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4 * This file is part of libFirm.
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15 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
16 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * @brief Naive spilling algorithm
23 * @author Matthias Braun
26 * This implements a naive spilling algorithm. It is designed to produce
27 * similar effects to the spill decisions produced by traditional graph
28 * coloring register allocators that spill while they are coloring the graph.
30 * This spiller walks over all blocks and looks for places with too high
31 * register pressure where it spills the values that are cheapest to spill.
32 * Spilling in this context means placing a spill instruction behind the
33 * definition of the value and a reload before each usage.
39 #include "irnodeset.h"
42 #include "iredges_t.h"
47 #include "bespillutil.h"
56 DEBUG_ONLY(static firm_dbg_module_t *dbg = NULL;)
58 static spill_env_t *spill_env;
59 static unsigned n_regs;
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 = (const spill_candidate_t*)d1;
73 const spill_candidate_t *c2 = (const spill_candidate_t*)d2;
75 return (int) (c1->costs - c2->costs);
78 static double get_spill_costs(ir_node *node)
80 ir_node *spill_place = skip_Proj(node);
81 double costs = be_get_spill_costs(spill_env, node, spill_place);
83 foreach_out_edge(node, edge) {
84 ir_node *use = get_edge_src_irn(edge);
86 /* keeps should be directly below the node */
87 if (be_is_Keep(use)) {
92 int in = get_edge_src_pos(edge);
93 ir_node *block = get_nodes_block(use);
95 costs += be_get_reload_costs_on_edge(spill_env, node, block, in);
97 costs += be_get_reload_costs(spill_env, node, use);
105 * spills a node by placing a reload before each usage
107 static void spill_node(ir_node *node)
109 DBG((dbg, LEVEL_3, "\tspilling %+F\n", node));
111 foreach_out_edge(node, edge) {
112 ir_node *use = get_edge_src_irn(edge);
119 int in = get_edge_src_pos(edge);
120 ir_node *block = get_nodes_block(use);
122 be_add_reload_on_edge(spill_env, node, block, in, cls, 1);
124 be_add_reload(spill_env, node, use, cls, 1);
128 bitset_set(spilled_nodes, get_irn_idx(node));
131 static unsigned get_value_width(const ir_node *node)
133 const arch_register_req_t *req = arch_get_irn_register_req(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;
153 be_foreach_definition(node, cls, value,
154 assert(req_->width >= 1);
155 values_defined += req_->width;
158 /* we need registers for the non-live argument values */
159 arity = get_irn_arity(node);
160 for (i = 0; i < arity; ++i) {
161 ir_node *pred = get_irn_n(node, i);
162 if (arch_irn_consider_in_reg_alloc(cls, pred)
163 && !ir_nodeset_contains(live_nodes, pred)) {
164 free_regs_needed += get_value_width(pred);
168 /* we can reuse all reloaded values for the defined values, but we might
169 * need even more registers */
170 if (values_defined > free_regs_needed)
171 free_regs_needed = values_defined;
173 spills_needed = (n_live_nodes + free_regs_needed) - n_regs;
174 if (spills_needed <= 0)
176 DBG((dbg, LEVEL_2, "\tspills needed after %+F: %d\n", node, spills_needed));
178 candidates = ALLOCAN(spill_candidate_t, n_live_nodes);
180 /* construct array with spill candidates and calculate their costs */
182 foreach_ir_nodeset(live_nodes, n, iter) {
183 spill_candidate_t *candidate = & candidates[c];
185 assert(!bitset_is_set(spilled_nodes, get_irn_idx(n)));
188 candidate->costs = get_spill_costs(n);
191 assert(c == n_live_nodes);
193 /* sort spill candidates */
194 qsort(candidates, n_live_nodes, sizeof(candidates[0]),
195 compare_spill_candidates_desc);
197 /* spill cheapest ones */
199 while (spills_needed > 0) {
201 spill_candidate_t *candidate;
204 if (cand_idx >= n_live_nodes) {
205 panic("can't spill enough values for node %+F", node);
208 candidate = &candidates[cand_idx];
209 cand_node = candidate->node;
212 if (arch_irn_is(skip_Proj_const(cand_node), dont_spill))
215 /* make sure the node is not an argument of the instruction */
216 for (i = 0; i < arity; ++i) {
