basic-block.h (FOR_ALL_BB_FN): New macro.

[gcc.git] / gcc / tree-ssa-loop-im.c

/* Loop invariant motion.
   Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc.
   
This file is part of GCC.
   
GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, 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 COPYING.  If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "tm_p.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "output.h"
#include "diagnostic.h"
#include "tree-flow.h"
#include "tree-dump.h"
#include "timevar.h"
#include "cfgloop.h"
#include "domwalk.h"
#include "params.h"
#include "tree-pass.h"
#include "flags.h"
#include "real.h"
#include "hashtab.h"

/* TODO:  Support for predicated code motion.  I.e.

   while (1)
     {
       if (cond)
         {
           a = inv;
           something;
         }
     }

   Where COND and INV are is invariants, but evaluating INV may trap or be
   invalid from some other reason if !COND.  This may be transformed to

   if (cond)
     a = inv;
   while (1)
     {
       if (cond)
         something;
     }  */

/* A type for the list of statements that have to be moved in order to be able
   to hoist an invariant computation.  */

struct depend
{
  tree stmt;
  struct depend *next;
};

/* The auxiliary data kept for each statement.  */

struct lim_aux_data
{
  struct loop *max_loop;        /* The outermost loop in that the statement
                                   is invariant.  */

  struct loop *tgt_loop;        /* The loop out of that we want to move the
                                   invariant.  */

  struct loop *always_executed_in;
                                /* The outermost loop for that we are sure
                                   the statement is executed if the loop
                                   is entered.  */

  bool sm_done;                 /* True iff the store motion for a memory
                                   reference in the statement has already
                                   been executed.  */

  unsigned cost;                /* Cost of the computation performed by the
                                   statement.  */

  struct depend *depends;       /* List of statements that must be also hoisted
                                   out of the loop when this statement is
                                   hoisted; i.e. those that define the operands
                                   of the statement and are inside of the
                                   MAX_LOOP loop.  */
};

#define LIM_DATA(STMT) (TREE_CODE (STMT) == PHI_NODE \
                        ? NULL \
                        : (struct lim_aux_data *) (stmt_ann (STMT)->aux))

/* Description of a memory reference location for store motion.  */

struct mem_ref_loc
{
  tree *ref;                    /* The reference itself.  */
  tree stmt;                    /* The statement in that it occurs.  */
  struct mem_ref_loc *next;     /* Next use in the chain.  */
};

/* Description of a memory reference for store motion.  */

struct mem_ref
{
  tree mem;                     /* The memory itself.  */
  hashval_t hash;               /* Its hash value.  */
  bool is_stored;               /* True if there is a store to the location
                                   in the loop.  */
  struct mem_ref_loc *locs;     /* The locations where it is found.  */
  bitmap vops;                  /* Vops corresponding to this memory
                                   location.  */
  struct mem_ref *next;         /* Next memory reference in the list.
                                   Memory references are stored in a hash
                                   table, but the hash function depends
                                   on values of pointers. Thus we cannot use
                                   htab_traverse, since then we would get
                                   misscompares during bootstrap (although the
                                   produced code would be correct).  */
};

/* Minimum cost of an expensive expression.  */
#define LIM_EXPENSIVE ((unsigned) PARAM_VALUE (PARAM_LIM_EXPENSIVE))

/* The outermost loop for that execution of the header guarantees that the
   block will be executed.  */
#define ALWAYS_EXECUTED_IN(BB) ((struct loop *) (BB)->aux)

/* Calls CBCK for each index in memory reference ADDR_P.  There are two
   kinds situations handled; in each of these cases, the memory reference
   and DATA are passed to the callback:
   
   Access to an array: ARRAY_{RANGE_}REF (base, index).  In this case we also
   pass the pointer to the index to the callback.

   Pointer dereference: INDIRECT_REF (addr).  In this case we also pass the
   pointer to addr to the callback.
   
   If the callback returns false, the whole search stops and false is returned.
   Otherwise the function returns true after traversing through the whole
   reference *ADDR_P.  */

bool
for_each_index (tree *addr_p, bool (*cbck) (tree, tree *, void *), void *data)
{
  tree *nxt, *idx;

  for (; ; addr_p = nxt)
    {
      switch (TREE_CODE (*addr_p))
        {
        case SSA_NAME:
          return cbck (*addr_p, addr_p, data);

        case MISALIGNED_INDIRECT_REF:
        case ALIGN_INDIRECT_REF:
        case INDIRECT_REF:
          nxt = &TREE_OPERAND (*addr_p, 0);
          return cbck (*addr_p, nxt, data);

        case BIT_FIELD_REF:
        case VIEW_CONVERT_EXPR:
        case ARRAY_RANGE_REF:
        case REALPART_EXPR:
        case IMAGPART_EXPR:
          nxt = &TREE_OPERAND (*addr_p, 0);
          break;

        case COMPONENT_REF:
          /* If the component has varying offset, it behaves like index
             as well.  */
          idx = &TREE_OPERAND (*addr_p, 2);
          if (*idx
              && !cbck (*addr_p, idx, data))
            return false;

          nxt = &TREE_OPERAND (*addr_p, 0);
          break;

        case ARRAY_REF:
          nxt = &TREE_OPERAND (*addr_p, 0);
          if (!cbck (*addr_p, &TREE_OPERAND (*addr_p, 1), data))
            return false;
          break;

        case VAR_DECL:
        case PARM_DECL:
        case STRING_CST:
        case RESULT_DECL:
          return true;

