xref: /aosp_15_r20/external/mesa3d/src/compiler/nir/nir_control_flow.c (revision 6104692788411f58d303aa86923a9ff6ecaded22)
1  /*
2   * Copyright © 2014 Intel Corporation
3   *
4   * Permission is hereby granted, free of charge, to any person obtaining a
5   * copy of this software and associated documentation files (the "Software"),
6   * to deal in the Software without restriction, including without limitation
7   * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8   * and/or sell copies of the Software, and to permit persons to whom the
9   * Software is furnished to do so, subject to the following conditions:
10   *
11   * The above copyright notice and this permission notice (including the next
12   * paragraph) shall be included in all copies or substantial portions of the
13   * Software.
14   *
15   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18   * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21   * IN THE SOFTWARE.
22   *
23   * Authors:
24   *    Connor Abbott (cwabbott0@gmail.com)
25   *
26   */
27  
28  #include "nir_control_flow_private.h"
29  
30  /**
31   * \name Control flow modification
32   *
33   * These functions modify the control flow tree while keeping the control flow
34   * graph up-to-date. The invariants respected are:
35   * 1. Each then statement, else statement, or loop body must have at least one
36   *    control flow node.
37   * 2. Each if-statement and loop must have one basic block before it and one
38   *    after.
39   * 3. Two basic blocks cannot be directly next to each other.
40   * 4. If a basic block has a jump instruction, there must be only one and it
41   *    must be at the end of the block.
42   *
43   * The purpose of the second one is so that we have places to insert code during
44   * GCM, as well as eliminating the possibility of critical edges.
45   */
46  /*@{*/
47  
48  static inline void
block_add_pred(nir_block * block,nir_block * pred)49  block_add_pred(nir_block *block, nir_block *pred)
50  {
51     _mesa_set_add(block->predecessors, pred);
52  }
53  
54  static inline void
block_remove_pred(nir_block * block,nir_block * pred)55  block_remove_pred(nir_block *block, nir_block *pred)
56  {
57     struct set_entry *entry = _mesa_set_search(block->predecessors, pred);
58  
59     assert(entry);
60  
61     _mesa_set_remove(block->predecessors, entry);
62  }
63  
64  static void
link_blocks(nir_block * pred,nir_block * succ1,nir_block * succ2)65  link_blocks(nir_block *pred, nir_block *succ1, nir_block *succ2)
66  {
67     pred->successors[0] = succ1;
68     if (succ1 != NULL)
69        block_add_pred(succ1, pred);
70  
71     pred->successors[1] = succ2;
72     if (succ2 != NULL)
73        block_add_pred(succ2, pred);
74  }
75  
76  static void
unlink_blocks(nir_block * pred,nir_block * succ)77  unlink_blocks(nir_block *pred, nir_block *succ)
78  {
79     if (pred->successors[0] == succ) {
80        pred->successors[0] = pred->successors[1];
81        pred->successors[1] = NULL;
82     } else {
83        assert(pred->successors[1] == succ);
84        pred->successors[1] = NULL;
85     }
86  
87     block_remove_pred(succ, pred);
88  }
89  
90  static void
unlink_block_successors(nir_block * block)91  unlink_block_successors(nir_block *block)
92  {
93     if (block->successors[1] != NULL)
94        unlink_blocks(block, block->successors[1]);
95     if (block->successors[0] != NULL)
96        unlink_blocks(block, block->successors[0]);
97  }
98  
99  static void
link_non_block_to_block(nir_cf_node * node,nir_block * block)100  link_non_block_to_block(nir_cf_node *node, nir_block *block)
101  {
102     if (node->type == nir_cf_node_if) {
103        /*
104         * We're trying to link an if to a block after it; this just means linking
105         * the last block of the then and else branches.
106         */
107  
108        nir_if *if_stmt = nir_cf_node_as_if(node);
109  
110        nir_block *last_then_block = nir_if_last_then_block(if_stmt);
111        nir_block *last_else_block = nir_if_last_else_block(if_stmt);
112  
113        if (!nir_block_ends_in_jump(last_then_block)) {
114           unlink_block_successors(last_then_block);
115           link_blocks(last_then_block, block, NULL);
116        }
117  
118        if (!nir_block_ends_in_jump(last_else_block)) {
119           unlink_block_successors(last_else_block);
120           link_blocks(last_else_block, block, NULL);
121        }
122     } else {
123        assert(node->type == nir_cf_node_loop);
124     }
125  }
126  
127  static void
link_block_to_non_block(nir_block * block,nir_cf_node * node)128  link_block_to_non_block(nir_block *block, nir_cf_node *node)
129  {
130     if (node->type == nir_cf_node_if) {
131        /*
132         * We're trying to link a block to an if after it; this just means linking
133         * the block to the first block of the then and else branches.
