gcc/web.c

   1 /* Web construction code for GNU compiler.
   2    Contributed by Jan Hubicka.
   3    Copyright (C) 2001, 2002, 2004, 2006
   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 2, 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 COPYING.  If not, write to the Free
  20 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  21 02110-1301, USA.  */
  22
  23 /* Simple optimization pass that splits independent uses of each pseudo,
  24    increasing effectiveness of other optimizations.  The optimization can
  25    serve as an example of use for the dataflow module.
  26
  27    We don't split registers with REG_USERVAR set unless -fmessy-debugging
  28    is specified, because debugging information about such split variables
  29    is almost unusable.
  30
  31    TODO
  32     - Add code to keep debugging up-to-date after splitting user variable
  33       pseudos.  This can be done by keeping track of all the pseudos used
  34       for the variable and using life analysis information before reload
  35       to determine which one is live and, in case more than one are live,
  36       choose the one with the latest definition.
  37
  38       Other optimization passes can benefit from the infrastructure too.
  39
  40     - We may use profile information and ignore infrequent use for the
  41       purpose of web unifying, inserting the compensation code later to
  42       implement full induction variable expansion for loops (currently
  43       we expand only if the induction variable is dead afterward, which
  44       is often the case).  */
  45
  46 #include "config.h"
  47 #include "system.h"
  48 #include "coretypes.h"
  49 #include "tm.h"
  50 #include "toplev.h"
  51
  52 #include "rtl.h"
  53 #include "hard-reg-set.h"
  54 #include "flags.h"
  55 #include "obstack.h"
  56 #include "basic-block.h"
  57 #include "output.h"
  58 #include "df.h"
  59 #include "function.h"
  60 #include "timevar.h"
  61 #include "tree-pass.h"
  62
  63
  64 /* This entry is allocated for each reference in the insn stream.  */
  65 struct web_entry
  66 {
  67   /* Pointer to the parent in the union/find tree.  */
  68   struct web_entry *pred;
  69   /* Newly assigned register to the entry.  Set only for roots.  */
  70   rtx reg;
  71 };
  72
  73 static struct web_entry *unionfind_root (struct web_entry *);
  74 static void unionfind_union (struct web_entry *, struct web_entry *);
  75 static void union_defs (struct df *, struct df_ref *, struct web_entry *,
  76                         struct web_entry *);
  77 static rtx entry_register (struct web_entry *, struct df_ref *, char *);
  78 static void replace_ref (struct df_ref *, rtx);
  79
  80 /* Find the root of unionfind tree (the representative of set).  */
  81
  82 static struct web_entry *
  83 unionfind_root (struct web_entry *element)
  84 {
  85   struct web_entry *element1 = element, *element2;
  86
  87   while (element->pred)
  88     element = element->pred;
  89   while (element1->pred)
  90     {
  91       element2 = element1->pred;
  92       element1->pred = element;
  93       element1 = element2;
  94     }
  95   return element;
  96 }
  97
  98 /* Union sets.  */
  99
 100 static void
 101 unionfind_union (struct web_entry *first, struct web_entry *second)
 102 {
 103   first = unionfind_root (first);
 104   second = unionfind_root (second);
 105   if (first == second)
 106     return;
 107   second->pred = first;
 108 }
 109
 110 /* For each use, all possible defs reaching it must come in the same
 111    register, union them.  */
 112
 113 static void
 114 union_defs (struct df *df, struct df_ref *use, struct web_entry *def_entry,
 115             struct web_entry *use_entry)
 116 {
 117   rtx insn = DF_REF_INSN (use);
 118   struct df_link *link = DF_REF_CHAIN (use);
 119   struct df_ref *use_link = DF_INSN_USES (df, insn);
 120   struct df_ref *def_link = DF_INSN_DEFS (df, insn);
 121   rtx set = single_set (insn);
 122
 123   /* Some instructions may use match_dup for their operands.  In case the
 124      operands are dead, we will assign them different pseudos, creating
 125      invalid instructions, so union all uses of the same operand for each
 126      insn.  */
 127
 128   while (use_link)
 129     {
 130       if (use != use_link
 131           && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (use_link))
 132         unionfind_union (use_entry + DF_REF_ID (use),
 133                          use_entry + DF_REF_ID (use_link));
 134       use_link = use_link->next_ref;
 135     }
 136
 137   /* Recognize trivial noop moves and attempt to keep them as noop.
