gcc/web.c

   1 /* Web construction code for GNU compiler.
   2    Contributed by Jan Hubicka.
   3    Copyright (C) 2001-2014 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 3, 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 COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 /* Simple optimization pass that splits independent uses of each pseudo,
  22    increasing effectiveness of other optimizations.  The optimization can
  23    serve as an example of use for the dataflow module.
  24
  25    We don't split registers with REG_USERVAR set unless -fmessy-debugging
  26    is specified, because debugging information about such split variables
  27    is almost unusable.
  28
  29    TODO
  30     - We may use profile information and ignore infrequent use for the
  31       purpose of web unifying, inserting the compensation code later to
  32       implement full induction variable expansion for loops (currently
  33       we expand only if the induction variable is dead afterward, which
  34       is often the case).  */
  35
  36 #include "config.h"
  37 #include "system.h"
  38 #include "coretypes.h"
  39 #include "tm.h"
  40 #include "diagnostic-core.h"
  41
  42 #include "rtl.h"
  43 #include "hard-reg-set.h"
  44 #include "flags.h"
  45 #include "obstack.h"
  46 #include "basic-block.h"
  47 #include "df.h"
  48 #include "hashtab.h"
  49 #include "hash-set.h"
  50 #include "vec.h"
  51 #include "machmode.h"
  52 #include "input.h"
  53 #include "function.h"
  54 #include "insn-config.h"
  55 #include "recog.h"
  56 #include "tree-pass.h"
  57
  58
  59 /* Find the root of unionfind tree (the representative of set).  */
  60
  61 web_entry_base *
  62 web_entry_base::unionfind_root ()
  63 {
  64   web_entry_base *element = this, *element1 = this, *element2;
  65
  66   while (element->pred ())
  67     element = element->pred ();
  68   while (element1->pred ())
  69     {
  70       element2 = element1->pred ();
  71       element1->set_pred (element);
  72       element1 = element2;
  73     }
  74   return element;
  75 }
  76
  77 /* Union sets.
  78    Return true if FIRST and SECOND points to the same web entry structure and
  79    nothing is done.  Otherwise, return false.  */
  80
  81 bool
  82 unionfind_union (web_entry_base *first, web_entry_base *second)
  83 {
  84   first = first->unionfind_root ();
  85   second = second->unionfind_root ();
  86   if (first == second)
  87     return true;
  88   second->set_pred (first);
  89   return false;
  90 }
  91
  92 class web_entry : public web_entry_base
  93 {
  94  private:
  95   rtx reg_pvt;
  96
  97  public:
  98   rtx reg () { return reg_pvt; }
  99   void set_reg (rtx r) { reg_pvt = r; }
 100 };
 101
 102 /* For INSN, union all defs and uses that are linked by match_dup.
 103    FUN is the function that does the union.  */
 104
 105 static void
 106 union_match_dups (rtx_insn *insn, web_entry *def_entry, web_entry *use_entry,
 107                   bool (*fun) (web_entry_base *, web_entry_base *))
 108 {
 109   struct df_insn_info *insn_info = DF_INSN_INFO_GET (insn);
 110   df_ref use_link = DF_INSN_INFO_USES (insn_info);
 111   df_ref def_link = DF_INSN_INFO_DEFS (insn_info);
 112   struct web_entry *dup_entry;
 113   int i;
 114
 115   extract_insn (insn);
 116
 117   for (i = 0; i < recog_data.n_dups; i++)
 118     {
 119       int op = recog_data.dup_num[i];
 120       enum op_type type = recog_data.operand_type[op];
 121       df_ref ref, dupref;
 122       struct web_entry *entry;
 123
 124       dup_entry = use_entry;
 125       for (dupref = use_link; dupref; dupref = DF_REF_NEXT_LOC (dupref))
 126         if (DF_REF_LOC (dupref) == recog_data.dup_loc[i])
 127           break;
 128
 129       if (dupref == NULL && type == OP_INOUT)
 130         {
 131           dup_entry = def_entry;
 132           for (dupref = def_link; dupref; dupref = DF_REF_NEXT_LOC (dupref))
 133             if (DF_REF_LOC (dupref) == recog_data.dup_loc[i])
 134               break;
 135         }
 136       /* ??? *DUPREF can still be zero, because when an operand matches
 137          a memory, DF_REF_LOC (use_link[n]) points to the register part
 138          of the address, whereas recog_data.dup_loc[m] points to the
 139          entire memory ref, thus we fail to find the duplicate entry,
 140          even though it is there.
