2 * Copyright (C) 1995-2008 University of Karlsruhe. All right reserved.
4 * This file is part of libFirm.
6 * This file may be distributed and/or modified under the terms of the
7 * GNU General Public License version 2 as published by the Free Software
8 * Foundation and appearing in the file LICENSE.GPL included in the
9 * packaging of this file.
11 * Licensees holding valid libFirm Professional Edition licenses may use
12 * this file in accordance with the libFirm Commercial License.
13 * Agreement provided with the Software.
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 Control flow optimizations.
23 * @author Goetz Lindenmaier, Michael Beck, Sebastian Hack
26 * Removes Bad control flow predecessors and empty blocks. A block is empty
27 * if it contains only a Jmp node. Blocks can only be removed if they are not
28 * needed for the semantics of Phi nodes. Further, we NEVER remove labeled
29 * blocks (even if we could move the label).
33 #include "iroptimize.h"
40 #include "irgraph_t.h"
54 #include "irbackedge_t.h"
59 #include "irphase_t.h"
61 #include "iropt_dbg.h"
63 /** An environment for merge_blocks and collect nodes. */
64 typedef struct merge_env {
65 bool changed; /**< Set if the graph was changed. */
66 bool phis_moved; /**< Set if Phi nodes were moved. */
69 static void set_Block_removable(ir_node *block, bool removable)
71 set_Block_mark(block, removable);
74 static bool is_Block_removable(ir_node *block)
76 return get_Block_mark(block);
79 static bool is_switch_Cond(ir_node *cond) {
80 ir_node *sel = get_Cond_selector(cond);
81 return get_irn_mode(sel) != mode_b;
84 static void clear_link(ir_node *node, void *ctx)
87 set_irn_link(node, NULL);
89 set_Block_removable(node, true);
93 * Collects all Phi nodes in link list of Block.
94 * Marks all blocks "non_removable" if they contain a node other
95 * than Jmp (and Proj).
96 * Links all Proj nodes to their predecessors.
97 * Collects all switch-Conds in a list.
99 static void collect_nodes(ir_node *n, void *ctx)
101 ir_node ***switch_conds = (ir_node***)ctx;
104 /* Collect Phi nodes to compact ins along with block's ins. */
105 ir_node *block = get_nodes_block(n);
106 set_irn_link(n, get_irn_link(block));
107 set_irn_link(block, n);
108 } else if (is_Block(n)) {
109 if (has_Block_entity(n))
110 set_Block_removable(n, false);
112 } else if (!is_Jmp(n)) { /* Check for non-empty block. */
113 ir_node *block = get_nodes_block(n);
114 set_Block_removable(block, false);
117 /* link Proj nodes */
118 ir_node *pred = get_Proj_pred(n);
119 set_irn_link(n, get_irn_link(pred));
120 set_irn_link(pred, n);
121 } else if (is_Cond(n) && is_switch_Cond(n)) {
122 /* found a switch-Cond, collect */
123 ARR_APP1(ir_node*, *switch_conds, n);
128 /** Returns true if pred is predecessor of block. */
129 static bool is_pred_of(ir_node *pred, ir_node *b)
133 for (i = get_Block_n_cfgpreds(b) - 1; i >= 0; --i) {
134 ir_node *b_pred = get_Block_cfgpred_block(b, i);
141 /** Test whether we can optimize away pred block pos of b.
143 * @param b A block node.
144 * @param pos The position of the predecessor block to judge about.
146 * @returns The number of predecessors
148 * The test is rather tricky.
150 * The situation is something like the following:
159 * b merges the control flow of an if-then-else. We may not remove
160 * the 'then' _and_ the 'else' block of an 'if' if there is a Phi
161 * node in b, even if both are empty. The destruction of this Phi
162 * requires that a copy is added before the merge. We have to
163 * keep one of the case blocks to place the copies in.
165 * To perform the test for pos, we must regard predecessors before pos
166 * as already removed.
