gcc/web.c

   1 /* Web construction code for GNU compiler.
   2    Contributed by Jan Hubicka.
   3    Copyright (C) 2001, 2002, 2004 Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 2, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING.  If not, write to the Free
  19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  20 02110-1301, USA.  */
  21
  22 /* Simple optimization pass that splits independent uses of each pseudo,
  23    increasing effectiveness of other optimizations.  The optimization can
  24    serve as an example of use for the dataflow module.
  25
  26    We don't split registers with REG_USERVAR set unless -fmessy-debugging
  27    is specified, because debugging information about such split variables
  28    is almost unusable.
  29
  30    TODO
  31     - Add code to keep debugging up-to-date after splitting user variable
  32       pseudos.  This can be done by keeping track of all the pseudos used
  33       for the variable and using life analysis information before reload
  34       to determine which one is live and, in case more than one are live,
  35       choose the one with the latest definition.
  36
  37       Other optimization passes can benefit from the infrastructure too.
  38
  39     - We may use profile information and ignore infrequent use for the
  40       purpose of web unifying, inserting the compensation code later to
  41       implement full induction variable expansion for loops (currently
  42       we expand only if the induction variable is dead afterward, which
  43       is often the case).  */
  44
  45 #include "config.h"
  46 #include "system.h"
  47 #include "coretypes.h"
  48 #include "tm.h"
  49 #include "toplev.h"
  50
  51 #include "rtl.h"
  52 #include "hard-reg-set.h"
  53 #include "flags.h"
  54 #include "obstack.h"
  55 #include "basic-block.h"
  56 #include "output.h"
  57 #include "df.h"
  58 #include "function.h"
  59 #include "timevar.h"
  60 #include "tree-pass.h"
  61
  62
  63 /* This entry is allocated for each reference in the insn stream.  */
  64 struct web_entry
  65 {
  66   /* Pointer to the parent in the union/find tree.  */
  67   struct web_entry *pred;
  68   /* Newly assigned register to the entry.  Set only for roots.  */
  69   rtx reg;
  70 };
  71
  72 static struct web_entry *unionfind_root (struct web_entry *);
  73 static void unionfind_union (struct web_entry *, struct web_entry *);
  74 static void union_defs (struct df *, struct ref *, struct web_entry *,
  75                         struct web_entry *);
  76 static rtx entry_register (struct web_entry *, struct ref *, char *);
  77 static void replace_ref (struct ref *, rtx);
  78
  79 /* Find the root of unionfind tree (the representative of set).  */
  80
  81 static struct web_entry *
  82 unionfind_root (struct web_entry *element)
  83 {
  84   struct web_entry *element1 = element, *element2;
  85
  86   while (element->pred)
  87     element = element->pred;
  88   while (element1->pred)
  89     {
  90       element2 = element1->pred;
  91       element1->pred = element;
  92       element1 = element2;
  93     }
  94   return element;
  95 }
  96
  97 /* Union sets.  */
  98
  99 static void
 100 unionfind_union (struct web_entry *first, struct web_entry *second)
 101 {
 102   first = unionfind_root (first);
 103   second = unionfind_root (second);
 104   if (first == second)
 105     return;
 106   second->pred = first;
 107 }
 108
 109 /* For each use, all possible defs reaching it must come in the same
 110    register, union them.  */
 111
 112 static void
 113 union_defs (struct df *df, struct ref *use, struct web_entry *def_entry,
 114             struct web_entry *use_entry)
 115 {
 116   rtx insn = DF_REF_INSN (use);
 117   struct df_link *link = DF_REF_CHAIN (use);
 118   struct df_link *use_link = DF_INSN_USES (df, insn);
 119   struct df_link *def_link = DF_INSN_DEFS (df, insn);
 120   rtx set = single_set (insn);
 121
 122   /* Some instructions may use match_dup for their operands.  In case the
 123      operands are dead, we will assign them different pseudos, creating
 124      invalid instructions, so union all uses of the same operand for each
 125      insn.  */
 126
 127   while (use_link)
 128     {
 129       if (use != use_link->ref
 130           && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (use_link->ref))
 131         unionfind_union (use_entry + DF_REF_ID (use),
 132                          use_entry + DF_REF_ID (use_link->ref));
 133       use_link = use_link->next;
 134     }
 135
 136   /* Recognize trivial noop moves and attempt to keep them as noop.
