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[official-gcc.git] / gcc / regrename.c

/* Register renaming for the GNU compiler.
   Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
   2010 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/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl-error.h"
#include "tm_p.h"
#include "insn-config.h"
#include "regs.h"
#include "addresses.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "reload.h"
#include "output.h"
#include "function.h"
#include "recog.h"
#include "flags.h"
#include "obstack.h"
#include "timevar.h"
#include "tree-pass.h"
#include "df.h"
#include "target.h"

/* This file implements the RTL register renaming pass of the compiler.  It is
   a semi-local pass whose goal is to maximize the usage of the register file
   of the processor by substituting registers for others in the solution given
   by the register allocator.  The algorithm is as follows:

     1. Local def/use chains are built: within each basic block, chains are
        opened and closed; if a chain isn't closed at the end of the block,
        it is dropped.

     2. For each chain, the set of possible renaming registers is computed.
        This takes into account the renaming of previously processed chains.
        Optionally, a preferred class is computed for the renaming register.

     3. The best renaming register is computed for the chain in the above set,
        using a round-robin allocation.  If a preferred class exists, then the
        round-robin allocation is done within the class first, if possible.
        The round-robin allocation of renaming registers itself is global.

     4. If a renaming register has been found, it is substituted in the chain.

  Targets can parameterize the pass by specifying a preferred class for the
  renaming register for a given (super)class of registers to be renamed.  */

#if HOST_BITS_PER_WIDE_INT <= MAX_RECOG_OPERANDS
#error "Use a different bitmap implementation for untracked_operands."
#endif

/* We keep linked lists of DU_HEAD structures, each of which describes
   a chain of occurrences of a reg.  */
struct du_head
{
  /* The next chain.  */
  struct du_head *next_chain;
  /* The first and last elements of this chain.  */
  struct du_chain *first, *last;
  /* Describes the register being tracked.  */
  unsigned regno, nregs;

  /* A unique id to be used as an index into the conflicts bitmaps.  */
  unsigned id;
  /* A bitmap to record conflicts with other chains.  */
  bitmap_head conflicts;
  /* Conflicts with untracked hard registers.  */
  HARD_REG_SET hard_conflicts;

  /* Nonzero if the chain is finished; zero if it is still open.  */
  unsigned int terminated:1;
  /* Nonzero if the chain crosses a call.  */
  unsigned int need_caller_save_reg:1;
  /* Nonzero if the register is used in a way that prevents renaming,
     such as the SET_DEST of a CALL_INSN or an asm operand that used
     to be a hard register.  */
  unsigned int cannot_rename:1;
};

/* This struct describes a single occurrence of a register.  */
struct du_chain
{
  /* Links to the next occurrence of the register.  */
  struct du_chain *next_use;

  /* The insn where the register appears.  */
  rtx insn;
  /* The location inside the insn.  */
  rtx *loc;
  /* The register class required by the insn at this location.  */
  ENUM_BITFIELD(reg_class) cl : 16;
};

enum scan_actions
{
  terminate_write,
  terminate_dead,
  mark_all_read,
  mark_read,
  mark_write,
  /* mark_access is for marking the destination regs in
     REG_FRAME_RELATED_EXPR notes (as if they were read) so that the
     note is updated properly.  */
  mark_access
};

static const char * const scan_actions_name[] =
{
  "terminate_write",
  "terminate_dead",
  "mark_all_read",
  "mark_read",
  "mark_write",
  "mark_access"
};

static struct obstack rename_obstack;

static void do_replace (struct du_head *, int);
static void scan_rtx_reg (rtx, rtx *, enum reg_class,
                          enum scan_actions, enum op_type);
static void scan_rtx_address (rtx, rtx *, enum reg_class,
                              enum scan_actions, enum machine_mode);
static void scan_rtx (rtx, rtx *, enum reg_class, enum scan_actions,
                      enum op_type);
static struct du_head *build_def_use (basic_block);
static void dump_def_use_chain (struct du_head *);

typedef struct du_head *du_head_p;
DEF_VEC_P (du_head_p);
DEF_VEC_ALLOC_P (du_head_p, heap);
static VEC(du_head_p, heap) *id_to_chain;

static void
free_chain_data (void)
{
  int i;
  du_head_p ptr;
  for (i = 0; VEC_iterate(du_head_p, id_to_chain, i, ptr); i++)
    bitmap_clear (&ptr->conflicts);

  VEC_free (du_head_p, heap, id_to_chain);
}

/* For a def-use chain HEAD, find which registers overlap its lifetime and
   set the corresponding bits in *PSET.  */

static void
merge_overlapping_regs (HARD_REG_SET *pset, struct du_head *head)
{
  bitmap_iterator bi;
  unsigned i;
  IOR_HARD_REG_SET (*pset, head->hard_conflicts);
  EXECUTE_IF_SET_IN_BITMAP (&head->conflicts, 0, i, bi)
    {
      du_head_p other = VEC_index (du_head_p, id_to_chain, i);
      unsigned j = other->nregs;
      while (j-- > 0)
        SET_HARD_REG_BIT (*pset, other->regno + j);
    }
}

/* Check if NEW_REG can be the candidate register to rename for
   REG in THIS_HEAD chain.  THIS_UNAVAILABLE is a set of unavailable hard
   registers.  */

static bool
check_new_reg_p (int reg ATTRIBUTE_UNUSED, int new_reg,
                 struct du_head *this_head, HARD_REG_SET this_unavailable)
{
  enum machine_mode mode = GET_MODE (*this_head->first->loc);
  int nregs = hard_regno_nregs[new_reg][mode];
  int i;
  struct du_chain *tmp;

  for (i = nregs - 1; i >= 0; --i)
    if (TEST_HARD_REG_BIT (this_unavailable, new_reg + i)
        || fixed_regs[new_reg + i]
        || global_regs[new_reg + i]
        /* Can't use regs which aren't saved by the prologue.  */
        || (! df_regs_ever_live_p (new_reg + i)
            && ! call_used_regs[new_reg + i])
#ifdef LEAF_REGISTERS
        /* We can't use a non-leaf register if we're in a
           leaf function.  */
        || (current_function_is_leaf
            && !LEAF_REGISTERS[new_reg + i])
#endif
#ifdef HARD_REGNO_RENAME_OK
        || ! HARD_REGNO_RENAME_OK (reg + i, new_reg + i)
#endif
        )
      return false;

