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, 59 Temple Place - Suite 330, Boston, MA
  20 02111-1307, 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 "basic-block.h"
  55 #include "output.h"
  56 #include "df.h"
  57 #include "function.h"
  58
  59
  60 /* This entry is allocated for each reference in the insn stream.  */
  61 struct web_entry
  62 {
  63   /* Pointer to the parent in the union/find tree.  */
  64   struct web_entry *pred;
  65   /* Newly assigned register to the entry.  Set only for roots.  */
  66   rtx reg;
  67 };
  68
  69 static struct web_entry *unionfind_root (struct web_entry *);
  70 static void unionfind_union (struct web_entry *, struct web_entry *);
  71 static void union_defs (struct df *, struct ref *, struct web_entry *,
  72                         struct web_entry *);
  73 static rtx entry_register (struct web_entry *, struct ref *, char *, char *);
  74 static void replace_ref (struct ref *, rtx);
  75 static int mark_addressof (rtx *, void *);
  76
  77 /* Find the root of unionfind tree (the representative of set).  */
  78
  79 static struct web_entry *
  80 unionfind_root (struct web_entry *element)
  81 {
  82   struct web_entry *element1 = element, *element2;
  83
  84   while (element->pred)
  85     element = element->pred;
  86   while (element1->pred)
  87     {
  88       element2 = element1->pred;
  89       element1->pred = element;
  90       element1 = element2;
  91     }
  92   return element;
  93 }
  94
  95 /* Union sets.  */
  96
  97 static void
  98 unionfind_union (struct web_entry *first, struct web_entry *second)
  99 {
 100   first = unionfind_root (first);
 101   second = unionfind_root (second);
 102   if (first == second)
 103     return;
 104   second->pred = first;
 105 }
 106
 107 /* For each use, all possible defs reaching it must come in the same
 108    register, union them.  */
 109
 110 static void
 111 union_defs (struct df *df, struct ref *use, struct web_entry *def_entry,
 112             struct web_entry *use_entry)
 113 {
 114   rtx insn = DF_REF_INSN (use);
 115   struct df_link *link = DF_REF_CHAIN (use);
 116   struct df_link *use_link = DF_INSN_USES (df, insn);
 117   struct df_link *def_link = DF_INSN_DEFS (df, insn);
 118   rtx set = single_set (insn);
 119
 120   /* Some instructions may use match_dup for their operands.  In case the
 121      operands are dead, we will assign them different pseudos, creating
 122      invalid instructions, so union all uses of the same operand for each
 123      insn.  */
 124
 125   while (use_link)
 126     {
 127       if (use != use_link->ref
 128           && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (use_link->ref))
 129         unionfind_union (use_entry + DF_REF_ID (use),
 130                          use_entry + DF_REF_ID (use_link->ref));
 131       use_link = use_link->next;
 132     }
 133
 134   /* Recognize trivial noop moves and attempt to keep them as noop.
 135      While most of noop moves should be removed, we still keep some
 136      of them at libcall boundaries and such.  */
 137
 138   if (set
 139       && SET_SRC (set) == DF_REF_REG (use)
 140       && SET_SRC (set) == SET_DEST (set))
 141     {
 142       while (def_link)
 143         {
 144           if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def_link->ref))
 145             unionfind_union (use_entry + DF_REF_ID (use),
 146                              def_entry + DF_REF_ID (def_link->ref));
 147           def_link = def_link->next;
 148         }
 149     }
 150   while (link)
 151     {
 152       unionfind_union (use_entry + DF_REF_ID (use),
 153                        def_entry + DF_REF_ID (link->ref));
 154       link = link->next;
 155     }
 156
 157   /* A READ_WRITE use requires the corresponding def to be in the same
 158      register.  Find it and union.  */
 159   if (use->flags & DF_REF_READ_WRITE)
 160     {
 161       struct df_link *link = DF_INSN_DEFS (df, DF_REF_INSN (use));
 162
 163       while (DF_REF_REAL_REG (link->ref) != DF_REF_REAL_REG (use))
 164         link = link->next;
 165
 166       unionfind_union (use_entry + DF_REF_ID (use),
 167                        def_entry + DF_REF_ID (link->ref));
 168     }
 169 }
 170
 171 /* Find the corresponding register for the given entry.  */
 172
 173 static rtx
 174 entry_register (struct web_entry *entry, struct ref *ref, char *used,