168 static unsigned test_whether_dispensable(ir_node *b, int pos)
170 ir_node *pred = get_Block_cfgpred(b, pos);
171 ir_node *predb = get_nodes_block(pred);
173 if (is_Bad(pred) || !is_Block_removable(predb))
176 /* can't remove self-loops */
178 goto non_dispensable;
179 if (is_unknown_jump(pred))
180 goto non_dispensable;
182 /* Seems to be empty. At least we detected this in collect_nodes. */
183 if (get_irn_link(b) != NULL) {
184 int n_cfgpreds = get_Block_n_cfgpreds(b);
186 /* there are Phi nodes */
188 /* b's pred blocks and pred's pred blocks must be pairwise disjunct.
189 * Handle all pred blocks with preds < pos as if they were already
191 for (i = 0; i < pos; i++) {
192 ir_node *other_pred = get_Block_cfgpred(b, i);
193 ir_node *other_predb = get_nodes_block(other_pred);
194 if (is_Bad(other_pred))
196 if (is_Block_removable(other_predb)
197 && !Block_block_visited(other_predb)) {
199 for (j = get_Block_n_cfgpreds(other_predb) - 1; j >= 0; --j) {
200 ir_node *other_predpred
201 = get_Block_cfgpred_block(other_predb, j);
202 if (is_pred_of(other_predpred, predb))
203 goto non_dispensable;
205 } else if (is_pred_of(other_predb, predb)) {
206 goto non_dispensable;
209 for (i = pos+1; i < n_cfgpreds; i++) {
210 ir_node *other_predb = get_Block_cfgpred_block(b, i);
211 if (is_pred_of(other_predb, predb))
212 goto non_dispensable;
215 /* we will not dispense already visited blocks */
216 if (Block_block_visited(predb))
218 /* if we get here, the block is dispensable, count useful preds */
219 return get_irn_arity(predb);
222 set_Block_removable(predb, false);
227 * This method removes empty blocks. A block is empty if it only contains Phi
230 * We first adapt Phi nodes, then Block nodes, as we need the old ins
231 * of the Block to adapt the Phi nodes. We do this by computing new
232 * in arrays, and then replacing the old ones. So far we compute new in arrays
233 * for all nodes, not regarding whether there is a possibility for optimization.
235 * For each predecessor p of a Block b there are three cases:
236 * - The predecessor p is a Bad node: just skip it. The in array of b shrinks
238 * - The predecessor p is empty. Remove p. All predecessors of p are now
240 * - The predecessor p is a block containing useful code. Just keep p as is.
242 * For Phi nodes f we have to check the conditions at the Block of f.
243 * For cases 1 and 3 we proceed as for Blocks. For case 2 we can have two
245 * -2a: The old predecessor of the Phi f is a Phi pred_f IN THE BLOCK REMOVED.
246 * In this case we proceed as for blocks. We remove pred_f. All
247 * predecessors of pred_f now are predecessors of f.
248 * -2b: The old predecessor of f is NOT in the block removed. It might be a Phi
249 * too. We have to replicate f for each predecessor of the removed block.
250 * Or, with other words, the removed predecessor block has exactly one
253 * Further there is a special case for self referencing blocks:
256 * then_b else_b then_b else_b
262 * | | | === optimized to ===> \ | | |
269 * If there is a Phi in pred_b, but we remove pred_b, we have to generate a
270 * Phi in loop_b, that has the ins of the Phi in pred_b and a self referencing
273 static void optimize_blocks(ir_node *b, void *ctx)
275 int i, j, k, n, max_preds, n_preds, p_preds = -1;
276 ir_node *pred, *phi, *next;
278 merge_env *env = (merge_env*)ctx;
280 /* Count the number of predecessor if this block is merged with pred blocks