        default:
          gcc_unreachable ();
        }
    }
}

/* If it is possible to hoist the statement STMT unconditionally,
   returns MOVE_POSSIBLE.
   If it is possible to hoist the statement STMT, but we must avoid making
   it executed if it would not be executed in the original program (e.g.
   because it may trap), return MOVE_PRESERVE_EXECUTION.
   Otherwise return MOVE_IMPOSSIBLE.  */

enum move_pos
movement_possibility (tree stmt)
{
  tree lhs, rhs;

  if (flag_unswitch_loops
      && TREE_CODE (stmt) == COND_EXPR)
    {
      /* If we perform unswitching, force the operands of the invariant
         condition to be moved out of the loop.  */
      return MOVE_POSSIBLE;
    }

  if (TREE_CODE (stmt) != MODIFY_EXPR)
    return MOVE_IMPOSSIBLE;

  if (stmt_ends_bb_p (stmt))
    return MOVE_IMPOSSIBLE;

  if (stmt_ann (stmt)->has_volatile_ops)
    return MOVE_IMPOSSIBLE;

  lhs = TREE_OPERAND (stmt, 0);
  if (TREE_CODE (lhs) == SSA_NAME
      && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs))
    return MOVE_IMPOSSIBLE;

  rhs = TREE_OPERAND (stmt, 1);

  if (TREE_SIDE_EFFECTS (rhs))
    return MOVE_IMPOSSIBLE;

  if (TREE_CODE (lhs) != SSA_NAME
      || tree_could_trap_p (rhs))
    return MOVE_PRESERVE_EXECUTION;

  if (get_call_expr_in (stmt))
    {
      /* While pure or const call is guaranteed to have no side effects, we
         cannot move it arbitrarily.  Consider code like

         char *s = something ();

         while (1)
           {
             if (s)
               t = strlen (s);
             else
               t = 0;
           }

         Here the strlen call cannot be moved out of the loop, even though
         s is invariant.  In addition to possibly creating a call with
         invalid arguments, moving out a function call that is not executed
         may cause performance regressions in case the call is costly and
         not executed at all.  */
      return MOVE_PRESERVE_EXECUTION;
    }
  return MOVE_POSSIBLE;
}

/* Suppose that operand DEF is used inside the LOOP.  Returns the outermost
   loop to that we could move the expression using DEF if it did not have
   other operands, i.e. the outermost loop enclosing LOOP in that the value
   of DEF is invariant.  */

static struct loop *
outermost_invariant_loop (tree def, struct loop *loop)
{
  tree def_stmt;
  basic_block def_bb;
  struct loop *max_loop;

  if (TREE_CODE (def) != SSA_NAME)
    return superloop_at_depth (loop, 1);

  def_stmt = SSA_NAME_DEF_STMT (def);
  def_bb = bb_for_stmt (def_stmt);
  if (!def_bb)
    return superloop_at_depth (loop, 1);

  max_loop = find_common_loop (loop, def_bb->loop_father);

  if (LIM_DATA (def_stmt) && LIM_DATA (def_stmt)->max_loop)
    max_loop = find_common_loop (max_loop,
                                 LIM_DATA (def_stmt)->max_loop->outer);
  if (max_loop == loop)
    return NULL;
  max_loop = superloop_at_depth (loop, max_loop->depth + 1);

  return max_loop;
}

/* Returns the outermost superloop of LOOP in that the expression EXPR is
   invariant.  */

static struct loop *
outermost_invariant_loop_expr (tree expr, struct loop *loop)
{
  enum tree_code_class class = TREE_CODE_CLASS (TREE_CODE (expr));
  unsigned i, nops;
  struct loop *max_loop = superloop_at_depth (loop, 1), *aloop;

  if (TREE_CODE (expr) == SSA_NAME
      || TREE_CODE (expr) == INTEGER_CST
      || is_gimple_min_invariant (expr))
    return outermost_invariant_loop (expr, loop);

  if (class != tcc_unary
      && class != tcc_binary
      && class != tcc_expression
      && class != tcc_comparison)
    return NULL;

  nops = TREE_CODE_LENGTH (TREE_CODE (expr));
  for (i = 0; i < nops; i++)
    {
      aloop = outermost_invariant_loop_expr (TREE_OPERAND (expr, i), loop);
      if (!aloop)
        return NULL;

      if (flow_loop_nested_p (max_loop, aloop))
        max_loop = aloop;
    }

  return max_loop;
}

/* DATA is a structure containing information associated with a statement
   inside LOOP.  DEF is one of the operands of this statement.
   
   Find the outermost loop enclosing LOOP in that value of DEF is invariant
   and record this in DATA->max_loop field.  If DEF itself is defined inside
   this loop as well (i.e. we need to hoist it out of the loop if we want
   to hoist the statement represented by DATA), record the statement in that
   DEF is defined to the DATA->depends list.  Additionally if ADD_COST is true,
   add the cost of the computation of DEF to the DATA->cost.
   
