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 static rtx entry_register (struct web_entry *, struct df_ref *, char *);
  65 static void replace_ref (struct df_ref *, rtx);
  66
  67 /* Find the root of unionfind tree (the representative of set).  */
  68
  69 struct web_entry *
  70 unionfind_root (struct web_entry *element)
  71 {
  72   struct web_entry *element1 = element, *element2;
  73
  74   while (element->pred)
  75     element = element->pred;
  76   while (element1->pred)
  77     {
  78       element2 = element1->pred;
  79       element1->pred = element;
  80       element1 = element2;
  81     }
  82   return element;
  83 }
  84
  85 /* Union sets.
  86    Return true if FIRST and SECOND points to the same web entry structure and
  87    nothing is done.  Otherwise, return false.  */
  88
  89 bool
  90 unionfind_union (struct web_entry *first, struct web_entry *second)
  91 {
  92   first = unionfind_root (first);
  93   second = unionfind_root (second);
  94   if (first == second)
  95     return true;
  96   second->pred = first;
  97   return false;
  98 }
  99
 100 /* For each use, all possible defs reaching it must come in the same
 101    register, union them.
 102    FUN is the function that does the union.  */
 103
 104 void
 105 union_defs (struct df *df, struct df_ref *use, struct web_entry *def_entry,
 106             struct web_entry *use_entry,
 107             bool (*fun) (struct web_entry *, struct web_entry *))
 108 {
 109   rtx insn = DF_REF_INSN (use);
 110   struct df_link *link = DF_REF_CHAIN (use);
 111   struct df_ref *use_link;
 112   struct df_ref *def_link;
 113   rtx set;
 114
 115   if (insn)
 116     {
 117       use_link = DF_INSN_USES (df, insn);
 118       def_link = DF_INSN_DEFS (df, insn);
 119       set = single_set (insn);
 120     }
 121   else
 122     {
 123       use_link = NULL;
 124       def_link = NULL;
 125       set = NULL;
 126     }
 127
 128   /* Some instructions may use match_dup for their operands.  In case the
 129      operands are dead, we will assign them different pseudos, creating
 130      invalid instructions, so union all uses of the same operand for each
 131      insn.  */
 132
 133   while (use_link)
 134     {
 135       if (use != use_link
 136           && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (use_link))
 137         (*fun) (use_entry + DF_REF_ID (use),
 138                 use_entry + DF_REF_ID (use_link));
 139       use_link = use_link->next_ref;
 140     }
 141
 142   /* Recognize trivial noop moves and attempt to keep them as noop.
 143      While most of noop moves should be removed, we still keep some
 144      of them at libcall boundaries and such.  */
 145
 146   if (set
 147       && SET_SRC (set) == DF_REF_REG (use)
 148       && SET_SRC (set) == SET_DEST (set))
 149     {
 150       while (def_link)
 151         {
 152           if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def_link))
 153             (*fun) (use_entry + DF_REF_ID (use),
 154                     def_entry + DF_REF_ID (def_link));
 155           def_link = def_link->next_ref;
 156         }
 157     }
 158   while (link)
 159     {
 160       (*fun) (use_entry + DF_REF_ID (use),
 161               def_entry + DF_REF_ID (link->ref));
 162       link = link->next;
 163     }
 164
 165   /* A READ_WRITE use requires the corresponding def to be in the same
 166      register.  Find it and union.  */
 167   if (use->flags & DF_REF_READ_WRITE)
 168     {
 169       struct df_ref *link;
 170
 171       if (DF_REF_INSN (use))
 172         link = DF_INSN_DEFS (df, DF_REF_INSN (use));
 173       else
 174         link = NULL;
 175
 176       while (link)
 177         {
 178           if (DF_REF_REAL_REG (link) == DF_REF_REAL_REG (use))
 179             (*fun) (use_entry + DF_REF_ID (use),
 180                     def_entry + DF_REF_ID (link));
 181           link = link->next_ref;
 182         }
 183     }
 184 }
 185
 186 /* Find the corresponding register for the given entry.  */
 187
 188 static rtx
 189 entry_register (struct web_entry *entry, struct df_ref *ref, char *used)
 190 {
 191   struct web_entry *root;
 192   rtx reg, newreg;
 193
 194   /* Find the corresponding web and see if it has been visited.  */
 195   root = unionfind_root (entry);
 196   if (root->reg)