283 for (i = 0, k = get_Block_n_cfgpreds(b); i < k; ++i) {
284 max_preds += test_whether_dispensable(b, i);
286 in = XMALLOCN(ir_node*, max_preds);
288 /*- Fix the Phi nodes of the current block -*/
289 for (phi = (ir_node*)get_irn_link(b); phi != NULL; phi = (ir_node*)next) {
291 next = (ir_node*)get_irn_link(phi);
293 /* Find the new predecessors for the Phi */
295 for (i = 0, n = get_Block_n_cfgpreds(b); i < n; ++i) {
296 ir_graph *irg = get_irn_irg(b);
297 pred = get_Block_cfgpred_block(b, i);
300 /* case Phi 1: maintain Bads, as somebody else is responsible to remove them */
301 in[p_preds++] = new_r_Bad(irg, get_irn_mode(phi));
302 } else if (is_Block_removable(pred) && !Block_block_visited(pred)) {
303 /* case Phi 2: It's an empty block and not yet visited. */
304 ir_node *phi_pred = get_Phi_pred(phi, i);
306 for (j = 0, k = get_Block_n_cfgpreds(pred); j < k; j++) {
307 ir_node *pred_pred = get_Block_cfgpred(pred, j);
309 if (is_Bad(pred_pred)) {
310 in[p_preds++] = new_r_Bad(irg, get_irn_mode(phi));
314 if (get_nodes_block(phi_pred) == pred) {
316 assert(is_Phi(phi_pred)); /* Block is empty!! */
318 in[p_preds++] = get_Phi_pred(phi_pred, j);
321 in[p_preds++] = phi_pred;
326 in[p_preds++] = get_Phi_pred(phi, i);
329 assert(p_preds == max_preds);
333 exchange(phi, in[0]);
335 set_irn_in(phi, p_preds, in);
339 /*- This happens only if merge between loop backedge and single loop entry.
340 Moreover, it is only needed if predb is the direct dominator of b,
341 else there can be no uses of the Phi's in predb ... -*/
342 for (k = 0, n = get_Block_n_cfgpreds(b); k < n; ++k) {
343 ir_node *pred = get_Block_cfgpred(b, k);
344 ir_node *predb = get_nodes_block(pred);
348 if (is_Block_removable(predb) && !Block_block_visited(predb)) {
351 /* we found a predecessor block at position k that will be removed */
352 for (phi = (ir_node*)get_irn_link(predb); phi; phi = next_phi) {
354 next_phi = (ir_node*)get_irn_link(phi);
358 if (get_Block_idom(b) != predb) {
359 /* predb is not the dominator. There can't be uses of pred's Phi nodes, kill them .*/
360 ir_graph *irg = get_irn_irg(b);
361 ir_mode *mode = get_irn_mode(phi);
362 exchange(phi, new_r_Bad(irg, mode));
364 /* predb is the direct dominator of b. There might be uses of the Phi nodes from
365 predb in further block, so move this phi from the predecessor into the block b */
366 set_nodes_block(phi, b);
367 set_irn_link(phi, get_irn_link(b));
368 set_irn_link(b, phi);
369 env->phis_moved = true;
371 /* first, copy all 0..k-1 predecessors */
372 for (i = 0; i < k; i++) {
373 pred = get_Block_cfgpred_block(b, i);
376 in[q_preds++] = pred;
377 } else if (is_Block_removable(pred) && !Block_block_visited(pred)) {
378 /* It's an empty block and not yet visited. */
379 for (j = 0; j < get_Block_n_cfgpreds(pred); j++) {
380 if (! is_Bad(get_Block_cfgpred(pred, j)))
388 /* now we are at k, copy the phi predecessors */
389 pred = get_nodes_block(get_Block_cfgpred(b, k));
390 for (i = 0; i < get_Phi_n_preds(phi); i++) {
391 in[q_preds++] = get_Phi_pred(phi, i);
394 /* and now all the rest */
395 for (i = k+1; i < get_Block_n_cfgpreds(b); i++) {
396 pred = get_Block_cfgpred_block(b, i);
399 ir_graph *irg = get_irn_irg(b);
400 ir_mode *mode = get_irn_mode(phi);
401 in[q_preds++] = new_r_Bad(irg, mode);
402 } else if (is_Block_removable(pred) && !Block_block_visited(pred)) {
403 /* It's an empty block and not yet visited. */