  /* See whether it accepts all modes that occur in
     definition and uses.  */
  for (tmp = this_head->first; tmp; tmp = tmp->next_use)
    if ((! HARD_REGNO_MODE_OK (new_reg, GET_MODE (*tmp->loc))
         && ! DEBUG_INSN_P (tmp->insn))
        || (this_head->need_caller_save_reg
            && ! (HARD_REGNO_CALL_PART_CLOBBERED
                  (reg, GET_MODE (*tmp->loc)))
            && (HARD_REGNO_CALL_PART_CLOBBERED
                (new_reg, GET_MODE (*tmp->loc)))))
      return false;

  return true;
}

/* Perform register renaming on the current function.  */

static unsigned int
regrename_optimize (void)
{
  int tick[FIRST_PSEUDO_REGISTER];
  int this_tick = 0;
  basic_block bb;
  char *first_obj;

  df_set_flags (DF_LR_RUN_DCE);
  df_note_add_problem ();
  df_analyze ();
  df_set_flags (DF_DEFER_INSN_RESCAN);

  memset (tick, 0, sizeof tick);

  gcc_obstack_init (&rename_obstack);
  first_obj = XOBNEWVAR (&rename_obstack, char, 0);

  FOR_EACH_BB (bb)
    {
      struct du_head *all_chains = 0;
      HARD_REG_SET unavailable;
#if 0
      HARD_REG_SET regs_seen;
      CLEAR_HARD_REG_SET (regs_seen);
#endif

      id_to_chain = VEC_alloc (du_head_p, heap, 0);

      CLEAR_HARD_REG_SET (unavailable);

      if (dump_file)
        fprintf (dump_file, "\nBasic block %d:\n", bb->index);

      all_chains = build_def_use (bb);

      if (dump_file)
        dump_def_use_chain (all_chains);

      CLEAR_HARD_REG_SET (unavailable);
      /* Don't clobber traceback for noreturn functions.  */
      if (frame_pointer_needed)
        {
          add_to_hard_reg_set (&unavailable, Pmode, FRAME_POINTER_REGNUM);
#if !HARD_FRAME_POINTER_IS_FRAME_POINTER
          add_to_hard_reg_set (&unavailable, Pmode, HARD_FRAME_POINTER_REGNUM);
#endif
        }

      while (all_chains)
        {
          int new_reg, best_new_reg, best_nregs;
          int n_uses;
          struct du_head *this_head = all_chains;
          struct du_chain *tmp;
          HARD_REG_SET this_unavailable;
          int reg = this_head->regno;
          int pass;
          enum reg_class super_class = NO_REGS;
          enum reg_class preferred_class;
          bool has_preferred_class;

          all_chains = this_head->next_chain;

          if (this_head->cannot_rename)
            continue;

          best_new_reg = reg;
          best_nregs = this_head->nregs;

#if 0 /* This just disables optimization opportunities.  */
          /* Only rename once we've seen the reg more than once.  */
          if (! TEST_HARD_REG_BIT (regs_seen, reg))
            {
              SET_HARD_REG_BIT (regs_seen, reg);
              continue;
            }
#endif

          if (fixed_regs[reg] || global_regs[reg]
#if !HARD_FRAME_POINTER_IS_FRAME_POINTER
              || (frame_pointer_needed && reg == HARD_FRAME_POINTER_REGNUM)
#else
              || (frame_pointer_needed && reg == FRAME_POINTER_REGNUM)
#endif
              )
            continue;

          COPY_HARD_REG_SET (this_unavailable, unavailable);

          /* Iterate over elements in the chain in order to:
             1. Count number of uses, and narrow the set of registers we can
                use for renaming.
             2. Compute the superunion of register classes in this chain.  */
          n_uses = 0;
          super_class = NO_REGS;
          for (tmp = this_head->first; tmp; tmp = tmp->next_use)
            {
              if (DEBUG_INSN_P (tmp->insn))
                continue;
              n_uses++;
              IOR_COMPL_HARD_REG_SET (this_unavailable,
                                      reg_class_contents[tmp->cl]);
              super_class
                = reg_class_superunion[(int) super_class][(int) tmp->cl];
            }

          if (n_uses < 2)
            continue;

          /* Further narrow the set of registers we can use for renaming.
             If the chain needs a call-saved register, mark the call-used
             registers as unavailable.  */
          if (this_head->need_caller_save_reg)
            IOR_HARD_REG_SET (this_unavailable, call_used_reg_set);

          /* And mark registers that overlap its lifetime as unavailable.  */
          merge_overlapping_regs (&this_unavailable, this_head);

          /* Compute preferred rename class of super union of all the classes
             in the chain.  */
          preferred_class
            = (enum reg_class) targetm.preferred_rename_class (super_class);

          /* If PREFERRED_CLASS is not NO_REGS, we iterate in the first pass
             over registers that belong to PREFERRED_CLASS and try to find the
             best register within the class.  If that failed, we iterate in
             the second pass over registers that don't belong to the class.
             If PREFERRED_CLASS is NO_REGS, we iterate over all registers in
             ascending order without any preference.  */
          has_preferred_class = (preferred_class != NO_REGS);
          for (pass = (has_preferred_class ? 0 : 1); pass < 2; pass++)
            {
              for (new_reg = 0; new_reg < FIRST_PSEUDO_REGISTER; new_reg++)
                {
                  if (has_preferred_class
                      && (pass == 0)
                         != TEST_HARD_REG_BIT
                            (reg_class_contents[preferred_class], new_reg))
                    continue;