 175                 char *use_addressof)
 176 {
 177   struct web_entry *root;
 178   rtx reg, newreg;
 179
 180   /* Find the corresponding web and see if it has been visited.  */
 181   root = unionfind_root (entry);
 182   if (root->reg)
 183     return root->reg;
 184
 185   /* We are seeing this web for the first time, do the assignment.  */
 186   reg = DF_REF_REAL_REG (ref);
 187
 188   /* In case the original register is already assigned, generate new one.  */
 189   if (!used[REGNO (reg)])
 190     newreg = reg, used[REGNO (reg)] = 1;
 191   else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
 192     {
 193       newreg = reg;
 194       if (dump_file)
 195         fprintf (dump_file,
 196                  "New web forced to keep reg=%i (user variable)\n",
 197                  REGNO (reg));
 198     }
 199   else if (use_addressof [REGNO (reg)])
 200     {
 201       newreg = reg;
 202       if (dump_file)
 203         fprintf (dump_file,
 204                  "New web forced to keep reg=%i (address taken)\n",
 205                  REGNO (reg));
 206     }
 207   else
 208     {
 209       newreg = gen_reg_rtx (GET_MODE (reg));
 210       REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
 211       REG_POINTER (newreg) = REG_POINTER (reg);
 212       REG_LOOP_TEST_P (newreg) = REG_LOOP_TEST_P (reg);
 213       RTX_UNCHANGING_P (newreg) = RTX_UNCHANGING_P (reg);
 214       REG_ATTRS (newreg) = REG_ATTRS (reg);
 215       if (dump_file)
 216         fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
 217                  REGNO (newreg));
 218     }
 219
 220   root->reg = newreg;
 221   return newreg;
 222 }
 223
 224 /* Replace the reference by REG.  */
 225
 226 static void
 227 replace_ref (struct ref *ref, rtx reg)
 228 {
 229   rtx oldreg = DF_REF_REAL_REG (ref);
 230   rtx *loc = DF_REF_REAL_LOC (ref);
 231
 232   if (oldreg == reg)
 233     return;
 234   if (dump_file)
 235     fprintf (dump_file, "Updating insn %i (%i->%i)\n",
 236              INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
 237   *loc = reg;
 238 }
 239
 240 /* Mark each pseudo whose address is taken.  */
 241
 242 static int
 243 mark_addressof (rtx *rtl, void *data)
 244 {
 245   if (!*rtl)
 246     return 0;
 247   if (GET_CODE (*rtl) == ADDRESSOF
 248       && REG_P (XEXP (*rtl, 0)))
 249     ((char *)data)[REGNO (XEXP (*rtl, 0))] = 1;
 250   return 0;
 251 }
 252
 253 /* Main entry point.  */
 254
 255 void
 256 web_main (void)
 257 {
 258   struct df *df;
 259   struct web_entry *def_entry;
 260   struct web_entry *use_entry;
 261   unsigned int i;
 262   int max = max_reg_num ();
 263   char *used;
 264   char *use_addressof;
 265   basic_block bb;
 266   rtx insn;
 267
 268   df = df_init ();
 269   df_analyze (df, 0, DF_UD_CHAIN | DF_EQUIV_NOTES);
 270
 271   def_entry = xcalloc (df->n_defs, sizeof (struct web_entry));
 272   use_entry = xcalloc (df->n_uses, sizeof (struct web_entry));
 273   used = xcalloc (max, sizeof (char));
 274   use_addressof = xcalloc (max, sizeof (char));
 275
 276   if (dump_file)
 277     df_dump (df, DF_UD_CHAIN | DF_DU_CHAIN, dump_file);
 278
 279   /* Produce the web.  */
 280   for (i = 0; i < df->n_uses; i++)
 281     union_defs (df, df->uses[i], def_entry, use_entry);
 282
 283   /* We can not safely rename registers whose address is taken.  */
 284   FOR_EACH_BB (bb)
 285     FOR_BB_INSNS (bb, insn)
 286       {
 287         if (INSN_P (insn))
 288           for_each_rtx (&PATTERN (insn), mark_addressof, use_addressof);
 289       }
 290
 291   /* Update the instruction stream, allocating new registers for split pseudos
 292      in progress.  */
 293   for (i = 0; i < df->n_uses; i++)
 294     replace_ref (df->uses[i], entry_register (use_entry + i, df->uses[i],
 295                                               used, use_addressof));
 296   for (i = 0; i < df->n_defs; i++)
 297     replace_ref (df->defs[i], entry_register (def_entry + i, df->defs[i],
 298                                               used, use_addressof));
 299
 300   /* Dataflow information is corrupt here, but it can be easily updated
 301      by creating new entries for new registers and updates or calling
 302      df_insns_modify.  */
 303   free (def_entry);
 304   free (use_entry);
 305   free (used);
 306   free (use_addressof);
 307   df_finish (df);
 308 }