134         */
135  
136        nir_if *if_stmt = nir_cf_node_as_if(node);
137  
138        nir_block *first_then_block = nir_if_first_then_block(if_stmt);
139        nir_block *first_else_block = nir_if_first_else_block(if_stmt);
140  
141        unlink_block_successors(block);
142        link_blocks(block, first_then_block, first_else_block);
143     } else if (node->type == nir_cf_node_loop) {
144        /*
145         * For similar reasons as the corresponding case in
146         * link_non_block_to_block(), don't worry about if the loop header has
147         * any predecessors that need to be unlinked.
148         */
149  
150        nir_loop *loop = nir_cf_node_as_loop(node);
151  
152        nir_block *loop_header_block = nir_loop_first_block(loop);
153  
154        unlink_block_successors(block);
155        link_blocks(block, loop_header_block, NULL);
156     }
157  }
158  
159  /**
160   * Replace a block's successor with a different one.
161   */
162  static void
replace_successor(nir_block * block,nir_block * old_succ,nir_block * new_succ)163  replace_successor(nir_block *block, nir_block *old_succ, nir_block *new_succ)
164  {
165     if (block->successors[0] == old_succ) {
166        block->successors[0] = new_succ;
167     } else {
168        assert(block->successors[1] == old_succ);
169        block->successors[1] = new_succ;
170     }
171  
172     block_remove_pred(old_succ, block);
173     block_add_pred(new_succ, block);
174  }
175  
176  /**
177   * Takes a basic block and inserts a new empty basic block before it, making its
178   * predecessors point to the new block. This essentially splits the block into
179   * an empty header and a body so that another non-block CF node can be inserted
180   * between the two. Note that this does *not* link the two basic blocks, so
181   * some kind of cleanup *must* be performed after this call.
182   */
183  
184  static nir_block *
split_block_beginning(nir_block * block)185  split_block_beginning(nir_block *block)
186  {
187     nir_block *new_block = nir_block_create(ralloc_parent(block));
188     new_block->cf_node.parent = block->cf_node.parent;
189     exec_node_insert_node_before(&block->cf_node.node, &new_block->cf_node.node);
190  
191     set_foreach(block->predecessors, entry) {
192        nir_block *pred = (nir_block *)entry->key;
193        replace_successor(pred, block, new_block);
194     }
195  
196     /* Any phi nodes must stay part of the new block, or else their
197      * sources will be messed up.
198      */
199     nir_foreach_phi_safe(phi, block) {
200        exec_node_remove(&phi->instr.node);
201        phi->instr.block = new_block;
202        exec_list_push_tail(&new_block->instr_list, &phi->instr.node);
203     }
204  
205     return new_block;
206  }
207  
208  static void
rewrite_phi_preds(nir_block * block,nir_block * old_pred,nir_block * new_pred)209  rewrite_phi_preds(nir_block *block, nir_block *old_pred, nir_block *new_pred)
210  {
211     nir_foreach_phi_safe(phi, block) {
212        nir_foreach_phi_src(src, phi) {
213           if (src->pred == old_pred) {
214              src->pred = new_pred;
215              break;
216           }
217        }
218     }
219  }
220  
221  void
nir_insert_phi_undef(nir_block * block,nir_block * pred)222  nir_insert_phi_undef(nir_block *block, nir_block *pred)
223  {
224     nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
225     nir_foreach_phi(phi, block) {
226        nir_undef_instr *undef =
227           nir_undef_instr_create(impl->function->shader,
228                                  phi->def.num_components,
229                                  phi->def.bit_size);
230        nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
231        nir_phi_src *src = nir_phi_instr_add_src(phi, pred, &undef->def);
232        list_addtail(&src->src.use_link, &undef->def.uses);
233     }
234  }
235  
236  /**
237   * Moves the successors of source to the successors of dest, leaving both
238   * successors of source NULL.
