gcc/gcc/loop-invariant.c

/* RTL-level loop invariant motion.
   Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
   Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3, or (at your option) any
later version.

GCC is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

/* This implements the loop invariant motion pass.  It is very simple
   (no calls, no loads/stores, etc.).  This should be sufficient to cleanup
   things like address arithmetics -- other more complicated invariants should
   be eliminated on GIMPLE either in tree-ssa-loop-im.c or in tree-ssa-pre.c.

   We proceed loop by loop -- it is simpler than trying to handle things
   globally and should not lose much.  First we inspect all sets inside loop
   and create a dependency graph on insns (saying "to move this insn, you must
   also move the following insns").

   We then need to determine what to move.  We estimate the number of registers
   used and move as many invariants as possible while we still have enough free
   registers.  We prefer the expensive invariants.

   Then we move the selected invariants out of the loop, creating a new
   temporaries for them if necessary.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "tm_p.h"
#include "hard-reg-set.h"
#include "obstack.h"
#include "basic-block.h"
#include "cfgloop.h"
#include "expr.h"
#include "recog.h"
#include "output.h"
#include "function.h"
#include "flags.h"
#include "df.h"
#include "hashtab.h"
#include "except.h"
#include "params.h"

/* The data stored for the loop.  */

struct loop_data
{
  struct loop *outermost_exit;	/* The outermost exit of the loop.  */
  bool has_call;		/* True if the loop contains a call.  */
};

#define LOOP_DATA(LOOP) ((struct loop_data *) (LOOP)->aux)

/* The description of an use.  */

struct use
{
  rtx *pos;			/* Position of the use.  */
  rtx insn;			/* The insn in that the use occurs.  */
  unsigned addr_use_p;		/* Whether the use occurs in an address.  */
  struct use *next;		/* Next use in the list.  */
};

/* The description of a def.  */

struct def
{
  struct use *uses;		/* The list of uses that are uniquely reached
				   by it.  */
  unsigned n_uses;		/* Number of such uses.  */
  unsigned n_addr_uses;		/* Number of uses in addresses.  */
  unsigned invno;		/* The corresponding invariant.  */
};

/* The data stored for each invariant.  */

struct invariant
{
  /* The number of the invariant.  */
  unsigned invno;

  /* The number of the invariant with the same value.  */
  unsigned eqto;

  /* If we moved the invariant out of the loop, the register that contains its
     value.  */
  rtx reg;

  /* The definition of the invariant.  */
  struct def *def;

  /* The insn in that it is defined.  */
  rtx insn;

  /* Whether it is always executed.  */
  bool always_executed;

  /* Whether to move the invariant.  */
  bool move;

  /* Whether the invariant is cheap when used as an address.  */
  bool cheap_address;

  /* Cost of the invariant.  */
  unsigned cost;

  /* The invariants it depends on.  */
  bitmap depends_on;

  /* Used for detecting already visited invariants during determining
     costs of movements.  */
  unsigned stamp;
};

/* Table of invariants indexed by the df_ref uid field.  */

static unsigned int invariant_table_size = 0;
static struct invariant ** invariant_table;

/* Entry for hash table of invariant expressions.  */

struct invariant_expr_entry
{
  /* The invariant.  */
  struct invariant *inv;

  /* Its value.  */
  rtx expr;

  /* Its mode.  */
  enum machine_mode mode;

  /* Its hash.  */
  hashval_t hash;
};

/* The actual stamp for marking already visited invariants during determining
   costs of movements.  */

static unsigned actual_stamp;

typedef struct invariant *invariant_p;

DEF_VEC_P(invariant_p);
DEF_VEC_ALLOC_P(invariant_p, heap);

/* The invariants.  */

static VEC(invariant_p,heap) *invariants;

/* Check the size of the invariant table and realloc if necessary.  */

static void 
check_invariant_table_size (void)
{
  if (invariant_table_size < DF_DEFS_TABLE_SIZE())
    {
      unsigned int new_size = DF_DEFS_TABLE_SIZE () + (DF_DEFS_TABLE_SIZE () / 4);
      invariant_table = XRESIZEVEC (struct invariant *, invariant_table, new_size);
      memset (&invariant_table[invariant_table_size], 0, 
	      (new_size - invariant_table_size) * sizeof (struct rtx_iv *));
      invariant_table_size = new_size;
    }
}

/* Test for possibility of invariantness of X.  */

static bool
check_maybe_invariant (rtx x)
{
  enum rtx_code code = GET_CODE (x);
  int i, j;
  const char *fmt;

  switch (code)
    {
    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
    case SYMBOL_REF:
    case CONST:
    case LABEL_REF:
      return true;

    case PC:
    case CC0:
    case UNSPEC_VOLATILE:
    case CALL:
      return false;

    case REG:
      return true;

    case MEM:
      /* Load/store motion is done elsewhere.  ??? Perhaps also add it here?
	 It should not be hard, and might be faster than "elsewhere".  */

