gcc/web.c

   1 /* Web construction code for GNU compiler.
   2    Contributed by Jan Hubicka.
   3    Copyright (C) 2001, 2002, 2004, 2006, 2007, 2008
   4    Free Software Foundation, Inc.
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it under
   9 the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 3, or (at your option) any later
  11 version.
  12
  13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  16 for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with GCC; see the file COPYING3.  If not see
  20 <http://www.gnu.org/licenses/>.  */
  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 static rtx entry_register (struct web_entry *, df_ref, char *);
  64 static void replace_ref (df_ref, rtx);
  65
  66 /* Find the root of unionfind tree (the representative of set).  */
  67
  68 struct web_entry *
  69 unionfind_root (struct web_entry *element)
  70 {
  71   struct web_entry *element1 = element, *element2;
  72
  73   while (element->pred)
  74     element = element->pred;
  75   while (element1->pred)
  76     {
  77       element2 = element1->pred;
  78       element1->pred = element;
  79       element1 = element2;
  80     }
  81   return element;
  82 }
  83
  84 /* Union sets.
  85    Return true if FIRST and SECOND points to the same web entry structure and
  86    nothing is done.  Otherwise, return false.  */
  87
  88 bool
  89 unionfind_union (struct web_entry *first, struct web_entry *second)
  90 {
  91   first = unionfind_root (first);
  92   second = unionfind_root (second);
  93   if (first == second)
  94     return true;
  95   second->pred = first;
  96   return false;
  97 }
  98
  99 /* For each use, all possible defs reaching it must come in the same
 100    register, union them.
 101    FUN is the function that does the union.  */
 102
 103 void
 104 union_defs (df_ref use, struct web_entry *def_entry,
 105             struct web_entry *use_entry,
 106             bool (*fun) (struct web_entry *, struct web_entry *))
 107 {
 108   struct df_insn_info *insn_info = DF_REF_INSN_INFO (use);
 109   struct df_link *link = DF_REF_CHAIN (use);
 110   df_ref *use_link;
 111   df_ref *eq_use_link;
 112   df_ref *def_link;
 113   rtx set;
 114
 115   if (insn_info)
 116     {
 117       rtx insn = insn_info->insn;
 118       use_link = DF_INSN_INFO_USES (insn_info);
 119       eq_use_link = DF_INSN_INFO_EQ_USES (insn_info);
 120       def_link = DF_INSN_INFO_DEFS (insn_info);
 121       set = single_set (insn);
 122     }
 123   else
 124     {
 125       /* An artificial use.  It links up with nothing.  */
 126       use_link = NULL;
 127       eq_use_link = NULL;
 128       def_link = NULL;
 129       set = NULL;
 130     }
 131
 132   /* Some instructions may use match_dup for their operands.  In case the
 133      operands are dead, we will assign them different pseudos, creating
 134      invalid instructions, so union all uses of the same operand for each
 135      insn.  */
 136
 137   if (use_link)
 138     while (*use_link)
 139       {
 140         if (use != *use_link
 141             && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*use_link))
 142           (*fun) (use_entry + DF_REF_ID (use),
 143                   use_entry + DF_REF_ID (*use_link));
 144         use_link++;
 145       }
 146
 147   if (eq_use_link)
 148     while (*eq_use_link)
 149       {
 150         if (use != *eq_use_link
 151             && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*eq_use_link))
 152           (*fun) (use_entry + DF_REF_ID (use),
 153                   use_entry + DF_REF_ID (*eq_use_link));
 154         eq_use_link++;
 155     }
 156
 157   /* Recognize trivial noop moves and attempt to keep them as noop.  */
 158
 159   if (set
 160       && SET_SRC (set) == DF_REF_REG (use)
 161       && SET_SRC (set) == SET_DEST (set))
 162     {
 163       if (def_link)
 164         while (*def_link)
 165           {
 166             if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*def_link))
 167               (*fun) (use_entry + DF_REF_ID (use),
 168                       def_entry + DF_REF_ID (*def_link));
 169             def_link++;
 170           }
 171     }
 172   while (link)
 173     {
 174       (*fun) (use_entry + DF_REF_ID (use),
 175               def_entry + DF_REF_ID (link->ref));
 176       link = link->next;
 177     }
 178
 179   /* A READ_WRITE use requires the corresponding def to be in the same
 180      register.  Find it and union.  */
 181   if (DF_REF_FLAGS (use) & DF_REF_READ_WRITE)
 182     {
 183       df_ref *link;
 184
 185       if (insn_info)
 186         link = DF_INSN_INFO_DEFS (insn_info);
 187       else
 188         link = NULL;
 189
 190       if (link)
 191         while (*link)
 192           {
 193             if (DF_REF_REAL_REG (*link) == DF_REF_REAL_REG (use))
 194               (*fun) (use_entry + DF_REF_ID (use),
 195                       def_entry + DF_REF_ID (*link));
 196             link++;
 197           }
 198     }
 199 }
 200
 201 /* Find the corresponding register for the given entry.  */
 202
 203 static rtx
 204 entry_register (struct web_entry *entry, df_ref ref, char *used)
 205 {
 206   struct web_entry *root;
 207   rtx reg, newreg;
 208
 209   /* Find the corresponding web and see if it has been visited.  */
 210   root = unionfind_root (entry);
 211   if (root->reg)
 212     return root->reg;
 213
 214   /* We are seeing this web for the first time, do the assignment.  */
 215   reg = DF_REF_REAL_REG (ref);
 216
 217   /* In case the original register is already assigned, generate new one.  */
 218   if (!used[REGNO (reg)])
 219     newreg = reg, used[REGNO (reg)] = 1;
 220   else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
 221     {
 222       newreg = reg;
 223       if (dump_file)
 224         fprintf (dump_file,
