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/* Web construction code for GNU compiler.

   Contributed by Jan Hubicka.

   Copyright (C) 2001, 2002, 2004, 2006, 2007, 2008, 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/>.  */

/* Simple optimization pass that splits independent uses of each pseudo,

   increasing effectiveness of other optimizations.  The optimization can

   serve as an example of use for the dataflow module.

   We don't split registers with REG_USERVAR set unless -fmessy-debugging

   is specified, because debugging information about such split variables

   is almost unusable.

   TODO

    - We may use profile information and ignore infrequent use for the

      purpose of web unifying, inserting the compensation code later to

      implement full induction variable expansion for loops (currently

      we expand only if the induction variable is dead afterward, which

      is often the case).  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "toplev.h"

#include "rtl.h"

#include "hard-reg-set.h"

#include "flags.h"

#include "obstack.h"

#include "basic-block.h"

#include "output.h"

#include "df.h"

#include "function.h"

#include "timevar.h"

#include "tree-pass.h"

/* Find the root of unionfind tree (the representative of set).  */

struct web_entry *

unionfind_root (struct web_entry *element)

{

  struct web_entry *element1 = element, *element2;

  while (element->pred)

    element = element->pred;

  while (element1->pred)

    {

      element2 = element1->pred;

      element1->pred = element;

      element1 = element2;

    }

  return element;

}

/* Union sets.

   Return true if FIRST and SECOND points to the same web entry structure and

   nothing is done.  Otherwise, return false.  */

bool

unionfind_union (struct web_entry *first, struct web_entry *second)

{

  first = unionfind_root (first);

  second = unionfind_root (second);

  if (first == second)

    return true;

  second->pred = first;

  return false;

}

/* For each use, all possible defs reaching it must come in the same

   register, union them.

   FUN is the function that does the union.

   In USED, we keep the DF_REF_ID of the first uninitialized uses of a

   register, so that all uninitialized uses of the register can be

   combined into a single web.  We actually offset it by 2, because

   the values 0 and 1 are reserved for use by entry_register.  */

void

union_defs (df_ref use, struct web_entry *def_entry,

            unsigned int *used, struct web_entry *use_entry,

            bool (*fun) (struct web_entry *, struct web_entry *))

{

  struct df_insn_info *insn_info = DF_REF_INSN_INFO (use);

  struct df_link *link = DF_REF_CHAIN (use);

  df_ref *use_link;

  df_ref *eq_use_link;

  df_ref *def_link;

  rtx set;

  if (insn_info)

    {

      rtx insn = insn_info->insn;

      use_link = DF_INSN_INFO_USES (insn_info);

      eq_use_link = DF_INSN_INFO_EQ_USES (insn_info);

      def_link = DF_INSN_INFO_DEFS (insn_info);

      set = single_set (insn);

    }

  else

    {

      /* An artificial use.  It links up with nothing.  */

      use_link = NULL;

      eq_use_link = NULL;

      def_link = NULL;

      set = NULL;

    }

  /* Some instructions may use match_dup for their operands.  In case the

     operands are dead, we will assign them different pseudos, creating

     invalid instructions, so union all uses of the same operand for each

     insn.  */

  if (use_link)

    while (*use_link)

      {

        if (use != *use_link

            && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*use_link))

          (*fun) (use_entry + DF_REF_ID (use),

                  use_entry + DF_REF_ID (*use_link));

        use_link++;

      }

  if (eq_use_link)

    while (*eq_use_link)

      {

        if (use != *eq_use_link

            && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*eq_use_link))

          (*fun) (use_entry + DF_REF_ID (use),

                  use_entry + DF_REF_ID (*eq_use_link));

        eq_use_link++;

    }

  /* Recognize trivial noop moves and attempt to keep them as noop.  */

  if (set

      && SET_SRC (set) == DF_REF_REG (use)

      && SET_SRC (set) == SET_DEST (set))

    {

      if (def_link)

        while (*def_link)

          {

            if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*def_link))

              (*fun) (use_entry + DF_REF_ID (use),

                      def_entry + DF_REF_ID (*def_link));

            def_link++;

          }

    }

  /* UD chains of uninitialized REGs are empty.  Keeping all uses of

     the same uninitialized REG in a single web is not necessary for

     correctness, since the uses are undefined, but it's wasteful to

     allocate one register or slot for each reference.  Furthermore,

     creating new pseudos for uninitialized references in debug insns

     (see PR 42631) causes -fcompare-debug failures.  We record the

     number of the first uninitialized reference we found, and merge

     with it any other uninitialized references to the same

     register.  */

  if (!link)

    {

      int regno = REGNO (DF_REF_REAL_REG (use));

      if (used[regno])

        (*fun) (use_entry + DF_REF_ID (use), use_entry + used[regno] - 2);

      else

        used[regno] = DF_REF_ID (use) + 2;

    }

  while (link)

    {

      (*fun) (use_entry + DF_REF_ID (use),

              def_entry + DF_REF_ID (link->ref));

      link = link->next;

    }

  /* A READ_WRITE use requires the corresponding def to be in the same

     register.  Find it and union.  */

  if (DF_REF_FLAGS (use) & DF_REF_READ_WRITE)

    {

      df_ref *link;

      if (insn_info)

        link = DF_INSN_INFO_DEFS (insn_info);

      else

        link = NULL;

      if (link)

        while (*link)

          {

            if (DF_REF_REAL_REG (*link) == DF_REF_REAL_REG (use))