      /* Just handle the most trivial case where we load from an unchanging
	 location (most importantly, pic tables).  */
      if (MEM_READONLY_P (x) && !MEM_VOLATILE_P (x))
	break;

      return false;

    case ASM_OPERANDS:
      /* Don't mess with insns declared volatile.  */
      if (MEM_VOLATILE_P (x))
	return false;
      break;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
	{
	  if (!check_maybe_invariant (XEXP (x, i)))
	    return false;
	}
      else if (fmt[i] == 'E')
	{
	  for (j = 0; j < XVECLEN (x, i); j++)
	    if (!check_maybe_invariant (XVECEXP (x, i, j)))
	      return false;
	}
    }

  return true;
}

/* Returns the invariant definition for USE, or NULL if USE is not
   invariant.  */

static struct invariant *
invariant_for_use (df_ref use)
{
  struct df_link *defs;
  df_ref def;
  basic_block bb = DF_REF_BB (use), def_bb;

  if (DF_REF_FLAGS (use) & DF_REF_READ_WRITE)
    return NULL;

  defs = DF_REF_CHAIN (use);
  if (!defs || defs->next)
    return NULL;
  def = defs->ref;
  check_invariant_table_size ();
  if (!invariant_table[DF_REF_ID(def)])
    return NULL;

  def_bb = DF_REF_BB (def);
  if (!dominated_by_p (CDI_DOMINATORS, bb, def_bb))
    return NULL;
  return invariant_table[DF_REF_ID(def)];
}

/* Computes hash value for invariant expression X in INSN.  */

static hashval_t
hash_invariant_expr_1 (rtx insn, rtx x)
{
  enum rtx_code code = GET_CODE (x);
  int i, j;
  const char *fmt;
  hashval_t val = code;
  int do_not_record_p;
  df_ref use;
  struct invariant *inv;

  switch (code)
    {
    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
    case SYMBOL_REF:
    case CONST:
    case LABEL_REF:
      return hash_rtx (x, GET_MODE (x), &do_not_record_p, NULL, false);

    case REG:
      use = df_find_use (insn, x);
      if (!use)
	return hash_rtx (x, GET_MODE (x), &do_not_record_p, NULL, false);
      inv = invariant_for_use (use);
      if (!inv)
	return hash_rtx (x, GET_MODE (x), &do_not_record_p, NULL, false);

      gcc_assert (inv->eqto != ~0u);
      return inv->eqto;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
	val ^= hash_invariant_expr_1 (insn, XEXP (x, i));
      else if (fmt[i] == 'E')
	{
	  for (j = 0; j < XVECLEN (x, i); j++)
	    val ^= hash_invariant_expr_1 (insn, XVECEXP (x, i, j));
	}
      else if (fmt[i] == 'i' || fmt[i] == 'n')
	val ^= XINT (x, i);
    }

  return val;
}

/* Returns true if the invariant expressions E1 and E2 used in insns INSN1
   and INSN2 have always the same value.  */

static bool
invariant_expr_equal_p (rtx insn1, rtx e1, rtx insn2, rtx e2)
{
  enum rtx_code code = GET_CODE (e1);
  int i, j;
  const char *fmt;
  df_ref use1, use2;
  struct invariant *inv1 = NULL, *inv2 = NULL;
  rtx sub1, sub2;

  /* If mode of only one of the operands is VOIDmode, it is not equivalent to
     the other one.  If both are VOIDmode, we rely on the caller of this
     function to verify that their modes are the same.  */
  if (code != GET_CODE (e2) || GET_MODE (e1) != GET_MODE (e2))
    return false;

  switch (code)
    {
    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
    case SYMBOL_REF:
    case CONST:
    case LABEL_REF:
      return rtx_equal_p (e1, e2);

    case REG:
      use1 = df_find_use (insn1, e1);
      use2 = df_find_use (insn2, e2);
      if (use1)
	inv1 = invariant_for_use (use1);
      if (use2)
	inv2 = invariant_for_use (use2);

      if (!inv1 && !inv2)
	return rtx_equal_p (e1, e2);

      if (!inv1 || !inv2)
	return false;

      gcc_assert (inv1->eqto != ~0u);
      gcc_assert (inv2->eqto != ~0u);
      return inv1->eqto == inv2->eqto;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
	{
	  sub1 = XEXP (e1, i);
	  sub2 = XEXP (e2, i);

	  if (!invariant_expr_equal_p (insn1, sub1, insn2, sub2))
	    return false;
	}

      else if (fmt[i] == 'E')
	{
	  if (XVECLEN (e1, i) != XVECLEN (e2, i))
	    return false;

	  for (j = 0; j < XVECLEN (e1, i); j++)
	    {
	      sub1 = XVECEXP (e1, i, j);
	      sub2 = XVECEXP (e2, i, j);