 225                  "New web forced to keep reg=%i (user variable)\n",
 226                  REGNO (reg));
 227     }
 228   else
 229     {
 230       newreg = gen_reg_rtx (GET_MODE (reg));
 231       REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
 232       REG_POINTER (newreg) = REG_POINTER (reg);
 233       REG_ATTRS (newreg) = REG_ATTRS (reg);
 234       if (dump_file)
 235         fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
 236                  REGNO (newreg));
 237     }
 238
 239   root->reg = newreg;
 240   return newreg;
 241 }
 242
 243 /* Replace the reference by REG.  */
 244
 245 static void
 246 replace_ref (df_ref ref, rtx reg)
 247 {
 248   rtx oldreg = DF_REF_REAL_REG (ref);
 249   rtx *loc = DF_REF_REAL_LOC (ref);
 250   unsigned int uid = DF_REF_INSN_UID (ref);
 251
 252   if (oldreg == reg)
 253     return;
 254   if (dump_file)
 255     fprintf (dump_file, "Updating insn %i (%i->%i)\n",
 256              uid, REGNO (oldreg), REGNO (reg));
 257   *loc = reg;
 258   df_insn_rescan (DF_REF_INSN (ref));
 259 }
 260
 261 \f
 262 static bool
 263 gate_handle_web (void)
 264 {
 265   return (optimize > 0 && flag_web);
 266 }
 267
 268 /* Main entry point.  */
 269
 270 static unsigned int
 271 web_main (void)
 272 {
 273   struct web_entry *def_entry;
 274   struct web_entry *use_entry;
 275   unsigned int max = max_reg_num ();
 276   char *used;
 277   basic_block bb;
 278   unsigned int uses_num = 0;
 279   rtx insn;
 280
 281   df_set_flags (DF_NO_HARD_REGS + DF_EQ_NOTES);
 282   df_chain_add_problem (DF_UD_CHAIN);
 283   df_analyze ();
 284   df_set_flags (DF_DEFER_INSN_RESCAN);
 285
 286   /* Assign ids to the uses.  */
 287   FOR_ALL_BB (bb)
 288     FOR_BB_INSNS (bb, insn)
 289     {
 290       unsigned int uid = INSN_UID (insn);
 291       if (INSN_P (insn))
 292         {
 293           df_ref *use_rec;
 294           for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
 295             {
 296               df_ref use = *use_rec;
 297               if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 298                 DF_REF_ID (use) = uses_num++;
 299             }
 300           for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)
 301             {
 302               df_ref use = *use_rec;
 303               if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 304                 DF_REF_ID (use) = uses_num++;
 305             }
 306         }
 307     }
 308
 309   /* Record the number of uses and defs at the beginning of the optimization.  */
 310   def_entry = XCNEWVEC (struct web_entry, DF_DEFS_TABLE_SIZE());
 311   used = XCNEWVEC (char, max);
 312   use_entry = XCNEWVEC (struct web_entry, uses_num);
 313
 314   /* Produce the web.  */
 315   FOR_ALL_BB (bb)
 316     FOR_BB_INSNS (bb, insn)
 317     {
 318       unsigned int uid = INSN_UID (insn);
 319       if (INSN_P (insn))
 320         {
 321           df_ref *use_rec;
 322           for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
 323             {
 324               df_ref use = *use_rec;
 325               if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 326                 union_defs (use, def_entry, use_entry, unionfind_union);
 327             }
 328           for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)
 329             {
 330               df_ref use = *use_rec;
 331               if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 332                 union_defs (use, def_entry, use_entry, unionfind_union);
 333             }
 334         }
 335     }
 336
 337   /* Update the instruction stream, allocating new registers for split pseudos
 338      in progress.  */
 339   FOR_ALL_BB (bb)
 340     FOR_BB_INSNS (bb, insn)
 341     {
 342       unsigned int uid = INSN_UID (insn);
 343       if (INSN_P (insn))
 344         {
 345           df_ref *use_rec;
 346           df_ref *def_rec;
 347           for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
 348             {
 349               df_ref use = *use_rec;
 350               if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 351                 replace_ref (use, entry_register (use_entry + DF_REF_ID (use), use, used));
 352             }
 353           for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)
 354             {
 355               df_ref use = *use_rec;
 356               if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 357                 replace_ref (use, entry_register (use_entry + DF_REF_ID (use), use, used));
 358             }
 359           for (def_rec = DF_INSN_UID_DEFS (uid); *def_rec; def_rec++)
 360             {
 361               df_ref def = *def_rec;
 362               if (DF_REF_REGNO (def) >= FIRST_PSEUDO_REGISTER)
 363                 replace_ref (def, entry_register (def_entry + DF_REF_ID (def), def, used));
 364             }
 365         }
 366     }
 367
 368   free (def_entry);
 369   free (use_entry);
 370   free (used);
 371   return 0;
 372 }
 373 \f
 374 struct rtl_opt_pass pass_web =
 375 {
 376  {
 377   RTL_PASS,
 378   "web",                                /* name */
 379   gate_handle_web,                      /* gate */
 380   web_main,                             /* execute */
 381   NULL,                                 /* sub */
 382   NULL,                                 /* next */
 383   0,                                    /* static_pass_number */
 384   TV_WEB,                               /* tv_id */
 385   0,                                    /* properties_required */
 386   0,                                    /* properties_provided */
 387   0,                                    /* properties_destroyed */
 388   0,                                    /* todo_flags_start */
 389   TODO_df_finish | TODO_verify_rtl_sharing |
 390   TODO_dump_func                        /* todo_flags_finish */
 391  }
 392 };
 393