 197     return root->reg;
 198
 199   /* We are seeing this web for the first time, do the assignment.  */
 200   reg = DF_REF_REAL_REG (ref);
 201
 202   /* In case the original register is already assigned, generate new one.  */
 203   if (!used[REGNO (reg)])
 204     newreg = reg, used[REGNO (reg)] = 1;
 205   else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
 206     {
 207       newreg = reg;
 208       if (dump_file)
 209         fprintf (dump_file,
 210                  "New web forced to keep reg=%i (user variable)\n",
 211                  REGNO (reg));
 212     }
 213   else
 214     {
 215       newreg = gen_reg_rtx (GET_MODE (reg));
 216       REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
 217       REG_POINTER (newreg) = REG_POINTER (reg);
 218       REG_ATTRS (newreg) = REG_ATTRS (reg);
 219       if (dump_file)
 220         fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
 221                  REGNO (newreg));
 222     }
 223
 224   root->reg = newreg;
 225   return newreg;
 226 }
 227
 228 /* Replace the reference by REG.  */
 229
 230 static void
 231 replace_ref (struct df_ref *ref, rtx reg)
 232 {
 233   rtx oldreg = DF_REF_REAL_REG (ref);
 234   rtx *loc = DF_REF_REAL_LOC (ref);
 235
 236   if (oldreg == reg)
 237     return;
 238   if (dump_file)
 239     fprintf (dump_file, "Updating insn %i (%i->%i)\n",
 240              INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
 241   *loc = reg;
 242 }
 243
 244 /* Main entry point.  */
 245
 246 static void
 247 web_main (void)
 248 {
 249   struct df *df;
 250   struct web_entry *def_entry;
 251   struct web_entry *use_entry;
 252   unsigned int i;
 253   int max = max_reg_num ();
 254   char *used;
 255
 256   df = df_init (DF_EQUIV_NOTES);
 257   df_chain_add_problem (df, DF_UD_CHAIN);
 258   df_analyze (df);
 259   df_reorganize_refs (&df->def_info);
 260   df_reorganize_refs (&df->use_info);
 261
 262   def_entry = XCNEWVEC (struct web_entry, DF_DEFS_SIZE (df));
 263   use_entry = XCNEWVEC (struct web_entry, DF_USES_SIZE (df));
 264   used = XCNEWVEC (char, max);
 265
 266   if (dump_file)
 267     df_dump (df, dump_file);
 268
 269   /* Produce the web.  */
 270   for (i = 0; i < DF_USES_SIZE (df); i++)
 271     union_defs (df, DF_USES_GET (df, i), def_entry, use_entry, unionfind_union);
 272
 273   /* Update the instruction stream, allocating new registers for split pseudos
 274      in progress.  */
 275   for (i = 0; i < DF_USES_SIZE (df); i++)
 276     replace_ref (DF_USES_GET (df, i),
 277                  entry_register (use_entry + i, DF_USES_GET (df, i), used));
 278   for (i = 0; i < DF_DEFS_SIZE (df); i++)
 279     replace_ref (DF_DEFS_GET (df, i),
 280                  entry_register (def_entry + i, DF_DEFS_GET (df, i), used));
 281
 282   /* Dataflow information is corrupt here, but it can be easily updated
 283      by creating new entries for new registers and updates or calling
 284      df_insns_modify.  */
 285   free (def_entry);
 286   free (use_entry);
 287   free (used);
 288   df_finish (df);
 289   df = NULL;
 290 }
 291 \f
 292 static bool
 293 gate_handle_web (void)
 294 {
 295   return (optimize > 0 && flag_web);
 296 }
 297
 298 static unsigned int
 299 rest_of_handle_web (void)
 300 {
 301   web_main ();
 302   delete_trivially_dead_insns (get_insns (), max_reg_num ());
 303   cleanup_cfg (CLEANUP_EXPENSIVE);
 304   reg_scan (get_insns (), max_reg_num ());
 305   return 0;
 306 }
 307
 308 struct tree_opt_pass pass_web =
 309 {
 310   "web",                                /* name */
 311   gate_handle_web,                      /* gate */
 312   rest_of_handle_web,                   /* execute */
 313   NULL,                                 /* sub */
 314   NULL,                                 /* next */
 315   0,                                    /* static_pass_number */
 316   TV_WEB,                               /* tv_id */
 317   0,                                    /* properties_required */
 318   0,                                    /* properties_provided */
 319   0,                                    /* properties_destroyed */
 320   0,                                    /* todo_flags_start */
 321   TODO_dump_func,                       /* todo_flags_finish */
 322   'Z'                                   /* letter */
 323 };
 324