	      if (!invariant_expr_equal_p (insn1, sub1, insn2, sub2))
		return false;
	    }
	}
      else if (fmt[i] == 'i' || fmt[i] == 'n')
	{
	  if (XINT (e1, i) != XINT (e2, i))
	    return false;
	}
      /* Unhandled type of subexpression, we fail conservatively.  */
      else
	return false;
    }

  return true;
}

/* Returns hash value for invariant expression entry E.  */

static hashval_t
hash_invariant_expr (const void *e)
{
  const struct invariant_expr_entry *const entry =
    (const struct invariant_expr_entry *) e;

  return entry->hash;
}

/* Compares invariant expression entries E1 and E2.  */

static int
eq_invariant_expr (const void *e1, const void *e2)
{
  const struct invariant_expr_entry *const entry1 =
    (const struct invariant_expr_entry *) e1;
  const struct invariant_expr_entry *const entry2 =
    (const struct invariant_expr_entry *) e2;

  if (entry1->mode != entry2->mode)
    return 0;

  return invariant_expr_equal_p (entry1->inv->insn, entry1->expr,
				 entry2->inv->insn, entry2->expr);
}

/* Checks whether invariant with value EXPR in machine mode MODE is
   recorded in EQ.  If this is the case, return the invariant.  Otherwise
   insert INV to the table for this expression and return INV.  */

static struct invariant *
find_or_insert_inv (htab_t eq, rtx expr, enum machine_mode mode,
		    struct invariant *inv)
{
  hashval_t hash = hash_invariant_expr_1 (inv->insn, expr);
  struct invariant_expr_entry *entry;
  struct invariant_expr_entry pentry;
  PTR *slot;

  pentry.expr = expr;
  pentry.inv = inv;
  pentry.mode = mode;
  slot = htab_find_slot_with_hash (eq, &pentry, hash, INSERT);
  entry = (struct invariant_expr_entry *) *slot;

  if (entry)
    return entry->inv;

  entry = XNEW (struct invariant_expr_entry);
  entry->inv = inv;
  entry->expr = expr;
  entry->mode = mode;
  entry->hash = hash;
  *slot = entry;

  return inv;
}

/* Finds invariants identical to INV and records the equivalence.  EQ is the
   hash table of the invariants.  */

static void
find_identical_invariants (htab_t eq, struct invariant *inv)
{
  unsigned depno;
  bitmap_iterator bi;
  struct invariant *dep;
  rtx expr, set;
  enum machine_mode mode;

  if (inv->eqto != ~0u)
    return;

  EXECUTE_IF_SET_IN_BITMAP (inv->depends_on, 0, depno, bi)
    {
      dep = VEC_index (invariant_p, invariants, depno);
      find_identical_invariants (eq, dep);
    }

  set = single_set (inv->insn);
  expr = SET_SRC (set);
  mode = GET_MODE (expr);
  if (mode == VOIDmode)
    mode = GET_MODE (SET_DEST (set));
  inv->eqto = find_or_insert_inv (eq, expr, mode, inv)->invno;

  if (dump_file && inv->eqto != inv->invno)
    fprintf (dump_file,
	     "Invariant %d is equivalent to invariant %d.\n",
	     inv->invno, inv->eqto);
}

/* Find invariants with the same value and record the equivalences.  */

static void
merge_identical_invariants (void)
{
  unsigned i;
  struct invariant *inv;
  htab_t eq = htab_create (VEC_length (invariant_p, invariants),
			   hash_invariant_expr, eq_invariant_expr, free);

  for (i = 0; VEC_iterate (invariant_p, invariants, i, inv); i++)
    find_identical_invariants (eq, inv);

  htab_delete (eq);
}

/* Determines the basic blocks inside LOOP that are always executed and
   stores their bitmap to ALWAYS_REACHED.  MAY_EXIT is a bitmap of
   basic blocks that may either exit the loop, or contain the call that
   does not have to return.  BODY is body of the loop obtained by
   get_loop_body_in_dom_order.  */

static void
compute_always_reached (struct loop *loop, basic_block *body,
			bitmap may_exit, bitmap always_reached)
{
  unsigned i;

  for (i = 0; i < loop->num_nodes; i++)
    {
      if (dominated_by_p (CDI_DOMINATORS, loop->latch, body[i]))
	bitmap_set_bit (always_reached, i);

      if (bitmap_bit_p (may_exit, i))
	return;
    }
}

/* Finds exits out of the LOOP with body BODY.  Marks blocks in that we may
   exit the loop by cfg edge to HAS_EXIT and MAY_EXIT.  In MAY_EXIT
   additionally mark blocks that may exit due to a call.  */

static void
find_exits (struct loop *loop, basic_block *body,
	    bitmap may_exit, bitmap has_exit)
{
  unsigned i;
  edge_iterator ei;
  edge e;
  struct loop *outermost_exit = loop, *aexit;
  bool has_call = false;
  rtx insn;

  for (i = 0; i < loop->num_nodes; i++)
    {
      if (body[i]->loop_father == loop)
	{
	  FOR_BB_INSNS (body[i], insn)
	    {
	      if (CALL_P (insn)
		  && (RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)
		      || !RTL_CONST_OR_PURE_CALL_P (insn)))
		{
		  has_call = true;
		  bitmap_set_bit (may_exit, i);
		  break;
		}
	    }