 137      While most of noop moves should be removed, we still keep some
 138      of them at libcall boundaries and such.  */
 139
 140   if (set
 141       && SET_SRC (set) == DF_REF_REG (use)
 142       && SET_SRC (set) == SET_DEST (set))
 143     {
 144       while (def_link)
 145         {
 146           if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def_link->ref))
 147             unionfind_union (use_entry + DF_REF_ID (use),
 148                              def_entry + DF_REF_ID (def_link->ref));
 149           def_link = def_link->next;
 150         }
 151     }
 152   while (link)
 153     {
 154       unionfind_union (use_entry + DF_REF_ID (use),
 155                        def_entry + DF_REF_ID (link->ref));
 156       link = link->next;
 157     }
 158
 159   /* A READ_WRITE use requires the corresponding def to be in the same
 160      register.  Find it and union.  */
 161   if (use->flags & DF_REF_READ_WRITE)
 162     {
 163       struct df_link *link = DF_INSN_DEFS (df, DF_REF_INSN (use));
 164
 165       while (link)
 166         {
 167           if (DF_REF_REAL_REG (link->ref) == DF_REF_REAL_REG (use))
 168             unionfind_union (use_entry + DF_REF_ID (use),
 169                              def_entry + DF_REF_ID (link->ref));
 170           link = link->next;
 171         }
 172     }
 173 }
 174
 175 /* Find the corresponding register for the given entry.  */
 176
 177 static rtx
 178 entry_register (struct web_entry *entry, struct ref *ref, char *used)
 179 {
 180   struct web_entry *root;
 181   rtx reg, newreg;
 182
 183   /* Find the corresponding web and see if it has been visited.  */
 184   root = unionfind_root (entry);
 185   if (root->reg)
 186     return root->reg;
 187
 188   /* We are seeing this web for the first time, do the assignment.  */
 189   reg = DF_REF_REAL_REG (ref);
 190
 191   /* In case the original register is already assigned, generate new one.  */
 192   if (!used[REGNO (reg)])
 193     newreg = reg, used[REGNO (reg)] = 1;
 194   else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
 195     {
 196       newreg = reg;
 197       if (dump_file)
 198         fprintf (dump_file,
 199                  "New web forced to keep reg=%i (user variable)\n",
 200                  REGNO (reg));
 201     }
 202   else
 203     {
 204       newreg = gen_reg_rtx (GET_MODE (reg));
 205       REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
 206       REG_POINTER (newreg) = REG_POINTER (reg);
 207       REG_ATTRS (newreg) = REG_ATTRS (reg);
 208       if (dump_file)
 209         fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
 210                  REGNO (newreg));
 211     }
 212
 213   root->reg = newreg;
 214   return newreg;
 215 }
 216
 217 /* Replace the reference by REG.  */
 218
 219 static void
 220 replace_ref (struct ref *ref, rtx reg)
 221 {
 222   rtx oldreg = DF_REF_REAL_REG (ref);
 223   rtx *loc = DF_REF_REAL_LOC (ref);
 224
 225   if (oldreg == reg)
 226     return;
 227   if (dump_file)
 228     fprintf (dump_file, "Updating insn %i (%i->%i)\n",
 229              INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
 230   *loc = reg;
 231 }
 232
 233 /* Main entry point.  */
 234
 235 void
 236 web_main (void)
 237 {
 238   struct df *df;
 239   struct web_entry *def_entry;
 240   struct web_entry *use_entry;
 241   unsigned int i;
 242   int max = max_reg_num ();
 243   char *used;
 244
 245   df = df_init ();
 246   df_analyze (df, 0, DF_UD_CHAIN | DF_EQUIV_NOTES);
 247
 248   def_entry = xcalloc (df->n_defs, sizeof (struct web_entry));
 249   use_entry = xcalloc (df->n_uses, sizeof (struct web_entry));
 250   used = xcalloc (max, sizeof (char));
 251
 252   if (dump_file)
 253     df_dump (df, DF_UD_CHAIN | DF_DU_CHAIN, dump_file);
 254
 255   /* Produce the web.  */
 256   for (i = 0; i < df->n_uses; i++)
 257     union_defs (df, df->uses[i], def_entry, use_entry);
 258
 259   /* Update the instruction stream, allocating new registers for split pseudos
 260      in progress.  */
 261   for (i = 0; i < df->n_uses; i++)
 262     replace_ref (df->uses[i], entry_register (use_entry + i, df->uses[i],
 263                                               used));
 264   for (i = 0; i < df->n_defs; i++)
 265     replace_ref (df->defs[i], entry_register (def_entry + i, df->defs[i],
 266                                               used));
 267
 268   /* Dataflow information is corrupt here, but it can be easily updated
 269      by creating new entries for new registers and updates or calling
 270      df_insns_modify.  */
 271   free (def_entry);
 272   free (use_entry);
 273   free (used);
 274   df_finish (df);
 275 }
 276 \f
 277 static bool
 278 gate_handle_web (void)
 279 {
 280   return (optimize > 0 && flag_web);
 281 }
 282
 283 static void
 284 rest_of_handle_web (void)
 285 {
 286   web_main ();
 287   delete_trivially_dead_insns (get_insns (), max_reg_num ());
 288   cleanup_cfg (CLEANUP_EXPENSIVE);
 289   reg_scan (get_insns (), max_reg_num ());
 290 }
 291
 292 struct tree_opt_pass pass_web =
 293 {
 294   "web",                                /* name */
 295   gate_handle_web,                      /* gate */
 296   rest_of_handle_web,                   /* execute */
 297   NULL,                                 /* sub */
 298   NULL,                                 /* next */
 299   0,                                    /* static_pass_number */
 300   TV_WEB,                               /* tv_id */
 301   0,                                    /* properties_required */
 302   0,                                    /* properties_provided */
 303   0,                                    /* properties_destroyed */
 304   0,                                    /* todo_flags_start */
 305   TODO_dump_func,                       /* todo_flags_finish */
 306   'Z'                                   /* letter */
 307 };
 308