                  /* In the first pass, we force the renaming of registers that
                     don't belong to PREFERRED_CLASS to registers that do, even
                     though the latters were used not very long ago.  */
                  if (check_new_reg_p (reg, new_reg, this_head,
                                       this_unavailable)
                      && ((pass == 0
                           && !TEST_HARD_REG_BIT
                               (reg_class_contents[preferred_class],
                                best_new_reg))
                          || tick[best_new_reg] > tick[new_reg]))
                    {
                      enum machine_mode mode
                        = GET_MODE (*this_head->first->loc);
                      best_new_reg = new_reg;
                      best_nregs = hard_regno_nregs[new_reg][mode];
                    }
                }
              if (pass == 0 && best_new_reg != reg)
                break;
            }

          if (dump_file)
            {
              fprintf (dump_file, "Register %s in insn %d",
                       reg_names[reg], INSN_UID (this_head->first->insn));
              if (this_head->need_caller_save_reg)
                fprintf (dump_file, " crosses a call");
            }

          if (best_new_reg == reg)
            {
              tick[reg] = ++this_tick;
              if (dump_file)
                fprintf (dump_file, "; no available better choice\n");
              continue;
            }

          if (dump_file)
            fprintf (dump_file, ", renamed as %s\n", reg_names[best_new_reg]);

          do_replace (this_head, best_new_reg);
          this_head->regno = best_new_reg;
          this_head->nregs = best_nregs;
          tick[best_new_reg] = ++this_tick;
          df_set_regs_ever_live (best_new_reg, true);
        }

      free_chain_data ();
      obstack_free (&rename_obstack, first_obj);
    }

  obstack_free (&rename_obstack, NULL);

  if (dump_file)
    fputc ('\n', dump_file);

  return 0;
}

static void
do_replace (struct du_head *head, int reg)
{
  struct du_chain *chain;
  unsigned int base_regno = head->regno;
  bool found_note = false;

  gcc_assert (! DEBUG_INSN_P (head->first->insn));

  for (chain = head->first; chain; chain = chain->next_use)
    {
      unsigned int regno = ORIGINAL_REGNO (*chain->loc);
      struct reg_attrs *attr = REG_ATTRS (*chain->loc);
      int reg_ptr = REG_POINTER (*chain->loc);

      if (DEBUG_INSN_P (chain->insn) && REGNO (*chain->loc) != base_regno)
        INSN_VAR_LOCATION_LOC (chain->insn) = gen_rtx_UNKNOWN_VAR_LOC ();
      else
        {
          rtx note;

          *chain->loc = gen_raw_REG (GET_MODE (*chain->loc), reg);
          if (regno >= FIRST_PSEUDO_REGISTER)
            ORIGINAL_REGNO (*chain->loc) = regno;
          REG_ATTRS (*chain->loc) = attr;
          REG_POINTER (*chain->loc) = reg_ptr;

          for (note = REG_NOTES (chain->insn); note; note = XEXP (note, 1))
            {
              enum reg_note kind = REG_NOTE_KIND (note);
              if (kind == REG_DEAD || kind == REG_UNUSED)
                {
                  rtx reg = XEXP (note, 0);
                  gcc_assert (HARD_REGISTER_P (reg));

                  if (REGNO (reg) == base_regno)
                    {
                      found_note = true;
                      if (kind == REG_DEAD
                          && reg_set_p (*chain->loc, chain->insn))
                        remove_note (chain->insn, note);
                      else
                        XEXP (note, 0) = *chain->loc;
                      break;
                    }
                }
            }
        }

      df_insn_rescan (chain->insn);
    }
  if (!found_note)
    {
      /* If the chain's first insn is the same as the last, we should have
         found a REG_UNUSED note.  */
      gcc_assert (head->first->insn != head->last->insn);
      if (!reg_set_p (*head->last->loc, head->last->insn))
        add_reg_note (head->last->insn, REG_DEAD, *head->last->loc);
    }
}


/* Walk all chains starting with CHAINS and record that they conflict with
   another chain whose id is ID.  */

static void
mark_conflict (struct du_head *chains, unsigned id)
{
  while (chains)
    {
      bitmap_set_bit (&chains->conflicts, id);
      chains = chains->next_chain;
    }
}

/* True if we found a register with a size mismatch, which means that we
   can't track its lifetime accurately.  If so, we abort the current block
   without renaming.  */
static bool fail_current_block;

/* The id to be given to the next opened chain.  */
static unsigned current_id;

/* List of currently open chains, and closed chains that can be renamed.  */
static struct du_head *open_chains;
static struct du_head *closed_chains;

/* Bitmap of open chains.  The bits set always match the list found in
   open_chains.  */
static bitmap_head open_chains_set;

/* Record the registers being tracked in open_chains.  */
static HARD_REG_SET live_in_chains;

/* Record the registers that are live but not tracked.  The intersection
   between this and live_in_chains is empty.  */
static HARD_REG_SET live_hard_regs;

/* Return true if OP is a reg for which all bits are set in PSET, false
   if all bits are clear.
   In other cases, set fail_current_block and return false.  */

static bool
verify_reg_in_set (rtx op, HARD_REG_SET *pset)
{
  unsigned regno, nregs;
  bool all_live, all_dead;
  if (!REG_P (op))
    return false;

  regno = REGNO (op);
  nregs = hard_regno_nregs[regno][GET_MODE (op)];
  all_live = all_dead = true;
  while (nregs-- > 0)
    if (TEST_HARD_REG_BIT (*pset, regno + nregs))
      all_dead = false;
    else
      all_live = false;
  if (!all_dead && !all_live)
    {
      fail_current_block = true;
      return false;
    }
  return all_live;
}

/* Return true if OP is a reg that is being tracked already in some form.
   May set fail_current_block if it sees an unhandled case of overlap.  */

static bool
verify_reg_tracked (rtx op)
{
  return (verify_reg_in_set (op, &live_hard_regs)
          || verify_reg_in_set (op, &live_in_chains));
}