239   */
240  
241  static void
move_successors(nir_block * source,nir_block * dest)242  move_successors(nir_block *source, nir_block *dest)
243  {
244     nir_block *succ1 = source->successors[0];
245     nir_block *succ2 = source->successors[1];
246  
247     if (succ1) {
248        unlink_blocks(source, succ1);
249        rewrite_phi_preds(succ1, source, dest);
250     }
251  
252     if (succ2) {
253        unlink_blocks(source, succ2);
254        rewrite_phi_preds(succ2, source, dest);
255     }
256  
257     unlink_block_successors(dest);
258     link_blocks(dest, succ1, succ2);
259  }
260  
261  /* Given a basic block with no successors that has been inserted into the
262   * control flow tree, gives it the successors it would normally have assuming
263   * it doesn't end in a jump instruction. Also inserts phi sources with undefs
264   * if necessary.
265   */
266  static void
block_add_normal_succs(nir_block * block)267  block_add_normal_succs(nir_block *block)
268  {
269     if (exec_node_is_tail_sentinel(block->cf_node.node.next)) {
270        nir_cf_node *parent = block->cf_node.parent;
271        if (parent->type == nir_cf_node_if) {
272           nir_cf_node *next = nir_cf_node_next(parent);
273           nir_block *next_block = nir_cf_node_as_block(next);
274  
275           link_blocks(block, next_block, NULL);
276           nir_insert_phi_undef(next_block, block);
277        } else if (parent->type == nir_cf_node_loop) {
278           nir_loop *loop = nir_cf_node_as_loop(parent);
279  
280           nir_block *cont_block;
281           if (block == nir_loop_last_block(loop)) {
282              cont_block = nir_loop_continue_target(loop);
283           } else {
284              assert(block == nir_loop_last_continue_block(loop));
285              cont_block = nir_loop_first_block(loop);
286           }
287  
288           link_blocks(block, cont_block, NULL);
289           nir_insert_phi_undef(cont_block, block);
290        } else {
291           nir_function_impl *impl = nir_cf_node_as_function(parent);
292           link_blocks(block, impl->end_block, NULL);
293        }
294     } else {
295        nir_cf_node *next = nir_cf_node_next(&block->cf_node);
296        if (next->type == nir_cf_node_if) {
297           nir_if *next_if = nir_cf_node_as_if(next);
298  
299           nir_block *first_then_block = nir_if_first_then_block(next_if);
300           nir_block *first_else_block = nir_if_first_else_block(next_if);
301  
302           link_blocks(block, first_then_block, first_else_block);
303           nir_insert_phi_undef(first_then_block, block);
304           nir_insert_phi_undef(first_else_block, block);
305        } else if (next->type == nir_cf_node_loop) {
306           nir_loop *next_loop = nir_cf_node_as_loop(next);
307  
308           nir_block *first_block = nir_loop_first_block(next_loop);
309  
310           link_blocks(block, first_block, NULL);
311           nir_insert_phi_undef(first_block, block);
312        }
313     }
314  }
315  
316  static nir_block *
split_block_end(nir_block * block)317  split_block_end(nir_block *block)
318  {
319     nir_block *new_block = nir_block_create(ralloc_parent(block));
320     new_block->cf_node.parent = block->cf_node.parent;
321     exec_node_insert_after(&block->cf_node.node, &new_block->cf_node.node);
322  
323     if (nir_block_ends_in_jump(block)) {
324        /* Figure out what successor block would've had if it didn't have a jump
325         * instruction, and make new_block have that successor.
326         */
327        block_add_normal_succs(new_block);
328     } else {
329        move_successors(block, new_block);
330     }
331  
332     return new_block;
333  }
334  
335  static nir_block *
split_block_before_instr(nir_instr * instr)336  split_block_before_instr(nir_instr *instr)
337  {
338     assert(instr->type != nir_instr_type_phi);
339     nir_block *new_block = split_block_beginning(instr->block);
340  
341     nir_foreach_instr_safe(cur_instr, instr->block) {
342        if (cur_instr == instr)
343           break;
344  
345        exec_node_remove(&cur_instr->node);
346        cur_instr->block = new_block;
347        exec_list_push_tail(&new_block->instr_list, &cur_instr->node);
348     }
349  
350     return new_block;
351  }
352  
353  /* Splits a basic block at the point specified by the cursor. The "before" and
354   * "after" arguments are filled out with the blocks resulting from the split
355   * if non-NULL. Note that the "beginning" of the block is actually interpreted
356   * as before the first non-phi instruction, and it's illegal to split a block
357   * before a phi instruction.