 141          Example: i686-pc-linux-gnu gcc.c-torture/compile/950607-1.c
 142                   -O3 -fomit-frame-pointer -funroll-loops  */
 143       if (dupref == NULL
 144           || DF_REF_REGNO (dupref) < FIRST_PSEUDO_REGISTER)
 145         continue;
 146
 147       ref = type == OP_IN ? use_link : def_link;
 148       entry = type == OP_IN ? use_entry : def_entry;
 149       for (; ref; ref = DF_REF_NEXT_LOC (ref))
 150         {
 151           rtx *l = DF_REF_LOC (ref);
 152           if (l == recog_data.operand_loc[op])
 153             break;
 154           if (l && DF_REF_REAL_LOC (ref) == recog_data.operand_loc[op])
 155             break;
 156         }
 157
 158       if (!ref && type == OP_INOUT)
 159         {
 160           entry = use_entry;
 161           for (ref = use_link; ref; ref = DF_REF_NEXT_LOC (ref))
 162             {
 163               rtx *l = DF_REF_LOC (ref);
 164               if (l == recog_data.operand_loc[op])
 165                 break;
 166               if (l && DF_REF_REAL_LOC (ref) == recog_data.operand_loc[op])
 167                 break;
 168             }
 169         }
 170
 171       gcc_assert (ref);
 172       (*fun) (dup_entry + DF_REF_ID (dupref), entry + DF_REF_ID (ref));
 173     }
 174 }
 175
 176 /* For each use, all possible defs reaching it must come in the same
 177    register, union them.
 178    FUN is the function that does the union.
 179
 180    In USED, we keep the DF_REF_ID of the first uninitialized uses of a
 181    register, so that all uninitialized uses of the register can be
 182    combined into a single web.  We actually offset it by 2, because
 183    the values 0 and 1 are reserved for use by entry_register.  */
 184
 185 void
 186 union_defs (df_ref use, web_entry *def_entry,
 187             unsigned int *used, web_entry *use_entry,
 188             bool (*fun) (web_entry_base *, web_entry_base *))
 189 {
 190   struct df_insn_info *insn_info = DF_REF_INSN_INFO (use);
 191   struct df_link *link = DF_REF_CHAIN (use);
 192   rtx set;
 193
 194   if (insn_info)
 195     {
 196       df_ref eq_use;
 197
 198       set = single_set (insn_info->insn);
 199       FOR_EACH_INSN_INFO_EQ_USE (eq_use, insn_info)
 200         if (use != eq_use
 201             && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (eq_use))
 202           (*fun) (use_entry + DF_REF_ID (use), use_entry + DF_REF_ID (eq_use));
 203     }
 204   else
 205     set = NULL;
 206
 207   /* Union all occurrences of the same register in reg notes.  */
 208
 209   /* Recognize trivial noop moves and attempt to keep them as noop.  */
 210
 211   if (set
 212       && SET_SRC (set) == DF_REF_REG (use)
 213       && SET_SRC (set) == SET_DEST (set))
 214     {
 215       df_ref def;
 216
 217       FOR_EACH_INSN_INFO_DEF (def, insn_info)
 218         if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def))
 219           (*fun) (use_entry + DF_REF_ID (use), def_entry + DF_REF_ID (def));
 220     }
 221
 222   /* UD chains of uninitialized REGs are empty.  Keeping all uses of
 223      the same uninitialized REG in a single web is not necessary for
 224      correctness, since the uses are undefined, but it's wasteful to
 225      allocate one register or slot for each reference.  Furthermore,
 226      creating new pseudos for uninitialized references in debug insns
 227      (see PR 42631) causes -fcompare-debug failures.  We record the
 228      number of the first uninitialized reference we found, and merge
 229      with it any other uninitialized references to the same
 230      register.  */
 231   if (!link)
 232     {
 233       int regno = REGNO (DF_REF_REAL_REG (use));
 234       if (used[regno])
