in
   PARTITIONS.  */

static void
sort_partitions_by_post_order (struct graph *pg,
                               vec<struct partition *> *partitions)
{
  int i;
  struct pg_vdata *data;

  /* Now order the remaining nodes in descending postorder.  */
  qsort (pg->vertices, pg->n_vertices, sizeof (vertex), pgcmp);
  partitions->truncate (0);
  for (i = 0; i < pg->n_vertices; ++i)
    {
      data = (struct pg_vdata *)pg->vertices[i].data;
      if (data->partition)
        partitions->safe_push (data->partition);
    }
}

void
loop_distribution::merge_dep_scc_partitions (struct graph *rdg,
                                             vec<struct partition *> *partitions,
                                             bool ignore_alias_p)
{
  struct partition *partition1, *partition2;
  struct pg_vdata *data;
  graph *pg = build_partition_graph (rdg, partitions, ignore_alias_p);
  int i, j, num_sccs = graphds_scc (pg, NULL);

  /* Strong connected compoenent means dependence cycle, we cannot distribute
     them.  So fuse them together.  */
  if ((unsigned) num_sccs < partitions->length ())
    {
      for (i = 0; i < num_sccs; ++i)
        {
          for (j = 0; partitions->iterate (j, &partition1); ++j)
            if (pg->vertices[j].component == i)
              break;
          for (j = j + 1; partitions->iterate (j, &partition2); ++j)
            if (pg->vertices[j].component == i)
              {
                partition_merge_into (NULL, partition1,
                                      partition2, FUSE_SAME_SCC);
                partition1->type = PTYPE_SEQUENTIAL;
                (*partitions)[j] = NULL;
                partition_free (partition2);
                data = (struct pg_vdata *)pg->vertices[j].data;
                data->partition = NULL;
              }
        }
    }

  sort_partitions_by_post_order (pg, partitions);
  gcc_assert (partitions->length () == (unsigned)num_sccs);
  free_partition_graph_vdata (pg);
  for_each_edge (pg, free_partition_graph_edata_cb, NULL);
  free_graph (pg);
}

/* Callback function for traversing edge E in graph G.  DATA is private
   callback data.  */

static void
pg_collect_alias_ddrs (struct graph *g, struct graph_edge *e, void *data)
{
  int i, j, component;
  struct pg_edge_callback_data *cbdata;
  struct pg_edata *edata = (struct pg_edata *) e->data;

  /* If the edge doesn't have attached data dependence, it represents
     compilation time known dependences.  This type dependence cannot
     be resolved by runtime alias check.  */
  if (edata == NULL || edata->alias_ddrs.length () == 0)
    return;

  cbdata = (struct pg_edge_callback_data *) data;
  i = e->src;
  j = e->dest;
  component = cbdata->vertices_component[i];
  /* Vertices are topologically sorted according to compilation time
     known dependences, so we can break strong connected components
     by removing edges of the opposite direction, i.e, edges pointing
     from vertice with smaller post number to vertice with bigger post
     number.  */
  if (g->vertices[i].post < g->vertices[j].post
      /* We only need to remove edges connecting vertices in the same
         strong connected component to break it.  */
      && component == cbdata->vertices_component[j]
      /* Check if we want to break the strong connected component or not.  */
      && !bitmap_bit_p (cbdata->sccs_to_merge, component))
    cbdata->alias_ddrs->safe_splice (edata->alias_ddrs);
}

/* Callback function for traversing edge E.  DATA is private
   callback data.  */

static void
pg_unmark_merged_alias_ddrs (struct graph *, struct graph_edge *e, void *data)
{
  int i, j, component;
  struct pg_edge_callback_data *cbdata;
  struct pg_edata *edata = (struct pg_edata *) e->data;

  if (edata == NULL || edata->alias_ddrs.length () == 0)
    return;

  cbdata = (struct pg_edge_callback_data *) data;
  i = e->src;
  j = e->dest;
  component = cbdata->vertices_component[i];
  /* Make sure to not skip vertices inside SCCs we are going to merge.  */
  if (component == cbdata->vertices_component[j]
      && bitmap_bit_p (cbdata->sccs_to_merge, component))
    {
      edata->alias_ddrs.release ();
      delete edata;
      e->data = NULL;
    }
}

/* This is the main function breaking strong conected components in
   PARTITIONS giving reduced depdendence graph RDG.  Store data dependence
   relations for runtime alias check in ALIAS_DDRS.  */
void
loop_distribution::break_alias_scc_partitions (struct graph *rdg,
                                               vec<struct partition *> *partitions,
                                               vec<ddr_p> *alias_ddrs)
{
  int i, j, k, num_sccs, num_sccs_no_alias = 0;
  /* Build partition dependence graph.  */
  graph *pg = build_partition_graph (rdg, partitions, false);

  alias_ddrs->truncate (0);
  /* Find strong connected components in the graph, with all dependence edges
     considered.  */
  num_sccs = graphds_scc (pg, NULL);
  /* All SCCs now can be broken by runtime alias checks because SCCs caused by
     compilation time known dependences are merged before this function.  */
  if ((unsigned) num_sccs < partitions->length ())
    {
      struct pg_edge_callback_data cbdata;
      auto_bitmap sccs_to_merge;
      auto_vec<enum partition_type> scc_types;
      struct partition *partition, *first;

      /* If all partitions in a SCC have the same type, we can simply merge the
         SCC.  This loop finds out such SCCS and record them in bitmap.  */
      bitmap_set_range (sccs_to_merge, 0, (unsigned) num_sccs);
      for (i = 0; i < num_sccs; ++i)
        {
          for (j = 0; partitions->iterate (j, &first); ++j)
            if (pg->vertices[j].component == i)
              break;

          bool same_type = true, all_builtins = partition_builtin_p (first);
          for (++j; partitions->iterate (j, &partition); ++j)
            {
              if (pg->vertices[j].component != i)
                continue;

              if (first->type != partition->type)
                {
                  same_type = false;
                  break;
                }
              all_builtins &= partition_builtin_p (partition);
            }
          /* Merge SCC if all partitions in SCC have the same type, though the
             result partition is sequential, because vectorizer can do better
             runtime alias check.  One expecption is all partitions in SCC are
             builtins.  */
          if (!same_type || all_builtins)
            bitmap_clear_bit (sccs_to_merge, i);
        }

      /* Initialize callback data for traversing.  */
      cbdata.sccs_to_merge = sccs_to_merge;
      cbdata.alias_ddrs = alias_ddrs;
      cbdata.vertices_component = XNEWVEC (int, pg->n_vertices);
      /* Record the component information which will be corrupted by next
         graph scc finding call.  */
      for (i = 0; i < pg->n_vertices; ++i)
        cbdata.vertices_component[i] = pg->vertices[i].component;

      /* Collect data dependences for runtime alias checks to break SCCs.  */
      if (bitmap_count_bits (sccs_to_merge) != (unsigned) num_sccs)
        {
          /* For SCCs we want to merge clear all alias_ddrs for edges
             inside the component.  */
          for_each_edge (pg, pg_unmark_merged_alias_ddrs, &cbdata);