	  FOR_EACH_EDGE (e, ei, body[i]->succs)
	    {
	      if (flow_bb_inside_loop_p (loop, e->dest))
		continue;

	      bitmap_set_bit (may_exit, i);
	      bitmap_set_bit (has_exit, i);
	      outermost_exit = find_common_loop (outermost_exit,
						 e->dest->loop_father);
	    }
	  continue;
	}

      /* Use the data stored for the subloop to decide whether we may exit
	 through it.  It is sufficient to do this for header of the loop,
	 as other basic blocks inside it must be dominated by it.  */
      if (body[i]->loop_father->header != body[i])
	continue;

      if (LOOP_DATA (body[i]->loop_father)->has_call)
	{
	  has_call = true;
	  bitmap_set_bit (may_exit, i);
	}
      aexit = LOOP_DATA (body[i]->loop_father)->outermost_exit;
      if (aexit != loop)
	{
	  bitmap_set_bit (may_exit, i);
	  bitmap_set_bit (has_exit, i);

	  if (flow_loop_nested_p (aexit, outermost_exit))
	    outermost_exit = aexit;
	}
    }

  loop->aux = xcalloc (1, sizeof (struct loop_data));
  LOOP_DATA (loop)->outermost_exit = outermost_exit;
  LOOP_DATA (loop)->has_call = has_call;
}

/* Check whether we may assign a value to X from a register.  */

static bool
may_assign_reg_p (rtx x)
{
  return (GET_MODE (x) != VOIDmode
	  && GET_MODE (x) != BLKmode
	  && can_copy_p (GET_MODE (x))
	  && (!REG_P (x)
	      || !HARD_REGISTER_P (x)
	      || REGNO_REG_CLASS (REGNO (x)) != NO_REGS));
}

/* Finds definitions that may correspond to invariants in LOOP with body
   BODY.  */

static void
find_defs (struct loop *loop, basic_block *body)
{
  unsigned i;
  bitmap blocks = BITMAP_ALLOC (NULL);

  for (i = 0; i < loop->num_nodes; i++)
    bitmap_set_bit (blocks, body[i]->index);

  df_remove_problem (df_chain);
  df_process_deferred_rescans ();
  df_chain_add_problem (DF_UD_CHAIN);
  df_set_blocks (blocks);
  df_analyze ();

  if (dump_file)
    {
      df_dump_region (dump_file);
      fprintf (dump_file, "*****starting processing of loop  ******\n");
      print_rtl_with_bb (dump_file, get_insns ());
      fprintf (dump_file, "*****ending processing of loop  ******\n");
    }
  check_invariant_table_size ();

  BITMAP_FREE (blocks);
}

/* Creates a new invariant for definition DEF in INSN, depending on invariants
   in DEPENDS_ON.  ALWAYS_EXECUTED is true if the insn is always executed,
   unless the program ends due to a function call.  The newly created invariant
   is returned.  */

static struct invariant *
create_new_invariant (struct def *def, rtx insn, bitmap depends_on,
		      bool always_executed)
{
  struct invariant *inv = XNEW (struct invariant);
  rtx set = single_set (insn);
  bool speed = optimize_bb_for_speed_p (BLOCK_FOR_INSN (insn));

  inv->def = def;
  inv->always_executed = always_executed;
  inv->depends_on = depends_on;

  /* If the set is simple, usually by moving it we move the whole store out of
     the loop.  Otherwise we save only cost of the computation.  */
  if (def)
    {
      inv->cost = rtx_cost (set, SET, speed);
      inv->cheap_address = address_cost (SET_SRC (set), word_mode,
					 speed) < COSTS_N_INSNS (1);
    }
  else
    {
      inv->cost = rtx_cost (SET_SRC (set), SET, speed);
      inv->cheap_address = false;
    }

  inv->move = false;
  inv->reg = NULL_RTX;
  inv->stamp = 0;
  inv->insn = insn;

  inv->invno = VEC_length (invariant_p, invariants);
  inv->eqto = ~0u;
  if (def)
    def->invno = inv->invno;
  VEC_safe_push (invariant_p, heap, invariants, inv);

  if (dump_file)
    {
      fprintf (dump_file,
	       "Set in insn %d is invariant (%d), cost %d, depends on ",
	       INSN_UID (insn), inv->invno, inv->cost);
      dump_bitmap (dump_file, inv->depends_on);
    }

  return inv;
}

/* Record USE at DEF.  */

static void
record_use (struct def *def, df_ref use)
{
  struct use *u = XNEW (struct use);

  u->pos = DF_REF_REAL_LOC (use);
  u->insn = DF_REF_INSN (use);
  u->addr_use_p = (DF_REF_TYPE (use) == DF_REF_REG_MEM_LOAD
		   || DF_REF_TYPE (use) == DF_REF_REG_MEM_STORE);
  u->next = def->uses;
  def->uses = u;
  def->n_uses++;
  if (u->addr_use_p)
    def->n_addr_uses++;
}