/* Called through note_stores.  DATA points to a rtx_code, either SET or
   CLOBBER, which tells us which kind of rtx to look at.  If we have a
   match, record the set register in live_hard_regs and in the hard_conflicts
   bitmap of open chains.  */

static void
note_sets_clobbers (rtx x, const_rtx set, void *data)
{
  enum rtx_code code = *(enum rtx_code *)data;
  struct du_head *chain;

  if (GET_CODE (x) == SUBREG)
    x = SUBREG_REG (x);
  if (!REG_P (x) || GET_CODE (set) != code)
    return;
  /* There must not be pseudos at this point.  */
  gcc_assert (HARD_REGISTER_P (x));
  add_to_hard_reg_set (&live_hard_regs, GET_MODE (x), REGNO (x));
  for (chain = open_chains; chain; chain = chain->next_chain)
    add_to_hard_reg_set (&chain->hard_conflicts, GET_MODE (x), REGNO (x));
}

/* Create a new chain for THIS_NREGS registers starting at THIS_REGNO,
   and record its occurrence in *LOC, which is being written to in INSN.
   This access requires a register of class CL.  */

static void
create_new_chain (unsigned this_regno, unsigned this_nregs, rtx *loc,
                  rtx insn, enum reg_class cl)
{
  struct du_head *head = XOBNEW (&rename_obstack, struct du_head);
  struct du_chain *this_du;
  int nregs;

  head->next_chain = open_chains;
  open_chains = head;
  head->regno = this_regno;
  head->nregs = this_nregs;
  head->need_caller_save_reg = 0;
  head->cannot_rename = 0;
  head->terminated = 0;

  VEC_safe_push (du_head_p, heap, id_to_chain, head);
  head->id = current_id++;

  bitmap_initialize (&head->conflicts, &bitmap_default_obstack);
  bitmap_copy (&head->conflicts, &open_chains_set);
  mark_conflict (open_chains, head->id);

  /* Since we're tracking this as a chain now, remove it from the
     list of conflicting live hard registers and track it in
     live_in_chains instead.  */
  nregs = head->nregs;
  while (nregs-- > 0)
    {
      SET_HARD_REG_BIT (live_in_chains, head->regno + nregs);
      CLEAR_HARD_REG_BIT (live_hard_regs, head->regno + nregs);
    }

  COPY_HARD_REG_SET (head->hard_conflicts, live_hard_regs);
  bitmap_set_bit (&open_chains_set, head->id);

  open_chains = head;

  if (dump_file)
    {
      fprintf (dump_file, "Creating chain %s (%d)",
               reg_names[head->regno], head->id);
      if (insn != NULL_RTX)
        fprintf (dump_file, " at insn %d", INSN_UID (insn));
      fprintf (dump_file, "\n");
    }

  if (insn == NULL_RTX)
    {
      head->first = head->last = NULL;
      return;
    }

  this_du = XOBNEW (&rename_obstack, struct du_chain);
  head->first = head->last = this_du;

  this_du->next_use = 0;
  this_du->loc = loc;
  this_du->insn = insn;
  this_du->cl = cl;
}

static void
scan_rtx_reg (rtx insn, rtx *loc, enum reg_class cl, enum scan_actions action,
              enum op_type type)
{
  struct du_head **p;
  rtx x = *loc;
  enum machine_mode mode = GET_MODE (x);
  unsigned this_regno = REGNO (x);
  unsigned this_nregs = hard_regno_nregs[this_regno][mode];

  if (action == mark_write)
    {
      if (type == OP_OUT)
        create_new_chain (this_regno, this_nregs, loc, insn, cl);
      return;
    }

  if ((type == OP_OUT) != (action == terminate_write || action == mark_access))
    return;

  for (p = &open_chains; *p;)
    {
      struct du_head *head = *p;
      struct du_head *next = head->next_chain;
      int exact_match = (head->regno == this_regno
                         && head->nregs == this_nregs);
      int superset = (this_regno <= head->regno
                      && this_regno + this_nregs >= head->regno + head->nregs);
      int subset = (this_regno >= head->regno
                      && this_regno + this_nregs <= head->regno + head->nregs);

      if (head->terminated
          || head->regno + head->nregs <= this_regno
          || this_regno + this_nregs <= head->regno)
        {
          p = &head->next_chain;
          continue;
        }

      if (action == mark_read || action == mark_access)
        {
          /* ??? Class NO_REGS can happen if the md file makes use of
             EXTRA_CONSTRAINTS to match registers.  Which is arguably
             wrong, but there we are.  */

          if (cl == NO_REGS || (!exact_match && !DEBUG_INSN_P (insn)))
            {
              if (dump_file)
                fprintf (dump_file,
                         "Cannot rename chain %s (%d) at insn %d (%s)\n",
                         reg_names[head->regno], head->id, INSN_UID (insn),
                         scan_actions_name[(int) action]);
              head->cannot_rename = 1;
              if (superset)
                {
                  unsigned nregs = this_nregs;
                  head->regno = this_regno;
                  head->nregs = this_nregs;
                  while (nregs-- > 0)
                    SET_HARD_REG_BIT (live_in_chains, head->regno + nregs);
                  if (dump_file)
                    fprintf (dump_file,
                             "Widening register in chain %s (%d) at insn %d\n",
                             reg_names[head->regno], head->id, INSN_UID (insn));
                }
              else if (!subset)
                {
                  fail_current_block = true;
                  if (dump_file)
                    fprintf (dump_file,
                             "Failing basic block due to unhandled overlap\n");
                }
            }
          else
            {
              struct du_chain *this_du;
              this_du = XOBNEW (&rename_obstack, struct du_chain);
              this_du->next_use = 0;
              this_du->loc = loc;
              this_du->insn = insn;
              this_du->cl = cl;
              if (head->first == NULL)
                head->first = this_du;
              else
                head->last->next_use = this_du;
              head->last = this_du;
            }
          /* Avoid adding the same location in a DEBUG_INSN multiple times,
             which could happen with non-exact overlap.  */
          if (DEBUG_INSN_P (insn))
            return;
          /* Otherwise, find any other chains that do not match exactly;
             ensure they all get marked unrenamable.  */
          p = &head->next_chain;
          continue;
        }

      /* Whether the terminated chain can be used for renaming
         depends on the action and this being an exact match.
         In either case, we remove this element from open_chains.  */

      if ((action == terminate_dead || action == terminate_write)
          && superset)
        {
          unsigned nregs;

          head->terminated = 1;
          head->next_chain = closed_chains;
          closed_chains = head;
          bitmap_clear_bit (&open_chains_set, head->id);

          nregs = head->nregs;
          while (nregs-- > 0)
            CLEAR_HARD_REG_BIT (live_in_chains, head->regno + nregs);