   If DEF is not invariant in LOOP, return false.  Otherwise return TRUE.  */

static bool
add_dependency (tree def, struct lim_aux_data *data, struct loop *loop,
                bool add_cost)
{
  tree def_stmt = SSA_NAME_DEF_STMT (def);
  basic_block def_bb = bb_for_stmt (def_stmt);
  struct loop *max_loop;
  struct depend *dep;

  if (!def_bb)
    return true;

  max_loop = outermost_invariant_loop (def, loop);
  if (!max_loop)
    return false;

  if (flow_loop_nested_p (data->max_loop, max_loop))
    data->max_loop = max_loop;

  if (!LIM_DATA (def_stmt))
    return true;

  if (add_cost
      /* Only add the cost if the statement defining DEF is inside LOOP,
         i.e. if it is likely that by moving the invariants dependent
         on it, we will be able to avoid creating a new register for
         it (since it will be only used in these dependent invariants).  */
      && def_bb->loop_father == loop)
    data->cost += LIM_DATA (def_stmt)->cost;

  dep = xmalloc (sizeof (struct depend));
  dep->stmt = def_stmt;
  dep->next = data->depends;
  data->depends = dep;

  return true;
}

/* Returns an estimate for a cost of statement STMT.  TODO -- the values here
   are just ad-hoc constants.  The estimates should be based on target-specific
   values.  */

static unsigned
stmt_cost (tree stmt)
{
  tree rhs;
  unsigned cost = 1;

  /* Always try to create possibilities for unswitching.  */
  if (TREE_CODE (stmt) == COND_EXPR)
    return LIM_EXPENSIVE;

  rhs = TREE_OPERAND (stmt, 1);

  /* Hoisting memory references out should almost surely be a win.  */
  if (stmt_references_memory_p (stmt))
    cost += 20;

  switch (TREE_CODE (rhs))
    {
    case CALL_EXPR:
      /* We should be hoisting calls if possible.  */

      /* Unless the call is a builtin_constant_p; this always folds to a
         constant, so moving it is useless.  */
      rhs = get_callee_fndecl (rhs);
      if (DECL_BUILT_IN_CLASS (rhs) == BUILT_IN_NORMAL
          && DECL_FUNCTION_CODE (rhs) == BUILT_IN_CONSTANT_P)
        return 0;

      cost += 20;
      break;

    case MULT_EXPR:
    case TRUNC_DIV_EXPR:
    case CEIL_DIV_EXPR:
    case FLOOR_DIV_EXPR:
    case ROUND_DIV_EXPR:
    case EXACT_DIV_EXPR:
    case CEIL_MOD_EXPR:
    case FLOOR_MOD_EXPR:
    case ROUND_MOD_EXPR:
    case TRUNC_MOD_EXPR:
    case RDIV_EXPR:
      /* Division and multiplication are usually expensive.  */
      cost += 20;
      break;

    default:
      break;
    }

  return cost;
}

/* Determine the outermost loop to that it is possible to hoist a statement
   STMT and store it to LIM_DATA (STMT)->max_loop.  To do this we determine
   the outermost loop in that the value computed by STMT is invariant.
   If MUST_PRESERVE_EXEC is true, additionally choose such a loop that
   we preserve the fact whether STMT is executed.  It also fills other related
   information to LIM_DATA (STMT).
   
   The function returns false if STMT cannot be hoisted outside of the loop it
   is defined in, and true otherwise.  */

static bool
determine_max_movement (tree stmt, bool must_preserve_exec)
{
  basic_block bb = bb_for_stmt (stmt);
  struct loop *loop = bb->loop_father;
  struct loop *level;
  struct lim_aux_data *lim_data = LIM_DATA (stmt);
  tree val;
  ssa_op_iter iter;
  
  if (must_preserve_exec)
    level = ALWAYS_EXECUTED_IN (bb);
  else
    level = superloop_at_depth (loop, 1);
  lim_data->max_loop = level;

  FOR_EACH_SSA_TREE_OPERAND (val, stmt, iter, SSA_OP_USE)
    if (!add_dependency (val, lim_data, loop, true))
      return false;

  FOR_EACH_SSA_TREE_OPERAND (val, stmt, iter, SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_KILLS)
    if (!add_dependency (val, lim_data, loop, false))
      return false;

  lim_data->cost += stmt_cost (stmt);

  return true;
}

/* Suppose that some statement in ORIG_LOOP is hoisted to the loop LEVEL,
   and that one of the operands of this statement is computed by STMT.
   Ensure that STMT (together with all the statements that define its
   operands) is hoisted at least out of the loop LEVEL.  */

static void
set_level (tree stmt, struct loop *orig_loop, struct loop *level)
{
  struct loop *stmt_loop = bb_for_stmt (stmt)->loop_father;
  struct depend *dep;

  stmt_loop = find_common_loop (orig_loop, stmt_loop);
  if (LIM_DATA (stmt) && LIM_DATA (stmt)->tgt_loop)
    stmt_loop = find_common_loop (stmt_loop,
                                  LIM_DATA (stmt)->tgt_loop->outer);
  if (flow_loop_nested_p (stmt_loop, level))
    return;

  gcc_assert (LIM_DATA (stmt));
  gcc_assert (level == LIM_DATA (stmt)->max_loop
              || flow_loop_nested_p (LIM_DATA (stmt)->max_loop, level));

  LIM_DATA (stmt)->tgt_loop = level;
  for (dep = LIM_DATA (stmt)->depends; dep; dep = dep->next)
    set_level (dep->stmt, orig_loop, level);
}

/* Determines an outermost loop from that we want to hoist the statement STMT.
   For now we chose the outermost possible loop.  TODO -- use profiling
   information to set it more sanely.  */

static void
set_profitable_level (tree stmt)
{
  set_level (stmt, bb_for_stmt (stmt)->loop_father, LIM_DATA (stmt)->max_loop);
}