          /* Run SCC finding algorithm again, with alias dependence edges
             skipped.  This is to topologically sort partitions according to
             compilation time known dependence.  Note the topological order
             is stored in the form of pg's post order number.  */
          num_sccs_no_alias = graphds_scc (pg, NULL, pg_skip_alias_edge);
          /* We cannot assert partitions->length () == num_sccs_no_alias
             since we are not ignoring alias edges in cycles we are
             going to merge.  That's required to compute correct postorder.  */
          /* With topological order, we can construct two subgraphs L and R.
             L contains edge <x, y> where x < y in terms of post order, while
             R contains edge <x, y> where x > y.  Edges for compilation time
             known dependence all fall in R, so we break SCCs by removing all
             (alias) edges of in subgraph L.  */
          for_each_edge (pg, pg_collect_alias_ddrs, &cbdata);
        }

      /* For SCC that doesn't need to be broken, merge it.  */
      for (i = 0; i < num_sccs; ++i)
        {
          if (!bitmap_bit_p (sccs_to_merge, i))
            continue;

          for (j = 0; partitions->iterate (j, &first); ++j)
            if (cbdata.vertices_component[j] == i)
              break;
          for (k = j + 1; partitions->iterate (k, &partition); ++k)
            {
              struct pg_vdata *data;

              if (cbdata.vertices_component[k] != i)
                continue;

              partition_merge_into (NULL, first, partition, FUSE_SAME_SCC);
              (*partitions)[k] = NULL;
              partition_free (partition);
              data = (struct pg_vdata *)pg->vertices[k].data;
              gcc_assert (data->id == k);
              data->partition = NULL;
              /* The result partition of merged SCC must be sequential.  */
              first->type = PTYPE_SEQUENTIAL;
            }
        }
      /* If reduction partition's SCC is broken by runtime alias checks,
         we force a negative post order to it making sure it will be scheduled
         in the last.  */
      if (num_sccs_no_alias > 0)
        {
          j = -1;
          for (i = 0; i < pg->n_vertices; ++i)
            {
              struct pg_vdata *data = (struct pg_vdata *)pg->vertices[i].data;
              if (data->partition && partition_reduction_p (data->partition))
                {
                  gcc_assert (j == -1);
                  j = i;
                }
            }
          if (j >= 0)
            pg->vertices[j].post = -1;
        }

      free (cbdata.vertices_component);
    }

  sort_partitions_by_post_order (pg, partitions);
  free_partition_graph_vdata (pg);
  for_each_edge (pg, free_partition_graph_edata_cb, NULL);
  free_graph (pg);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "Possible alias data dependence to break:\n");
      dump_data_dependence_relations (dump_file, *alias_ddrs);
    }
}

/* Compute and return an expression whose value is the segment length which
   will be accessed by DR in NITERS iterations.  */

static tree
data_ref_segment_size (struct data_reference *dr, tree niters)
{
  niters = size_binop (MINUS_EXPR,
                       fold_convert (sizetype, niters),
                       size_one_node);
  return size_binop (MULT_EXPR,
                     fold_convert (sizetype, DR_STEP (dr)),
                     fold_convert (sizetype, niters));
}

/* Return true if LOOP's latch is dominated by statement for data reference
   DR.  */

static inline bool
latch_dominated_by_data_ref (class loop *loop, data_reference *dr)
{
  return dominated_by_p (CDI_DOMINATORS, single_exit (loop)->src,
                         gimple_bb (DR_STMT (dr)));
}

/* Compute alias check pairs and store them in COMP_ALIAS_PAIRS for LOOP's
   data dependence relations ALIAS_DDRS.  */

static void
compute_alias_check_pairs (class loop *loop, vec<ddr_p> *alias_ddrs,
                           vec<dr_with_seg_len_pair_t> *comp_alias_pairs)
{
  unsigned int i;
  unsigned HOST_WIDE_INT factor = 1;
  tree niters_plus_one, niters = number_of_latch_executions (loop);

  gcc_assert (niters != NULL_TREE && niters != chrec_dont_know);
  niters = fold_convert (sizetype, niters);
  niters_plus_one = size_binop (PLUS_EXPR, niters, size_one_node);

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "Creating alias check pairs:\n");

  /* Iterate all data dependence relations and compute alias check pairs.  */
  for (i = 0; i < alias_ddrs->length (); i++)
    {
      ddr_p ddr = (*alias_ddrs)[i];
      struct data_reference *dr_a = DDR_A (ddr);
      struct data_reference *dr_b = DDR_B (ddr);
      tree seg_length_a, seg_length_b;

      if (latch_dominated_by_data_ref (loop, dr_a))
        seg_length_a = data_ref_segment_size (dr_a, niters_plus_one);
      else
        seg_length_a = data_ref_segment_size (dr_a, niters);

      if (latch_dominated_by_data_ref (loop, dr_b))
        seg_length_b = data_ref_segment_size (dr_b, niters_plus_one);
      else
        seg_length_b = data_ref_segment_size (dr_b, niters);

      unsigned HOST_WIDE_INT access_size_a
        = tree_to_uhwi (TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr_a))));
      unsigned HOST_WIDE_INT access_size_b
        = tree_to_uhwi (TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr_b))));
      unsigned int align_a = TYPE_ALIGN_UNIT (TREE_TYPE (DR_REF (dr_a)));
      unsigned int align_b = TYPE_ALIGN_UNIT (TREE_TYPE (DR_REF (dr_b)));

      dr_with_seg_len_pair_t dr_with_seg_len_pair
        (dr_with_seg_len (dr_a, seg_length_a, access_size_a, align_a),
         dr_with_seg_len (dr_b, seg_length_b, access_size_b, align_b),
         /* ??? Would WELL_ORDERED be safe?  */
         dr_with_seg_len_pair_t::REORDERED);

      comp_alias_pairs->safe_push (dr_with_seg_len_pair);
    }

  if (tree_fits_uhwi_p (niters))
    factor = tree_to_uhwi (niters);

  /* Prune alias check pairs.  */
  prune_runtime_alias_test_list (comp_alias_pairs, factor);
  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file,
             "Improved number of alias checks from %d to %d\n",
             alias_ddrs->length (), comp_alias_pairs->length ());
}

/* Given data dependence relations in ALIAS_DDRS, generate runtime alias
   checks and version LOOP under condition of these runtime alias checks.  */

static void
version_loop_by_alias_check (vec<struct partition *> *partitions,
                             class loop *loop, vec<ddr_p> *alias_ddrs)
{
  profile_probability prob;
  basic_block cond_bb;
  class loop *nloop;
  tree lhs, arg0, cond_expr = NULL_TREE;
  gimple_seq cond_stmts = NULL;
  gimple *call_stmt = NULL;
  auto_vec<dr_with_seg_len_pair_t> comp_alias_pairs;

  /* Generate code for runtime alias checks if necessary.  */
  gcc_assert (alias_ddrs->length () > 0);

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file,
             "Version loop <%d> with runtime alias check\n", loop->num);

  compute_alias_check_pairs (loop, alias_ddrs, &comp_alias_pairs);
  create_runtime_alias_checks (loop, &comp_alias_pairs, &cond_expr);
  cond_expr = force_gimple_operand_1 (cond_expr, &cond_stmts,
                                      is_gimple_val, NULL_TREE);