          *p = next;
          if (dump_file)
            fprintf (dump_file,
                     "Closing chain %s (%d) at insn %d (%s)\n",
                     reg_names[head->regno], head->id, INSN_UID (insn),
                     scan_actions_name[(int) action]);
        }
      else if (action == terminate_dead || action == terminate_write)
        {
          /* In this case, tracking liveness gets too hard.  Fail the
             entire basic block.  */
          if (dump_file)
            fprintf (dump_file,
                     "Failing basic block due to unhandled overlap\n");
          fail_current_block = true;
          return;
        }
      else
        {
          head->cannot_rename = 1;
          if (dump_file)
            fprintf (dump_file,
                     "Cannot rename chain %s (%d) at insn %d (%s)\n",
                     reg_names[head->regno], head->id, INSN_UID (insn),
                     scan_actions_name[(int) action]);
          p = &head->next_chain;
        }
    }
}

/* Adapted from find_reloads_address_1.  CL is INDEX_REG_CLASS or
   BASE_REG_CLASS depending on how the register is being considered.  */

static void
scan_rtx_address (rtx insn, rtx *loc, enum reg_class cl,
                  enum scan_actions action, enum machine_mode mode)
{
  rtx x = *loc;
  RTX_CODE code = GET_CODE (x);
  const char *fmt;
  int i, j;

  if (action == mark_write || action == mark_access)
    return;

  switch (code)
    {
    case PLUS:
      {
        rtx orig_op0 = XEXP (x, 0);
        rtx orig_op1 = XEXP (x, 1);
        RTX_CODE code0 = GET_CODE (orig_op0);
        RTX_CODE code1 = GET_CODE (orig_op1);
        rtx op0 = orig_op0;
        rtx op1 = orig_op1;
        rtx *locI = NULL;
        rtx *locB = NULL;
        enum rtx_code index_code = SCRATCH;

        if (GET_CODE (op0) == SUBREG)
          {
            op0 = SUBREG_REG (op0);
            code0 = GET_CODE (op0);
          }

        if (GET_CODE (op1) == SUBREG)
          {
            op1 = SUBREG_REG (op1);
            code1 = GET_CODE (op1);
          }

        if (code0 == MULT || code0 == SIGN_EXTEND || code0 == TRUNCATE
            || code0 == ZERO_EXTEND || code1 == MEM)
          {
            locI = &XEXP (x, 0);
            locB = &XEXP (x, 1);
            index_code = GET_CODE (*locI);
          }
        else if (code1 == MULT || code1 == SIGN_EXTEND || code1 == TRUNCATE
                 || code1 == ZERO_EXTEND || code0 == MEM)
          {
            locI = &XEXP (x, 1);
            locB = &XEXP (x, 0);
            index_code = GET_CODE (*locI);
          }
        else if (code0 == CONST_INT || code0 == CONST
                 || code0 == SYMBOL_REF || code0 == LABEL_REF)
          {
            locB = &XEXP (x, 1);
            index_code = GET_CODE (XEXP (x, 0));
          }
        else if (code1 == CONST_INT || code1 == CONST
                 || code1 == SYMBOL_REF || code1 == LABEL_REF)
          {
            locB = &XEXP (x, 0);
            index_code = GET_CODE (XEXP (x, 1));
          }
        else if (code0 == REG && code1 == REG)
          {
            int index_op;
            unsigned regno0 = REGNO (op0), regno1 = REGNO (op1);

            if (REGNO_OK_FOR_INDEX_P (regno1)
                && regno_ok_for_base_p (regno0, mode, PLUS, REG))
              index_op = 1;
            else if (REGNO_OK_FOR_INDEX_P (regno0)
                     && regno_ok_for_base_p (regno1, mode, PLUS, REG))
              index_op = 0;
            else if (regno_ok_for_base_p (regno0, mode, PLUS, REG)
                     || REGNO_OK_FOR_INDEX_P (regno1))
              index_op = 1;
            else if (regno_ok_for_base_p (regno1, mode, PLUS, REG))
              index_op = 0;
            else
              index_op = 1;

            locI = &XEXP (x, index_op);
            locB = &XEXP (x, !index_op);
            index_code = GET_CODE (*locI);
          }
        else if (code0 == REG)
          {
            locI = &XEXP (x, 0);
            locB = &XEXP (x, 1);
            index_code = GET_CODE (*locI);
          }
        else if (code1 == REG)
          {
            locI = &XEXP (x, 1);
            locB = &XEXP (x, 0);
            index_code = GET_CODE (*locI);
          }

        if (locI)
          scan_rtx_address (insn, locI, INDEX_REG_CLASS, action, mode);
        if (locB)
          scan_rtx_address (insn, locB, base_reg_class (mode, PLUS, index_code),
                            action, mode);

        return;
      }

    case POST_INC:
    case POST_DEC:
    case POST_MODIFY:
    case PRE_INC:
    case PRE_DEC:
    case PRE_MODIFY:
#ifndef AUTO_INC_DEC
      /* If the target doesn't claim to handle autoinc, this must be
         something special, like a stack push.  Kill this chain.  */
      action = mark_all_read;
#endif
      break;

    case MEM:
      scan_rtx_address (insn, &XEXP (x, 0),
                        base_reg_class (GET_MODE (x), MEM, SCRATCH), action,
                        GET_MODE (x));
      return;

    case REG:
      scan_rtx_reg (insn, loc, cl, action, OP_IN);
      return;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        scan_rtx_address (insn, &XEXP (x, i), cl, action, mode);
      else if (fmt[i] == 'E')
        for (j = XVECLEN (x, i) - 1; j >= 0; j--)
          scan_rtx_address (insn, &XVECEXP (x, i, j), cl, action, mode);
    }
}

static void
scan_rtx (rtx insn, rtx *loc, enum reg_class cl, enum scan_actions action,
          enum op_type type)
{
  const char *fmt;
  rtx x = *loc;
  enum rtx_code code = GET_CODE (x);
  int i, j;