404 for (j = 0; j < get_Block_n_cfgpreds(pred); j++) {
405 if (! is_Bad(get_Block_cfgpred(pred, j)))
415 exchange(phi, in[0]);
417 set_irn_in(phi, q_preds, in);
420 assert(q_preds <= max_preds);
421 // assert(p_preds == q_preds && "Wrong Phi Fix");
427 /*- Fix the block -*/
429 for (i = 0; i < get_Block_n_cfgpreds(b); i++) {
430 ir_node *pred = get_Block_cfgpred(b, i);
431 ir_node *predb = get_nodes_block(pred);
432 ir_graph *irg = get_irn_irg(pred);
434 /* case 1: Bad predecessor */
436 in[n_preds++] = new_r_Bad(irg, mode_X);
439 if (is_Block_removable(predb) && !Block_block_visited(predb)) {
440 /* case 2: It's an empty block and not yet visited. */
441 for (j = 0; j < get_Block_n_cfgpreds(predb); j++) {
442 ir_node *predpred = get_Block_cfgpred(predb, j);
444 if (is_Bad(predpred)) {
445 in[n_preds++] = new_r_Bad(irg, mode_X);
449 in[n_preds++] = predpred;
451 /* Remove block+jump as it might be kept alive. */
452 exchange(pred, new_r_Bad(get_irn_irg(b), mode_X));
453 exchange(predb, new_r_Bad(get_irn_irg(b), mode_BB));
456 in[n_preds++] = pred;
459 assert(n_preds == max_preds);
461 set_irn_in(b, n_preds, in);
464 /* see if phi-fix was correct */
465 assert(get_irn_link(b) == NULL || p_preds == -1 || (n_preds == p_preds));
470 * Optimize table-switch Conds.
472 * @param cond the switch-Cond
473 * @return true if the switch-Cond was optimized
475 static bool handle_switch_cond(ir_node *cond)
477 ir_node *sel = get_Cond_selector(cond);
478 ir_node *proj1 = (ir_node*)get_irn_link(cond);
479 ir_node *proj2 = (ir_node*)get_irn_link(proj1);
480 ir_node *blk = get_nodes_block(cond);
482 /* exactly 1 Proj on the Cond node: must be the defaultProj */
484 ir_node *jmp = new_r_Jmp(blk);
485 assert(get_Cond_default_proj(cond) == get_Proj_proj(proj1));
486 /* convert it into a Jmp */
487 exchange(proj1, jmp);
491 /* handle Cond nodes with constant argument. In this case the localopt rules
492 * should have killed all obviously impossible cases.
493 * So the only case left to handle here is 1 defaultProj + 1case
494 * (this one case should be the one taken) */
495 if (get_irn_link(proj2) == NULL) {
496 ir_tarval *tv = value_of(sel);
498 if (tv != tarval_bad) {
499 /* we have a constant switch */
500 long num = get_tarval_long(tv);
501 long def_num = get_Cond_default_proj(cond);
502 ir_graph *irg = get_irn_irg(cond);
503 ir_node *bad = new_r_Bad(irg, mode_X);
505 if (def_num == get_Proj_proj(proj1)) {
506 /* first one is the defProj */
507 if (num == get_Proj_proj(proj2)) {
508 ir_node *jmp = new_r_Jmp(blk);
509 exchange(proj2, jmp);
510 exchange(proj1, bad);
513 } else if (def_num == get_Proj_proj(proj2)) {
514 /* second one is the defProj */
515 if (num == get_Proj_proj(proj1)) {
516 ir_node *jmp = new_r_Jmp(blk);
517 exchange(proj1, jmp);
518 exchange(proj2, bad);
522 /* neither: strange, Cond was not optimized so far */
523 if (num == get_Proj_proj(proj1)) {
524 ir_node *jmp = new_r_Jmp(blk);
525 exchange(proj1, jmp);
526 exchange(proj2, bad);
528 } else if (num == get_Proj_proj(proj2)) {
529 ir_node *jmp = new_r_Jmp(blk);
530 exchange(proj2, jmp);
531 exchange(proj1, bad);
540 static bool get_phase_flag(ir_phase *block_info, ir_node *block, int offset) {
541 return ((int)phase_get_irn_data(block_info, block)) & (1<<offset);
543 static void set_phase_flag(ir_phase *block_info, ir_node *block, int offset) {
544 int data = (int)phase_get_irn_data(block_info, block);
546 phase_set_irn_data(block_info, block, (void*)data);