/* Returns true if STMT is not a pure call.  */

static bool
nonpure_call_p (tree stmt)
{
  tree call = get_call_expr_in (stmt);

  if (!call)
    return false;

  return TREE_SIDE_EFFECTS (call) != 0;
}

/* Releases the memory occupied by DATA.  */

static void
free_lim_aux_data (struct lim_aux_data *data)
{
  struct depend *dep, *next;

  for (dep = data->depends; dep; dep = next)
    {
      next = dep->next;
      free (dep);
    }
  free (data);
}

/* Determine the outermost loops in that statements in basic block BB are
   invariant, and record them to the LIM_DATA associated with the statements.
   Callback for walk_dominator_tree.  */

static void
determine_invariantness_stmt (struct dom_walk_data *dw_data ATTRIBUTE_UNUSED,
                              basic_block bb)
{
  enum move_pos pos;
  block_stmt_iterator bsi;
  tree stmt, rhs;
  bool maybe_never = ALWAYS_EXECUTED_IN (bb) == NULL;
  struct loop *outermost = ALWAYS_EXECUTED_IN (bb);

  if (!bb->loop_father->outer)
    return;

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "Basic block %d (loop %d -- depth %d):\n\n",
             bb->index, bb->loop_father->num, bb->loop_father->depth);

  for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
    {
      stmt = bsi_stmt (bsi);

      pos = movement_possibility (stmt);
      if (pos == MOVE_IMPOSSIBLE)
        {
          if (nonpure_call_p (stmt))
            {
              maybe_never = true;
              outermost = NULL;
            }
          continue;
        }

      /* If divisor is invariant, convert a/b to a*(1/b), allowing reciprocal
         to be hoisted out of loop, saving expensive divide.  */
      if (pos == MOVE_POSSIBLE
          && (rhs = TREE_OPERAND (stmt, 1)) != NULL
          && TREE_CODE (rhs) == RDIV_EXPR
          && flag_unsafe_math_optimizations
          && outermost_invariant_loop_expr (TREE_OPERAND (rhs, 1),
                                            loop_containing_stmt (stmt)) != NULL
          && outermost_invariant_loop_expr (rhs,
                                            loop_containing_stmt (stmt)) == NULL)
        {
          tree lhs, stmt1, stmt2, var, name;

          lhs = TREE_OPERAND (stmt, 0);

          /* stmt must be MODIFY_EXPR.  */
          var = create_tmp_var (TREE_TYPE (rhs), "reciptmp");
          add_referenced_tmp_var (var);

          stmt1 = build2 (MODIFY_EXPR, void_type_node, var,
                          build2 (RDIV_EXPR, TREE_TYPE (rhs),
                                  build_real (TREE_TYPE (rhs), dconst1),
                                  TREE_OPERAND (rhs, 1)));
          name = make_ssa_name (var, stmt1);
          TREE_OPERAND (stmt1, 0) = name;
          stmt2 = build2 (MODIFY_EXPR, void_type_node, lhs,
                          build2 (MULT_EXPR, TREE_TYPE (rhs),
                                  name, TREE_OPERAND (rhs, 0)));

          /* Replace division stmt with reciprocal and multiply stmts.
             The multiply stmt is not invariant, so update iterator
             and avoid rescanning.  */
          bsi_replace (&bsi, stmt1, true);
          bsi_insert_after (&bsi, stmt2, BSI_NEW_STMT);
          SSA_NAME_DEF_STMT (lhs) = stmt2;

          /* Continue processing with invariant reciprocal statment.  */
          stmt = stmt1;
        }

      stmt_ann (stmt)->aux = xcalloc (1, sizeof (struct lim_aux_data));
      LIM_DATA (stmt)->always_executed_in = outermost;

      if (maybe_never && pos == MOVE_PRESERVE_EXECUTION)
        continue;

      if (!determine_max_movement (stmt, pos == MOVE_PRESERVE_EXECUTION))
        {
          LIM_DATA (stmt)->max_loop = NULL;
          continue;
        }

      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          print_generic_stmt_indented (dump_file, stmt, 0, 2);
          fprintf (dump_file, "  invariant up to level %d, cost %d.\n\n",
                   LIM_DATA (stmt)->max_loop->depth,
                   LIM_DATA (stmt)->cost);
        }

      if (LIM_DATA (stmt)->cost >= LIM_EXPENSIVE)
        set_profitable_level (stmt);
    }
}

/* For each statement determines the outermost loop in that it is invariant,
   statements on whose motion it depends and the cost of the computation.
   This information is stored to the LIM_DATA structure associated with
   each statement.  */

static void
determine_invariantness (void)
{
  struct dom_walk_data walk_data;

  memset (&walk_data, 0, sizeof (struct dom_walk_data));
  walk_data.before_dom_children_before_stmts = determine_invariantness_stmt;

  init_walk_dominator_tree (&walk_data);
  walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR);
  fini_walk_dominator_tree (&walk_data);
}

/* Commits edge insertions and updates loop structures.  */

void
loop_commit_inserts (void)
{
  unsigned old_last_basic_block, i;
  basic_block bb;

  old_last_basic_block = last_basic_block;
  bsi_commit_edge_inserts ();
  for (i = old_last_basic_block; i < (unsigned) last_basic_block; i++)
    {
      bb = BASIC_BLOCK (i);
      add_bb_to_loop (bb,
                      find_common_loop (single_pred (bb)->loop_father,
                                        single_succ (bb)->loop_father));
    }
}