  code = GET_CODE (x);
  switch (code)
    {
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
    case CONST_VECTOR:
    case SYMBOL_REF:
    case LABEL_REF:
    case CC0:
    case PC:
      return;

    case REG:
      scan_rtx_reg (insn, loc, cl, action, type);
      return;

    case MEM:
      scan_rtx_address (insn, &XEXP (x, 0),
                        base_reg_class (GET_MODE (x), MEM, SCRATCH), action,
                        GET_MODE (x));
      return;

    case SET:
      scan_rtx (insn, &SET_SRC (x), cl, action, OP_IN);
      scan_rtx (insn, &SET_DEST (x), cl, action,
                (GET_CODE (PATTERN (insn)) == COND_EXEC
                 && verify_reg_tracked (SET_DEST (x))) ? OP_INOUT : OP_OUT);
      return;

    case STRICT_LOW_PART:
      scan_rtx (insn, &XEXP (x, 0), cl, action,
                verify_reg_tracked (XEXP (x, 0)) ? OP_INOUT : OP_OUT);
      return;

    case ZERO_EXTRACT:
    case SIGN_EXTRACT:
      scan_rtx (insn, &XEXP (x, 0), cl, action,
                (type == OP_IN ? OP_IN :
                 verify_reg_tracked (XEXP (x, 0)) ? OP_INOUT : OP_OUT));
      scan_rtx (insn, &XEXP (x, 1), cl, action, OP_IN);
      scan_rtx (insn, &XEXP (x, 2), cl, action, OP_IN);
      return;

    case POST_INC:
    case PRE_INC:
    case POST_DEC:
    case PRE_DEC:
    case POST_MODIFY:
    case PRE_MODIFY:
      /* Should only happen inside MEM.  */
      gcc_unreachable ();

    case CLOBBER:
      scan_rtx (insn, &SET_DEST (x), cl, action,
                (GET_CODE (PATTERN (insn)) == COND_EXEC
                 && verify_reg_tracked (SET_DEST (x))) ? OP_INOUT : OP_OUT);
      return;

    case EXPR_LIST:
      scan_rtx (insn, &XEXP (x, 0), cl, action, type);
      if (XEXP (x, 1))
        scan_rtx (insn, &XEXP (x, 1), cl, action, type);
      return;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        scan_rtx (insn, &XEXP (x, i), cl, action, type);
      else if (fmt[i] == 'E')
        for (j = XVECLEN (x, i) - 1; j >= 0; j--)
          scan_rtx (insn, &XVECEXP (x, i, j), cl, action, type);
    }
}

/* Hide operands of the current insn (of which there are N_OPS) by
   substituting cc0 for them.
   Previous values are stored in the OLD_OPERANDS and OLD_DUPS.
   For every bit set in DO_NOT_HIDE, we leave the operand alone.
   If INOUT_AND_EC_ONLY is set, we only do this for OP_INOUT type operands
   and earlyclobbers.  */

static void
hide_operands (int n_ops, rtx *old_operands, rtx *old_dups,
               unsigned HOST_WIDE_INT do_not_hide, bool inout_and_ec_only)
{
  int i;
  int alt = which_alternative;
  for (i = 0; i < n_ops; i++)
    {
      old_operands[i] = recog_data.operand[i];
      /* Don't squash match_operator or match_parallel here, since
         we don't know that all of the contained registers are
         reachable by proper operands.  */
      if (recog_data.constraints[i][0] == '\0')
        continue;
      if (do_not_hide & (1 << i))
        continue;
      if (!inout_and_ec_only || recog_data.operand_type[i] == OP_INOUT
          || recog_op_alt[i][alt].earlyclobber)
        *recog_data.operand_loc[i] = cc0_rtx;
    }
  for (i = 0; i < recog_data.n_dups; i++)
    {
      int opn = recog_data.dup_num[i];
      old_dups[i] = *recog_data.dup_loc[i];
      if (do_not_hide & (1 << opn))
        continue;
      if (!inout_and_ec_only || recog_data.operand_type[opn] == OP_INOUT
          || recog_op_alt[opn][alt].earlyclobber)
        *recog_data.dup_loc[i] = cc0_rtx;
    }
}

/* Undo the substitution performed by hide_operands.  INSN is the insn we
   are processing; the arguments are the same as in hide_operands.  */

static void
restore_operands (rtx insn, int n_ops, rtx *old_operands, rtx *old_dups)
{
  int i;
  for (i = 0; i < recog_data.n_dups; i++)
    *recog_data.dup_loc[i] = old_dups[i];
  for (i = 0; i < n_ops; i++)
    *recog_data.operand_loc[i] = old_operands[i];
  if (recog_data.n_dups)
    df_insn_rescan (insn);
}

/* For each output operand of INSN, call scan_rtx to create a new
   open chain.  Do this only for normal or earlyclobber outputs,
   depending on EARLYCLOBBER.  */

static void
record_out_operands (rtx insn, bool earlyclobber)
{
  int n_ops = recog_data.n_operands;
  int alt = which_alternative;

  int i;

  for (i = 0; i < n_ops + recog_data.n_dups; i++)
    {
      int opn = i < n_ops ? i : recog_data.dup_num[i - n_ops];
      rtx *loc = (i < n_ops
                  ? recog_data.operand_loc[opn]
                  : recog_data.dup_loc[i - n_ops]);
      rtx op = *loc;
      enum reg_class cl = recog_op_alt[opn][alt].cl;

      struct du_head *prev_open;

      if (recog_data.operand_type[opn] != OP_OUT
          || recog_op_alt[opn][alt].earlyclobber != earlyclobber)
        continue;

      prev_open = open_chains;
      scan_rtx (insn, loc, cl, mark_write, OP_OUT);

      /* ??? Many targets have output constraints on the SET_DEST
         of a call insn, which is stupid, since these are certainly
         ABI defined hard registers.  For these, and for asm operands
         that originally referenced hard registers, we must record that
         the chain cannot be renamed.  */
      if (CALL_P (insn)
          || (asm_noperands (PATTERN (insn)) > 0
              && REG_P (op)
              && REGNO (op) == ORIGINAL_REGNO (op)))
        {
          if (prev_open != open_chains)
            open_chains->cannot_rename = 1;
        }
    }
}