/* Finds the invariants USE depends on and store them to the DEPENDS_ON
   bitmap.  Returns true if all dependencies of USE are known to be
   loop invariants, false otherwise.  */

static bool
check_dependency (basic_block bb, df_ref use, bitmap depends_on)
{
  df_ref def;
  basic_block def_bb;
  struct df_link *defs;
  struct def *def_data;
  struct invariant *inv;
  
  if (DF_REF_FLAGS (use) & DF_REF_READ_WRITE)
    return false;
  
  defs = DF_REF_CHAIN (use);
  if (!defs)
    return true;
  
  if (defs->next)
    return false;
  
  def = defs->ref;
  check_invariant_table_size ();
  inv = invariant_table[DF_REF_ID(def)];
  if (!inv)
    return false;
  
  def_data = inv->def;
  gcc_assert (def_data != NULL);
  
  def_bb = DF_REF_BB (def);
  /* Note that in case bb == def_bb, we know that the definition
     dominates insn, because def has invariant_table[DF_REF_ID(def)]
     defined and we process the insns in the basic block bb
     sequentially.  */
  if (!dominated_by_p (CDI_DOMINATORS, bb, def_bb))
    return false;
  
  bitmap_set_bit (depends_on, def_data->invno);
  return true;
}


/* Finds the invariants INSN depends on and store them to the DEPENDS_ON
   bitmap.  Returns true if all dependencies of INSN are known to be
   loop invariants, false otherwise.  */

static bool
check_dependencies (rtx insn, bitmap depends_on)
{
  struct df_insn_info *insn_info = DF_INSN_INFO_GET (insn);
  df_ref *use_rec;
  basic_block bb = BLOCK_FOR_INSN (insn);

  for (use_rec = DF_INSN_INFO_USES (insn_info); *use_rec; use_rec++)
    if (!check_dependency (bb, *use_rec, depends_on))
      return false;
  for (use_rec = DF_INSN_INFO_EQ_USES (insn_info); *use_rec; use_rec++)
    if (!check_dependency (bb, *use_rec, depends_on))
      return false;
	
  return true;
}

/* Finds invariant in INSN.  ALWAYS_REACHED is true if the insn is always
   executed.  ALWAYS_EXECUTED is true if the insn is always executed,
   unless the program ends due to a function call.  */

static void
find_invariant_insn (rtx insn, bool always_reached, bool always_executed)
{
  df_ref ref;
  struct def *def;
  bitmap depends_on;
  rtx set, dest;
  bool simple = true;
  struct invariant *inv;

#ifdef HAVE_cc0
  /* We can't move a CC0 setter without the user.  */
  if (sets_cc0_p (insn))
    return;
#endif

  set = single_set (insn);
  if (!set)
    return;
  dest = SET_DEST (set);

  if (!REG_P (dest)
      || HARD_REGISTER_P (dest))
    simple = false;

  if (!may_assign_reg_p (SET_DEST (set))
      || !check_maybe_invariant (SET_SRC (set)))
    return;

  /* If the insn can throw exception, we cannot move it at all without changing
     cfg.  */
  if (can_throw_internal (insn))
    return;

  /* We cannot make trapping insn executed, unless it was executed before.  */
  if (may_trap_or_fault_p (PATTERN (insn)) && !always_reached)
    return;

  depends_on = BITMAP_ALLOC (NULL);
  if (!check_dependencies (insn, depends_on))
    {
      BITMAP_FREE (depends_on);
      return;
    }

  if (simple)
    def = XCNEW (struct def);
  else
    def = NULL;

  inv = create_new_invariant (def, insn, depends_on, always_executed);

  if (simple)
    {
      ref = df_find_def (insn, dest);
      check_invariant_table_size ();
      invariant_table[DF_REF_ID(ref)] = inv;
    }
}

/* Record registers used in INSN that have a unique invariant definition.  */

static void
record_uses (rtx insn)
{
  struct df_insn_info *insn_info = DF_INSN_INFO_GET (insn);
  df_ref *use_rec;
  struct invariant *inv;

  for (use_rec = DF_INSN_INFO_USES (insn_info); *use_rec; use_rec++)
    {
      df_ref use = *use_rec;
      inv = invariant_for_use (use);
      if (inv)
	record_use (inv->def, use);
    }
  for (use_rec = DF_INSN_INFO_EQ_USES (insn_info); *use_rec; use_rec++)
    {
      df_ref use = *use_rec;
      inv = invariant_for_use (use);
      if (inv)
	record_use (inv->def, use);
    }
}