549 static bool has_operations(ir_phase *block_info, ir_node *block) {
550 return get_phase_flag(block_info, block, 1);
552 static void set_has_operations(ir_phase *block_info, ir_node *block) {
553 set_phase_flag(block_info, block, 1);
556 static bool has_phis(ir_phase *block_info, ir_node *block) {
557 return get_phase_flag(block_info, block, 2);
559 static void set_has_phis(ir_phase *block_info, ir_node *block) {
560 set_phase_flag(block_info, block, 2);
563 static bool is_unknown_jump_target(ir_phase *block_info, ir_node *block) {
564 return get_phase_flag(block_info, block, 3);
566 static void set_is_unknown_jump_target(ir_phase *block_info, ir_node *block) {
567 set_phase_flag(block_info, block, 3);
571 * Optimize Conds, where true and false jump to the same block into a Jmp
575 * projA projB => Jmp Bad
579 static bool optimize_pred_cond(ir_node *block, int i, int j)
581 ir_node *projA, *projB, *cond, *pred_block, *jmp, *bad;
584 projA = get_Block_cfgpred(block, i);
585 if (!is_Proj(projA)) return false;
586 projB = get_Block_cfgpred(block, j);
587 if (!is_Proj(projB)) return false;
588 cond = get_Proj_pred(projA);
589 if (!is_Cond(cond)) return false;
591 if (cond != get_Proj_pred(projB)) return false;
592 if (is_switch_Cond(cond)) return false;
594 /* cond should actually be a Jmp */
595 pred_block = get_nodes_block(cond);
596 jmp = new_r_Jmp(pred_block);
597 bad = new_r_Bad(get_irn_irg(block), mode_X);
599 assert(projA != projB);
600 exchange(projA, jmp);
601 exchange(projB, bad);
605 static void compute_block_info(ir_node *n, void *x)
607 ir_phase *block_info = (ir_phase *)x;
610 int i, max = get_Block_n_cfgpreds(n);
611 for (i=0; i<max; i++) {
612 ir_node *pred = get_Block_cfgpred(n,i);
613 if (is_unknown_jump(pred)) {
614 set_is_unknown_jump_target(block_info, n);
617 } else if (is_Phi(n)) {
618 ir_node *block = get_nodes_block(n);
619 set_has_phis(block_info, block);
620 } else if (is_Jmp(n) || is_Cond(n) || is_Cmp(n) || is_Proj(n)) {
623 ir_node *block = get_nodes_block(n);
624 set_has_operations(block_info, block);
628 typedef struct skip_env {
633 static void optimize_conds(ir_node *b, void *x)
635 skip_env *env = (skip_env*)x;
637 int n_preds = get_Block_n_cfgpreds(b);
639 if (has_phis(env->phase,b)) return;
641 /* optimize Cond predecessors (might produce Bad predecessors) */
642 for (i = 0; i < n_preds; i++) {
643 for (j = i+1; j < n_preds; j++) {
644 optimize_pred_cond(b, i, j);
649 static void remove_empty_blocks(ir_node *b, void *x)
651 skip_env *env = (skip_env*)x;
653 int n_preds = get_Block_n_cfgpreds(b);
655 for (i = 0; i < n_preds; ++i) {
656 ir_node *jmp, *jmp_block, *pred, *pred_block;
658 jmp = get_Block_cfgpred(b, i);
659 if (!is_Jmp(jmp)) continue;
660 if (is_unknown_jump(jmp)) continue;
661 jmp_block = get_nodes_block(jmp);
662 if (is_unknown_jump_target(env->phase, jmp_block)) continue;
663 if (has_operations(env->phase,jmp_block)) continue;
664 /* jmp_block is an empty block! */
666 if (get_Block_n_cfgpreds(jmp_block) != 1) continue;
667 pred = get_Block_cfgpred(jmp_block, 0);
671 /* cleanup: jmp_block might have a Keep edge! */
672 pred_block = get_nodes_block(pred);
673 exchange(jmp_block, pred_block);
678 * Some cfg optimizations, which do not touch Phi nodes */
679 static void cfgopt_ignoring_phis(ir_graph *irg) {
680 ir_phase *block_info = new_phase(irg, NULL);
681 skip_env env = { false, block_info };