/* Hoist the statements in basic block BB out of the loops prescribed by
   data stored in LIM_DATA structures associated with each statement.  Callback
   for walk_dominator_tree.  */

static void
move_computations_stmt (struct dom_walk_data *dw_data ATTRIBUTE_UNUSED,
                        basic_block bb)
{
  struct loop *level;
  block_stmt_iterator bsi;
  tree stmt;
  unsigned cost = 0;

  if (!bb->loop_father->outer)
    return;

  for (bsi = bsi_start (bb); !bsi_end_p (bsi); )
    {
      stmt = bsi_stmt (bsi);

      if (!LIM_DATA (stmt))
        {
          bsi_next (&bsi);
          continue;
        }

      cost = LIM_DATA (stmt)->cost;
      level = LIM_DATA (stmt)->tgt_loop;
      free_lim_aux_data (LIM_DATA (stmt));
      stmt_ann (stmt)->aux = NULL;

      if (!level)
        {
          bsi_next (&bsi);
          continue;
        }

      /* We do not really want to move conditionals out of the loop; we just
         placed it here to force its operands to be moved if necessary.  */
      if (TREE_CODE (stmt) == COND_EXPR)
        continue;

      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          fprintf (dump_file, "Moving statement\n");
          print_generic_stmt (dump_file, stmt, 0);
          fprintf (dump_file, "(cost %u) out of loop %d.\n\n",
                   cost, level->num);
        }
      bsi_insert_on_edge (loop_preheader_edge (level), stmt);
      bsi_remove (&bsi);
    }
}

/* Hoist the statements out of the loops prescribed by data stored in
   LIM_DATA structures associated with each statement.*/

static void
move_computations (void)
{
  struct dom_walk_data walk_data;

  memset (&walk_data, 0, sizeof (struct dom_walk_data));
  walk_data.before_dom_children_before_stmts = move_computations_stmt;

  init_walk_dominator_tree (&walk_data);
  walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR);
  fini_walk_dominator_tree (&walk_data);

  loop_commit_inserts ();
  if (need_ssa_update_p ())
    rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa);
}

/* Checks whether the statement defining variable *INDEX can be hoisted
   out of the loop passed in DATA.  Callback for for_each_index.  */

static bool
may_move_till (tree ref, tree *index, void *data)
{
  struct loop *loop = data, *max_loop;

  /* If REF is an array reference, check also that the step and the lower
     bound is invariant in LOOP.  */
  if (TREE_CODE (ref) == ARRAY_REF)
    {
      tree step = array_ref_element_size (ref);
      tree lbound = array_ref_low_bound (ref);

      max_loop = outermost_invariant_loop_expr (step, loop);
      if (!max_loop)
        return false;

      max_loop = outermost_invariant_loop_expr (lbound, loop);
      if (!max_loop)
        return false;
    }

  max_loop = outermost_invariant_loop (*index, loop);
  if (!max_loop)
    return false;

  return true;
}

/* Forces statements defining (invariant) SSA names in expression EXPR to be
   moved out of the LOOP.  ORIG_LOOP is the loop in that EXPR is used.  */

static void
force_move_till_expr (tree expr, struct loop *orig_loop, struct loop *loop)
{
  enum tree_code_class class = TREE_CODE_CLASS (TREE_CODE (expr));
  unsigned i, nops;

  if (TREE_CODE (expr) == SSA_NAME)
    {
      tree stmt = SSA_NAME_DEF_STMT (expr);
      if (IS_EMPTY_STMT (stmt))
        return;

      set_level (stmt, orig_loop, loop);
      return;
    }

  if (class != tcc_unary
      && class != tcc_binary
      && class != tcc_expression
      && class != tcc_comparison)
    return;

  nops = TREE_CODE_LENGTH (TREE_CODE (expr));
  for (i = 0; i < nops; i++)
    force_move_till_expr (TREE_OPERAND (expr, i), orig_loop, loop);
}

/* Forces statement defining invariants in REF (and *INDEX) to be moved out of
   the LOOP.  The reference REF is used in the loop ORIG_LOOP.  Callback for
   for_each_index.  */

struct fmt_data
{
  struct loop *loop;
  struct loop *orig_loop;
};

static bool
force_move_till (tree ref, tree *index, void *data)
{
  tree stmt;
  struct fmt_data *fmt_data = data;

  if (TREE_CODE (ref) == ARRAY_REF)
    {
      tree step = array_ref_element_size (ref);
      tree lbound = array_ref_low_bound (ref);

      force_move_till_expr (step, fmt_data->orig_loop, fmt_data->loop);
      force_move_till_expr (lbound, fmt_data->orig_loop, fmt_data->loop);
    }

  if (TREE_CODE (*index) != SSA_NAME)
    return true;

  stmt = SSA_NAME_DEF_STMT (*index);
  if (IS_EMPTY_STMT (stmt))
    return true;

  set_level (stmt, fmt_data->orig_loop, fmt_data->loop);

  return true;
}

/* Records memory reference location *REF to the list MEM_REFS.  The reference
   occurs in statement STMT.  */

static void
record_mem_ref_loc (struct mem_ref_loc **mem_refs, tree stmt, tree *ref)
{
  struct mem_ref_loc *aref = xmalloc (sizeof (struct mem_ref_loc));

  aref->stmt = stmt;
  aref->ref = ref;

  aref->next = *mem_refs;
  *mem_refs = aref;
}

/* Releases list of memory reference locations MEM_REFS.  */

static void
free_mem_ref_locs (struct mem_ref_loc *mem_refs)
{
  struct mem_ref_loc *act;

  while (mem_refs)
    {
      act = mem_refs;
      mem_refs = mem_refs->next;
      free (act);
    }
}