 235         (*fun) (use_entry + DF_REF_ID (use), use_entry + used[regno] - 2);
 236       else
 237         used[regno] = DF_REF_ID (use) + 2;
 238     }
 239
 240   while (link)
 241     {
 242       (*fun) (use_entry + DF_REF_ID (use),
 243               def_entry + DF_REF_ID (link->ref));
 244       link = link->next;
 245     }
 246
 247   /* A READ_WRITE use requires the corresponding def to be in the same
 248      register.  Find it and union.  */
 249   if (DF_REF_FLAGS (use) & DF_REF_READ_WRITE)
 250     if (insn_info)
 251       {
 252         df_ref def;
 253
 254         FOR_EACH_INSN_INFO_DEF (def, insn_info)
 255           if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def))
 256             (*fun) (use_entry + DF_REF_ID (use), def_entry + DF_REF_ID (def));
 257       }
 258 }
 259
 260 /* Find the corresponding register for the given entry.  */
 261
 262 static rtx
 263 entry_register (web_entry *entry, df_ref ref, unsigned int *used)
 264 {
 265   web_entry *root;
 266   rtx reg, newreg;
 267
 268   /* Find the corresponding web and see if it has been visited.  */
 269   root = (web_entry *)entry->unionfind_root ();
 270   if (root->reg ())
 271     return root->reg ();
 272
 273   /* We are seeing this web for the first time, do the assignment.  */
 274   reg = DF_REF_REAL_REG (ref);
 275
 276   /* In case the original register is already assigned, generate new
 277      one.  Since we use USED to merge uninitialized refs into a single
 278      web, we might found an element to be nonzero without our having
 279      used it.  Test for 1, because union_defs saves it for our use,
 280      and there won't be any use for the other values when we get to
 281      this point.  */
 282   if (used[REGNO (reg)] != 1)
 283     newreg = reg, used[REGNO (reg)] = 1;
 284   else
 285     {
 286       newreg = gen_reg_rtx (GET_MODE (reg));
 287       REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
 288       REG_POINTER (newreg) = REG_POINTER (reg);
 289       REG_ATTRS (newreg) = REG_ATTRS (reg);
 290       if (dump_file)
 291         fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
 292                  REGNO (newreg));
 293     }
 294
 295   root->set_reg (newreg);
 296   return newreg;
 297 }
 298
 299 /* Replace the reference by REG.  */
 300
 301 static void
 302 replace_ref (df_ref ref, rtx reg)
 303 {
 304   rtx oldreg = DF_REF_REAL_REG (ref);
 305   rtx *loc = DF_REF_REAL_LOC (ref);
 306   unsigned int uid = DF_REF_INSN_UID (ref);
 307
 308   if (oldreg == reg)
 309     return;
 310   if (dump_file)
 311     fprintf (dump_file, "Updating insn %i (%i->%i)\n",
 312              uid, REGNO (oldreg), REGNO (reg));
 313   *loc = reg;
 314   df_insn_rescan (DF_REF_INSN (ref));
 315 }
 316
 317 \f
 318 namespace {
 319
 320 const pass_data pass_data_web =
 321 {
 322   RTL_PASS, /* type */
 323   "web", /* name */
 324   OPTGROUP_NONE, /* optinfo_flags */
 325   TV_WEB, /* tv_id */
 326   0, /* properties_required */
 327   0, /* properties_provided */
 328   0, /* properties_destroyed */
 329   0, /* todo_flags_start */
 330   TODO_df_finish, /* todo_flags_finish */
 331 };
 332
 333 class pass_web : public rtl_opt_pass
 334 {
 335 public:
 336   pass_web (gcc::context *ctxt)
 337     : rtl_opt_pass (pass_data_web, ctxt)
 338   {}
 339
 340   /* opt_pass methods: */
 341   virtual bool gate (function *) { return (optimize > 0 && flag_web); }
 342   virtual unsigned int execute (function *);
 343
 344 }; // class pass_web
 345
 346 unsigned int
 347 pass_web::execute (function *fun)
 348 {
 349   web_entry *def_entry;
 350   web_entry *use_entry;
 351   unsigned int max = max_reg_num ();
 352   unsigned int *used;
 353   basic_block bb;
 354   unsigned int uses_num = 0;
