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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 values_defined = 0;
145 be_foreach_definition(node, cls, value,
146 assert(req_->width >= 1);
147 values_defined += req_->width;
150 /* we need registers for the non-live argument values */
151 size_t free_regs_needed = 0;
152 int arity = get_irn_arity(node);
153 for (int i = 0; i < arity; ++i) {
154 ir_node *pred = get_irn_n(node, i);
155 if (arch_irn_consider_in_reg_alloc(cls, pred)
156 && !ir_nodeset_contains(live_nodes, pred)) {
157 free_regs_needed += get_value_width(pred);
161 /* we can reuse all reloaded values for the defined values, but we might
162 * need even more registers */
163 if (values_defined > free_regs_needed)
164 free_regs_needed = values_defined;
166 size_t n_live_nodes = ir_nodeset_size(live_nodes);
167 int spills_needed = (n_live_nodes + free_regs_needed) - n_regs;
168 if (spills_needed <= 0)
170 DBG((dbg, LEVEL_2, "\tspills needed after %+F: %d\n", node, spills_needed));
172 spill_candidate_t *candidates = ALLOCAN(spill_candidate_t, n_live_nodes);
174 /* construct array with spill candidates and calculate their costs */
176 foreach_ir_nodeset(live_nodes, n, iter) {
177 spill_candidate_t *candidate = & candidates[c];
179 assert(!bitset_is_set(spilled_nodes, get_irn_idx(n)));
182 candidate->costs = get_spill_costs(n);
185 assert(c == n_live_nodes);
187 /* sort spill candidates */
188 qsort(candidates, n_live_nodes, sizeof(candidates[0]),
189 compare_spill_candidates_desc);
191 /* spill cheapest ones */
193 while (spills_needed > 0) {
194 if (cand_idx >= n_live_nodes) {
195 panic("can't spill enough values for node %+F", node);
198 spill_candidate_t *candidate = &candidates[cand_idx];
199 ir_node *cand_node = candidate->node;
202 if (arch_irn_is(skip_Proj_const(cand_node), dont_spill))
205 /* make sure the node is not an argument of the instruction */
207 for (int i = 0; i < arity; ++i) {
208 ir_node *in = get_irn_n(node, i);
209 if (in == cand_node) {
217 spill_node(cand_node);
218 ir_nodeset_remove(live_nodes, cand_node);
219 spills_needed -= get_value_width(cand_node);
224 * removes all values from the nodeset that are defined by node
226 static void remove_defs(ir_node *node, ir_nodeset_t *nodeset)
228 /* You must break out of your loop when hitting the first phi function. */
229 assert(!is_Phi(node));
232 be_foreach_definition(node, cls, value,
233 ir_nodeset_remove(nodeset, value);
237 static void add_uses(ir_node *node, ir_nodeset_t *nodeset)
239 int arity = get_irn_arity(node);
240 for (int i = 0; i < arity; ++i) {
241 ir_node *op = get_irn_n(node, i);
243 if (arch_irn_consider_in_reg_alloc(cls, op) &&
244 !bitset_is_set(spilled_nodes, get_irn_idx(op))) {
245 ir_nodeset_insert(nodeset, op);
250 static __attribute__((unused))
251 void print_nodeset(ir_nodeset_t *nodeset)
253 foreach_ir_nodeset(nodeset, node, iter) {
254 ir_fprintf(stderr, "%+F ", node);
256 fprintf(stderr, "\n");
260 * make sure register pressure in a block is always equal or below the number
261 * of available registers
263 static void spill_block(ir_node *block, void *data)
266 DBG((dbg, LEVEL_1, "spilling block %+F\n", block));
268 /* construct set of live nodes at end of block */
269 ir_nodeset_t live_nodes;
270 ir_nodeset_init(&live_nodes);
271 be_liveness_end_of_block(lv, cls, block, &live_nodes);
273 /* remove already spilled nodes from liveset */
274 foreach_ir_nodeset(&live_nodes, node, iter) {
275 DBG((dbg, LEVEL_2, "\t%+F is live-end... ", node));
276 if (bitset_is_set(spilled_nodes, get_irn_idx(node))) {
277 DBG((dbg, LEVEL_2, "but spilled; removing.\n"));
278 ir_nodeset_remove_iterator(&live_nodes, &iter);
280 DBG((dbg, LEVEL_2, "keeping.\n"));
284 /* walk schedule backwards and spill until register pressure is fine at
286 sched_foreach_reverse(block, node) {
290 remove_defs(node, &live_nodes);
291 do_spilling(&live_nodes, node);
292 add_uses(node, &live_nodes);
295 /* until now only the values of some phis have been spilled the phis itself
296 * are still there and occupy registers, so we need to count them and might
297 * have to spill some of them. */
298 int n_phi_values_spilled = 0;
299 sched_foreach(block, node) {
303 if (bitset_is_set(spilled_nodes, get_irn_idx(node))) {
304 n_phi_values_spilled += get_value_width(node);
308 int live_nodes_pressure = 0;
309 foreach_ir_nodeset(&live_nodes, node, iter) {
310 live_nodes_pressure += get_value_width(node);
313 /* calculate how many of the phis need to be spilled */
314 int regpressure = live_nodes_pressure + n_phi_values_spilled;
315 int phi_spills_needed = regpressure - n_regs;
316 DBG((dbg, LEVEL_3, "Regpressure before phis: %d phispills: %d\n",
317 regpressure, phi_spills_needed));
319 /* spill as many phis as needed */
320 /* TODO: we should really estimate costs of the phi spill as well...
321 * and preferably spill phis with lower costs... */
322 sched_foreach(block, node) {
325 if (phi_spills_needed <= 0)
328 if (!bitset_is_set(spilled_nodes, get_irn_idx(node)))
331 be_spill_phi(spill_env, node);
332 phi_spills_needed -= get_value_width(node);
334 assert(phi_spills_needed <= 0);
336 ir_nodeset_destroy(&live_nodes);
339 static void be_spill_daemel(ir_graph *irg, const arch_register_class_t *new_cls)
341 n_regs = be_get_n_allocatable_regs(irg, new_cls);
345 be_assure_live_sets(irg);
347 spill_env = be_new_spill_env(irg);
349 lv = be_get_irg_liveness(irg);
350 spilled_nodes = bitset_malloc(get_irg_last_idx(irg));
352 DBG((dbg, LEVEL_1, "*** RegClass %s\n", cls->name));
354 irg_block_walk_graph(irg, spill_block, NULL, NULL);
356 bitset_free(spilled_nodes);
358 be_insert_spills_reloads(spill_env);
359 be_delete_spill_env(spill_env);
362 BE_REGISTER_MODULE_CONSTRUCTOR(be_init_daemelspill)
363 void be_init_daemelspill(void)
365 static be_spiller_t daemel_spiller = {
369 be_register_spiller("daemel", &daemel_spiller);
370 FIRM_DBG_REGISTER(dbg, "firm.be.spilldaemel");