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"
60 #include "iropt_dbg.h"
62 /** An environment for merge_blocks and collect nodes. */
63 typedef struct merge_env {
64 bool changed; /**< Set if the graph was changed. */
65 bool phis_moved; /**< Set if Phi nodes were moved. */
66 ir_node **switch_conds; /**< Helper list for all found Switch Conds. */
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 void clear_link(ir_node *node, void *ctx)
82 set_irn_link(node, NULL);
84 set_Block_removable(node, true);
88 * Collects all Phi nodes in link list of Block.
89 * Marks all blocks "non_removable" if they contain a node other
90 * than Jmp (and Proj).
91 * Links all Proj nodes to their predecessors.
92 * Collects all switch-Conds in a list.
94 static void collect_nodes(ir_node *n, void *ctx)
96 merge_env *env = (merge_env*)ctx;
99 /* Collect Phi nodes to compact ins along with block's ins. */
100 ir_node *block = get_nodes_block(n);
101 set_irn_link(n, get_irn_link(block));
102 set_irn_link(block, n);
103 } else if (is_Block(n)) {
104 if (has_Block_entity(n))
105 set_Block_removable(n, false);
107 } else if (!is_Jmp(n)) { /* Check for non-empty block. */
108 ir_node *block = get_nodes_block(n);
109 set_Block_removable(block, false);
112 /* link Proj nodes */
113 ir_node *pred = get_Proj_pred(n);
114 set_irn_link(n, get_irn_link(pred));
115 set_irn_link(pred, n);
116 } else if (is_Cond(n)) {
117 ir_node *sel = get_Cond_selector(n);
118 if (get_irn_mode(sel) != mode_b) {
119 /* found a switch-Cond, collect */
120 ARR_APP1(ir_node*, env->switch_conds, n);
126 /** Returns true if pred is predecessor of block. */
127 static bool is_pred_of(ir_node *pred, ir_node *b)
131 for (i = get_Block_n_cfgpreds(b) - 1; i >= 0; --i) {
132 ir_node *b_pred = get_Block_cfgpred_block(b, i);
139 /** Test whether we can optimize away pred block pos of b.
141 * @param b A block node.
142 * @param pos The position of the predecessor block to judge about.
144 * @returns The number of predecessors
146 * The test is rather tricky.
148 * The situation is something like the following:
157 * b merges the control flow of an if-then-else. We may not remove
158 * the 'then' _and_ the 'else' block of an 'if' if there is a Phi
159 * node in b, even if both are empty. The destruction of this Phi
160 * requires that a copy is added before the merge. We have to
161 * keep one of the case blocks to place the copies in.
163 * To perform the test for pos, we must regard predecessors before pos
164 * as already removed.
166 static unsigned test_whether_dispensable(ir_node *b, int pos)
168 ir_node *pred = get_Block_cfgpred(b, pos);
169 ir_node *predb = get_nodes_block(pred);
171 if (is_Bad(pred) || !is_Block_removable(predb))
174 /* can't remove self-loops */
176 goto non_dispensable;
177 if (is_unknown_jump(pred))
178 goto non_dispensable;
180 /* Seems to be empty. At least we detected this in collect_nodes. */
181 if (get_irn_link(b) != NULL) {
182 int n_cfgpreds = get_Block_n_cfgpreds(b);
184 /* there are Phi nodes */
186 /* b's pred blocks and pred's pred blocks must be pairwise disjunct.
187 * Handle all pred blocks with preds < pos as if they were already
189 for (i = 0; i < pos; i++) {
190 ir_node *other_pred = get_Block_cfgpred(b, i);
191 ir_node *other_predb = get_nodes_block(other_pred);
192 if (is_Bad(other_pred))
194 if (is_Block_removable(other_predb)
195 && !Block_block_visited(other_predb)) {
197 for (j = get_Block_n_cfgpreds(other_predb) - 1; j >= 0; --j) {
198 ir_node *other_predpred
199 = get_Block_cfgpred_block(other_predb, j);
200 if (is_pred_of(other_predpred, predb))
201 goto non_dispensable;
203 } else if (is_pred_of(other_predb, predb)) {
204 goto non_dispensable;
207 for (i = pos+1; i < n_cfgpreds; i++) {
208 ir_node *other_predb = get_Block_cfgpred_block(b, i);
209 if (is_pred_of(other_predb, predb))
210 goto non_dispensable;
213 /* we will not dispense already visited blocks */
214 if (Block_block_visited(predb))
216 /* if we get here, the block is dispensable, count useful preds */
217 return get_irn_arity(predb);
220 set_Block_removable(predb, false);
225 * This method removes empty blocks. A block is empty if it only contains Phi
228 * We first adapt Phi nodes, then Block nodes, as we need the old ins
229 * of the Block to adapt the Phi nodes. We do this by computing new
230 * in arrays, and then replacing the old ones. So far we compute new in arrays
231 * for all nodes, not regarding whether there is a possibility for optimization.