/* Build def/use chain.  */

static struct du_head *
build_def_use (basic_block bb)
{
  rtx insn;
  df_ref *def_rec;
  unsigned HOST_WIDE_INT untracked_operands;

  open_chains = closed_chains = NULL;

  fail_current_block = false;

  current_id = 0;
  bitmap_initialize (&open_chains_set, &bitmap_default_obstack);
  CLEAR_HARD_REG_SET (live_in_chains);
  REG_SET_TO_HARD_REG_SET (live_hard_regs, df_get_live_in (bb));
  for (def_rec = df_get_artificial_defs (bb->index); *def_rec; def_rec++)
    {
      df_ref def = *def_rec;
      if (DF_REF_FLAGS (def) & DF_REF_AT_TOP)
        SET_HARD_REG_BIT (live_hard_regs, DF_REF_REGNO (def));
    }

  for (insn = BB_HEAD (bb); ; insn = NEXT_INSN (insn))
    {
      if (NONDEBUG_INSN_P (insn))
        {
          int n_ops;
          rtx note;
          rtx old_operands[MAX_RECOG_OPERANDS];
          rtx old_dups[MAX_DUP_OPERANDS];
          int i;
          int alt;
          int predicated;
          enum rtx_code set_code = SET;
          enum rtx_code clobber_code = CLOBBER;

          /* Process the insn, determining its effect on the def-use
             chains and live hard registers.  We perform the following
             steps with the register references in the insn, simulating
             its effect:
             (1) Deal with earlyclobber operands and CLOBBERs of non-operands
                 by creating chains and marking hard regs live.
             (2) Any read outside an operand causes any chain it overlaps
                 with to be marked unrenamable.
             (3) Any read inside an operand is added if there's already
                 an open chain for it.
             (4) For any REG_DEAD note we find, close open chains that
                 overlap it.
             (5) For any non-earlyclobber write we find, close open chains
                 that overlap it.
             (6) For any non-earlyclobber write we find in an operand, make
                 a new chain or mark the hard register as live.
             (7) For any REG_UNUSED, close any chains we just opened.

             We cannot deal with situations where we track a reg in one mode
             and see a reference in another mode; these will cause the chain
             to be marked unrenamable or even cause us to abort the entire
             basic block.  */

          extract_insn (insn);
          if (! constrain_operands (1))
            fatal_insn_not_found (insn);
          preprocess_constraints ();
          alt = which_alternative;
          n_ops = recog_data.n_operands;
          untracked_operands = 0;

          /* Simplify the code below by rewriting things to reflect
             matching constraints.  Also promote OP_OUT to OP_INOUT in
             predicated instructions, but only for register operands
             that are already tracked, so that we can create a chain
             when the first SET makes a register live.  */

          predicated = GET_CODE (PATTERN (insn)) == COND_EXEC;
          for (i = 0; i < n_ops; ++i)
            {
              rtx op = recog_data.operand[i];
              int matches = recog_op_alt[i][alt].matches;
              if (matches >= 0)
                recog_op_alt[i][alt].cl = recog_op_alt[matches][alt].cl;
              if (matches >= 0 || recog_op_alt[i][alt].matched >= 0
                  || (predicated && recog_data.operand_type[i] == OP_OUT))
                {
                  recog_data.operand_type[i] = OP_INOUT;
                  /* A special case to deal with instruction patterns that
                     have matching operands with different modes.  If we're
                     not already tracking such a reg, we won't start here,
                     and we must instead make sure to make the operand visible
                     to the machinery that tracks hard registers.  */
                  if (matches >= 0
                      && (GET_MODE_SIZE (recog_data.operand_mode[i])
                          != GET_MODE_SIZE (recog_data.operand_mode[matches]))
                      && !verify_reg_in_set (op, &live_in_chains))
                    {
                      untracked_operands |= 1 << i;
                      untracked_operands |= 1 << matches;
                    }
                }
              /* If there's an in-out operand with a register that is not
                 being tracked at all yet, open a chain.  */
              if (recog_data.operand_type[i] == OP_INOUT
                  && !(untracked_operands & (1 << i))
                  && REG_P (op)
                  && !verify_reg_tracked (op))
                {
                  enum machine_mode mode = GET_MODE (op);
                  unsigned this_regno = REGNO (op);
                  unsigned this_nregs = hard_regno_nregs[this_regno][mode];
                  create_new_chain (this_regno, this_nregs, NULL, NULL_RTX,
                                    NO_REGS);
                }
            }

          if (fail_current_block)
            break;

          /* Step 1a: Mark hard registers that are clobbered in this insn,
             outside an operand, as live.  */
          hide_operands (n_ops, old_operands, old_dups, untracked_operands,
                         false);
          note_stores (PATTERN (insn), note_sets_clobbers, &clobber_code);
          restore_operands (insn, n_ops, old_operands, old_dups);

          /* Step 1b: Begin new chains for earlyclobbered writes inside
             operands.  */
          record_out_operands (insn, true);

          /* Step 2: Mark chains for which we have reads outside operands
             as unrenamable.
             We do this by munging all operands into CC0, and closing
             everything remaining.  */

          hide_operands (n_ops, old_operands, old_dups, untracked_operands,
                         false);
          scan_rtx (insn, &PATTERN (insn), NO_REGS, mark_all_read, OP_IN);
          restore_operands (insn, n_ops, old_operands, old_dups);

          /* Step 2B: Can't rename function call argument registers.  */
          if (CALL_P (insn) && CALL_INSN_FUNCTION_USAGE (insn))
            scan_rtx (insn, &CALL_INSN_FUNCTION_USAGE (insn),
                      NO_REGS, mark_all_read, OP_IN);