/* Finds invariants in INSN.  ALWAYS_REACHED is true if the insn is always
   executed.  ALWAYS_EXECUTED is true if the insn is always executed,
   unless the program ends due to a function call.  */

static void
find_invariants_insn (rtx insn, bool always_reached, bool always_executed)
{
  find_invariant_insn (insn, always_reached, always_executed);
  record_uses (insn);
}

/* Finds invariants in basic block BB.  ALWAYS_REACHED is true if the
   basic block is always executed.  ALWAYS_EXECUTED is true if the basic
   block is always executed, unless the program ends due to a function
   call.  */

static void
find_invariants_bb (basic_block bb, bool always_reached, bool always_executed)
{
  rtx insn;

  FOR_BB_INSNS (bb, insn)
    {
      if (!NONDEBUG_INSN_P (insn))
	continue;

      find_invariants_insn (insn, always_reached, always_executed);

      if (always_reached
	  && CALL_P (insn)
	  && (RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)
	      || ! RTL_CONST_OR_PURE_CALL_P (insn)))
	always_reached = false;
    }
}

/* Finds invariants in LOOP with body BODY.  ALWAYS_REACHED is the bitmap of
   basic blocks in BODY that are always executed.  ALWAYS_EXECUTED is the
   bitmap of basic blocks in BODY that are always executed unless the program
   ends due to a function call.  */

static void
find_invariants_body (struct loop *loop, basic_block *body,
		      bitmap always_reached, bitmap always_executed)
{
  unsigned i;

  for (i = 0; i < loop->num_nodes; i++)
    find_invariants_bb (body[i],
			bitmap_bit_p (always_reached, i),
			bitmap_bit_p (always_executed, i));
}

/* Finds invariants in LOOP.  */

static void
find_invariants (struct loop *loop)
{
  bitmap may_exit = BITMAP_ALLOC (NULL);
  bitmap always_reached = BITMAP_ALLOC (NULL);
  bitmap has_exit = BITMAP_ALLOC (NULL);
  bitmap always_executed = BITMAP_ALLOC (NULL);
  basic_block *body = get_loop_body_in_dom_order (loop);

  find_exits (loop, body, may_exit, has_exit);
  compute_always_reached (loop, body, may_exit, always_reached);
  compute_always_reached (loop, body, has_exit, always_executed);

  find_defs (loop, body);
  find_invariants_body (loop, body, always_reached, always_executed);
  merge_identical_invariants ();

  BITMAP_FREE (always_reached);
  BITMAP_FREE (always_executed);
  BITMAP_FREE (may_exit);
  BITMAP_FREE (has_exit);
  free (body);
}

/* Frees a list of uses USE.  */

static void
free_use_list (struct use *use)
{
  struct use *next;

  for (; use; use = next)
    {
      next = use->next;
      free (use);
    }
}

/* Calculates cost and number of registers needed for moving invariant INV
   out of the loop and stores them to *COST and *REGS_NEEDED.  */

static void
get_inv_cost (struct invariant *inv, int *comp_cost, unsigned *regs_needed)
{
  int acomp_cost;
  unsigned aregs_needed;
  unsigned depno;
  struct invariant *dep;
  bitmap_iterator bi;

  /* Find the representative of the class of the equivalent invariants.  */
  inv = VEC_index (invariant_p, invariants, inv->eqto);

  *comp_cost = 0;
  *regs_needed = 0;
  if (inv->move
      || inv->stamp == actual_stamp)
    return;
  inv->stamp = actual_stamp;

  (*regs_needed)++;
  if (!inv->cheap_address
      || inv->def->n_addr_uses < inv->def->n_uses)
    (*comp_cost) += inv->cost;

#ifdef STACK_REGS
  {
    /* Hoisting constant pool constants into stack regs may cost more than
       just single register.  On x87, the balance is affected both by the
       small number of FP registers, and by its register stack organization,
       that forces us to add compensation code in and around the loop to
       shuffle the operands to the top of stack before use, and pop them
       from the stack after the loop finishes.

       To model this effect, we increase the number of registers needed for
       stack registers by two: one register push, and one register pop.
       This usually has the effect that FP constant loads from the constant
       pool are not moved out of the loop.