233 * For each predecessor p of a Block b there are three cases:
234 * - The predecessor p is a Bad node: just skip it. The in array of b shrinks
236 * - The predecessor p is empty. Remove p. All predecessors of p are now
238 * - The predecessor p is a block containing useful code. Just keep p as is.
240 * For Phi nodes f we have to check the conditions at the Block of f.
241 * For cases 1 and 3 we proceed as for Blocks. For case 2 we can have two
243 * -2a: The old predecessor of the Phi f is a Phi pred_f IN THE BLOCK REMOVED.
244 * In this case we proceed as for blocks. We remove pred_f. All
245 * predecessors of pred_f now are predecessors of f.
246 * -2b: The old predecessor of f is NOT in the block removed. It might be a Phi
247 * too. We have to replicate f for each predecessor of the removed block.
248 * Or, with other words, the removed predecessor block has exactly one
251 * Further there is a special case for self referencing blocks:
254 * then_b else_b then_b else_b
260 * | | | === optimized to ===> \ | | |
267 * If there is a Phi in pred_b, but we remove pred_b, we have to generate a
268 * Phi in loop_b, that has the ins of the Phi in pred_b and a self referencing
271 static void optimize_blocks(ir_node *b, void *ctx)
273 int i, j, k, n, max_preds, n_preds, p_preds = -1;
274 ir_node *pred, *phi, *next;
276 merge_env *env = (merge_env*)ctx;
278 /* Count the number of predecessor if this block is merged with pred blocks
281 for (i = 0, k = get_Block_n_cfgpreds(b); i < k; ++i) {
282 max_preds += test_whether_dispensable(b, i);
284 in = XMALLOCN(ir_node*, max_preds);
286 /*- Fix the Phi nodes of the current block -*/
287 for (phi = (ir_node*)get_irn_link(b); phi != NULL; phi = (ir_node*)next) {
289 next = (ir_node*)get_irn_link(phi);
291 /* Find the new predecessors for the Phi */
293 for (i = 0, n = get_Block_n_cfgpreds(b); i < n; ++i) {
294 ir_graph *irg = get_irn_irg(b);
295 pred = get_Block_cfgpred_block(b, i);
298 /* case Phi 1: maintain Bads, as somebody else is responsible to remove them */
299 in[p_preds++] = new_r_Bad(irg, get_irn_mode(phi));
300 } else if (is_Block_removable(pred) && !Block_block_visited(pred)) {
301 /* case Phi 2: It's an empty block and not yet visited. */
302 ir_node *phi_pred = get_Phi_pred(phi, i);
304 for (j = 0, k = get_Block_n_cfgpreds(pred); j < k; j++) {
305 ir_node *pred_pred = get_Block_cfgpred(pred, j);
307 if (is_Bad(pred_pred)) {
308 in[p_preds++] = new_r_Bad(irg, get_irn_mode(phi));
312 if (get_nodes_block(phi_pred) == pred) {
314 assert(is_Phi(phi_pred)); /* Block is empty!! */
316 in[p_preds++] = get_Phi_pred(phi_pred, j);
319 in[p_preds++] = phi_pred;
324 in[p_preds++] = get_Phi_pred(phi, i);
327 assert(p_preds == max_preds);
331 exchange(phi, in[0]);
333 set_irn_in(phi, p_preds, in);
337 /*- This happens only if merge between loop backedge and single loop entry.
