1 /* Register conflict graph computation routines.
2 Copyright (C) 2000 Free Software Foundation, Inc.
3 Contributed by CodeSourcery, LLC
5 This file is part of GNU CC.
7 GNU CC is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2, or (at your option)
12 GNU CC is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GNU CC; see the file COPYING. If not, write to
19 the Free Software Foundation, 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
24 Building an Optimizing Compiler
26 Butterworth-Heinemann, 1998 */
34 #include "basic-block.h"
36 /* Use malloc to allocate obstack chunks. */
37 #define obstack_chunk_alloc xmalloc
38 #define obstack_chunk_free free
40 /* A register conflict graph is an undirected graph containing nodes
41 for some or all of the regs used in a function. Arcs represent
42 conflicts, i.e. two nodes are connected by an arc if there is a
43 point in the function at which the regs corresponding to the two
46 The conflict graph is represented by the data structures described
47 in Morgan section 11.3.1. Nodes are not stored explicitly; only
48 arcs are. An arc stores the numbers of the regs it connects.
50 Arcs can be located by two methods:
52 - The two reg numbers for each arc are hashed into a single
53 value, and the arc is placed in a hash table according to this
54 value. This permits quick determination of whether a specific
55 conflict is present in the graph.
57 - Additionally, the arc data structures are threaded by a set of
58 linked lists by single reg number. Since each arc references
59 two regs, there are two next pointers, one for the
60 smaller-numbered reg and one for the larger-numbered reg. This
61 permits the quick enumeration of conflicts for a single
64 Arcs are allocated from an obstack. */
66 /* An arc in a conflict graph. */
68 struct conflict_graph_arc_def
70 /* The next element of the list of conflicts involving the
71 smaller-numbered reg, as an index in the table of arcs of this
72 graph. Contains NULL if this is the tail. */
73 struct conflict_graph_arc_def *smaller_next;
75 /* The next element of the list of conflicts involving the
76 larger-numbered reg, as an index in the table of arcs of this
77 graph. Contains NULL if this is the tail. */
78 struct conflict_graph_arc_def *larger_next;
80 /* The smaller-numbered reg involved in this conflict. */
83 /* The larger-numbered reg involved in this conflict. */
87 typedef struct conflict_graph_arc_def *conflict_graph_arc;
90 /* A conflict graph. */
92 struct conflict_graph_def
94 /* A hash table of arcs. Used to search for a specific conflict. */
95 htab_t arc_hash_table;
97 /* The number of regs this conflict graph handles. */
100 /* For each reg, the arc at the head of a list that threads through
101 all the arcs involving that reg. An entry is NULL if no
102 conflicts exist involving that reg. */
103 conflict_graph_arc *neighbor_heads;
105 /* Arcs are allocated from here. */
106 struct obstack arc_obstack;
109 /* The initial capacity (number of conflict arcs) for newly-created
111 #define INITIAL_ARC_CAPACITY (64)
114 /* Computes the hash value of the conflict graph arc connecting regs
115 R1__ and R2__. R1__ is assumed to be smaller or equal to R2__. */
116 #define CONFLICT_HASH_FN(r1__, r2__) ((r2__) * ((r2__) - 1) / 2 + (r1__))
118 static unsigned arc_hash
119 PARAMS ((const void *arcp));
121 PARAMS ((const void *arcp1, const void *arcp2));
122 static int print_conflict
123 PARAMS ((int reg1, int reg2, void *contextp));
125 PARAMS ((rtx reg, rtx setter, void *data));
128 /* Callback function to compute the hash value of an arc. Uses
129 current_graph to locate the graph to which the arc belongs. */
135 conflict_graph_arc arc = (conflict_graph_arc) arcp;
136 return CONFLICT_HASH_FN (arc->smaller, arc->larger);
139 /* Callback function to determine the equality of two arcs in the hash
143 arc_eq (arcp1, arcp2)
147 conflict_graph_arc arc1 = (conflict_graph_arc) arcp1;
148 conflict_graph_arc arc2 = (conflict_graph_arc) arcp2;
149 return arc1->smaller == arc2->smaller && arc1->larger == arc2->larger;
152 /* Creates an empty conflict graph to hold conflicts among NUM_REGS
156 conflict_graph_new (num_regs)
159 conflict_graph graph =
160 (conflict_graph) xmalloc (sizeof (struct conflict_graph_def));