358   */
359  
360  static void
split_block_cursor(nir_cursor cursor,nir_block ** _before,nir_block ** _after)361  split_block_cursor(nir_cursor cursor,
362                     nir_block **_before, nir_block **_after)
363  {
364     nir_block *before, *after;
365     switch (cursor.option) {
366     case nir_cursor_before_block:
367        after = cursor.block;
368        before = split_block_beginning(cursor.block);
369        break;
370  
371     case nir_cursor_after_block:
372        before = cursor.block;
373        after = split_block_end(cursor.block);
374        break;
375  
376     case nir_cursor_before_instr:
377        after = cursor.instr->block;
378        before = split_block_before_instr(cursor.instr);
379        break;
380  
381     case nir_cursor_after_instr:
382        /* We lower this to split_block_before_instr() so that we can keep the
383         * after-a-jump-instr case contained to split_block_end().
384         */
385        if (nir_instr_is_last(cursor.instr)) {
386           before = cursor.instr->block;
387           after = split_block_end(cursor.instr->block);
388        } else {
389           after = cursor.instr->block;
390           before = split_block_before_instr(nir_instr_next(cursor.instr));
391        }
392        break;
393  
394     default:
395        unreachable("not reached");
396     }
397  
398     if (_before)
399        *_before = before;
400     if (_after)
401        *_after = after;
402  }
403  
404  /**
405   * Inserts a non-basic block between two basic blocks and links them together.
406   */
407  
408  static void
insert_non_block(nir_block * before,nir_cf_node * node,nir_block * after)409  insert_non_block(nir_block *before, nir_cf_node *node, nir_block *after)
410  {
411     node->parent = before->cf_node.parent;
412     exec_node_insert_after(&before->cf_node.node, &node->node);
413     if (!nir_block_ends_in_jump(before))
414        link_block_to_non_block(before, node);
415     link_non_block_to_block(node, after);
416  }
417  
418  /* walk up the control flow tree to find the innermost enclosed loop */
419  static nir_loop *
nearest_loop(nir_cf_node * node)420  nearest_loop(nir_cf_node *node)
421  {
422     while (node->type != nir_cf_node_loop) {
423        node = node->parent;
424     }
425  
426     return nir_cf_node_as_loop(node);
427  }
428  
429  void
nir_loop_add_continue_construct(nir_loop * loop)430  nir_loop_add_continue_construct(nir_loop *loop)
431  {
432     assert(!nir_loop_has_continue_construct(loop));
433  
434     nir_block *cont = nir_block_create(ralloc_parent(loop));
435     exec_list_push_tail(&loop->continue_list, &cont->cf_node.node);
436     cont->cf_node.parent = &loop->cf_node;
437  
438     /* change predecessors and successors */
439     nir_block *header = nir_loop_first_block(loop);
440     nir_block *preheader = nir_block_cf_tree_prev(header);
441     set_foreach(header->predecessors, entry) {
442        nir_block *pred = (nir_block *)entry->key;
443        if (pred != preheader)
444           replace_successor(pred, header, cont);
445     }
446  
447     link_blocks(cont, header, NULL);
448  }
449  
450  void
nir_loop_remove_continue_construct(nir_loop * loop)451  nir_loop_remove_continue_construct(nir_loop *loop)
452  {
453     assert(nir_cf_list_is_empty_block(&loop->continue_list));
454  
455     /* change predecessors and successors */
456     nir_block *header = nir_loop_first_block(loop);
457     nir_block *cont = nir_loop_first_continue_block(loop);
458     set_foreach(cont->predecessors, entry) {
459        nir_block *pred = (nir_block *)entry->key;
460        replace_successor(pred, cont, header);
461     }
462     block_remove_pred(header, cont);
463  
464     exec_node_remove(&cont->cf_node.node);
465  }
466  
467  static void
remove_phi_src(nir_block * block,nir_block * pred)468  remove_phi_src(nir_block *block, nir_block *pred)
469  {
470     nir_foreach_phi(phi, block) {
471        nir_foreach_phi_src_safe(src, phi) {
