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22 * @brief Naive spilling algorithm
23 * @author Matthias Braun
25 * @version $Id: bespillbelady.c 13913 2007-05-18 12:48:56Z matze $
27 * This implements a naive spilling algorithm. It is designed to produce similar
28 * effects to the spill decisions produced by traditional graph coloring
29 * register allocators that spill while they are coloring the graph.
31 * This spiller walks over all blocks and looks for places with too high
32 * register pressure where it spills the values that are cheapest to spill.
33 * Spilling in this context means placing a spill instruction behind the
34 * definition of the value and a reload before each usage.
40 #include "irnodeset.h"
43 #include "iredges_t.h"
47 #include "bespilloptions.h"
56 DEBUG_ONLY(static firm_dbg_module_t *dbg = NULL;)
58 static spill_env_t *spill_env;
60 static const arch_register_class_t *cls;
61 static const be_lv_t *lv;
62 static bitset_t *spilled_nodes;
64 typedef struct spill_candidate_t spill_candidate_t;
65 struct spill_candidate_t {
70 static int compare_spill_candidates_desc(const void *d1, const void *d2)
72 const spill_candidate_t *c1 = d1;
73 const spill_candidate_t *c2 = d2;
75 return (int) (c1->costs - c2->costs);
78 static double get_spill_costs(ir_node *node)
80 const ir_edge_t *edge;
81 ir_node *spill_place = skip_Proj(node);
82 double costs = be_get_spill_costs(spill_env, node,
85 foreach_out_edge(node, edge) {
86 ir_node *use = get_edge_src_irn(edge);
88 /* keeps should be directly below the node */
94 int in = get_edge_src_pos(edge);
95 ir_node *block = get_nodes_block(use);
97 costs += be_get_reload_costs_on_edge(spill_env, node, block, in);
99 costs += be_get_reload_costs(spill_env, node, use);
103 /* TODO cache costs? */
109 * spills a node by placing a reload before each usage
111 static void spill_node(ir_node *node)
113 const ir_edge_t *edge;
115 DBG((dbg, LEVEL_3, "\tspilling %+F\n", node));
117 foreach_out_edge(node, edge) {
118 ir_node *use = get_edge_src_irn(edge);
125 int in = get_edge_src_pos(edge);
126 ir_node *block = get_nodes_block(use);
128 be_add_reload_on_edge(spill_env, node, block, in, cls, 1);
130 be_add_reload(spill_env, node, use, cls, 1);
134 bitset_set(spilled_nodes, get_irn_idx(node));
138 * spill @p n nodes from a nodeset. Removes the nodes from the nodeset and
139 * sets the spilled bits in spilled_nodes.
141 static void do_spilling(ir_nodeset_t *live_nodes, ir_node *node)
143 size_t n_live_nodes = ir_nodeset_size(live_nodes);
144 size_t values_defined = 0;
145 size_t free_regs_needed = 0;
146 spill_candidate_t *candidates;
147 ir_nodeset_iterator_t iter;
153 /* mode_T nodes define several values at once. Count them */
154 if(get_irn_mode(node) == mode_T) {
155 const ir_edge_t *edge;
157 foreach_out_edge(node, edge) {
158 const ir_node *proj = get_edge_src_irn(edge);
160 if (arch_irn_consider_in_reg_alloc(cls, proj)) {
164 } else if (arch_irn_consider_in_reg_alloc(cls, node)) {
168 /* we need registers for the non-live argument values */
169 arity = get_irn_arity(node);
170 for(i = 0; i < arity; ++i) {
171 ir_node *pred = get_irn_n(node, i);
172 if (arch_irn_consider_in_reg_alloc(cls, pred)
173 && !ir_nodeset_contains(live_nodes, pred)) {
178 /* we can reuse all reloaded values for the defined values, but we might
179 need even more registers */
180 if(values_defined > free_regs_needed)
181 free_regs_needed = values_defined;
183 spills_needed = (n_live_nodes + free_regs_needed) - n_regs;
184 if(spills_needed <= 0)
186 DBG((dbg, LEVEL_2, "\tspills needed after %+F: %d\n", node, spills_needed));
188 candidates = alloca(n_live_nodes * sizeof(candidates[0]));
190 /* construct array with spill candidates and calculate their costs */
192 foreach_ir_nodeset(live_nodes, n, iter) {
193 spill_candidate_t *candidate = & candidates[i];
195 assert(!bitset_is_set(spilled_nodes, get_irn_idx(n)));
198 candidate->costs = get_spill_costs(n);
201 assert(i == n_live_nodes);
203 /* sort spill candidates */
204 qsort(candidates, n_live_nodes, sizeof(candidates[0]),
205 compare_spill_candidates_desc);
207 /* spill cheapest ones */
209 while(spills_needed > 0) {
210 spill_candidate_t *candidate;
214 if (cand_idx >= n_live_nodes) {
215 panic("can't spill enough values for node %+F", node);
219 candidate = &candidates[cand_idx];
220 cand_node = candidate->node;