/* Rewrites memory references in list MEM_REFS by variable TMP_VAR.  */

static void
rewrite_mem_refs (tree tmp_var, struct mem_ref_loc *mem_refs)
{
  tree var;
  ssa_op_iter iter;

  for (; mem_refs; mem_refs = mem_refs->next)
    {
      FOR_EACH_SSA_TREE_OPERAND (var, mem_refs->stmt, iter, SSA_OP_ALL_VIRTUALS)
        mark_sym_for_renaming (SSA_NAME_VAR (var));

      *mem_refs->ref = tmp_var;
      update_stmt (mem_refs->stmt);
    }
}

/* Records request for store motion of memory reference REF from LOOP.
   MEM_REFS is the list of occurrences of the reference REF inside LOOP;
   these references are rewritten by a new temporary variable.
   Exits from the LOOP are stored in EXITS, there are N_EXITS of them.
   The initialization of the temporary variable is put to the preheader
   of the loop, and assignments to the reference from the temporary variable
   are emitted to exits.  */

static void
schedule_sm (struct loop *loop, edge *exits, unsigned n_exits, tree ref,
             struct mem_ref_loc *mem_refs)
{
  struct mem_ref_loc *aref;
  tree tmp_var;
  unsigned i;
  tree load, store;
  struct fmt_data fmt_data;

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "Executing store motion of ");
      print_generic_expr (dump_file, ref, 0);
      fprintf (dump_file, " from loop %d\n", loop->num);
    }

  tmp_var = make_rename_temp (TREE_TYPE (ref), "lsm_tmp");

  fmt_data.loop = loop;
  fmt_data.orig_loop = loop;
  for_each_index (&ref, force_move_till, &fmt_data);

  rewrite_mem_refs (tmp_var, mem_refs);
  for (aref = mem_refs; aref; aref = aref->next)
    if (LIM_DATA (aref->stmt))
      LIM_DATA (aref->stmt)->sm_done = true;

  /* Emit the load & stores.  */
  load = build (MODIFY_EXPR, void_type_node, tmp_var, ref);
  get_stmt_ann (load)->aux = xcalloc (1, sizeof (struct lim_aux_data));
  LIM_DATA (load)->max_loop = loop;
  LIM_DATA (load)->tgt_loop = loop;

  /* Put this into the latch, so that we are sure it will be processed after
     all dependencies.  */
  bsi_insert_on_edge (loop_latch_edge (loop), load);

  for (i = 0; i < n_exits; i++)
    {
      store = build (MODIFY_EXPR, void_type_node,
                     unshare_expr (ref), tmp_var);
      bsi_insert_on_edge (exits[i], store);
    }
}

/* Check whether memory reference REF can be hoisted out of the LOOP.  If this
   is true, prepare the statements that load the value of the memory reference
   to a temporary variable in the loop preheader, store it back on the loop
   exits, and replace all the references inside LOOP by this temporary variable.
   LOOP has N_EXITS stored in EXITS.  CLOBBERED_VOPS is the bitmap of virtual
   operands that are clobbered by a call or accessed through multiple references
   in loop.  */

static void
determine_lsm_ref (struct loop *loop, edge *exits, unsigned n_exits,
                   bitmap clobbered_vops, struct mem_ref *ref)
{
  struct mem_ref_loc *aref;
  struct loop *must_exec;

  /* In case the memory is not stored to, there is nothing for SM to do.  */
  if (!ref->is_stored)
    return;

  /* If the reference is aliased with any different ref, or killed by call
     in function, then fail.  */
  if (bitmap_intersect_p (ref->vops, clobbered_vops))
    return;

  if (tree_could_trap_p (ref->mem))
    {
      /* If the memory access is unsafe (i.e. it might trap), ensure that some
         of the statements in that it occurs is always executed when the loop
         is entered.  This way we know that by moving the load from the
         reference out of the loop we will not cause the error that would not
         occur otherwise.

         TODO -- in fact we would like to check for anticipability of the
         reference, i.e. that on each path from loop entry to loop exit at
         least one of the statements containing the memory reference is
         executed.  */

      for (aref = ref->locs; aref; aref = aref->next)
        {
          if (!LIM_DATA (aref->stmt))
            continue;

          must_exec = LIM_DATA (aref->stmt)->always_executed_in;
          if (!must_exec)
            continue;

          if (must_exec == loop
              || flow_loop_nested_p (must_exec, loop))
            break;
        }

      if (!aref)
        return;
    }

  schedule_sm (loop, exits, n_exits, ref->mem, ref->locs);
}

/* Hoists memory references MEM_REFS out of LOOP.  CLOBBERED_VOPS is the list
   of vops clobbered by call in loop or accessed by multiple memory references.
   EXITS is the list of N_EXITS exit edges of the LOOP.  */

static void
hoist_memory_references (struct loop *loop, struct mem_ref *mem_refs,
                         bitmap clobbered_vops, edge *exits, unsigned n_exits)
{
  struct mem_ref *ref;

  for (ref = mem_refs; ref; ref = ref->next)
    determine_lsm_ref (loop, exits, n_exits, clobbered_vops, ref);
}