472           if (src->pred == pred) {
473              list_del(&src->src.use_link);
474              exec_node_remove(&src->node);
475              gc_free(src);
476           }
477        }
478     }
479  }
480  
481  /*
482   * update the CFG after a jump instruction has been added to the end of a block
483   */
484  
485  void
nir_handle_add_jump(nir_block * block)486  nir_handle_add_jump(nir_block *block)
487  {
488     nir_instr *instr = nir_block_last_instr(block);
489     nir_jump_instr *jump_instr = nir_instr_as_jump(instr);
490  
491     if (block->successors[0])
492        remove_phi_src(block->successors[0], block);
493     if (block->successors[1])
494        remove_phi_src(block->successors[1], block);
495     unlink_block_successors(block);
496  
497     nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
498     nir_metadata_preserve(impl, nir_metadata_none);
499  
500     switch (jump_instr->type) {
501     case nir_jump_return:
502     case nir_jump_halt:
503        link_blocks(block, impl->end_block, NULL);
504        break;
505  
506     case nir_jump_break: {
507        nir_loop *loop = nearest_loop(&block->cf_node);
508        nir_cf_node *after = nir_cf_node_next(&loop->cf_node);
509        nir_block *after_block = nir_cf_node_as_block(after);
510        link_blocks(block, after_block, NULL);
511        break;
512     }
513  
514     case nir_jump_continue: {
515        nir_loop *loop = nearest_loop(&block->cf_node);
516        nir_block *cont_block = nir_loop_continue_target(loop);
517        link_blocks(block, cont_block, NULL);
518        break;
519     }
520  
521     case nir_jump_goto:
522        link_blocks(block, jump_instr->target, NULL);
523        break;
524  
525     case nir_jump_goto_if:
526        link_blocks(block, jump_instr->else_target, jump_instr->target);
527        break;
528  
529     default:
530        unreachable("Invalid jump type");
531     }
532  }
533  
534  /* Removes the successor of a block with a jump. Note that the jump to be
535   * eliminated may be free-floating.
536   */
537  
538  static void
unlink_jump(nir_block * block,nir_jump_type type,bool add_normal_successors)539  unlink_jump(nir_block *block, nir_jump_type type, bool add_normal_successors)
540  {
541     if (block->successors[0])
542        remove_phi_src(block->successors[0], block);
543     if (block->successors[1])
544        remove_phi_src(block->successors[1], block);
545  
546     unlink_block_successors(block);
547     if (add_normal_successors)
548        block_add_normal_succs(block);
549  }
550  
551  void
nir_handle_remove_jump(nir_block * block,nir_jump_type type)552  nir_handle_remove_jump(nir_block *block, nir_jump_type type)
553  {
554     unlink_jump(block, type, true);
555  
556     nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
557     nir_metadata_preserve(impl, nir_metadata_none);
558  }
559  
560  static void
update_if_uses(nir_cf_node * node)561  update_if_uses(nir_cf_node *node)
562  {
563     if (node->type != nir_cf_node_if)
564        return;
565  
566     nir_if *if_stmt = nir_cf_node_as_if(node);
567     nir_src_set_parent_if(&if_stmt->condition, if_stmt);
568  
569     list_addtail(&if_stmt->condition.use_link,
570                  &if_stmt->condition.ssa->uses);
571  }
572  
573  /**
574   * Stitch two basic blocks together into one. The aggregate must have the same
575   * predecessors as the first and the same successors as the second.
576   *
577   * Returns a cursor pointing at the end of the before block (i.e.m between the
578   * two blocks) once stiched together.
579   */
580  
581  static nir_cursor
stitch_blocks(nir_block * before,nir_block * after)582  stitch_blocks(nir_block *before, nir_block *after)
583  {
584     /*
585      * We move after into before, so we have to deal with up to 2 successors vs.
586      * possibly a large number of predecessors.
587      *
588      * TODO: special case when before is empty and after isn't?
