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22 * @brief modifies schedule so flags dependencies are respected.
23 * @author Matthias Braun, Christoph Mallon
24 * @version $Id: besched.h 14693 2007-06-21 15:35:49Z beck $
26 * Fixup schedule to respect flag constraints by moving and rematerialisation of
29 * Flags are modeled as register classes with ignore registers. However to avoid
30 * bloating the graph, only flag-consumer -> producer dependencies are
31 * explicitely modeled in the graph. Nodes that just change the flags are only
32 * marked with the arch_irn_flags_modify_flags flag.
34 * Flags are usually a limited resource that can't (or at least shouldn't) be
35 * spilled. So in some situations (for example 2 adc-nodes that use the flags of
36 * a single add node on x86) operations have to be repeated to work correctly.
46 #include "iredges_t.h"
57 static const arch_register_class_t *flag_class;
58 static const arch_register_t *flags_reg;
59 static func_rematerialize remat;
60 static check_modifies_flags check_modify;
63 static ir_node *default_remat(ir_node *node, ir_node *after)
65 ir_node *block, *copy;
69 block = get_nodes_block(after);
71 copy = exact_copy(node);
72 set_nodes_block(copy, block);
73 sched_add_after(after, copy);
78 static bool default_check_modifies(const ir_node *node)
80 return arch_irn_is(node, modify_flags);
84 * tests whether we can legally move node node after node after
85 * (only works for nodes in same block)
87 static bool can_move(ir_node *node, ir_node *after)
89 const ir_edge_t *edge;
90 ir_node *node_block = get_nodes_block(node);
91 assert(node_block == get_nodes_block(after));
93 /* TODO respect dep edges */
94 assert(get_irn_n_edges_kind(node, EDGE_KIND_DEP) == 0);
96 /** all users have to be after the after node */
97 foreach_out_edge(node, edge) {
98 ir_node *out = get_edge_src_irn(edge);
100 const ir_edge_t *edge2;
101 assert(get_irn_n_edges_kind(out, EDGE_KIND_DEP) == 0);
102 foreach_out_edge(out, edge2) {
103 ir_node *out2 = get_edge_src_irn(edge2);
104 if (get_nodes_block(out2) != node_block)
106 /* Phi or End represents a usage at block end. */
107 if (is_Phi(out2) || is_End(out2))
110 const ir_edge_t *edge3;
111 foreach_out_edge(out2, edge3) {
112 ir_node *out3 = get_edge_src_irn(edge3);
113 /* Phi or End represents a usage at block end. */
114 if (is_Phi(out3) || is_End(out3))
116 assert(!is_Sync(out3));
117 if (sched_get_time_step(out3) <= sched_get_time_step(after)) {
121 } else if (sched_get_time_step(out2) <= sched_get_time_step(after)) {
126 if (get_nodes_block(out) != node_block)
128 /* phi represents a usage at block end */
131 if (sched_get_time_step(out) <= sched_get_time_step(after)) {
140 static void rematerialize_or_move(ir_node *flags_needed, ir_node *node,
141 ir_node *flag_consumers, int pn)
147 if (!is_Block(node) &&
148 get_nodes_block(flags_needed) == get_nodes_block(node) &&
149 can_move(flags_needed, node)) {
151 sched_remove(flags_needed);
152 sched_add_after(node, flags_needed);
153 /* No need to update liveness, because the node stays in the same block */
158 copy = remat(flags_needed, node);
160 if (get_irn_mode(copy) == mode_T) {
161 ir_mode *mode = flag_class->mode;
162 value = new_rd_Proj(NULL, copy, mode, pn);
170 int arity = get_irn_arity(n);
171 for (i = 0; i < arity; ++i) {
172 ir_node *in = get_irn_n(n, i);
174 if (in == flags_needed) {
175 set_irn_n(n, i, value);
179 n = (ir_node*)get_irn_link(n);
182 /* No need to introduce the copy, because it only lives in this block, but
183 * we have to update the liveness of all operands */
184 if (is_Block(node) ||
185 get_nodes_block(node) != get_nodes_block(flags_needed)) {
186 ir_graph *irg = get_irn_irg(node);
187 be_lv_t *lv = be_get_irg_liveness(irg);
191 for (i = get_irn_arity(copy) - 1; i >= 0; --i) {
192 be_liveness_update(lv, get_irn_n(copy, i));
199 * walks up the schedule and makes sure there are no flag-destroying nodes
200 * between a flag-consumer -> flag-producer chain. Fixes problematic situations
201 * by moving and/or rematerialisation of the flag-producers.
202 * (This can be extended in the future to do some register allocation on targets
203 * like ppc32 where we conceptually have 8 flag registers)
205 static void fix_flags_walker(ir_node *block, void *env)
208 ir_node *flags_needed = NULL;
209 ir_node *flag_consumers = NULL;
213 sched_foreach_reverse(block, node) {
215 ir_node *new_flags_needed = NULL;
221 if (node == flags_needed) {
224 flag_consumers = NULL;
227 /* test whether node destroys the flags */
229 if (be_is_Keep(test))
230 test = sched_prev(test);
232 if (flags_needed != NULL && check_modify(test)) {
234 rematerialize_or_move(flags_needed, node, flag_consumers, pn);
236 flag_consumers = NULL;
239 /* test whether the current node needs flags */
240 arity = get_irn_arity(node);
241 for (i = 0; i < arity; ++i) {
242 const arch_register_class_t *cls = arch_get_irn_reg_class(node, i);
243 if (cls == flag_class) {
244 assert(new_flags_needed == NULL);
245 new_flags_needed = get_irn_n(node, i);
249 if (new_flags_needed == NULL)
252 /* spiller can't (correctly) remat flag consumers at the moment */
253 assert(!arch_irn_is(node, rematerializable));
255 if (skip_Proj(new_flags_needed) != flags_needed) {
256 if (flags_needed != NULL) {
257 /* rematerialize node */
258 rematerialize_or_move(flags_needed, node, flag_consumers, pn);
260 flag_consumers = NULL;
263 flags_needed = new_flags_needed;
264 arch_set_irn_register(flags_needed, flags_reg);
265 if (is_Proj(flags_needed)) {
266 pn = get_Proj_proj(flags_needed);
267 flags_needed = get_Proj_pred(flags_needed);
269 flag_consumers = node;
270 set_irn_link(flag_consumers, NULL);
271 assert(arch_irn_is(flags_needed, rematerializable));
273 /* link all consumers in a list */
274 set_irn_link(node, flag_consumers);
275 flag_consumers = node;
279 if (flags_needed != NULL) {
280 assert(get_nodes_block(flags_needed) != block);
281 rematerialize_or_move(flags_needed, node, flag_consumers, pn);
283 flag_consumers = NULL;
286 assert(flags_needed == NULL);
287 assert(flag_consumers == NULL);
290 void be_sched_fix_flags(ir_graph *irg, const arch_register_class_t *flag_cls,
291 func_rematerialize remat_func,
292 check_modifies_flags check_modifies_flags_func)
294 flag_class = flag_cls;
295 flags_reg = & flag_class->regs[0];
297 check_modify = check_modifies_flags_func;
300 remat = &default_remat;
301 if (check_modify == NULL)
302 check_modify = &default_check_modifies;
304 ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK);
305 irg_block_walk_graph(irg, fix_flags_walker, NULL, NULL);
306 ir_free_resources(irg, IR_RESOURCE_IRN_LINK);
309 be_remove_dead_nodes_from_schedule(irg);