       Note that this also means that dependent invariants can not be moved.
       However, the primary purpose of this pass is to move loop invariant
       address arithmetic out of loops, and address arithmetic that depends
       on floating point constants is unlikely to ever occur.  */
    rtx set = single_set (inv->insn);
    if (set
       && IS_STACK_MODE (GET_MODE (SET_SRC (set)))
       && constant_pool_constant_p (SET_SRC (set)))
      (*regs_needed) += 2;
  }
#endif

  EXECUTE_IF_SET_IN_BITMAP (inv->depends_on, 0, depno, bi)
    {
      dep = VEC_index (invariant_p, invariants, depno);

      get_inv_cost (dep, &acomp_cost, &aregs_needed);

      if (aregs_needed
	  /* We need to check always_executed, since if the original value of
	     the invariant may be preserved, we may need to keep it in a
	     separate register.  TODO check whether the register has an
	     use outside of the loop.  */
	  && dep->always_executed
	  && !dep->def->uses->next)
	{
	  /* If this is a single use, after moving the dependency we will not
	     need a new register.  */
	  aregs_needed--;
	}

      (*regs_needed) += aregs_needed;
      (*comp_cost) += acomp_cost;
    }
}

/* Calculates gain for eliminating invariant INV.  REGS_USED is the number
   of registers used in the loop, NEW_REGS is the number of new variables
   already added due to the invariant motion.  The number of registers needed
   for it is stored in *REGS_NEEDED.  */

static int
gain_for_invariant (struct invariant *inv, unsigned *regs_needed,
		    unsigned new_regs, unsigned regs_used, bool speed)
{
  int comp_cost, size_cost;

  get_inv_cost (inv, &comp_cost, regs_needed);
  actual_stamp++;

  size_cost = (estimate_reg_pressure_cost (new_regs + *regs_needed, regs_used, speed)
	       - estimate_reg_pressure_cost (new_regs, regs_used, speed));

  return comp_cost - size_cost;
}

/* Finds invariant with best gain for moving.  Returns the gain, stores
   the invariant in *BEST and number of registers needed for it to
   *REGS_NEEDED.  REGS_USED is the number of registers used in the loop.
   NEW_REGS is the number of new variables already added due to invariant
   motion.  */

static int
best_gain_for_invariant (struct invariant **best, unsigned *regs_needed,
			 unsigned new_regs, unsigned regs_used, bool speed)
{
  struct invariant *inv;
  int gain = 0, again;
  unsigned aregs_needed, invno;

  for (invno = 0; VEC_iterate (invariant_p, invariants, invno, inv); invno++)
    {
      if (inv->move)
	continue;

      /* Only consider the "representatives" of equivalent invariants.  */
      if (inv->eqto != inv->invno)
	continue;

      again = gain_for_invariant (inv, &aregs_needed, new_regs, regs_used,
      				  speed);
      if (again > gain)
	{
	  gain = again;
	  *best = inv;
	  *regs_needed = aregs_needed;
	}
    }

  return gain;
}

/* Marks invariant INVNO and all its dependencies for moving.  */

static void
set_move_mark (unsigned invno)
{
  struct invariant *inv = VEC_index (invariant_p, invariants, invno);
  bitmap_iterator bi;

  /* Find the representative of the class of the equivalent invariants.  */
  inv = VEC_index (invariant_p, invariants, inv->eqto);

  if (inv->move)
    return;
  inv->move = true;

  if (dump_file)
    fprintf (dump_file, "Decided to move invariant %d\n", invno);

  EXECUTE_IF_SET_IN_BITMAP (inv->depends_on, 0, invno, bi)
    {
      set_move_mark (invno);
    }
}

/* Determines which invariants to move.  */

static void
find_invariants_to_move (bool speed)
{
  unsigned i, regs_used, regs_needed = 0, new_regs;
  struct invariant *inv = NULL;
  unsigned int n_regs = DF_REG_SIZE (df);

  if (!VEC_length (invariant_p, invariants))
    return;

  /* We do not really do a good job in estimating number of registers used;
     we put some initial bound here to stand for induction variables etc.
     that we do not detect.  */
  regs_used = 2;

  for (i = 0; i < n_regs; i++)
    {
      if (!DF_REGNO_FIRST_DEF (i) && DF_REGNO_LAST_USE (i))
	{
	  /* This is a value that is used but not changed inside loop.  */
	  regs_used++;
	}
    }

  new_regs = 0;
  while (best_gain_for_invariant (&inv, &regs_needed, new_regs, regs_used, speed) > 0)
    {
      set_move_mark (inv->invno);
      new_regs += regs_needed;
    }
}

/* Move invariant INVNO out of the LOOP.  Returns true if this succeeds, false
   otherwise.  */

static bool
move_invariant_reg (struct loop *loop, unsigned invno)
{
  struct invariant *inv = VEC_index (invariant_p, invariants, invno);
  struct invariant *repr = VEC_index (invariant_p, invariants, inv->eqto);
  unsigned i;
  basic_block preheader = loop_preheader_edge (loop)->src;
  rtx reg, set, dest, note;
  struct use *use;
  bitmap_iterator bi;

  if (inv->reg)
    return true;
  if (!repr->move)
    return false;
  /* If this is a representative of the class of equivalent invariants,
     really move the invariant.  Otherwise just replace its use with
     the register used for the representative.  */
  if (inv == repr)
    {
      if (inv->depends_on)
	{
	  EXECUTE_IF_SET_IN_BITMAP (inv->depends_on, 0, i, bi)
	    {
	      if (!move_invariant_reg (loop, i))
		goto fail;
	    }
	}