/* Checks whether LOOP (with N_EXITS exits stored in EXITS array) is suitable
   for a store motion optimization (i.e. whether we can insert statement
   on its exits).  */

static bool
loop_suitable_for_sm (struct loop *loop ATTRIBUTE_UNUSED, edge *exits,
                      unsigned n_exits)
{
  unsigned i;

  for (i = 0; i < n_exits; i++)
    if (exits[i]->flags & EDGE_ABNORMAL)
      return false;

  return true;
}

/* A hash function for struct mem_ref object OBJ.  */

static hashval_t
memref_hash (const void *obj)
{
  const struct mem_ref *mem = obj;

  return mem->hash;
}

/* An equality function for struct mem_ref object OBJ1 with
   memory reference OBJ2.  */

static int
memref_eq (const void *obj1, const void *obj2)
{
  const struct mem_ref *mem1 = obj1;

  return operand_equal_p (mem1->mem, (tree) obj2, 0);
}

/* Gathers memory references in statement STMT in LOOP, storing the
   information about them in MEM_REFS hash table.  Note vops accessed through
   unrecognized statements in CLOBBERED_VOPS.  The newly created references
   are also stored to MEM_REF_LIST.  */

static void
gather_mem_refs_stmt (struct loop *loop, htab_t mem_refs,
                      bitmap clobbered_vops, tree stmt,
                      struct mem_ref **mem_ref_list)
{
  tree *lhs, *rhs, *mem = NULL;
  hashval_t hash;
  PTR *slot;
  struct mem_ref *ref = NULL;
  ssa_op_iter oi;
  tree vname;
  bool is_stored;

  if (ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS))
    return;

  /* Recognize MEM = (SSA_NAME | invariant) and SSA_NAME = MEM patterns.  */
  if (TREE_CODE (stmt) != MODIFY_EXPR)
    goto fail;

  lhs = &TREE_OPERAND (stmt, 0);
  rhs = &TREE_OPERAND (stmt, 1);

  if (TREE_CODE (*lhs) == SSA_NAME)
    {
      if (!is_gimple_addressable (*rhs))
        goto fail;

      mem = rhs;
      is_stored = false;
    }
  else if (TREE_CODE (*rhs) == SSA_NAME
           || is_gimple_min_invariant (*rhs))
    {
      mem = lhs;
      is_stored = true;
    }
  else
    goto fail;

  /* If we cannot create an SSA name for the result, give up.  */
  if (!is_gimple_reg_type (TREE_TYPE (*mem))
      || TREE_THIS_VOLATILE (*mem))
    goto fail;

  /* If we cannot move the reference out of the loop, fail.  */
  if (!for_each_index (mem, may_move_till, loop))
    goto fail;

  hash = iterative_hash_expr (*mem, 0);
  slot = htab_find_slot_with_hash (mem_refs, *mem, hash, INSERT);

  if (*slot)
    ref = *slot;
  else
    {
      ref = xmalloc (sizeof (struct mem_ref));
      ref->mem = *mem;
      ref->hash = hash;
      ref->locs = NULL;
      ref->is_stored = false;
      ref->vops = BITMAP_ALLOC (NULL);
      ref->next = *mem_ref_list;
      *mem_ref_list = ref;
      *slot = ref;
    }
  ref->is_stored |= is_stored;

  FOR_EACH_SSA_TREE_OPERAND (vname, stmt, oi,
                             SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_KILLS)
    {
      bitmap_set_bit (ref->vops,
                      var_ann (SSA_NAME_VAR (vname))->uid);
    }
  record_mem_ref_loc (&ref->locs, stmt, mem);
  return;

fail:
  FOR_EACH_SSA_TREE_OPERAND (vname, stmt, oi,
                             SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_KILLS)
    {
      bitmap_set_bit (clobbered_vops,
                      var_ann (SSA_NAME_VAR (vname))->uid);
    }
}

/* Gathers memory references in LOOP.  Notes vops accessed through unrecognized
   statements in CLOBBERED_VOPS.  The list of the references found by
   the function is returned.  */

static struct mem_ref *
gather_mem_refs (struct loop *loop, bitmap clobbered_vops)
{
  basic_block *body = get_loop_body (loop);
  block_stmt_iterator bsi;
  unsigned i;
  struct mem_ref *mem_ref_list = NULL;
  htab_t mem_refs = htab_create (100, memref_hash, memref_eq, NULL);

  for (i = 0; i < loop->num_nodes; i++)
    {
      for (bsi = bsi_start (body[i]); !bsi_end_p (bsi); bsi_next (&bsi))
        gather_mem_refs_stmt (loop, mem_refs, clobbered_vops, bsi_stmt (bsi),
                              &mem_ref_list);
    }

  free (body);

  htab_delete (mem_refs);
  return mem_ref_list;
}

/* Finds the vops accessed by more than one of the memory references described
   in MEM_REFS and marks them in CLOBBERED_VOPS.  */

static void
find_more_ref_vops (struct mem_ref *mem_refs, bitmap clobbered_vops)
{
  bitmap_head tmp, all_vops;
  struct mem_ref *ref;

  bitmap_initialize (&tmp, &bitmap_default_obstack);
  bitmap_initialize (&all_vops, &bitmap_default_obstack);

  for (ref = mem_refs; ref; ref = ref->next)
    {
      /* The vops that are already in all_vops are accessed by more than
         one memory reference.  */
      bitmap_and (&tmp, &all_vops, ref->vops);
      bitmap_ior_into (clobbered_vops, &tmp);
      bitmap_clear (&tmp);

      bitmap_ior_into (&all_vops, ref->vops);
    }

  bitmap_clear (&all_vops);
}

/* Releases the memory occupied by REF.  */

static void
free_mem_ref (struct mem_ref *ref)
{
  free_mem_ref_locs (ref->locs);
  BITMAP_FREE (ref->vops);
  free (ref);
}