589      */
590  
591     if (nir_block_ends_in_jump(before)) {
592        assert(exec_list_is_empty(&after->instr_list));
593        if (after->successors[0])
594           remove_phi_src(after->successors[0], after);
595        if (after->successors[1])
596           remove_phi_src(after->successors[1], after);
597        unlink_block_successors(after);
598        exec_node_remove(&after->cf_node.node);
599  
600        return nir_after_block(before);
601     } else {
602        nir_instr *last_before_instr = nir_block_last_instr(before);
603  
604        move_successors(after, before);
605  
606        foreach_list_typed(nir_instr, instr, node, &after->instr_list) {
607           instr->block = before;
608        }
609  
610        exec_list_append(&before->instr_list, &after->instr_list);
611        exec_node_remove(&after->cf_node.node);
612  
613        return last_before_instr ? nir_after_instr(last_before_instr) : nir_before_block(before);
614     }
615  }
616  
617  void
nir_cf_node_insert(nir_cursor cursor,nir_cf_node * node)618  nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node)
619  {
620     nir_block *before, *after;
621  
622     split_block_cursor(cursor, &before, &after);
623  
624     if (node->type == nir_cf_node_block) {
625        nir_block *block = nir_cf_node_as_block(node);
626        exec_node_insert_after(&before->cf_node.node, &block->cf_node.node);
627        block->cf_node.parent = before->cf_node.parent;
628        /* stitch_blocks() assumes that any block that ends with a jump has
629         * already been setup with the correct successors, so we need to set
630         * up jumps here as the block is being inserted.
631         */
632        if (nir_block_ends_in_jump(block))
633           nir_handle_add_jump(block);
634  
635        stitch_blocks(block, after);
636        stitch_blocks(before, block);
637     } else {
638        update_if_uses(node);
639        insert_non_block(before, node, after);
640     }
641  }
642  
643  static bool
replace_ssa_def_uses(nir_def * def,void * void_impl)644  replace_ssa_def_uses(nir_def *def, void *void_impl)
645  {
646     nir_function_impl *impl = void_impl;
647  
648     nir_undef_instr *undef =
649        nir_undef_instr_create(impl->function->shader,
650                               def->num_components,
651                               def->bit_size);
652     nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
653     nir_def_rewrite_uses(def, &undef->def);
654     return true;
655  }
656  
657  static void
cleanup_cf_node(nir_cf_node * node,nir_function_impl * impl)658  cleanup_cf_node(nir_cf_node *node, nir_function_impl *impl)
659  {
660     switch (node->type) {
661     case nir_cf_node_block: {
662        nir_block *block = nir_cf_node_as_block(node);
663        /* We need to walk the instructions and clean up defs/uses */
664        nir_foreach_instr_safe(instr, block) {
665           if (instr->type == nir_instr_type_jump) {
666              nir_jump_instr *jump = nir_instr_as_jump(instr);
667              unlink_jump(block, jump->type, false);
668              if (jump->type == nir_jump_goto_if)
669                 nir_instr_clear_src(instr, &jump->condition);
670           } else {
671              nir_foreach_def(instr, replace_ssa_def_uses, impl);
672              nir_instr_remove(instr);
673           }
674        }
675        break;
676     }
677  
678     case nir_cf_node_if: {
679        nir_if *if_stmt = nir_cf_node_as_if(node);
680        foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list)
681           cleanup_cf_node(child, impl);
682        foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list)
683           cleanup_cf_node(child, impl);
684  
685        list_del(&if_stmt->condition.use_link);
686        break;
687     }
688  
689     case nir_cf_node_loop: {
690        nir_loop *loop = nir_cf_node_as_loop(node);
691        foreach_list_typed(nir_cf_node, child, node, &loop->body)
692           cleanup_cf_node(child, impl);
693        foreach_list_typed(nir_cf_node, child, node, &loop->continue_list)
694           cleanup_cf_node(child, impl);
695        break;
696     }
697     case nir_cf_node_function: {
698        nir_function_impl *impl = nir_cf_node_as_function(node);
699        foreach_list_typed(nir_cf_node, child, node, &impl->body)
700           cleanup_cf_node(child, impl);
701        break;
702     }
703     default:
704        unreachable("Invalid CF node type");
705     }
706  }
707  
708  /**
709   * Extracts everything between two cursors.  Returns the cursor which is
710   * equivalent to the old begin/end curosors.
711   */
712  nir_cursor
nir_cf_extract(nir_cf_list * extracted,nir_cursor begin,nir_cursor end)713  nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end)
714  {
715     nir_block *block_begin, *block_end, *block_before, *block_after;
716  
717     if (nir_cursors_equal(begin, end)) {
718        exec_list_make_empty(&extracted->list);
719        extracted->impl = NULL; /* we shouldn't need this */
720        return begin;
721     }
722  
723     split_block_cursor(begin, &block_before, &block_begin);
724  
725     /* Splitting a block twice with two cursors created before either split is
726      * tricky and there are a couple of places it can go wrong if both cursors
727      * point to the same block.  One is if the second cursor is an block-based
728      * cursor and, thanks to the split above, it ends up pointing to the wrong
729      * block.  If it's a before_block cursor and it's in the same block as
730      * begin, then begin must also be a before_block cursor and it should be
731      * caught by the nir_cursors_equal check above and we won't get here.  If
732      * it's an after_block cursor, we need to re-adjust to ensure that it
733      * points to the second one of the split blocks, regardless of which it is.