683 irg_walk_graph(irg, compute_block_info, NULL, block_info);
688 /* Conds => Jmp optimization; might produce empty blocks */
689 irg_block_walk_graph(irg, optimize_conds, NULL, &env);
691 /* Remove empty blocks */
692 irg_block_walk_graph(irg, remove_empty_blocks, NULL, &env);
694 set_irg_doms_inconsistent(irg);
695 /* Removing blocks might enable more Cond optimizations */
702 phase_free(block_info);
705 /* Optimizations of the control flow that also require changes of Phi nodes. */
706 void optimize_cf(ir_graph *irg)
710 ir_node *end = get_irg_end(irg);
714 assert(get_irg_phase_state(irg) != phase_building);
716 /* if the graph is not pinned, we cannot determine empty blocks */
717 assert(get_irg_pinned(irg) != op_pin_state_floats &&
718 "Control flow optimization need a pinned graph");
720 /* FIXME: control flow opt destroys block edges. So edges are deactivated
721 * here. Fix the edges! */
722 edges_deactivate(irg);
724 cfgopt_ignoring_phis(irg);
726 /* we use the mark flag to mark removable blocks */
727 ir_reserve_resources(irg, IR_RESOURCE_BLOCK_MARK | IR_RESOURCE_IRN_LINK);
729 /* The switch Cond optimization might expose unreachable code, so we loop */
732 ir_node **switch_conds = NULL;
734 env.phis_moved = false;
739 * This pass collects all Phi nodes in a link list in the block
740 * nodes. Further it performs simple control flow optimizations.
741 * Finally it marks all blocks that do not contain useful
742 * computations, i.e., these blocks might be removed.
744 switch_conds = NEW_ARR_F(ir_node*, 0);
745 irg_walk(end, clear_link, collect_nodes, &switch_conds);
747 /* handle all collected switch-Conds */
748 length = ARR_LEN(switch_conds);
749 for (i = 0; i < length; ++i) {
750 ir_node *cond = switch_conds[i];
751 env.changed |= handle_switch_cond(cond);
753 DEL_ARR_F(switch_conds);
755 if (!env.changed) break;
757 set_irg_doms_inconsistent(irg);
758 set_irg_extblk_inconsistent(irg);
759 set_irg_entity_usage_state(irg, ir_entity_usage_not_computed);
762 /* assert due to collect_nodes:
763 * 1. removable blocks are now marked as such
764 * 2. phi lists are up to date
767 /* Optimize the standard code.
768 * It walks only over block nodes and adapts these and the Phi nodes in these
769 * blocks, which it finds in a linked list computed before.
772 irg_block_walk_graph(irg, optimize_blocks, NULL, &env);
774 new_end = optimize_in_place(end);
775 if (new_end != end) {
776 set_irg_end(irg, new_end);
779 remove_End_Bads_and_doublets(end);
781 ir_free_resources(irg, IR_RESOURCE_BLOCK_MARK | IR_RESOURCE_IRN_LINK);
783 if (env.phis_moved) {
784 /* Bad: when we moved Phi's, we might produce dead Phi nodes
786 Some other phases cannot copy with this, so will them.
788 n = get_End_n_keepalives(end);
790 NEW_ARR_A(ir_node *, in, n);
791 assure_irg_outs(irg);
793 for (i = j = 0; i < n; ++i) {
794 ir_node *ka = get_End_keepalive(end, i);
799 for (k = get_irn_n_outs(ka) - 1; k >= 0; --k) {
800 ir_node *user = get_irn_out(ka, k);
802 if (user != ka && user != end) {
803 /* Is it a real user or just a self loop ? */
813 set_End_keepalives(end, j, in);
820 /* Handle graph state if was changed. */
821 set_irg_doms_inconsistent(irg);
822 set_irg_extblk_inconsistent(irg);
823 set_irg_entity_usage_state(irg, ir_entity_usage_not_computed);
827 /* Creates an ir_graph pass for optimize_cf. */
828 ir_graph_pass_t *optimize_cf_pass(const char *name)
830 return def_graph_pass(name ? name : "optimize_cf", optimize_cf);