338 Moreover, it is only needed if predb is the direct dominator of b,
339 else there can be no uses of the Phi's in predb ... -*/
340 for (k = 0, n = get_Block_n_cfgpreds(b); k < n; ++k) {
341 ir_node *pred = get_Block_cfgpred(b, k);
342 ir_node *predb = get_nodes_block(pred);
346 if (is_Block_removable(predb) && !Block_block_visited(predb)) {
349 /* we found a predecessor block at position k that will be removed */
350 for (phi = (ir_node*)get_irn_link(predb); phi; phi = next_phi) {
352 next_phi = (ir_node*)get_irn_link(phi);
356 if (get_Block_idom(b) != predb) {
357 /* predb is not the dominator. There can't be uses of pred's Phi nodes, kill them .*/
358 ir_graph *irg = get_irn_irg(b);
359 ir_mode *mode = get_irn_mode(phi);
360 exchange(phi, new_r_Bad(irg, mode));
362 /* predb is the direct dominator of b. There might be uses of the Phi nodes from
363 predb in further block, so move this phi from the predecessor into the block b */
364 set_nodes_block(phi, b);
365 set_irn_link(phi, get_irn_link(b));
366 set_irn_link(b, phi);
367 env->phis_moved = true;
369 /* first, copy all 0..k-1 predecessors */
370 for (i = 0; i < k; i++) {
371 pred = get_Block_cfgpred_block(b, i);
374 in[q_preds++] = pred;
375 } else if (is_Block_removable(pred) && !Block_block_visited(pred)) {
376 /* It's an empty block and not yet visited. */
377 for (j = 0; j < get_Block_n_cfgpreds(pred); j++) {
378 if (! is_Bad(get_Block_cfgpred(pred, j)))
386 /* now we are at k, copy the phi predecessors */
387 pred = get_nodes_block(get_Block_cfgpred(b, k));
388 for (i = 0; i < get_Phi_n_preds(phi); i++) {
389 in[q_preds++] = get_Phi_pred(phi, i);
392 /* and now all the rest */
393 for (i = k+1; i < get_Block_n_cfgpreds(b); i++) {
394 pred = get_Block_cfgpred_block(b, i);
397 ir_graph *irg = get_irn_irg(b);
398 ir_mode *mode = get_irn_mode(phi);
399 in[q_preds++] = new_r_Bad(irg, mode);
400 } else if (is_Block_removable(pred) && !Block_block_visited(pred)) {
401 /* It's an empty block and not yet visited. */
402 for (j = 0; j < get_Block_n_cfgpreds(pred); j++) {
403 if (! is_Bad(get_Block_cfgpred(pred, j)))
413 exchange(phi, in[0]);
415 set_irn_in(phi, q_preds, in);
418 assert(q_preds <= max_preds);
419 // assert(p_preds == q_preds && "Wrong Phi Fix");
425 /*- Fix the block -*/
427 for (i = 0; i < get_Block_n_cfgpreds(b); i++) {
428 ir_node *pred = get_Block_cfgpred(b, i);
429 ir_node *predb = get_nodes_block(pred);
430 ir_graph *irg = get_irn_irg(pred);
432 /* case 1: Bad predecessor */
434 in[n_preds++] = new_r_Bad(irg, mode_X);
437 if (is_Block_removable(predb) && !Block_block_visited(predb)) {
438 /* case 2: It's an empty block and not yet visited. */
439 for (j = 0; j < get_Block_n_cfgpreds(predb); j++) {
440 ir_node *predpred = get_Block_cfgpred(predb, j);
442 if (is_Bad(predpred)) {
443 in[n_preds++] = new_r_Bad(irg, mode_X);
447 in[n_preds++] = predpred;
449 /* Remove block+jump as it might be kept alive. */
450 exchange(pred, new_r_Bad(get_irn_irg(b), mode_X));
451 exchange(predb, new_r_Bad(get_irn_irg(b), mode_BB));
454 in[n_preds++] = pred;
457 assert(n_preds == max_preds);
459 set_irn_in(b, n_preds, in);
462 /* see if phi-fix was correct */
463 assert(get_irn_link(b) == NULL || p_preds == -1 || (n_preds == p_preds));
468 * Block walker: optimize all blocks using the default optimizations.
469 * This removes Blocks with only a Jmp predecessor.
471 static void remove_simple_blocks(ir_node *block, void *ctx)
473 merge_env *env = (merge_env*)ctx;
474 ir_node *new_blk = equivalent_node(block);
476 if (new_blk != block) {
477 exchange(block, new_blk);
483 * Optimize table-switch Conds.
485 * @param cond the switch-Cond
486 * @return true if the switch-Cond was optimized
488 static bool handle_switch_cond(ir_node *cond)
490 ir_node *sel = get_Cond_selector(cond);
491 ir_node *proj1 = (ir_node*)get_irn_link(cond);
492 ir_node *proj2 = (ir_node*)get_irn_link(proj1);
493 ir_node *blk = get_nodes_block(cond);
495 /* exactly 1 Proj on the Cond node: must be the defaultProj */
497 ir_node *jmp = new_r_Jmp(blk);
498 assert(get_Cond_default_proj(cond) == get_Proj_proj(proj1));
499 /* convert it into a Jmp */
500 exchange(proj1, jmp);
504 /* handle Cond nodes with constant argument. In this case the localopt rules
505 * should have killed all obviously impossible cases.
