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 "obstack.h"
  55 #include "basic-block.h"
  56 #include "output.h"
  57 #include "df.h"
  58 #include "function.h"
  59
  60
  61 /* This entry is allocated for each reference in the insn stream.  */
  62 struct web_entry
  63 {
  64   /* Pointer to the parent in the union/find tree.  */
  65   struct web_entry *pred;
  66   /* Newly assigned register to the entry.  Set only for roots.  */
  67   rtx reg;
  68 };
  69
  70 static struct web_entry *unionfind_root (struct web_entry *);
  71 static void unionfind_union (struct web_entry *, struct web_entry *);
  72 static void union_defs (struct df *, struct ref *, struct web_entry *,
  73                         struct web_entry *);
  74 static rtx entry_register (struct web_entry *, struct ref *, char *);
  75 static void replace_ref (struct ref *, rtx);
  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 (link)
 164         {
 165           if (DF_REF_REAL_REG (link->ref) == DF_REF_REAL_REG (use))
 166             unionfind_union (use_entry + DF_REF_ID (use),
 167                              def_entry + DF_REF_ID (link->ref));
 168           link = link->next;
 169         }
 170     }
 171 }
 172
 173 /* Find the corresponding register for the given entry.  */
 174
 175 static rtx
 176 entry_register (struct web_entry *entry, struct ref *ref, char *used)
 177 {
 178   struct web_entry *root;
 179   rtx reg, newreg;
 180
 181   /* Find the corresponding web and see if it has been visited.  */
 182   root = unionfind_root (entry);
 183   if (root->reg)
 184     return root->reg;
 185
 186   /* We are seeing this web for the first time, do the assignment.  */
 187   reg = DF_REF_REAL_REG (ref);
 188
 189   /* In case the original register is already assigned, generate new one.  */
 190   if (!used[REGNO (reg)])
 191     newreg = reg, used[REGNO (reg)] = 1;
 192   else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
 193     {
 194       newreg = reg;
 195       if (dump_file)
 196         fprintf (dump_file,
 197                  "New web forced to keep reg=%i (user variable)\n",
 198                  REGNO (reg));
 199     }
 200   else
 201     {
 202       newreg = gen_reg_rtx (GET_MODE (reg));
 203       REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
 204       REG_POINTER (newreg) = REG_POINTER (reg);
 205       REG_ATTRS (newreg) = REG_ATTRS (reg);
 206       if (dump_file)
 207         fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
 208                  REGNO (newreg));
 209     }
 210
 211   root->reg = newreg;
 212   return newreg;
 213 }
 214
 215 /* Replace the reference by REG.  */
 216
 217 static void
 218 replace_ref (struct ref *ref, rtx reg)
 219 {
 220   rtx oldreg = DF_REF_REAL_REG (ref);
 221   rtx *loc = DF_REF_REAL_LOC (ref);
 222
 223   if (oldreg == reg)
 224     return;
 225   if (dump_file)
 226     fprintf (dump_file, "Updating insn %i (%i->%i)\n",
 227              INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
 228   *loc = reg;
 229 }
 230
 231 /* Main entry point.  */
 232
 233 void
 234 web_main (void)
 235 {
 236   struct df *df;
 237   struct web_entry *def_entry;
 238   struct web_entry *use_entry;
 239   unsigned int i;
 240   int max = max_reg_num ();
 241   char *used;
 242
 243   df = df_init ();
 244   df_analyze (df, 0, DF_UD_CHAIN | DF_EQUIV_NOTES);
 245
 246   def_entry = xcalloc (df->n_defs, sizeof (struct web_entry));
 247   use_entry = xcalloc (df->n_uses, sizeof (struct web_entry));
 248   used = xcalloc (max, sizeof (char));
 249
 250   if (dump_file)
 251     df_dump (df, DF_UD_CHAIN | DF_DU_CHAIN, dump_file);
 252
 253   /* Produce the web.  */
 254   for (i = 0; i < df->n_uses; i++)
 255     union_defs (df, df->uses[i], def_entry, use_entry);
 256
 257   /* Update the instruction stream, allocating new registers for split pseudos
 258      in progress.  */
 259   for (i = 0; i < df->n_uses; i++)
 260     replace_ref (df->uses[i], entry_register (use_entry + i, df->uses[i],
 261                                               used));
 262   for (i = 0; i < df->n_defs; i++)
 263     replace_ref (df->defs[i], entry_register (def_entry + i, df->defs[i],
 264                                               used));
 265
 266   /* Dataflow information is corrupt here, but it can be easily updated
 267      by creating new entries for new registers and updates or calling
 268      df_insns_modify.  */
 269   free (def_entry);
 270   free (use_entry);
 271   free (used);
 272   df_finish (df);
 273 }