734      */
735     if (end.option == nir_cursor_after_block && end.block == block_before)
736        end.block = block_begin;
737  
738     split_block_cursor(end, &block_end, &block_after);
739  
740     /* The second place this can all go wrong is that it could be that the
741      * second split places the original block after the new block in which case
742      * the block_begin pointer that we saved off above is pointing to the block
743      * at the end rather than the block in the middle like it's supposed to be.
744      * In this case, we have to re-adjust begin_block to point to the middle
745      * one.
746      */
747     if (block_begin == block_after)
748        block_begin = block_end;
749  
750     extracted->impl = nir_cf_node_get_function(&block_begin->cf_node);
751     exec_list_make_empty(&extracted->list);
752  
753     /* Dominance and other block-related information is toast. */
754     nir_metadata_preserve(extracted->impl, nir_metadata_none);
755  
756     nir_cf_node *cf_node = &block_begin->cf_node;
757     nir_cf_node *cf_node_end = &block_end->cf_node;
758     while (true) {
759        nir_cf_node *next = nir_cf_node_next(cf_node);
760  
761        exec_node_remove(&cf_node->node);
762        cf_node->parent = NULL;
763        exec_list_push_tail(&extracted->list, &cf_node->node);
764  
765        if (cf_node == cf_node_end)
766           break;
767  
768        cf_node = next;
769     }
770  
771     return stitch_blocks(block_before, block_after);
772  }
773  
774  static void
relink_jump_halt_cf_node(nir_cf_node * node,nir_block * end_block)775  relink_jump_halt_cf_node(nir_cf_node *node, nir_block *end_block)
776  {
777     switch (node->type) {
778     case nir_cf_node_block: {
779        nir_block *block = nir_cf_node_as_block(node);
780        nir_instr *last_instr = nir_block_last_instr(block);
781        if (last_instr == NULL || last_instr->type != nir_instr_type_jump)
782           break;
783  
784        nir_jump_instr *jump = nir_instr_as_jump(last_instr);
785        /* We can't move a CF list from one function to another while we still
786         * have returns.
787         */
788        assert(jump->type != nir_jump_return);
789  
790        if (jump->type == nir_jump_halt) {
791           unlink_block_successors(block);
792           link_blocks(block, end_block, NULL);
793        }
794        break;
795     }
796  
797     case nir_cf_node_if: {
798        nir_if *if_stmt = nir_cf_node_as_if(node);
799        foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list)
800           relink_jump_halt_cf_node(child, end_block);
801        foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list)
802           relink_jump_halt_cf_node(child, end_block);
803        break;
804     }
805  
806     case nir_cf_node_loop: {
807        nir_loop *loop = nir_cf_node_as_loop(node);
808        foreach_list_typed(nir_cf_node, child, node, &loop->body)
809           relink_jump_halt_cf_node(child, end_block);
810        foreach_list_typed(nir_cf_node, child, node, &loop->continue_list)
811           relink_jump_halt_cf_node(child, end_block);
812        break;
813     }
814  
815     case nir_cf_node_function:
816        unreachable("Cannot insert a function in a function");
817  
818     default:
819        unreachable("Invalid CF node type");
820     }
821  }
822  
823  /**
824   * Inserts a list at a given cursor. Returns the cursor at the end of the
825   * insertion (i.e., at the end of the instructions contained in cf_list).