  /* Depend on vectorizer to fold IFN_LOOP_DIST_ALIAS.  */
  bool cancelable_p = flag_tree_loop_vectorize;
  if (cancelable_p)
    {
      unsigned i = 0;
      struct partition *partition;
      for (; partitions->iterate (i, &partition); ++i)
        if (!partition_builtin_p (partition))
          break;

     /* If all partitions are builtins, distributing it would be profitable and
        we don't want to cancel the runtime alias checks.  */
      if (i == partitions->length ())
        cancelable_p = false;
    }

  /* Generate internal function call for loop distribution alias check if the
     runtime alias check should be cancelable.  */
  if (cancelable_p)
    {
      call_stmt = gimple_build_call_internal (IFN_LOOP_DIST_ALIAS,
                                              2, NULL_TREE, cond_expr);
      lhs = make_ssa_name (boolean_type_node);
      gimple_call_set_lhs (call_stmt, lhs);
    }
  else
    lhs = cond_expr;

  prob = profile_probability::guessed_always ().apply_scale (9, 10);
  initialize_original_copy_tables ();
  nloop = loop_version (loop, lhs, &cond_bb, prob, prob.invert (),
                        prob, prob.invert (), true);
  free_original_copy_tables ();
  /* Record the original loop number in newly generated loops.  In case of
     distribution, the original loop will be distributed and the new loop
     is kept.  */
  loop->orig_loop_num = nloop->num;
  nloop->orig_loop_num = nloop->num;
  nloop->dont_vectorize = true;
  nloop->force_vectorize = false;

  if (call_stmt)
    {
      /* Record new loop's num in IFN_LOOP_DIST_ALIAS because the original
         loop could be destroyed.  */
      arg0 = build_int_cst (integer_type_node, loop->orig_loop_num);
      gimple_call_set_arg (call_stmt, 0, arg0);
      gimple_seq_add_stmt_without_update (&cond_stmts, call_stmt);
    }

  if (cond_stmts)
    {
      gimple_stmt_iterator cond_gsi = gsi_last_bb (cond_bb);
      gsi_insert_seq_before (&cond_gsi, cond_stmts, GSI_SAME_STMT);
    }
  update_ssa (TODO_update_ssa_no_phi);
}

/* Return true if loop versioning is needed to distrubute PARTITIONS.
   ALIAS_DDRS are data dependence relations for runtime alias check.  */

static inline bool
version_for_distribution_p (vec<struct partition *> *partitions,
                            vec<ddr_p> *alias_ddrs)
{
  /* No need to version loop if we have only one partition.  */
  if (partitions->length () == 1)
    return false;

  /* Need to version loop if runtime alias check is necessary.  */
  return (alias_ddrs->length () > 0);
}

/* Compare base offset of builtin mem* partitions P1 and P2.  */

static int
offset_cmp (const void *vp1, const void *vp2)
{
  struct partition *p1 = *(struct partition *const *) vp1;
  struct partition *p2 = *(struct partition *const *) vp2;
  unsigned HOST_WIDE_INT o1 = p1->builtin->dst_base_offset;
  unsigned HOST_WIDE_INT o2 = p2->builtin->dst_base_offset;
  return (o2 < o1) - (o1 < o2);
}

/* Fuse adjacent memset builtin PARTITIONS if possible.  This is a special
   case optimization transforming below code:

     __builtin_memset (&obj, 0, 100);
     _1 = &obj + 100;
     __builtin_memset (_1, 0, 200);
     _2 = &obj + 300;
     __builtin_memset (_2, 0, 100);

   into:

     __builtin_memset (&obj, 0, 400);

   Note we don't have dependence information between different partitions
   at this point, as a result, we can't handle nonadjacent memset builtin
   partitions since dependence might be broken.  */

static void
fuse_memset_builtins (vec<struct partition *> *partitions)
{
  unsigned i, j;
  struct partition *part1, *part2;
  tree rhs1, rhs2;

  for (i = 0; partitions->iterate (i, &part1);)
    {
      if (part1->kind != PKIND_MEMSET)
        {
          i++;
          continue;
        }

      /* Find sub-array of memset builtins of the same base.  Index range
         of the sub-array is [i, j) with "j > i".  */
      for (j = i + 1; partitions->iterate (j, &part2); ++j)
        {
          if (part2->kind != PKIND_MEMSET
              || !operand_equal_p (part1->builtin->dst_base_base,
                                   part2->builtin->dst_base_base, 0))
            break;

          /* Memset calls setting different values can't be merged.  */
          rhs1 = gimple_assign_rhs1 (DR_STMT (part1->builtin->dst_dr));
          rhs2 = gimple_assign_rhs1 (DR_STMT (part2->builtin->dst_dr));
          if (!operand_equal_p (rhs1, rhs2, 0))
            break;
        }

      /* Stable sort is required in order to avoid breaking dependence.  */
      gcc_stablesort (&(*partitions)[i], j - i, sizeof (*partitions)[i],
                      offset_cmp);
      /* Continue with next partition.  */
      i = j;
    }

  /* Merge all consecutive memset builtin partitions.  */
  for (i = 0; i < partitions->length () - 1;)
    {
      part1 = (*partitions)[i];
      if (part1->kind != PKIND_MEMSET)
        {
          i++;
          continue;
        }

      part2 = (*partitions)[i + 1];
      /* Only merge memset partitions of the same base and with constant
         access sizes.  */
      if (part2->kind != PKIND_MEMSET
          || TREE_CODE (part1->builtin->size) != INTEGER_CST
          || TREE_CODE (part2->builtin->size) != INTEGER_CST
          || !operand_equal_p (part1->builtin->dst_base_base,
                               part2->builtin->dst_base_base, 0))
        {
          i++;
          continue;
        }
      rhs1 = gimple_assign_rhs1 (DR_STMT (part1->builtin->dst_dr));
      rhs2 = gimple_assign_rhs1 (DR_STMT (part2->builtin->dst_dr));
      int bytev1 = const_with_all_bytes_same (rhs1);
      int bytev2 = const_with_all_bytes_same (rhs2);
      /* Only merge memset partitions of the same value.  */
      if (bytev1 != bytev2 || bytev1 == -1)
        {
          i++;
          continue;
        }
      wide_int end1 = wi::add (part1->builtin->dst_base_offset,
                               wi::to_wide (part1->builtin->size));
      /* Only merge adjacent memset partitions.  */
      if (wi::ne_p (end1, part2->builtin->dst_base_offset))
        {
          i++;
          continue;
        }
      /* Merge partitions[i] and partitions[i+1].  */
      part1->builtin->size = fold_build2 (PLUS_EXPR, sizetype,
                                          part1->builtin->size,
                                          part2->builtin->size);
      partition_free (part2);
      partitions->ordered_remove (i + 1);
    }
}

void
loop_distribution::finalize_partitions (class loop *loop,
                                        vec<struct partition *> *partitions,
                                        vec<ddr_p> *alias_ddrs)
{
  unsigned i;
  struct partition *partition, *a;

  if (partitions->length () == 1
      || alias_ddrs->length () > 0)
    return;

  unsigned num_builtin = 0, num_normal = 0, num_partial_memset = 0;
  bool same_type_p = true;
  enum partition_type type = ((*partitions)[0])->type;
  for (i = 0; partitions->iterate (i, &partition); ++i)
    {
      same_type_p &= (type == partition->type);
      if (partition_builtin_p (partition))
        {
          num_builtin++;
          continue;
        }
      num_normal++;
      if (partition->kind == PKIND_PARTIAL_MEMSET)
        num_partial_memset++;
    }