      /* Move the set out of the loop.  If the set is always executed (we could
	 omit this condition if we know that the register is unused outside of the
	 loop, but it does not seem worth finding out) and it has no uses that
	 would not be dominated by it, we may just move it (TODO).  Otherwise we
	 need to create a temporary register.  */
      set = single_set (inv->insn);
      dest = SET_DEST (set);
      reg = gen_reg_rtx_and_attrs (dest);

      /* Try replacing the destination by a new pseudoregister.  */
      if (!validate_change (inv->insn, &SET_DEST (set), reg, false))
	goto fail;
      df_insn_rescan (inv->insn);

      emit_insn_after (gen_move_insn (dest, reg), inv->insn);
      reorder_insns (inv->insn, inv->insn, BB_END (preheader));

      /* If there is a REG_EQUAL note on the insn we just moved, and
	 insn is in a basic block that is not always executed, the note
	 may no longer be valid after we move the insn.
	 Note that uses in REG_EQUAL notes are taken into account in
	 the computation of invariants.  Hence it is safe to retain the
	 note even if the note contains register references.  */
      if (! inv->always_executed
	  && (note = find_reg_note (inv->insn, REG_EQUAL, NULL_RTX)))
	remove_note (inv->insn, note);
    }
  else
    {
      if (!move_invariant_reg (loop, repr->invno))
	goto fail;
      reg = repr->reg;
      set = single_set (inv->insn);
      emit_insn_after (gen_move_insn (SET_DEST (set), reg), inv->insn);
      delete_insn (inv->insn);
    }


  inv->reg = reg;

  /* Replace the uses we know to be dominated.  It saves work for copy
     propagation, and also it is necessary so that dependent invariants
     are computed right.  */
  if (inv->def)
    {
      for (use = inv->def->uses; use; use = use->next)
	{
	  *use->pos = reg;
	  df_insn_rescan (use->insn);
	}      
    }

  return true;

fail:
  /* If we failed, clear move flag, so that we do not try to move inv
     again.  */
  if (dump_file)
    fprintf (dump_file, "Failed to move invariant %d\n", invno);
  inv->move = false;
  inv->reg = NULL_RTX;

  return false;
}

/* Move selected invariant out of the LOOP.  Newly created regs are marked
   in TEMPORARY_REGS.  */

static void
move_invariants (struct loop *loop)
{
  struct invariant *inv;
  unsigned i;

  for (i = 0; VEC_iterate (invariant_p, invariants, i, inv); i++)
    move_invariant_reg (loop, i);
}

/* Initializes invariant motion data.  */

static void
init_inv_motion_data (void)
{
  actual_stamp = 1;

  invariants = VEC_alloc (invariant_p, heap, 100);
}

/* Frees the data allocated by invariant motion.  */

static void
free_inv_motion_data (void)
{
  unsigned i;
  struct def *def;
  struct invariant *inv;

  check_invariant_table_size ();
  for (i = 0; i < DF_DEFS_TABLE_SIZE (); i++)
    {
      inv = invariant_table[i];
      if (inv)
	{
	  def = inv->def;
	  gcc_assert (def != NULL);
	  
	  free_use_list (def->uses);
	  free (def);
	  invariant_table[i] = NULL;
	}
    }

  for (i = 0; VEC_iterate (invariant_p, invariants, i, inv); i++)
    {
      BITMAP_FREE (inv->depends_on);
      free (inv);
    }
  VEC_free (invariant_p, heap, invariants);
}

/* Move the invariants out of the LOOP.  */

static void
move_single_loop_invariants (struct loop *loop)
{
  init_inv_motion_data ();

  find_invariants (loop);
  find_invariants_to_move (optimize_loop_for_speed_p (loop));
  move_invariants (loop);

  free_inv_motion_data ();
}

/* Releases the auxiliary data for LOOP.  */

static void
free_loop_data (struct loop *loop)
{
  struct loop_data *data = LOOP_DATA (loop);

  free (data);
  loop->aux = NULL;
}

/* Move the invariants out of the loops.  */

void
move_loop_invariants (void)
{
  struct loop *loop;
  loop_iterator li;

  df_set_flags (DF_EQ_NOTES + DF_DEFER_INSN_RESCAN);
  /* Process the loops, innermost first.  */
  FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
    {
      /* move_single_loop_invariants for very large loops
	 is time consuming and might need a lot of memory.  */
      if (loop->num_nodes <= (unsigned) LOOP_INVARIANT_MAX_BBS_IN_LOOP)
	move_single_loop_invariants (loop);
    }

  FOR_EACH_LOOP (li, loop, 0)
    {
      free_loop_data (loop);
    }

  free (invariant_table);
  invariant_table = NULL;
  invariant_table_size = 0;

#ifdef ENABLE_CHECKING
  verify_flow_info ();
#endif
}