          /* Step 2C: Can't rename asm operands that were originally
             hard registers.  */
          if (asm_noperands (PATTERN (insn)) > 0)
            for (i = 0; i < n_ops; i++)
              {
                rtx *loc = recog_data.operand_loc[i];
                rtx op = *loc;

                if (REG_P (op)
                    && REGNO (op) == ORIGINAL_REGNO (op)
                    && (recog_data.operand_type[i] == OP_IN
                        || recog_data.operand_type[i] == OP_INOUT))
                  scan_rtx (insn, loc, NO_REGS, mark_all_read, OP_IN);
              }

          /* Step 3: Append to chains for reads inside operands.  */
          for (i = 0; i < n_ops + recog_data.n_dups; i++)
            {
              int opn = i < n_ops ? i : recog_data.dup_num[i - n_ops];
              rtx *loc = (i < n_ops
                          ? recog_data.operand_loc[opn]
                          : recog_data.dup_loc[i - n_ops]);
              enum reg_class cl = recog_op_alt[opn][alt].cl;
              enum op_type type = recog_data.operand_type[opn];

              /* Don't scan match_operand here, since we've no reg class
                 information to pass down.  Any operands that we could
                 substitute in will be represented elsewhere.  */
              if (recog_data.constraints[opn][0] == '\0'
                  || untracked_operands & (1 << opn))
                continue;

              if (recog_op_alt[opn][alt].is_address)
                scan_rtx_address (insn, loc, cl, mark_read, VOIDmode);
              else
                scan_rtx (insn, loc, cl, mark_read, type);
            }

          /* Step 3B: Record updates for regs in REG_INC notes, and
             source regs in REG_FRAME_RELATED_EXPR notes.  */
          for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
            if (REG_NOTE_KIND (note) == REG_INC
                || REG_NOTE_KIND (note) == REG_FRAME_RELATED_EXPR)
              scan_rtx (insn, &XEXP (note, 0), ALL_REGS, mark_read,
                        OP_INOUT);

          /* Step 4: Close chains for registers that die here.  */
          for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
            if (REG_NOTE_KIND (note) == REG_DEAD)
              {
                remove_from_hard_reg_set (&live_hard_regs,
                                          GET_MODE (XEXP (note, 0)),
                                          REGNO (XEXP (note, 0)));
                scan_rtx (insn, &XEXP (note, 0), NO_REGS, terminate_dead,
                          OP_IN);
              }

          /* Step 4B: If this is a call, any chain live at this point
             requires a caller-saved reg.  */
          if (CALL_P (insn))
            {
              struct du_head *p;
              for (p = open_chains; p; p = p->next_chain)
                p->need_caller_save_reg = 1;
            }

          /* Step 5: Close open chains that overlap writes.  Similar to
             step 2, we hide in-out operands, since we do not want to
             close these chains.  We also hide earlyclobber operands,
             since we've opened chains for them in step 1, and earlier
             chains they would overlap with must have been closed at
             the previous insn at the latest, as such operands cannot
             possibly overlap with any input operands.  */

          hide_operands (n_ops, old_operands, old_dups, untracked_operands,
                         true);
          scan_rtx (insn, &PATTERN (insn), NO_REGS, terminate_write, OP_IN);
          restore_operands (insn, n_ops, old_operands, old_dups);

          /* Step 6a: Mark hard registers that are set in this insn,
             outside an operand, as live.  */
          hide_operands (n_ops, old_operands, old_dups, untracked_operands,
                         false);
          note_stores (PATTERN (insn), note_sets_clobbers, &set_code);
          restore_operands (insn, n_ops, old_operands, old_dups);

          /* Step 6b: Begin new chains for writes inside operands.  */
          record_out_operands (insn, false);

          /* Step 6c: Record destination regs in REG_FRAME_RELATED_EXPR
             notes for update.  */
          for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
            if (REG_NOTE_KIND (note) == REG_FRAME_RELATED_EXPR)
              scan_rtx (insn, &XEXP (note, 0), ALL_REGS, mark_access,
                        OP_INOUT);

          /* Step 7: Close chains for registers that were never
             really used here.  */
          for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
            if (REG_NOTE_KIND (note) == REG_UNUSED)
              {
                remove_from_hard_reg_set (&live_hard_regs,
                                          GET_MODE (XEXP (note, 0)),
                                          REGNO (XEXP (note, 0)));
                scan_rtx (insn, &XEXP (note, 0), NO_REGS, terminate_dead,
                          OP_IN);
              }
        }
      else if (DEBUG_INSN_P (insn)
               && !VAR_LOC_UNKNOWN_P (INSN_VAR_LOCATION_LOC (insn)))
        {
          scan_rtx (insn, &INSN_VAR_LOCATION_LOC (insn),
                    ALL_REGS, mark_read, OP_IN);
        }
      if (insn == BB_END (bb))
        break;
    }

  bitmap_clear (&open_chains_set);

  if (fail_current_block)
    return NULL;

  /* Since we close every chain when we find a REG_DEAD note, anything that
     is still open lives past the basic block, so it can't be renamed.  */
  return closed_chains;
}

/* Dump all def/use chains in CHAINS to DUMP_FILE.  They are
   printed in reverse order as that's how we build them.  */

static void
dump_def_use_chain (struct du_head *head)
{
  while (head)
    {
      struct du_chain *this_du = head->first;
      fprintf (dump_file, "Register %s (%d):",
               reg_names[head->regno], head->nregs);
      while (this_du)
        {
          fprintf (dump_file, " %d [%s]", INSN_UID (this_du->insn),
                   reg_class_names[this_du->cl]);
          this_du = this_du->next_use;
        }
      fprintf (dump_file, "\n");
      head = head->next_chain;
    }
}

\f
static bool
gate_handle_regrename (void)
{
  return (optimize > 0 && (flag_rename_registers));
}

struct rtl_opt_pass pass_regrename =
{
 {
  RTL_PASS,
  "rnreg",                              /* name */
  gate_handle_regrename,                /* gate */
  regrename_optimize,                   /* execute */
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_RENAME_REGISTERS,                  /* tv_id */
  0,                                    /* properties_required */
  0,                                    /* properties_provided */
  0,                                    /* properties_destroyed */
  0,                                    /* todo_flags_start */
  TODO_df_finish | TODO_verify_rtl_sharing |
  TODO_dump_func                        /* todo_flags_finish */
 }
};