  /* Don't distribute current loop into too many loops given we don't have
     memory stream cost model.  Be even more conservative in case of loop
     nest distribution.  */
  if ((same_type_p && num_builtin == 0
       && (loop->inner == NULL || num_normal != 2 || num_partial_memset != 1))
      || (loop->inner != NULL
          && i >= NUM_PARTITION_THRESHOLD && num_normal > 1)
      || (loop->inner == NULL
          && i >= NUM_PARTITION_THRESHOLD && num_normal > num_builtin))
    {
      a = (*partitions)[0];
      for (i = 1; partitions->iterate (i, &partition); ++i)
        {
          partition_merge_into (NULL, a, partition, FUSE_FINALIZE);
          partition_free (partition);
        }
      partitions->truncate (1);
    }

  /* Fuse memset builtins if possible.  */
  if (partitions->length () > 1)
    fuse_memset_builtins (partitions);
}

/* Distributes the code from LOOP in such a way that producer statements
   are placed before consumer statements.  Tries to separate only the
   statements from STMTS into separate loops.  Returns the number of
   distributed loops.  Set NB_CALLS to number of generated builtin calls.
   Set *DESTROY_P to whether LOOP needs to be destroyed.  */

int
loop_distribution::distribute_loop (class loop *loop,
                 const vec<gimple *> &stmts,
                 control_dependences *cd, int *nb_calls, bool *destroy_p,
                 bool only_patterns_p)
{
  ddrs_table = new hash_table<ddr_hasher> (389);
  struct graph *rdg;
  partition *partition;
  int i, nbp;

  *destroy_p = false;
  *nb_calls = 0;
  loop_nest.create (0);
  if (!find_loop_nest (loop, &loop_nest))
    {
      loop_nest.release ();
      delete ddrs_table;
      return 0;
    }

  datarefs_vec.create (20);
  has_nonaddressable_dataref_p = false;
  rdg = build_rdg (loop, cd);
  if (!rdg)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Loop %d not distributed: failed to build the RDG.\n",
                 loop->num);

      loop_nest.release ();
      free_data_refs (datarefs_vec);
      delete ddrs_table;
      return 0;
    }

  if (datarefs_vec.length () > MAX_DATAREFS_NUM)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Loop %d not distributed: too many memory references.\n",
                 loop->num);

      free_rdg (rdg);
      loop_nest.release ();
      free_data_refs (datarefs_vec);
      delete ddrs_table;
      return 0;
    }

  data_reference_p dref;
  for (i = 0; datarefs_vec.iterate (i, &dref); ++i)
    dref->aux = (void *) (uintptr_t) i;

  if (dump_file && (dump_flags & TDF_DETAILS))
    dump_rdg (dump_file, rdg);

  auto_vec<struct partition *, 3> partitions;
  rdg_build_partitions (rdg, stmts, &partitions);

  auto_vec<ddr_p> alias_ddrs;

  auto_bitmap stmt_in_all_partitions;
  bitmap_copy (stmt_in_all_partitions, partitions[0]->stmts);
  for (i = 1; partitions.iterate (i, &partition); ++i)
    bitmap_and_into (stmt_in_all_partitions, partitions[i]->stmts);

  bool any_builtin = false;
  bool reduction_in_all = false;
  int reduction_partition_num = -1;
  FOR_EACH_VEC_ELT (partitions, i, partition)
    {
      reduction_in_all
        |= classify_partition (loop, rdg, partition, stmt_in_all_partitions);
      any_builtin |= partition_builtin_p (partition);
    }

  /* If we are only distributing patterns but did not detect any,
     simply bail out.  */
  if (only_patterns_p
      && !any_builtin)
    {
      nbp = 0;
      goto ldist_done;
    }

  /* If we are only distributing patterns fuse all partitions that
     were not classified as builtins.  This also avoids chopping
     a loop into pieces, separated by builtin calls.  That is, we
     only want no or a single loop body remaining.  */
  struct partition *into;
  if (only_patterns_p)
    {
      for (i = 0; partitions.iterate (i, &into); ++i)
        if (!partition_builtin_p (into))
          break;
      for (++i; partitions.iterate (i, &partition); ++i)
        if (!partition_builtin_p (partition))
          {
            partition_merge_into (NULL, into, partition, FUSE_NON_BUILTIN);
            partitions.unordered_remove (i);
            partition_free (partition);
            i--;
          }
    }

  /* Due to limitations in the transform phase we have to fuse all
     reduction partitions into the last partition so the existing
     loop will contain all loop-closed PHI nodes.  */
  for (i = 0; partitions.iterate (i, &into); ++i)
    if (partition_reduction_p (into))
      break;
  for (i = i + 1; partitions.iterate (i, &partition); ++i)
    if (partition_reduction_p (partition))
      {
        partition_merge_into (rdg, into, partition, FUSE_REDUCTION);
        partitions.unordered_remove (i);
        partition_free (partition);
        i--;
      }

  /* Apply our simple cost model - fuse partitions with similar
     memory accesses.  */
  for (i = 0; partitions.iterate (i, &into); ++i)
    {
      bool changed = false;
      for (int j = i + 1; partitions.iterate (j, &partition); ++j)
        {
          if (share_memory_accesses (rdg, into, partition))
            {
              partition_merge_into (rdg, into, partition, FUSE_SHARE_REF);
              partitions.unordered_remove (j);
              partition_free (partition);
              j--;
              changed = true;
            }
        }
      /* If we fused 0 1 2 in step 1 to 0,2 1 as 0 and 2 have similar
         accesses when 1 and 2 have similar accesses but not 0 and 1
         then in the next iteration we will fail to consider merging
         1 into 0,2.  So try again if we did any merging into 0.  */
      if (changed)
        i--;
    }

  /* Put a non-builtin partition last if we need to preserve a reduction.
     In most cases this helps to keep a normal partition last avoiding to
     spill a reduction result across builtin calls.
     ???  The proper way would be to use dependences to see whether we
     can move builtin partitions earlier during merge_dep_scc_partitions
     and its sort_partitions_by_post_order.  Especially when the
     dependence graph is composed of multiple independent subgraphs the
     heuristic does not work reliably.  */
  if (reduction_in_all
      && partition_builtin_p (partitions.last()))
    FOR_EACH_VEC_ELT (partitions, i, partition)
      if (!partition_builtin_p (partition))
        {
          partitions.unordered_remove (i);
          partitions.quick_push (partition);
          break;
        }

  /* Build the partition dependency graph and fuse partitions in strong
     connected component.  */
  if (partitions.length () > 1)
    {
      /* Don't support loop nest distribution under runtime alias check
         since it's not likely to enable many vectorization opportunities.
         Also if loop has any data reference which may be not addressable
         since alias check needs to take, compare address of the object.  */
      if (loop->inner || has_nonaddressable_dataref_p)
        merge_dep_scc_partitions (rdg, &partitions, false);
      else
        {
          merge_dep_scc_partitions (rdg, &partitions, true);
          if (partitions.length () > 1)
            break_alias_scc_partitions (rdg, &partitions, &alias_ddrs);
        }
    }

  finalize_partitions (loop, &partitions, &alias_ddrs);