 138      While most of noop moves should be removed, we still keep some
 139      of them at libcall boundaries and such.  */
 140
 141   if (set
 142       && SET_SRC (set) == DF_REF_REG (use)
 143       && SET_SRC (set) == SET_DEST (set))
 144     {
 145       while (def_link)
 146         {
 147           if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def_link))
 148             unionfind_union (use_entry + DF_REF_ID (use),
 149                              def_entry + DF_REF_ID (def_link));
 150           def_link = def_link->next_ref;
 151         }
 152     }
 153   while (link)
 154     {
 155       unionfind_union (use_entry + DF_REF_ID (use),
 156                        def_entry + DF_REF_ID (link->ref));
 157       link = link->next;
 158     }
 159
 160   /* A READ_WRITE use requires the corresponding def to be in the same
 161      register.  Find it and union.  */
 162   if (use->flags & DF_REF_READ_WRITE)
 163     {
 164       struct df_ref *link = DF_INSN_DEFS (df, DF_REF_INSN (use));
 165
 166       while (link)
 167         {
 168           if (DF_REF_REAL_REG (link) == DF_REF_REAL_REG (use))
 169             unionfind_union (use_entry + DF_REF_ID (use),
 170                              def_entry + DF_REF_ID (link));
 171           link = link->next_ref;
 172         }
 173     }
 174 }
 175
 176 /* Find the corresponding register for the given entry.  */
 177
 178 static rtx
 179 entry_register (struct web_entry *entry, struct df_ref *ref, char *used)
 180 {
 181   struct web_entry *root;
 182   rtx reg, newreg;
 183
 184   /* Find the corresponding web and see if it has been visited.  */
 185   root = unionfind_root (entry);
 186   if (root->reg)
 187     return root->reg;
 188
 189   /* We are seeing this web for the first time, do the assignment.  */
 190   reg = DF_REF_REAL_REG (ref);
 191
 192   /* In case the original register is already assigned, generate new one.  */
 193   if (!used[REGNO (reg)])
 194     newreg = reg, used[REGNO (reg)] = 1;
 195   else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
 196     {
 197       newreg = reg;
 198       if (dump_file)
 199         fprintf (dump_file,
 200                  "New web forced to keep reg=%i (user variable)\n",
 201                  REGNO (reg));
 202     }
 203   else
 204     {
 205       newreg = gen_reg_rtx (GET_MODE (reg));
 206       REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
 207       REG_POINTER (newreg) = REG_POINTER (reg);
 208       REG_ATTRS (newreg) = REG_ATTRS (reg);
 209       if (dump_file)
 210         fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
 211                  REGNO (newreg));
 212     }
 213
 214   root->reg = newreg;
 215   return newreg;
 216 }
 217
 218 /* Replace the reference by REG.  */
 219
 220 static void
 221 replace_ref (struct df_ref *ref, rtx reg)
 222 {
 223   rtx oldreg = DF_REF_REAL_REG (ref);
 224   rtx *loc = DF_REF_REAL_LOC (ref);
 225
 226   if (oldreg == reg)
 227     return;
 228   if (dump_file)
 229     fprintf (dump_file, "Updating insn %i (%i->%i)\n",
 230              INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
 231   *loc = reg;
 232 }
 233
 234 /* Main entry point.  */
 235
 236 static void
 237 web_main (void)
 238 {
 239   struct df *df;
 240   struct web_entry *def_entry;
 241   struct web_entry *use_entry;
 242   unsigned int i;
 243   int max = max_reg_num ();
 244   char *used;
 245
 246   df = df_init (DF_EQUIV_NOTES);
 247   df_chain_add_problem (df, DF_UD_CHAIN);
 248   df_analyze (df);
 249   df_reorganize_refs (&df->def_info);
 250   df_reorganize_refs (&df->use_info);
 251
 252   def_entry = XCNEWVEC (struct web_entry, DF_DEFS_SIZE (df));
 253   use_entry = XCNEWVEC (struct web_entry, DF_USES_SIZE (df));
 254   used = XCNEWVEC (char, max);
 255
 256   if (dump_file)
 257     df_dump (df, dump_file);
 258
 259   /* Produce the web.  */
 260   for (i = 0; i < DF_USES_SIZE (df); i++)
 261     union_defs (df, DF_USES_GET (df, i), def_entry, use_entry);
 262
 263   /* Update the instruction stream, allocating new registers for split pseudos
 264      in progress.  */
 265   for (i = 0; i < DF_USES_SIZE (df); i++)
 266     replace_ref (DF_USES_GET (df, i),
 267                  entry_register (use_entry + i, DF_USES_GET (df, i), used));
 268   for (i = 0; i < DF_DEFS_SIZE (df); i++)
 269     replace_ref (DF_DEFS_GET (df, i),
 270                  entry_register (def_entry + i, DF_DEFS_GET (df, i), used));
 271
 272   /* Dataflow information is corrupt here, but it can be easily updated
 273      by creating new entries for new registers and updates or calling
 274      df_insns_modify.  */
 275   free (def_entry);
 276   free (use_entry);
 277   free (used);
 278   df_finish (df);
 279   df = NULL;
 280 }
 281 \f
 282 static bool
 283 gate_handle_web (void)
 284 {
 285   return (optimize > 0 && flag_web);
 286 }
 287
 288 static void
 289 rest_of_handle_web (void)
 290 {
 291   web_main ();
 292   delete_trivially_dead_insns (get_insns (), max_reg_num ());
 293   cleanup_cfg (CLEANUP_EXPENSIVE);
 294   reg_scan (get_insns (), max_reg_num ());
 295 }
 296
 297 struct tree_opt_pass pass_web =
 298 {
 299   "web",                                /* name */
 300   gate_handle_web,                      /* gate */
 301   rest_of_handle_web,                   /* execute */
 302   NULL,                                 /* sub */
 303   NULL,                                 /* next */
 304   0,                                    /* static_pass_number */
 305   TV_WEB,                               /* tv_id */
 306   0,                                    /* properties_required */
 307   0,                                    /* properties_provided */
 308   0,                                    /* properties_destroyed */
 309   0,                                    /* todo_flags_start */
 310   TODO_dump_func,                       /* todo_flags_finish */
 311   'Z'                                   /* letter */
 312 };
 313