217 ir_node *in = get_irn_n(node, i);
218 if (in == cand_node) {
226 spill_node(cand_node);
227 ir_nodeset_remove(live_nodes, cand_node);
228 spills_needed -= get_value_width(cand_node);
233 * removes all values from the nodeset that are defined by node
235 static void remove_defs(ir_node *node, ir_nodeset_t *nodeset)
238 /* You must break out of your loop when hitting the first phi function. */
239 assert(!is_Phi(node));
241 be_foreach_definition(node, cls, value,
242 ir_nodeset_remove(nodeset, value);
246 static void add_uses(ir_node *node, ir_nodeset_t *nodeset)
250 arity = get_irn_arity(node);
251 for (i = 0; i < arity; ++i) {
252 ir_node *op = get_irn_n(node, i);
254 if (arch_irn_consider_in_reg_alloc(cls, op) &&
255 !bitset_is_set(spilled_nodes, get_irn_idx(op))) {
256 ir_nodeset_insert(nodeset, op);
261 static __attribute__((unused))
262 void print_nodeset(ir_nodeset_t *nodeset)
264 foreach_ir_nodeset(nodeset, node, iter) {
265 ir_fprintf(stderr, "%+F ", node);
267 fprintf(stderr, "\n");
271 * make sure register pressure in a block is always equal or below the number
272 * of available registers
274 static void spill_block(ir_node *block, void *data)
276 ir_nodeset_t live_nodes;
277 int n_phi_values_spilled;
279 int live_nodes_pressure;
280 int phi_spills_needed;
283 DBG((dbg, LEVEL_1, "spilling block %+F\n", block));
285 /* construct set of live nodes at end of block */
286 ir_nodeset_init(&live_nodes);
287 be_liveness_end_of_block(lv, cls, block, &live_nodes);
289 /* remove already spilled nodes from liveset */
290 foreach_ir_nodeset(&live_nodes, node, iter) {
291 DBG((dbg, LEVEL_2, "\t%+F is live-end... ", node));
292 if (bitset_is_set(spilled_nodes, get_irn_idx(node))) {
293 DBG((dbg, LEVEL_2, "but spilled; removing.\n"));
294 ir_nodeset_remove_iterator(&live_nodes, &iter);
296 DBG((dbg, LEVEL_2, "keeping.\n"));
300 /* walk schedule backwards and spill until register pressure is fine at
302 sched_foreach_reverse(block, node) {
306 remove_defs(node, &live_nodes);
307 do_spilling(&live_nodes, node);
308 add_uses(node, &live_nodes);
311 /* until now only the values of some phis have been spilled the phis itself
312 * are still there and occupy registers, so we need to count them and might
313 * have to spill some of them. */
314 n_phi_values_spilled = 0;
315 sched_foreach(block, node) {
319 if (bitset_is_set(spilled_nodes, get_irn_idx(node))) {
320 n_phi_values_spilled += get_value_width(node);
324 live_nodes_pressure = 0;
325 foreach_ir_nodeset(&live_nodes, node, iter) {
326 live_nodes_pressure += get_value_width(node);
329 /* calculate how many of the phis need to be spilled */
330 regpressure = live_nodes_pressure + n_phi_values_spilled;
331 phi_spills_needed = regpressure - n_regs;
332 DBG((dbg, LEVEL_3, "Regpressure before phis: %d phispills: %d\n",
333 regpressure, phi_spills_needed));
335 /* spill as many phis as needed */
336 /* TODO: we should really estimate costs of the phi spill as well...
337 * and preferably spill phis with lower costs... */
338 sched_foreach(block, node) {
341 if (phi_spills_needed <= 0)
344 if (!bitset_is_set(spilled_nodes, get_irn_idx(node)))
347 be_spill_phi(spill_env, node);
348 phi_spills_needed -= get_value_width(node);
350 assert(phi_spills_needed <= 0);
352 ir_nodeset_destroy(&live_nodes);
355 static void be_spill_daemel(ir_graph *irg, const arch_register_class_t *new_cls)
357 n_regs = be_get_n_allocatable_regs(irg, new_cls);
361 be_assure_live_sets(irg);
363 spill_env = be_new_spill_env(irg);
365 lv = be_get_irg_liveness(irg);
366 spilled_nodes = bitset_malloc(get_irg_last_idx(irg));
368 DBG((dbg, LEVEL_1, "*** RegClass %s\n", cls->name));
370 irg_block_walk_graph(irg, spill_block, NULL, NULL);
372 bitset_free(spilled_nodes);
374 be_insert_spills_reloads(spill_env);
375 be_delete_spill_env(spill_env);
378 BE_REGISTER_MODULE_CONSTRUCTOR(be_init_daemelspill)
379 void be_init_daemelspill(void)
381 static be_spiller_t daemel_spiller = {
385 be_register_spiller("daemel", &daemel_spiller);
386 FIRM_DBG_REGISTER(dbg, "firm.be.spilldaemel");