  /* If there is a reduction in all partitions make sure the last
     non-builtin partition provides the LC PHI defs.  */
  if (reduction_in_all)
    {
      FOR_EACH_VEC_ELT (partitions, i, partition)
        if (!partition_builtin_p (partition))
          reduction_partition_num = i;
      if (reduction_partition_num == -1)
        {
          /* If all partitions are builtin, force the last one to
             be code generated as normal partition.  */
          partition = partitions.last ();
          partition->kind = PKIND_NORMAL;
        }
    }

  nbp = partitions.length ();
  if (nbp == 0
      || (nbp == 1 && !partition_builtin_p (partitions[0]))
      || (nbp > 1 && partition_contains_all_rw (rdg, partitions)))
    {
      nbp = 0;
      goto ldist_done;
    }

  if (version_for_distribution_p (&partitions, &alias_ddrs))
    version_loop_by_alias_check (&partitions, loop, &alias_ddrs);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file,
               "distribute loop <%d> into partitions:\n", loop->num);
      dump_rdg_partitions (dump_file, partitions);
    }

  FOR_EACH_VEC_ELT (partitions, i, partition)
    {
      if (partition_builtin_p (partition))
        (*nb_calls)++;
      *destroy_p |= generate_code_for_partition (loop, partition, i < nbp - 1,
                                                 i == reduction_partition_num);
    }

 ldist_done:
  loop_nest.release ();
  free_data_refs (datarefs_vec);
  for (hash_table<ddr_hasher>::iterator iter = ddrs_table->begin ();
       iter != ddrs_table->end (); ++iter)
    {
      free_dependence_relation (*iter);
      *iter = NULL;
    }
  delete ddrs_table;

  FOR_EACH_VEC_ELT (partitions, i, partition)
    partition_free (partition);

  free_rdg (rdg);
  return nbp - *nb_calls;
}


void loop_distribution::bb_top_order_init (void)
{
  int rpo_num;
  int *rpo = XNEWVEC (int, n_basic_blocks_for_fn (cfun) - NUM_FIXED_BLOCKS);
  edge entry = single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun));
  bitmap exit_bbs = BITMAP_ALLOC (NULL);

  bb_top_order_index = XNEWVEC (int, last_basic_block_for_fn (cfun));
  bb_top_order_index_size = last_basic_block_for_fn (cfun);

  entry->flags &= ~EDGE_DFS_BACK;
  bitmap_set_bit (exit_bbs, EXIT_BLOCK);
  rpo_num = rev_post_order_and_mark_dfs_back_seme (cfun, entry, exit_bbs, true,
                                                   rpo, NULL);
  BITMAP_FREE (exit_bbs);

  for (int i = 0; i < rpo_num; i++)
    bb_top_order_index[rpo[i]] = i;

  free (rpo);
}

void loop_distribution::bb_top_order_destroy ()
{
  free (bb_top_order_index);
  bb_top_order_index = NULL;
  bb_top_order_index_size = 0;
}


/* Given LOOP, this function records seed statements for distribution in
   WORK_LIST.  Return false if there is nothing for distribution.  */

static bool
find_seed_stmts_for_distribution (class loop *loop, vec<gimple *> *work_list)
{
  basic_block *bbs = get_loop_body_in_dom_order (loop);

  /* Initialize the worklist with stmts we seed the partitions with.  */
  for (unsigned i = 0; i < loop->num_nodes; ++i)
    {
      /* In irreducible sub-regions we don't know how to redirect
         conditions, so fail.  See PR100492.  */
      if (bbs[i]->flags & BB_IRREDUCIBLE_LOOP)
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file, "loop %d contains an irreducible region.\n",
                     loop->num);
          work_list->truncate (0);
          break;
        }
      for (gphi_iterator gsi = gsi_start_phis (bbs[i]);
           !gsi_end_p (gsi); gsi_next (&gsi))
        {
          gphi *phi = gsi.phi ();
          if (virtual_operand_p (gimple_phi_result (phi)))
            continue;
          /* Distribute stmts which have defs that are used outside of
             the loop.  */
          if (!stmt_has_scalar_dependences_outside_loop (loop, phi))
            continue;
          work_list->safe_push (phi);
        }
      for (gimple_stmt_iterator gsi = gsi_start_bb (bbs[i]);
           !gsi_end_p (gsi); gsi_next (&gsi))
        {
          gimple *stmt = gsi_stmt (gsi);

          /* Ignore clobbers, they do not have true side effects.  */
          if (gimple_clobber_p (stmt))
            continue;

          /* If there is a stmt with side-effects bail out - we
             cannot and should not distribute this loop.  */
          if (gimple_has_side_effects (stmt))
            {
              free (bbs);
              return false;
            }

          /* Distribute stmts which have defs that are used outside of
             the loop.  */
          if (stmt_has_scalar_dependences_outside_loop (loop, stmt))
            ;
          /* Otherwise only distribute stores for now.  */
          else if (!gimple_vdef (stmt))
            continue;

          work_list->safe_push (stmt);
        }
    }
  bool res = work_list->length () > 0;
  if (res && !can_copy_bbs_p (bbs, loop->num_nodes))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file, "cannot copy loop %d.\n", loop->num);
      res = false;
    }
  free (bbs);
  return res;
}

/* A helper function for generate_{rawmemchr,strlen}_builtin functions in order
   to place new statements SEQ before LOOP and replace the old reduction
   variable with the new one.  */

static void
generate_reduction_builtin_1 (loop_p loop, gimple_seq &seq,
                              tree reduction_var_old, tree reduction_var_new,
                              const char *info, machine_mode load_mode)
{
  gcc_assert (flag_tree_loop_distribute_patterns);

  /* Place new statements before LOOP.  */
  gimple_stmt_iterator gsi = gsi_last_bb (loop_preheader_edge (loop)->src);
  gsi_insert_seq_after (&gsi, seq, GSI_CONTINUE_LINKING);

  /* Replace old reduction variable with new one.  */
  imm_use_iterator iter;
  gimple *stmt;
  use_operand_p use_p;
  FOR_EACH_IMM_USE_STMT (stmt, iter, reduction_var_old)
    {
      FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
        SET_USE (use_p, reduction_var_new);

      update_stmt (stmt);
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, info, GET_MODE_NAME (load_mode));
}

/* Generate a call to rawmemchr and place it before LOOP.  REDUCTION_VAR is
   replaced with a fresh SSA name representing the result of the call.  */

static void
generate_rawmemchr_builtin (loop_p loop, tree reduction_var,
                            data_reference_p store_dr, tree base, tree pattern,
                            location_t loc)
{
  gimple_seq seq = NULL;

  tree mem = force_gimple_operand (base, &seq, true, NULL_TREE);
  gimple *fn_call = gimple_build_call_internal (IFN_RAWMEMCHR, 2, mem, pattern);
  tree reduction_var_new = copy_ssa_name (reduction_var);
  gimple_call_set_lhs (fn_call, reduction_var_new);
  gimple_set_location (fn_call, loc);
  gimple_seq_add_stmt (&seq, fn_call);

  if (store_dr)
    {
      gassign *g = gimple_build_assign (DR_REF (store_dr), reduction_var_new);
      gimple_seq_add_stmt (&seq, g);
    }

  generate_reduction_builtin_1 (loop, seq, reduction_var, reduction_var_new,
                                "generated rawmemchr%s\n",
                                TYPE_MODE (TREE_TYPE (TREE_TYPE (base))));
}