              (*fun) (use_entry + DF_REF_ID (use),

                      def_entry + DF_REF_ID (*link));

            link++;

          }

    }

}

/* Find the corresponding register for the given entry.  */

static rtx

entry_register (struct web_entry *entry, df_ref ref, unsigned int *used)

{

  struct web_entry *root;

  rtx reg, newreg;

  /* Find the corresponding web and see if it has been visited.  */

  root = unionfind_root (entry);

  if (root->reg)

    return root->reg;

  /* We are seeing this web for the first time, do the assignment.  */

  reg = DF_REF_REAL_REG (ref);

  /* In case the original register is already assigned, generate new

     one.  Since we use USED to merge uninitialized refs into a single

     web, we might found an element to be nonzero without our having

     used it.  Test for 1, because union_defs saves it for our use,

     and there won't be any use for the other values when we get to

     this point.  */

  if (used[REGNO (reg)] != 1)

    newreg = reg, used[REGNO (reg)] = 1;

  else

    {

      newreg = gen_reg_rtx (GET_MODE (reg));

      REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);

      REG_POINTER (newreg) = REG_POINTER (reg);

      REG_ATTRS (newreg) = REG_ATTRS (reg);

      if (dump_file)

        fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),

                 REGNO (newreg));

    }

  root->reg = newreg;

  return newreg;

}

/* Replace the reference by REG.  */

static void

replace_ref (df_ref ref, rtx reg)

{

  rtx oldreg = DF_REF_REAL_REG (ref);

  rtx *loc = DF_REF_REAL_LOC (ref);

  unsigned int uid = DF_REF_INSN_UID (ref);

  if (oldreg == reg)

    return;

  if (dump_file)

    fprintf (dump_file, "Updating insn %i (%i->%i)\n",

             uid, REGNO (oldreg), REGNO (reg));

  *loc = reg;

  df_insn_rescan (DF_REF_INSN (ref));

}

static bool

gate_handle_web (void)

{

  return (optimize > 0 && flag_web);

}

/* Main entry point.  */

static unsigned int

web_main (void)

{

  struct web_entry *def_entry;

  struct web_entry *use_entry;

  unsigned int max = max_reg_num ();

  unsigned int *used;

  basic_block bb;

  unsigned int uses_num = 0;

  rtx insn;

  df_set_flags (DF_NO_HARD_REGS + DF_EQ_NOTES);

  df_chain_add_problem (DF_UD_CHAIN);

  df_analyze ();

  df_set_flags (DF_DEFER_INSN_RESCAN);

  /* Assign ids to the uses.  */

  FOR_ALL_BB (bb)

    FOR_BB_INSNS (bb, insn)

    {

      unsigned int uid = INSN_UID (insn);

      if (NONDEBUG_INSN_P (insn))

        {

          df_ref *use_rec;

          for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)

            {

              df_ref use = *use_rec;

              if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)

                DF_REF_ID (use) = uses_num++;

            }

          for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)

            {

              df_ref use = *use_rec;

              if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)

                DF_REF_ID (use) = uses_num++;

            }

        }

    }

  /* Record the number of uses and defs at the beginning of the optimization.  */

  def_entry = XCNEWVEC (struct web_entry, DF_DEFS_TABLE_SIZE());

  used = XCNEWVEC (unsigned, max);

  use_entry = XCNEWVEC (struct web_entry, uses_num);

  /* Produce the web.  */

  FOR_ALL_BB (bb)

    FOR_BB_INSNS (bb, insn)

    {

      unsigned int uid = INSN_UID (insn);

      if (NONDEBUG_INSN_P (insn))

        {

          df_ref *use_rec;

          for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)

            {

              df_ref use = *use_rec;

              if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)

                union_defs (use, def_entry, used, use_entry, unionfind_union);

            }

          for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)

            {

              df_ref use = *use_rec;

              if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)

                union_defs (use, def_entry, used, use_entry, unionfind_union);

            }

        }

    }

  /* Update the instruction stream, allocating new registers for split pseudos

     in progress.  */

  FOR_ALL_BB (bb)

    FOR_BB_INSNS (bb, insn)

    {

      unsigned int uid = INSN_UID (insn);

      if (NONDEBUG_INSN_P (insn))

        {

          df_ref *use_rec;

          df_ref *def_rec;

          for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)

            {

              df_ref use = *use_rec;

              if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)

                replace_ref (use, entry_register (use_entry + DF_REF_ID (use), use, used));

            }

          for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)

            {

              df_ref use = *use_rec;

              if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)

                replace_ref (use, entry_register (use_entry + DF_REF_ID (use), use, used));

            }

          for (def_rec = DF_INSN_UID_DEFS (uid); *def_rec; def_rec++)

            {

              df_ref def = *def_rec;

              if (DF_REF_REGNO (def) >= FIRST_PSEUDO_REGISTER)

                replace_ref (def, entry_register (def_entry + DF_REF_ID (def), def, used));

            }

        }

    }

  free (def_entry);

  free (use_entry);

  free (used);

  return 0;

}

struct rtl_opt_pass pass_web =

{

 {

  RTL_PASS,

  "web",                                /* name */

  gate_handle_web,                      /* gate */

  web_main,                             /* execute */

  NULL,                                 /* sub */

  NULL,                                 /* next */

  0,                                    /* static_pass_number */

  TV_WEB,                               /* 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 */

 }

};