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
6This file is part of GCC.
7
8GCC is free software; you can redistribute it and/or modify it under
9the terms of the GNU General Public License as published by the Free
10Software Foundation; either version 2, or (at your option) any later
11version.
12
13GCC is distributed in the hope that it will be useful, but WITHOUT ANY
14WARRANTY; without even the implied warranty of MERCHANTABILITY or
15FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
16for more details.
17
18You should have received a copy of the GNU General Public License
19along with GCC; see the file COPYING.  If not, write to the Free
20Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
2102110-1301, 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
64static rtx entry_register (struct web_entry *, struct df_ref *, char *);
65static void replace_ref (struct df_ref *, rtx);
66
67/* Find the root of unionfind tree (the representative of set).  */
68
69struct web_entry *
70unionfind_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
89bool
90unionfind_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
104void
105union_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
188static rtx
189entry_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
230static void
231replace_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
246static void
247web_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
292static bool
293gate_handle_web (void)
294{
295  return (optimize > 0 && flag_web);
296}
297
298static unsigned int
299rest_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
308struct 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
325