161 graph->num_regs = num_regs;
163 /* Set up the hash table. No delete action is specified; memory
164 management of arcs is through the obstack. */
165 graph->arc_hash_table =
166 htab_create (INITIAL_ARC_CAPACITY, &arc_hash, &arc_eq, NULL);
168 /* Create an obstack for allocating arcs. */
169 obstack_init (&(graph->arc_obstack));
171 /* Create and zero the lookup table by register number. */
172 graph->neighbor_heads = (conflict_graph_arc *)
173 xmalloc (num_regs * sizeof (conflict_graph_arc));
174 memset (graph->neighbor_heads, 0,
175 num_regs * sizeof (conflict_graph_arc));
180 /* Deletes a conflict graph. */
183 conflict_graph_delete (graph)
184 conflict_graph graph;
186 obstack_free (&(graph->arc_obstack), NULL);
187 htab_delete (graph->arc_hash_table);
188 free (graph->neighbor_heads);
192 /* Adds a conflict to GRAPH between regs REG1 and REG2, which must be
193 distinct. Returns non-zero, unless the conflict is already present
194 in GRAPH, in which case it does nothing and returns zero. */
197 conflict_graph_add (graph, reg1, reg2)
198 conflict_graph graph;
202 int smaller = MIN (reg1, reg2);
203 int larger = MAX (reg1, reg2);
204 struct conflict_graph_arc_def dummy;
205 conflict_graph_arc arc;
208 /* A reg cannot conflict with itself. */
212 dummy.smaller = smaller;
213 dummy.larger = larger;
214 slot = htab_find_slot (graph->arc_hash_table, (void *) &dummy, 1);
216 /* If the conflict is already there, do nothing. */
220 /* Allocate an arc. */
221 arc = (conflict_graph_arc)
222 obstack_alloc (&(graph->arc_obstack),
223 sizeof (struct conflict_graph_arc_def));
225 /* Record the reg numbers. */
226 arc->smaller = smaller;
227 arc->larger = larger;
229 /* Link the conflict into into two lists, one for each reg. */
230 arc->smaller_next = graph->neighbor_heads[smaller];
231 graph->neighbor_heads[smaller] = arc;
232 arc->larger_next = graph->neighbor_heads[larger];
233 graph->neighbor_heads[larger] = arc;
235 /* Put it in the hash table. */
236 *slot = (void *) arc;
241 /* Returns non-zero if a conflict exists in GRAPH between regs REG1
245 conflict_graph_conflict_p (graph, reg1, reg2)
246 conflict_graph graph;
250 /* Build an arc to search for. */
251 struct conflict_graph_arc_def arc;
252 arc.smaller = MIN (reg1, reg2);
253 arc.larger = MAX (reg1, reg2);
255 return htab_find (graph->arc_hash_table, (void *) &arc) != NULL;
258 /* Calls ENUM_FN for each conflict in GRAPH involving REG. EXTRA is
259 passed back to ENUM_FN. */
262 conflict_graph_enum (graph, reg, enum_fn, extra)
263 conflict_graph graph;
265 conflict_graph_enum_fn enum_fn;
268 conflict_graph_arc arc = graph->neighbor_heads[reg];
271 /* Invoke the callback. */
272 if ((*enum_fn) (arc->smaller, arc->larger, extra))
273 /* Stop if requested. */
276 /* Which next pointer to follow depends on whether REG is the
277 smaller or larger reg in this conflict. */
278 if (reg < arc->larger)
279 arc = arc->smaller_next;
281 arc = arc->larger_next;
285 /* For each conflict between a register x and SRC in GRAPH, adds a
286 conflict to GRAPH between x and TARGET. */
289 conflict_graph_merge_regs (graph, target, src)
290 conflict_graph graph;
294 conflict_graph_arc arc = graph->neighbor_heads[src];
301 int other = arc->smaller;
305 conflict_graph_add (graph, target, other);
307 /* Which next pointer to follow depends on whether REG is the
308 smaller or larger reg in this conflict. */
309 if (src < arc->larger)
310 arc = arc->smaller_next;
312 arc = arc->larger_next;
316 /* Holds context information while a conflict graph is being traversed
321 /* The file pointer to which we're printing. */
324 /* The reg whose conflicts we're printing. */
327 /* Whether a conflict has already been printed for this reg. */
331 /* Callback function when enumerating conflicts during printing. */
334 print_conflict (reg1, reg2, contextp)
339 struct print_context *context = (struct print_context *) contextp;
342 /* If this is the first conflict printed for this reg, start a new
344 if (! context->started)
346 fprintf (context->fp, " %d:", context->reg);
347 context->started = 1;
350 /* Figure out the reg whose conflicts we're printing. The other reg
351 is the interesting one. */
352 if (reg1 == context->reg)
354 else if (reg2 == context->reg)