/* Helper function for generate_strlen_builtin(,_using_rawmemchr)  */

static void
generate_strlen_builtin_1 (loop_p loop, gimple_seq &seq,
                           tree reduction_var_old, tree reduction_var_new,
                           machine_mode mode, tree start_len)
{
  /* REDUCTION_VAR_NEW has either size type or ptrdiff type and must be
     converted if types of old and new reduction variable are not compatible. */
  reduction_var_new = gimple_convert (&seq, TREE_TYPE (reduction_var_old),
                                      reduction_var_new);

  /* Loops of the form `for (i=42; s[i]; ++i);` have an additional start
     length.  */
  if (!integer_zerop (start_len))
    {
      tree lhs = make_ssa_name (TREE_TYPE (reduction_var_new));
      gimple *g = gimple_build_assign (lhs, PLUS_EXPR, reduction_var_new,
                                       start_len);
      gimple_seq_add_stmt (&seq, g);
      reduction_var_new = lhs;
    }

  generate_reduction_builtin_1 (loop, seq, reduction_var_old, reduction_var_new,
                                "generated strlen%s\n", mode);
}

/* Generate a call to strlen and place it before LOOP.  REDUCTION_VAR is
   replaced with a fresh SSA name representing the result of the call.  */

static void
generate_strlen_builtin (loop_p loop, tree reduction_var, tree base,
                         tree start_len, location_t loc)
{
  gimple_seq seq = NULL;

  tree reduction_var_new = make_ssa_name (size_type_node);

  tree mem = force_gimple_operand (base, &seq, true, NULL_TREE);
  tree fn = build_fold_addr_expr (builtin_decl_implicit (BUILT_IN_STRLEN));
  gimple *fn_call = gimple_build_call (fn, 1, mem);
  gimple_call_set_lhs (fn_call, reduction_var_new);
  gimple_set_location (fn_call, loc);
  gimple_seq_add_stmt (&seq, fn_call);

  generate_strlen_builtin_1 (loop, seq, reduction_var, reduction_var_new,
                             QImode, start_len);
}

/* Generate code in order to mimic the behaviour of strlen but this time over
   an array of elements with mode different than QI.  REDUCTION_VAR is replaced
   with a fresh SSA name representing the result, i.e., the length.  */

static void
generate_strlen_builtin_using_rawmemchr (loop_p loop, tree reduction_var,
                                         tree base, tree load_type,
                                         tree start_len, location_t loc)
{
  gimple_seq seq = NULL;

  tree start = force_gimple_operand (base, &seq, true, NULL_TREE);
  tree zero = build_zero_cst (load_type);
  gimple *fn_call = gimple_build_call_internal (IFN_RAWMEMCHR, 2, start, zero);
  tree end = make_ssa_name (TREE_TYPE (base));
  gimple_call_set_lhs (fn_call, end);
  gimple_set_location (fn_call, loc);
  gimple_seq_add_stmt (&seq, fn_call);

  /* Determine the number of elements between START and END by
     evaluating (END - START) / sizeof (*START).  */
  tree diff = make_ssa_name (ptrdiff_type_node);
  gimple *diff_stmt = gimple_build_assign (diff, POINTER_DIFF_EXPR, end, start);
  gimple_seq_add_stmt (&seq, diff_stmt);
  /* Let SIZE be the size of each character.  */
  tree size = gimple_convert (&seq, ptrdiff_type_node,
                              TYPE_SIZE_UNIT (load_type));
  tree count = make_ssa_name (ptrdiff_type_node);
  gimple *count_stmt = gimple_build_assign (count, TRUNC_DIV_EXPR, diff, size);
  gimple_seq_add_stmt (&seq, count_stmt);

  generate_strlen_builtin_1 (loop, seq, reduction_var, count,
                             TYPE_MODE (load_type),
                             start_len);
}

/* Return true if we can count at least as many characters by taking pointer
   difference as we can count via reduction_var without an overflow.  Thus
   compute 2^n < (2^(m-1) / s) where n = TYPE_PRECISION (reduction_var_type),
   m = TYPE_PRECISION (ptrdiff_type_node), and s = size of each character.  */
static bool
reduction_var_overflows_first (tree reduction_var_type, tree load_type)
{
  widest_int n2 = wi::lshift (1, TYPE_PRECISION (reduction_var_type));;
  widest_int m2 = wi::lshift (1, TYPE_PRECISION (ptrdiff_type_node) - 1);
  widest_int s = wi::to_widest (TYPE_SIZE_UNIT (load_type));
  return wi::ltu_p (n2, wi::udiv_trunc (m2, s));
}

static gimple *
determine_reduction_stmt_1 (const loop_p loop, const basic_block *bbs)
{
  gimple *reduction_stmt = NULL;

  for (unsigned i = 0, ninsns = 0; i < loop->num_nodes; ++i)
    {
      basic_block bb = bbs[i];

      for (gphi_iterator bsi = gsi_start_phis (bb); !gsi_end_p (bsi);
           gsi_next_nondebug (&bsi))
        {
          gphi *phi = bsi.phi ();
          if (virtual_operand_p (gimple_phi_result (phi)))
            continue;
          if (stmt_has_scalar_dependences_outside_loop (loop, phi))
            {
              if (reduction_stmt)
                return NULL;
              reduction_stmt = phi;
            }
        }

      for (gimple_stmt_iterator bsi = gsi_start_bb (bb); !gsi_end_p (bsi);
           gsi_next_nondebug (&bsi), ++ninsns)
        {
          /* Bail out early for loops which are unlikely to match.  */
          if (ninsns > 16)
            return NULL;
          gimple *stmt = gsi_stmt (bsi);
          if (gimple_clobber_p (stmt))
            continue;
          if (gimple_code (stmt) == GIMPLE_LABEL)
            continue;
          if (gimple_has_volatile_ops (stmt))
            return NULL;
          if (stmt_has_scalar_dependences_outside_loop (loop, stmt))
            {
              if (reduction_stmt)
                return NULL;
              reduction_stmt = stmt;
            }
        }
    }

  return reduction_stmt;
}

/* If LOOP has a single non-volatile reduction statement, then return a pointer
   to it.  Otherwise return NULL.  */
static gimple *
determine_reduction_stmt (const loop_p loop)
{
  basic_block *bbs = get_loop_body (loop);
  gimple *reduction_stmt = determine_reduction_stmt_1 (loop, bbs);
  XDELETEVEC (bbs);
  return reduction_stmt;
}