 355   rtx_insn *insn;
 356
 357   df_set_flags (DF_NO_HARD_REGS + DF_EQ_NOTES);
 358   df_set_flags (DF_RD_PRUNE_DEAD_DEFS);
 359   df_chain_add_problem (DF_UD_CHAIN);
 360   df_analyze ();
 361   df_set_flags (DF_DEFER_INSN_RESCAN);
 362
 363   /* Assign ids to the uses.  */
 364   FOR_ALL_BB_FN (bb, fun)
 365     FOR_BB_INSNS (bb, insn)
 366     {
 367       if (NONDEBUG_INSN_P (insn))
 368         {
 369           struct df_insn_info *insn_info = DF_INSN_INFO_GET (insn);
 370           df_ref use;
 371           FOR_EACH_INSN_INFO_USE (use, insn_info)
 372             if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 373               DF_REF_ID (use) = uses_num++;
 374           FOR_EACH_INSN_INFO_EQ_USE (use, insn_info)
 375             if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 376               DF_REF_ID (use) = uses_num++;
 377         }
 378     }
 379
 380   /* Record the number of uses and defs at the beginning of the optimization.  */
 381   def_entry = XCNEWVEC (web_entry, DF_DEFS_TABLE_SIZE ());
 382   used = XCNEWVEC (unsigned, max);
 383   use_entry = XCNEWVEC (web_entry, uses_num);
 384
 385   /* Produce the web.  */
 386   FOR_ALL_BB_FN (bb, fun)
 387     FOR_BB_INSNS (bb, insn)
 388       if (NONDEBUG_INSN_P (insn))
 389         {
 390           struct df_insn_info *insn_info = DF_INSN_INFO_GET (insn);
 391           df_ref use;
 392           union_match_dups (insn, def_entry, use_entry, unionfind_union);
 393           FOR_EACH_INSN_INFO_USE (use, insn_info)
 394             if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 395               union_defs (use, def_entry, used, use_entry, unionfind_union);
 396           FOR_EACH_INSN_INFO_EQ_USE (use, insn_info)
 397             if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 398               union_defs (use, def_entry, used, use_entry, unionfind_union);
 399         }
 400
 401   /* Update the instruction stream, allocating new registers for split pseudos
 402      in progress.  */
 403   FOR_ALL_BB_FN (bb, fun)
 404     FOR_BB_INSNS (bb, insn)
 405       if (NONDEBUG_INSN_P (insn)
 406           /* Ignore naked clobber.  For example, reg 134 in the second insn
 407              of the following sequence will not be replaced.
 408
 409                (insn (clobber (reg:SI 134)))
 410
 411                (insn (set (reg:SI 0 r0) (reg:SI 134)))
 412
 413              Thus the later passes can optimize them away.  */
 414           && GET_CODE (PATTERN (insn)) != CLOBBER)
 415         {
 416           struct df_insn_info *insn_info = DF_INSN_INFO_GET (insn);
 417           df_ref def, use;
 418           FOR_EACH_INSN_INFO_USE (use, insn_info)
 419             if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 420               replace_ref (use, entry_register (use_entry + DF_REF_ID (use),
 421                                                 use, used));
 422           FOR_EACH_INSN_INFO_EQ_USE (use, insn_info)
 423             if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
 424               replace_ref (use, entry_register (use_entry + DF_REF_ID (use),
 425                                                 use, used));
 426           FOR_EACH_INSN_INFO_DEF (def, insn_info)
 427             if (DF_REF_REGNO (def) >= FIRST_PSEUDO_REGISTER)
 428               replace_ref (def, entry_register (def_entry + DF_REF_ID (def),
 429                                                 def, used));
 430         }
 431
 432   free (def_entry);
 433   free (use_entry);
 434   free (used);
 435   return 0;
 436 }
 437 \f
 438 } // anon namespace
 439
 440 rtl_opt_pass *
 441 make_pass_web (gcc::context *ctxt)
 442 {
 443   return new pass_web (ctxt);
 444 }