359 /* Print the conflict. */
360 fprintf (context->fp, " %d", reg);
362 /* Continue enumerating. */
366 /* Prints the conflicts in GRAPH to FP. */
369 conflict_graph_print (graph, fp)
370 conflict_graph graph;
374 struct print_context context;
377 fprintf (fp, "Conflicts:\n");
378 /* Loop over registers supported in this graph. */
379 for (reg = 0; reg < graph->num_regs; ++reg)
383 /* Scan the conflicts for reg, printing as we go. A label for
384 this line will be printed the first time a conflict is
385 printed for the reg; we won't start a new line if this reg
387 conflict_graph_enum (graph, reg, &print_conflict, &context);
388 /* If this reg does have conflicts, end the line. */
394 /* Callback function for note_stores. */
397 mark_reg (reg, setter, data)
399 rtx setter ATTRIBUTE_UNUSED;
402 regset set = (regset) data;
404 if (GET_CODE (reg) == SUBREG)
405 reg = SUBREG_REG (reg);
407 /* We're only interested in regs. */
408 if (GET_CODE (reg) != REG)
411 SET_REGNO_REG_SET (set, REGNO (reg));
414 /* Allocates a conflict graph and computes conflicts over the current
415 function for the registers set in REGS. The caller is responsible
416 for deallocating the return value.
418 Preconditions: the flow graph must be in SSA form, and life
419 analysis (specifically, regs live at exit from each block) must be
422 This algorithm determines conflicts by walking the insns in each
423 block backwards. We maintain the set of live regs at each insn,
424 starting with the regs live on exit from the block. For each insn:
426 1. If a reg is set in this insns, it must be born here, since
427 we're in SSA. Therefore, it was not live before this insns,
428 so remove it from the set of live regs.
430 2. For each reg born in this insn, record a conflict between it
431 and every other reg live coming into this insn. For each
432 existing conflict, one of the two regs must be born while the
433 other is alive. See Morgan or elsewhere for a proof of this.
435 3. Regs clobbered by this insn must have been live coming into
436 it, so record them as such.
438 The resulting conflict graph is not built for regs in REGS
439 themselves; rather, partition P is used to obtain the canonical reg
440 for each of these. The nodes of the conflict graph are these
441 canonical regs instead. */
444 conflict_graph_compute (regs, p)
449 conflict_graph graph = conflict_graph_new (max_reg_num ());
451 for (b = n_basic_blocks; --b >= 0; )
453 basic_block bb = BASIC_BLOCK (b);
454 regset_head live_head;
455 regset live = &live_head;
456 regset_head born_head;
457 regset born = &born_head;
464 /* Start with the regs that are live on exit, limited to those
465 we're interested in. */
466 COPY_REG_SET (live, bb->global_live_at_end);
467 AND_REG_SET (live, regs);
469 /* Walk the instruction stream backwards. */
474 insn = PREV_INSN (insn))
480 /* Are we interested in this insn? */
483 /* Determine which regs are set in this insn. Since
484 we're in SSA form, if a reg is set here it isn't set
485 anywhere elso, so this insn is where the reg is born. */
486 CLEAR_REG_SET (born);
487 note_stores (PATTERN (insn), mark_reg, (void *) born);
489 for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
490 if (REG_NOTE_KIND (link) == REG_INC)
491 mark_reg (XEXP (link, 0), NULL_RTX, NULL);
493 AND_REG_SET (born, regs);
495 /* Regs born here were not live before this insn. */
496 AND_COMPL_REG_SET (live, born);
498 /* For every reg born here, add a conflict with every other
499 reg live coming into this insn. */
500 EXECUTE_IF_SET_IN_REG_SET (born,
501 FIRST_PSEUDO_REGISTER,
503 EXECUTE_IF_SET_IN_REG_SET (live,
504 FIRST_PSEUDO_REGISTER,
506 /* Build the conflict graph in terms of canonical
508 int b = partition_find (p, born_reg);
509 int l = partition_find (p, live_reg);
511 conflict_graph_add (graph, b, l);
515 /* Morgan's algorithm checks the operands of the insn
516 and adds them to the set of live regs. Instead, we
517 use death information added by life analysis. Regs
518 dead after this instruction were live before it. */
519 for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
520 if (REG_NOTE_KIND (link) == REG_DEAD)
522 int regno = REGNO (XEXP (link, 0));
523 if (REGNO_REG_SET_P (regs, regno))
524 SET_REGNO_REG_SET (live, regno);