/* Transform loops which mimic the effects of builtins rawmemchr or strlen and
   replace them accordingly.  For example, a loop of the form

     for (; *p != 42; ++p);

   is replaced by

     p = rawmemchr<MODE> (p, 42);

   under the assumption that rawmemchr is available for a particular MODE.
   Another example is

     int i;
     for (i = 42; s[i]; ++i);

   which is replaced by

     i = (int)strlen (&s[42]) + 42;

   for some character array S.  In case array S is not of type character array
   we end up with

     i = (int)(rawmemchr<MODE> (&s[42], 0) - &s[42]) + 42;

   assuming that rawmemchr is available for a particular MODE.  */

bool
loop_distribution::transform_reduction_loop (loop_p loop)
{
  gimple *reduction_stmt;
  data_reference_p load_dr = NULL, store_dr = NULL;

  edge e = single_exit (loop);
  gcond *cond = safe_dyn_cast <gcond *> (*gsi_last_bb (e->src));
  if (!cond)
    return false;
  /* Ensure loop condition is an (in)equality test and loop is exited either if
     the inequality test fails or the equality test succeeds.  */
  if (!(e->flags & EDGE_FALSE_VALUE && gimple_cond_code (cond) == NE_EXPR)
      && !(e->flags & EDGE_TRUE_VALUE && gimple_cond_code (cond) == EQ_EXPR))
    return false;
  /* A limitation of the current implementation is that we only support
     constant patterns in (in)equality tests.  */
  tree pattern = gimple_cond_rhs (cond);
  if (TREE_CODE (pattern) != INTEGER_CST)
    return false;

  reduction_stmt = determine_reduction_stmt (loop);

  /* A limitation of the current implementation is that we require a reduction
     statement.  Therefore, loops without a reduction statement as in the
     following are not recognized:
     int *p;
     void foo (void) { for (; *p; ++p); } */
  if (reduction_stmt == NULL)
    return false;

  /* Reduction variables are guaranteed to be SSA names.  */
  tree reduction_var;
  switch (gimple_code (reduction_stmt))
    {
    case GIMPLE_ASSIGN:
    case GIMPLE_PHI:
      reduction_var = gimple_get_lhs (reduction_stmt);
      break;
    default:
      /* Bail out e.g. for GIMPLE_CALL.  */
      return false;
    }

  struct graph *rdg = build_rdg (loop, NULL);
  if (rdg == NULL)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file,
                 "Loop %d not transformed: failed to build the RDG.\n",
                 loop->num);

      return false;
    }
  auto_bitmap partition_stmts;
  bitmap_set_range (partition_stmts, 0, rdg->n_vertices);
  find_single_drs (loop, rdg, partition_stmts, &store_dr, &load_dr);
  free_rdg (rdg);

  /* Bail out if there is no single load.  */
  if (load_dr == NULL)
    return false;

  /* Reaching this point we have a loop with a single reduction variable,
     a single load, and an optional single store.  */

  tree load_ref = DR_REF (load_dr);
  tree load_type = TREE_TYPE (load_ref);
  tree load_access_base = build_fold_addr_expr (load_ref);
  tree load_access_size = TYPE_SIZE_UNIT (load_type);
  affine_iv load_iv, reduction_iv;

  if (!INTEGRAL_TYPE_P (load_type)
      || !type_has_mode_precision_p (load_type))
    return false;

  /* We already ensured that the loop condition tests for (in)equality where the
     rhs is a constant pattern. Now ensure that the lhs is the result of the
     load.  */
  if (gimple_cond_lhs (cond) != gimple_assign_lhs (DR_STMT (load_dr)))
    return false;

  /* Bail out if no affine induction variable with constant step can be
     determined.  */
  if (!simple_iv (loop, loop, load_access_base, &load_iv, false))
    return false;

  /* Bail out if memory accesses are not consecutive or not growing.  */
  if (!operand_equal_p (load_iv.step, load_access_size, 0))
    return false;

  if (!simple_iv (loop, loop, reduction_var, &reduction_iv, false))
    return false;

  /* Handle rawmemchr like loops.  */
  if (operand_equal_p (load_iv.base, reduction_iv.base)
      && operand_equal_p (load_iv.step, reduction_iv.step))
    {
      if (store_dr)
        {
          /* Ensure that we store to X and load from X+I where I>0.  */
          if (TREE_CODE (load_iv.base) != POINTER_PLUS_EXPR
              || !integer_onep (TREE_OPERAND (load_iv.base, 1)))
            return false;
          tree ptr_base = TREE_OPERAND (load_iv.base, 0);
          if (TREE_CODE (ptr_base) != SSA_NAME)
            return false;
          gimple *def = SSA_NAME_DEF_STMT (ptr_base);
          if (!gimple_assign_single_p (def)
              || gimple_assign_rhs1 (def) != DR_REF (store_dr))
            return false;
          /* Ensure that the reduction value is stored.  */
          if (gimple_assign_rhs1 (DR_STMT (store_dr)) != reduction_var)
            return false;
        }
      /* Bail out if target does not provide rawmemchr for a certain mode.  */
      machine_mode mode = TYPE_MODE (load_type);
      if (direct_optab_handler (rawmemchr_optab, mode) == CODE_FOR_nothing)
        return false;
      location_t loc = gimple_location (DR_STMT (load_dr));
      generate_rawmemchr_builtin (loop, reduction_var, store_dr, load_iv.base,
                                  pattern, loc);
      return true;
    }

  /* Handle strlen like loops.  */
  if (store_dr == NULL
      && integer_zerop (pattern)
      && INTEGRAL_TYPE_P (TREE_TYPE (reduction_var))
      && TREE_CODE (reduction_iv.base) == INTEGER_CST
      && TREE_CODE (reduction_iv.step) == INTEGER_CST
      && integer_onep (reduction_iv.step))
    {
      location_t loc = gimple_location (DR_STMT (load_dr));
      tree reduction_var_type = TREE_TYPE (reduction_var);
      /* While determining the length of a string an overflow might occur.
         If an overflow only occurs in the loop implementation and not in the
         strlen implementation, then either the overflow is undefined or the
         truncated result of strlen equals the one of the loop.  Otherwise if
         an overflow may also occur in the strlen implementation, then
         replacing a loop by a call to strlen is sound whenever we ensure that
         if an overflow occurs in the strlen implementation, then also an
         overflow occurs in the loop implementation which is undefined.  It
         seems reasonable to relax this and assume that the strlen
         implementation cannot overflow in case sizetype is big enough in the
         sense that an overflow can only happen for string objects which are
         bigger than half of the address space; at least for 32-bit targets and
         up.

         For strlen which makes use of rawmemchr the maximal length of a string
         which can be determined without an overflow is PTRDIFF_MAX / S where
         each character has size S.  Since an overflow for ptrdiff type is
         undefined we have to make sure that if an overflow occurs, then an
         overflow occurs in the loop implementation, too, and this is
         undefined, too.  Similar as before we relax this and assume that no
         string object is larger than half of the address space; at least for
         32-bit targets and up.  */
      if (TYPE_MODE (load_type) == TYPE_MODE (char_type_node)
          && TYPE_PRECISION (load_type) == TYPE_PRECISION (char_type_node)
          && ((TYPE_PRECISION (sizetype) >= TYPE_PRECISION (ptr_type_node) - 1
               && TYPE_PRECISION (ptr_type_node) >= 32)
              || (TYPE_OVERFLOW_UNDEFINED (reduction_var_type)
                  && TYPE_PRECISION (reduction_var_type) <= TYPE_PRECISION (sizetype)))
          && builtin_decl_implicit (BUILT_IN_STRLEN))
        generate_strlen_builtin (loop, reduction_var, load_iv.base,
                                 reduction_iv.base, loc);
      else if (direct_optab_handler (rawmemchr_optab, TYPE_MODE (load_type))
               != CODE_FOR_nothing
               && ((TYPE_PRECISION (ptrdiff_type_node) == TYPE_PRECISION (ptr_type_node)
                    && TYPE_PRECISION (ptrdiff_type_node) >= 32)
                   || (TYPE_OVERFLOW_UNDEFINED (reduction_var_type)
                       && reduction_var_overflows_first (reduction_var_type, load_type))))
        generate_strlen_builtin_using_rawmemchr (loop, reduction_var,
                                                 load_iv.base,
                                                 load_type,
                                                 reduction_iv.base, loc);
      else
        return false;
      return true;
    }

  return false;
}

/* Given innermost LOOP, return the outermost enclosing loop that forms a
   perfect loop nest.  */

static class loop *
prepare_perfect_loop_nest (class loop *loop)
{
  class loop *outer = loop_outer (loop);
  tree niters = number_of_latch_executions (loop);