/* Releases the memory occupied by REFS.  */

static void
free_mem_refs (struct mem_ref *refs)
{
  struct mem_ref *ref, *next;

  for (ref = refs; ref; ref = next)
    {
      next = ref->next;
      free_mem_ref (ref);
    }
}

/* Try to perform store motion for all memory references modified inside
   LOOP.  */

static void
determine_lsm_loop (struct loop *loop)
{
  unsigned n_exits;
  edge *exits = get_loop_exit_edges (loop, &n_exits);
  bitmap clobbered_vops;
  struct mem_ref *mem_refs;

  if (!loop_suitable_for_sm (loop, exits, n_exits))
    {
      free (exits);
      return;
    }

  /* Find the memory references in LOOP.  */
  clobbered_vops = BITMAP_ALLOC (NULL);
  mem_refs = gather_mem_refs (loop, clobbered_vops);

  /* Find the vops that are used for more than one reference.  */
  find_more_ref_vops (mem_refs, clobbered_vops);

  /* Hoist all suitable memory references.  */
  hoist_memory_references (loop, mem_refs, clobbered_vops, exits, n_exits);

  free_mem_refs (mem_refs);
  free (exits);
  BITMAP_FREE (clobbered_vops);
}

/* Try to perform store motion for all memory references modified inside
   any of LOOPS.  */

static void
determine_lsm (struct loops *loops)
{
  struct loop *loop;

  if (!loops->tree_root->inner)
    return;

  /* Pass the loops from the outermost and perform the store motion as
     suitable.  */

  loop = loops->tree_root->inner;
  while (1)
    {
      determine_lsm_loop (loop);

      if (loop->inner)
        {
          loop = loop->inner;
          continue;
        }
      while (!loop->next)
        {
          loop = loop->outer;
          if (loop == loops->tree_root)
            {
              loop_commit_inserts ();
              return;
            }
        }
      loop = loop->next;
    }
}

/* Fills ALWAYS_EXECUTED_IN information for basic blocks of LOOP, i.e.
   for each such basic block bb records the outermost loop for that execution
   of its header implies execution of bb.  CONTAINS_CALL is the bitmap of
   blocks that contain a nonpure call.  */

static void
fill_always_executed_in (struct loop *loop, sbitmap contains_call)
{
  basic_block bb = NULL, *bbs, last = NULL;
  unsigned i;
  edge e;
  struct loop *inn_loop = loop;

  if (!loop->header->aux)
    {
      bbs = get_loop_body_in_dom_order (loop);

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

          if (dominated_by_p (CDI_DOMINATORS, loop->latch, bb))
            last = bb;

          if (TEST_BIT (contains_call, bb->index))
            break;

          FOR_EACH_EDGE (e, ei, bb->succs)
            if (!flow_bb_inside_loop_p (loop, e->dest))
              break;
          if (e)
            break;

          /* A loop might be infinite (TODO use simple loop analysis
             to disprove this if possible).  */
          if (bb->flags & BB_IRREDUCIBLE_LOOP)
            break;

          if (!flow_bb_inside_loop_p (inn_loop, bb))
            break;

          if (bb->loop_father->header == bb)
            {
              if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb))
                break;

              /* In a loop that is always entered we may proceed anyway.
                 But record that we entered it and stop once we leave it.  */
              inn_loop = bb->loop_father;
            }
        }

      while (1)
        {
          last->aux = loop;
          if (last == loop->header)
            break;
          last = get_immediate_dominator (CDI_DOMINATORS, last);
        }

      free (bbs);
    }

  for (loop = loop->inner; loop; loop = loop->next)
    fill_always_executed_in (loop, contains_call);
}

/* Compute the global information needed by the loop invariant motion pass.
   LOOPS is the loop tree.  */

static void
tree_ssa_lim_initialize (struct loops *loops)
{
  sbitmap contains_call = sbitmap_alloc (last_basic_block);
  block_stmt_iterator bsi;
  struct loop *loop;
  basic_block bb;

  sbitmap_zero (contains_call);
  FOR_EACH_BB (bb)
    {
      for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
        {
          if (nonpure_call_p (bsi_stmt (bsi)))
            break;
        }

      if (!bsi_end_p (bsi))
        SET_BIT (contains_call, bb->index);
    }

  for (loop = loops->tree_root->inner; loop; loop = loop->next)
    fill_always_executed_in (loop, contains_call);

  sbitmap_free (contains_call);
}

/* Cleans up after the invariant motion pass.  */

static void
tree_ssa_lim_finalize (void)
{
  basic_block bb;

  FOR_EACH_BB (bb)
    {
      bb->aux = NULL;
    }
}

/* Moves invariants from LOOPS.  Only "expensive" invariants are moved out --
   i.e. those that are likely to be win regardless of the register pressure.  */

void
tree_ssa_lim (struct loops *loops)
{
  tree_ssa_lim_initialize (loops);

  /* For each statement determine the outermost loop in that it is
     invariant and cost for computing the invariant.  */
  determine_invariantness ();

  /* For each memory reference determine whether it is possible to hoist it
     out of the loop.  Force the necessary invariants to be moved out of the
     loops as well.  */
  determine_lsm (loops);

  /* Move the expressions that are expensive enough.  */
  move_computations ();

  tree_ssa_lim_finalize ();
}