826   */
827  nir_cursor
nir_cf_reinsert(nir_cf_list * cf_list,nir_cursor cursor)828  nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor)
829  {
830     nir_block *before, *after;
831  
832     if (exec_list_is_empty(&cf_list->list))
833        return cursor;
834  
835     nir_function_impl *cursor_impl =
836        nir_cf_node_get_function(&nir_cursor_current_block(cursor)->cf_node);
837     if (cf_list->impl != cursor_impl) {
838        foreach_list_typed(nir_cf_node, node, node, &cf_list->list)
839           relink_jump_halt_cf_node(node, cursor_impl->end_block);
840     }
841  
842     split_block_cursor(cursor, &before, &after);
843  
844     foreach_list_typed_safe(nir_cf_node, node, node, &cf_list->list) {
845        exec_node_remove(&node->node);
846        node->parent = before->cf_node.parent;
847        exec_node_insert_node_before(&after->cf_node.node, &node->node);
848     }
849  
850     stitch_blocks(before,
851                   nir_cf_node_as_block(nir_cf_node_next(&before->cf_node)));
852     return stitch_blocks(nir_cf_node_as_block(nir_cf_node_prev(&after->cf_node)),
853                          after);
854  }
855  
856  void
nir_cf_delete(nir_cf_list * cf_list)857  nir_cf_delete(nir_cf_list *cf_list)
858  {
859     foreach_list_typed(nir_cf_node, node, node, &cf_list->list) {
860        cleanup_cf_node(node, cf_list->impl);
861     }
862  }
863  
864  struct block_index {
865     nir_block *block;
866     uint32_t index;
867  };
868  
869  static void
calc_cfg_post_dfs_indices(nir_function_impl * impl,nir_block * block,struct block_index * blocks,uint32_t * count)870  calc_cfg_post_dfs_indices(nir_function_impl *impl,
871                            nir_block *block,
872                            struct block_index *blocks,
873                            uint32_t *count)
874  {
875     if (block == impl->end_block)
876        return;
877  
878     assert(block->index < impl->num_blocks);
879  
880     if (blocks[block->index].block != NULL) {
881        assert(blocks[block->index].block == block);
882        return;
883     }
884  
885     blocks[block->index].block = block;
886  
887     for (uint32_t i = 0; i < ARRAY_SIZE(block->successors); i++) {
888        if (block->successors[i] != NULL)
889           calc_cfg_post_dfs_indices(impl, block->successors[i], blocks, count);
890     }
891  
892     /* Pre-increment so that unreachable blocks have an index of 0 */
893     blocks[block->index].index = ++(*count);
894  }
895  
896  static int
rev_cmp_block_index(const void * _a,const void * _b)897  rev_cmp_block_index(const void *_a, const void *_b)
898  {
899     const struct block_index *a = _a, *b = _b;
900  
901     return b->index - a->index;
902  }
903  
904  void
nir_sort_unstructured_blocks(nir_function_impl * impl)905  nir_sort_unstructured_blocks(nir_function_impl *impl)
906  {
907     /* Re-index the blocks.
908      *
909      * We hand-roll it here instead of calling the helper because we also want
910      * to assert that there are no structured control-flow constructs.
911      */
912     impl->num_blocks = 0;
913     foreach_list_typed(nir_cf_node, node, node, &impl->body) {
914        nir_block *block = nir_cf_node_as_block(node);
915        block->index = impl->num_blocks++;
916     }
917  
918     struct block_index *blocks =
919        rzalloc_array(NULL, struct block_index, impl->num_blocks);
920  
921     uint32_t count = 0;
922     calc_cfg_post_dfs_indices(impl, nir_start_block(impl), blocks, &count);
923     assert(count <= impl->num_blocks);
924  
925     qsort(blocks, impl->num_blocks, sizeof(*blocks), rev_cmp_block_index);
926  
927     struct exec_list dead_blocks;
928     exec_list_move_nodes_to(&impl->body, &dead_blocks);
929  
930     for (uint32_t i = 0; i < count; i++) {
931        nir_block *block = blocks[i].block;
932        exec_node_remove(&block->cf_node.node);
933        block->index = i;
934        exec_list_push_tail(&impl->body, &block->cf_node.node);
935     }
936     impl->end_block->index = count;
937  
938     for (uint32_t i = count; i < impl->num_blocks; i++) {
939        assert(blocks[i].index == 0);
940        assert(blocks[i].block == NULL);
941     }
942  
943     foreach_list_typed_safe(nir_cf_node, node, node, &dead_blocks)
944        cleanup_cf_node(node, impl);
945  
946     ralloc_free(blocks);
947  
948     /* Dominance is toast but we indexed blocks as part of this pass. */
949     impl->valid_metadata &= nir_metadata_dominance;
950     impl->valid_metadata |= nir_metadata_block_index;
951  }
952