  /* TODO: We only support the innermost 3-level loop nest distribution
     because of compilation time issue for now.  This should be relaxed
     in the future.  Note we only allow 3-level loop nest distribution
     when parallelizing loops.  */
  while ((loop->inner == NULL
          || (loop->inner->inner == NULL && flag_tree_parallelize_loops > 1))
         && loop_outer (outer)
         && outer->inner == loop && loop->next == NULL
         && single_exit (outer)
         && !chrec_contains_symbols_defined_in_loop (niters, outer->num)
         && (niters = number_of_latch_executions (outer)) != NULL_TREE
         && niters != chrec_dont_know)
    {
      loop = outer;
      outer = loop_outer (loop);
    }

  return loop;
}


unsigned int
loop_distribution::execute (function *fun)
{
  bool changed = false;
  basic_block bb;
  control_dependences *cd = NULL;
  auto_vec<loop_p> loops_to_be_destroyed;

  if (number_of_loops (fun) <= 1)
    return 0;

  bb_top_order_init ();

  FOR_ALL_BB_FN (bb, fun)
    {
      gimple_stmt_iterator gsi;
      for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
        gimple_set_uid (gsi_stmt (gsi), -1);
      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
        gimple_set_uid (gsi_stmt (gsi), -1);
    }

  /* We can at the moment only distribute non-nested loops, thus restrict
     walking to innermost loops.  */
  for (auto loop : loops_list (cfun, LI_ONLY_INNERMOST))
    {
      /* Don't distribute multiple exit edges loop, or cold loop when
         not doing pattern detection.  */
      if (!single_exit (loop)
          || (!flag_tree_loop_distribute_patterns
              && !optimize_loop_for_speed_p (loop)))
        continue;

      /* If niters is unknown don't distribute loop but rather try to transform
         it to a call to a builtin.  */
      tree niters = number_of_latch_executions (loop);
      if (niters == NULL_TREE || niters == chrec_dont_know)
        {
          datarefs_vec.create (20);
          if (flag_tree_loop_distribute_patterns
              && transform_reduction_loop (loop))
            {
              changed = true;
              loops_to_be_destroyed.safe_push (loop);
              if (dump_enabled_p ())
                {
                  dump_user_location_t loc = find_loop_location (loop);
                  dump_printf_loc (MSG_OPTIMIZED_LOCATIONS,
                                   loc, "Loop %d transformed into a builtin.\n",
                                   loop->num);
                }
            }
          free_data_refs (datarefs_vec);
          continue;
        }

      /* Get the perfect loop nest for distribution.  */
      loop = prepare_perfect_loop_nest (loop);
      for (; loop; loop = loop->inner)
        {
          auto_vec<gimple *> work_list;
          if (!find_seed_stmts_for_distribution (loop, &work_list))
            continue;

          const char *str = loop->inner ? " nest" : "";
          dump_user_location_t loc = find_loop_location (loop);
          if (!cd)
            {
              calculate_dominance_info (CDI_DOMINATORS);
              calculate_dominance_info (CDI_POST_DOMINATORS);
              cd = new control_dependences ();
              free_dominance_info (CDI_POST_DOMINATORS);
            }

          bool destroy_p;
          int nb_generated_loops, nb_generated_calls;
          bool only_patterns = !optimize_loop_for_speed_p (loop)
                               || !flag_tree_loop_distribution;
          /* do not try to distribute loops that are not expected to iterate.  */
          if (!only_patterns)
            {
              HOST_WIDE_INT iterations = estimated_loop_iterations_int (loop);
              if (iterations < 0)
                iterations = likely_max_loop_iterations_int (loop);
              if (!iterations)
                only_patterns = true;
            }
          nb_generated_loops
            = distribute_loop (loop, work_list, cd, &nb_generated_calls,
                               &destroy_p, only_patterns);
          if (destroy_p)
            loops_to_be_destroyed.safe_push (loop);

          if (nb_generated_loops + nb_generated_calls > 0)
            {
              changed = true;
              if (dump_enabled_p ())
                dump_printf_loc (MSG_OPTIMIZED_LOCATIONS,
                                 loc, "Loop%s %d distributed: split to %d loops "
                                 "and %d library calls.\n", str, loop->num,
                                 nb_generated_loops, nb_generated_calls);

              break;
            }

          if (dump_file && (dump_flags & TDF_DETAILS))
            fprintf (dump_file, "Loop%s %d not distributed.\n", str, loop->num);
        }
    }

  if (cd)
    delete cd;

  if (bb_top_order_index != NULL)
    bb_top_order_destroy ();

  if (changed)
    {
      /* Destroy loop bodies that could not be reused.  Do this late as we
         otherwise can end up refering to stale data in control dependences.  */
      unsigned i;
      class loop *loop;
      FOR_EACH_VEC_ELT (loops_to_be_destroyed, i, loop)
        destroy_loop (loop);

      /* Cached scalar evolutions now may refer to wrong or non-existing
         loops.  */
      scev_reset ();
      mark_virtual_operands_for_renaming (fun);
      rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa);
    }

  checking_verify_loop_structure ();

  return changed ? TODO_cleanup_cfg : 0;
}


/* Distribute all loops in the current function.  */

namespace {

const pass_data pass_data_loop_distribution =
{
  GIMPLE_PASS, /* type */
  "ldist", /* name */
  OPTGROUP_LOOP, /* optinfo_flags */
  TV_TREE_LOOP_DISTRIBUTION, /* tv_id */
  ( PROP_cfg | PROP_ssa ), /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  0, /* todo_flags_finish */
};

class pass_loop_distribution : public gimple_opt_pass
{
public:
  pass_loop_distribution (gcc::context *ctxt)
    : gimple_opt_pass (pass_data_loop_distribution, ctxt)
  {}

  /* opt_pass methods: */
  bool gate (function *) final override
    {
      return flag_tree_loop_distribution
        || flag_tree_loop_distribute_patterns;
    }

  unsigned int execute (function *) final override;

}; // class pass_loop_distribution

unsigned int
pass_loop_distribution::execute (function *fun)
{
  return loop_distribution ().execute (fun);
}

} // anon namespace

gimple_opt_pass *
make_pass_loop_distribution (gcc::context *ctxt)
{
  return new pass_loop_distribution (ctxt);
}