223 if (arch_irn_is(cand_node, dont_spill))
226 /* make sure the node is not an argument of the instruction */
228 for (i = 0; i < arity; ++i) {
229 ir_node *in = get_irn_n(node, i);
230 if(in == cand_node) {
239 spill_node(cand_node);
240 ir_nodeset_remove(live_nodes, cand_node);
246 * removes all values from the nodeset that are defined by node
248 static void remove_defs(ir_node *node, ir_nodeset_t *nodeset)
250 /* You should better break out of your loop when hitting the first phi
252 assert(!is_Phi(node) && "liveness_transfer produces invalid results for phi nodes");
254 if (get_irn_mode(node) == mode_T) {
255 const ir_edge_t *edge;
257 foreach_out_edge(node, edge) {
258 const ir_node *proj = get_edge_src_irn(edge);
260 if (arch_irn_consider_in_reg_alloc(cls, proj)) {
261 ir_nodeset_remove(nodeset, proj);
266 if (arch_irn_consider_in_reg_alloc(cls, node)) {
267 ir_nodeset_remove(nodeset, node);
271 static void add_uses(ir_node *node, ir_nodeset_t *nodeset)
275 arity = get_irn_arity(node);
276 for(i = 0; i < arity; ++i) {
277 ir_node *op = get_irn_n(node, i);
279 if (arch_irn_consider_in_reg_alloc(cls, op) &&
280 !bitset_is_set(spilled_nodes, get_irn_idx(op))) {
281 ir_nodeset_insert(nodeset, op);
286 static __attribute__((unused))
287 void print_nodeset(ir_nodeset_t *nodeset)
289 ir_nodeset_iterator_t iter;
292 foreach_ir_nodeset(nodeset, node, iter) {
293 ir_fprintf(stderr, "%+F ", node);
295 fprintf(stderr, "\n");
299 * make sure register pressure in a block is always equal or below the number
300 * of available registers
302 static void spill_block(ir_node *block, void *data)
304 ir_nodeset_t live_nodes;
305 ir_nodeset_iterator_t iter;
307 int n_phi_values_spilled;
309 int phi_spills_needed;
312 DBG((dbg, LEVEL_1, "spilling block %+F\n", block));
314 /* construct set of live nodes at end of block */
315 ir_nodeset_init(&live_nodes);
316 be_liveness_end_of_block(lv, cls, block, &live_nodes);
318 /* remove already spilled nodes from liveset */
319 foreach_ir_nodeset(&live_nodes, node, iter) {
320 DBG((dbg, LEVEL_2, "\t%+F is live-end... ", node));
321 if(bitset_is_set(spilled_nodes, get_irn_idx(node))) {
322 DBG((dbg, LEVEL_2, "but spilled; removing.\n"));
323 ir_nodeset_remove_iterator(&live_nodes, &iter);
325 DBG((dbg, LEVEL_2, "keeping.\n"));
329 /* walk schedule backwards and spill until register pressure is fine at
331 sched_foreach_reverse(block, node) {
335 remove_defs(node, &live_nodes);
336 do_spilling(&live_nodes, node);
337 add_uses(node, &live_nodes);
340 /* until now only the values of some phis have been spilled the phis itself
341 * are still there and occupy registers, so we need to count them and might
342 * have to spill some of them.
344 n_phi_values_spilled = 0;
345 sched_foreach(block, node) {
349 if(bitset_is_set(spilled_nodes, get_irn_idx(node))) {
350 ++n_phi_values_spilled;
354 /* calculate how many of the phis need to be spilled */
355 regpressure = ir_nodeset_size(&live_nodes) + n_phi_values_spilled;
356 phi_spills_needed = regpressure - n_regs;
357 DBG((dbg, LEVEL_3, "Regpressure before phis: %d phispills: %d\n",
358 regpressure, phi_spills_needed));
360 /* spill as many phis as needed */
361 /* TODO: we should really estimate costs of the phi spill as well...
362 * and preferably spill phis with lower costs... */
363 sched_foreach(block, node) {
366 if(phi_spills_needed <= 0)
369 if(bitset_is_set(spilled_nodes, get_irn_idx(node))) {
370 be_spill_phi(spill_env, node);
374 assert(phi_spills_needed <= 0);
376 ir_nodeset_destroy(&live_nodes);
379 void be_spill_daemel(be_irg_t *birg, const arch_register_class_t *new_cls)
381 ir_graph *irg = be_get_birg_irg(birg);
382 n_regs = new_cls->n_regs - be_put_ignore_regs(birg, new_cls, NULL);
387 be_liveness_assure_sets(be_assure_liveness(birg));
389 spill_env = be_new_spill_env(birg);
391 lv = be_get_birg_liveness(birg);
392 spilled_nodes = bitset_malloc(get_irg_last_idx(irg));
394 DBG((dbg, LEVEL_1, "*** RegClass %s\n", cls->name));
396 irg_block_walk_graph(irg, spill_block, NULL, NULL);
398 bitset_free(spilled_nodes);
399 spilled_nodes = NULL;
401 be_insert_spills_reloads(spill_env);
403 be_delete_spill_env(spill_env);
407 void be_init_daemelspill(void)
409 static be_spiller_t daemel_spiller = {
413 be_register_spiller("daemel", &daemel_spiller);
414 FIRM_DBG_REGISTER(dbg, "firm.be.spilldaemel");
417 BE_REGISTER_MODULE_CONSTRUCTOR(be_init_daemelspill);