506 * So the only case left to handle here is 1 defaultProj + 1case
507 * (this one case should be the one taken) */
508 if (get_irn_link(proj2) == NULL) {
509 ir_tarval *tv = value_of(sel);
511 if (tv != tarval_bad) {
512 /* we have a constant switch */
513 long num = get_tarval_long(tv);
514 long def_num = get_Cond_default_proj(cond);
515 ir_graph *irg = get_irn_irg(cond);
516 ir_node *bad = new_r_Bad(irg, mode_X);
518 if (def_num == get_Proj_proj(proj1)) {
519 /* first one is the defProj */
520 if (num == get_Proj_proj(proj2)) {
521 ir_node *jmp = new_r_Jmp(blk);
522 exchange(proj2, jmp);
523 exchange(proj1, bad);
526 } else if (def_num == get_Proj_proj(proj2)) {
527 /* second one is the defProj */
528 if (num == get_Proj_proj(proj1)) {
529 ir_node *jmp = new_r_Jmp(blk);
530 exchange(proj1, jmp);
531 exchange(proj2, bad);
535 /* neither: strange, Cond was not optimized so far */
536 if (num == get_Proj_proj(proj1)) {
537 ir_node *jmp = new_r_Jmp(blk);
538 exchange(proj1, jmp);
539 exchange(proj2, bad);
541 } else if (num == get_Proj_proj(proj2)) {
542 ir_node *jmp = new_r_Jmp(blk);
543 exchange(proj2, jmp);
544 exchange(proj1, bad);
553 /* Optimizations of the control flow that also require changes of Phi nodes.
555 * This optimization performs two passes over the graph.
557 * The first pass collects all Phi nodes in a link list in the block
558 * nodes. Further it performs simple control flow optimizations.
559 * Finally it marks all blocks that do not contain useful
560 * computations, i.e., these blocks might be removed.
562 * The second pass performs the optimizations intended by this algorithm.
563 * It walks only over block nodes and adapts these and the Phi nodes in these
564 * blocks, which it finds in a linked list computed by the first pass.
566 * We use the mark flag to mark removable blocks in the first phase.
568 void optimize_cf(ir_graph *irg)
572 ir_node *end = get_irg_end(irg);
576 assert(get_irg_phase_state(irg) != phase_building);
578 /* if the graph is not pinned, we cannot determine empty blocks */
579 assert(get_irg_pinned(irg) != op_pin_state_floats &&
580 "Control flow optimization need a pinned graph");
582 /* FIXME: control flow opt destroys block edges. So edges are deactivated
583 * here. Fix the edges! */
584 edges_deactivate(irg);
586 /* we use the mark flag to mark removable blocks */
587 ir_reserve_resources(irg, IR_RESOURCE_BLOCK_MARK | IR_RESOURCE_IRN_LINK);
590 env.phis_moved = false;
594 env.switch_conds = NEW_ARR_F(ir_node*, 0);
595 irg_walk(end, clear_link, collect_nodes, &env);
597 /* handle all collected switch-Conds */
598 n = ARR_LEN(env.switch_conds);
599 for (i = 0; i < n; ++i) {
600 ir_node *cond = env.switch_conds[i];
601 env.changed |= handle_switch_cond(cond);
603 DEL_ARR_F(env.switch_conds);
606 /* Handle graph state if was changed. */
607 set_irg_doms_inconsistent(irg);
608 set_irg_extblk_inconsistent(irg);
609 set_irg_entity_usage_state(irg, ir_entity_usage_not_computed);
611 /* The Cond optimization might generate unreachable code, so restart if
616 /* Optimize the standard code. */
618 irg_block_walk_graph(irg, optimize_blocks, remove_simple_blocks, &env);
620 new_end = optimize_in_place(end);
621 if (new_end != end) {
622 set_irg_end(irg, new_end);
625 remove_End_Bads_and_doublets(end);
627 ir_free_resources(irg, IR_RESOURCE_BLOCK_MARK | IR_RESOURCE_IRN_LINK);
629 if (env.phis_moved) {
630 /* Bad: when we moved Phi's, we might produce dead Phi nodes
632 Some other phases cannot copy with this, so will them.
634 n = get_End_n_keepalives(end);
636 NEW_ARR_A(ir_node *, in, n);
637 assure_irg_outs(irg);
639 for (i = j = 0; i < n; ++i) {
640 ir_node *ka = get_End_keepalive(end, i);
645 for (k = get_irn_n_outs(ka) - 1; k >= 0; --k) {
646 ir_node *user = get_irn_out(ka, k);
648 if (user != ka && user != end) {
649 /* Is it a real user or just a self loop ? */
659 set_End_keepalives(end, j, in);
666 /* Handle graph state if was changed. */
667 set_irg_doms_inconsistent(irg);
668 set_irg_extblk_inconsistent(irg);
669 set_irg_entity_usage_state(irg, ir_entity_usage_not_computed);
673 /* Creates an ir_graph pass for optimize_cf. */
674 ir_graph_pass_t *optimize_cf_pass(const char *name)
676 return def_graph_pass(name ? name : "optimize_cf", optimize_cf);