src/compiler/nir/nir_control_flow.c

   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 bool
  49 block_ends_in_jump(nir_block *block)
  50 {
  51    return !exec_list_is_empty(&block->instr_list) &&
  52           nir_block_last_instr(block)->type == nir_instr_type_jump;
  53 }
  54
  55 static inline void
  56 block_add_pred(nir_block *block, nir_block *pred)
  57 {
  58    _mesa_set_add(block->predecessors, pred);
  59 }
  60
  61 static inline void
  62 block_remove_pred(nir_block *block, nir_block *pred)
  63 {
  64    struct set_entry *entry = _mesa_set_search(block->predecessors, pred);
  65
  66    assert(entry);
  67
  68    _mesa_set_remove(block->predecessors, entry);
  69 }
  70
  71 static void
  72 link_blocks(nir_block *pred, nir_block *succ1, nir_block *succ2)
  73 {
  74    pred->successors[0] = succ1;
  75    if (succ1 != NULL)
  76       block_add_pred(succ1, pred);
  77
  78    pred->successors[1] = succ2;
  79    if (succ2 != NULL)
  80       block_add_pred(succ2, pred);
  81 }
  82
  83 static void
  84 unlink_blocks(nir_block *pred, nir_block *succ)
  85 {
  86    if (pred->successors[0] == succ) {
  87       pred->successors[0] = pred->successors[1];
  88       pred->successors[1] = NULL;
  89    } else {
  90       assert(pred->successors[1] == succ);
  91       pred->successors[1] = NULL;
  92    }
  93
  94    block_remove_pred(succ, pred);
  95 }
  96
  97 static void
  98 unlink_block_successors(nir_block *block)
  99 {
 100    if (block->successors[1] != NULL)
 101       unlink_blocks(block, block->successors[1]);
 102    if (block->successors[0] != NULL)
 103       unlink_blocks(block, block->successors[0]);
 104 }
 105
 106 static void
 107 link_non_block_to_block(nir_cf_node *node, nir_block *block)
 108 {
 109    if (node->type == nir_cf_node_if) {
 110       /*
 111        * We're trying to link an if to a block after it; this just means linking
 112        * the last block of the then and else branches.
 113        */
 114
 115       nir_if *if_stmt = nir_cf_node_as_if(node);
 116
 117       nir_cf_node *last_then = nir_if_last_then_node(if_stmt);
 118       assert(last_then->type == nir_cf_node_block);
 119       nir_block *last_then_block = nir_cf_node_as_block(last_then);
 120
 121       nir_cf_node *last_else = nir_if_last_else_node(if_stmt);
 122       assert(last_else->type == nir_cf_node_block);
 123       nir_block *last_else_block = nir_cf_node_as_block(last_else);
 124
 125       if (!block_ends_in_jump(last_then_block)) {
 126          unlink_block_successors(last_then_block);
 127          link_blocks(last_then_block, block, NULL);
 128       }
 129
 130       if (!block_ends_in_jump(last_else_block)) {
 131          unlink_block_successors(last_else_block);
 132          link_blocks(last_else_block, block, NULL);
 133       }
 134    } else {
 135       assert(node->type == nir_cf_node_loop);
 136    }
 137 }
 138
 139 static void
 140 link_block_to_non_block(nir_block *block, nir_cf_node *node)
 141 {
 142    if (node->type == nir_cf_node_if) {
 143       /*
 144        * We're trying to link a block to an if after it; this just means linking
 145        * the block to the first block of the then and else branches.
 146        */
 147
 148       nir_if *if_stmt = nir_cf_node_as_if(node);
 149
 150       nir_cf_node *first_then = nir_if_first_then_node(if_stmt);
 151       assert(first_then->type == nir_cf_node_block);
 152       nir_block *first_then_block = nir_cf_node_as_block(first_then);
 153
 154       nir_cf_node *first_else = nir_if_first_else_node(if_stmt);
 155       assert(first_else->type == nir_cf_node_block);
 156       nir_block *first_else_block = nir_cf_node_as_block(first_else);
 157
 158       unlink_block_successors(block);
 159       link_blocks(block, first_then_block, first_else_block);
 160    } else {
 161       /*
 162        * For similar reasons as the corresponding case in
 163        * link_non_block_to_block(), don't worry about if the loop header has
 164        * any predecessors that need to be unlinked.
 165        */
 166
 167       assert(node->type == nir_cf_node_loop);
 168
 169       nir_loop *loop = nir_cf_node_as_loop(node);
 170
 171       nir_cf_node *loop_header = nir_loop_first_cf_node(loop);
 172       assert(loop_header->type == nir_cf_node_block);
 173       nir_block *loop_header_block = nir_cf_node_as_block(loop_header);
 174
 175       unlink_block_successors(block);
 176       link_blocks(block, loop_header_block, NULL);
 177    }
 178
 179 }
 180
 181 /**
 182  * Replace a block's successor with a different one.
 183  */
 184 static void
 185 replace_successor(nir_block *block, nir_block *old_succ, nir_block *new_succ)
 186 {
 187    if (block->successors[0] == old_succ) {
 188       block->successors[0] = new_succ;
 189    } else {
 190       assert(block->successors[1] == old_succ);
 191       block->successors[1] = new_succ;
 192    }
 193
 194    block_remove_pred(old_succ, block);
 195    block_add_pred(new_succ, block);
 196 }
 197
 198 /**
 199  * Takes a basic block and inserts a new empty basic block before it, making its
 200  * predecessors point to the new block. This essentially splits the block into
 201  * an empty header and a body so that another non-block CF node can be inserted
 202  * between the two. Note that this does *not* link the two basic blocks, so
 203  * some kind of cleanup *must* be performed after this call.
 204  */
 205
 206 static nir_block *
 207 split_block_beginning(nir_block *block)
 208 {
 209    nir_block *new_block = nir_block_create(ralloc_parent(block));
 210    new_block->cf_node.parent = block->cf_node.parent;
 211    exec_node_insert_node_before(&block->cf_node.node, &new_block->cf_node.node);
 212
 213    struct set_entry *entry;
 214    set_foreach(block->predecessors, entry) {
 215       nir_block *pred = (nir_block *) entry->key;
 216       replace_successor(pred, block, new_block);
 217    }
 218
 219    /* Any phi nodes must stay part of the new block, or else their
 220     * sourcse will be messed up. This will reverse the order of the phi's, but
 221     * order shouldn't matter.
 222     */
 223    nir_foreach_instr_safe(instr, block) {
 224       if (instr->type != nir_instr_type_phi)
 225          break;
 226
 227       exec_node_remove(&instr->node);
 228       instr->block = new_block;
 229       exec_list_push_head(&new_block->instr_list, &instr->node);
 230    }
 231
 232    return new_block;
 233 }
 234
 235 static void
 236 rewrite_phi_preds(nir_block *block, nir_block *old_pred, nir_block *new_pred)
 237 {
 238    nir_foreach_instr_safe(instr, block) {
 239       if (instr->type != nir_instr_type_phi)
 240          break;
 241
 242       nir_phi_instr *phi = nir_instr_as_phi(instr);
 243       nir_foreach_phi_src(src, phi) {
 244          if (src->pred == old_pred) {
 245             src->pred = new_pred;
 246             break;
 247          }
 248       }
 249    }
 250 }
 251
 252 static void
 253 insert_phi_undef(nir_block *block, nir_block *pred)
 254 {
 255    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 256    nir_foreach_instr(instr, block) {
 257       if (instr->type != nir_instr_type_phi)
 258          break;
 259
 260       nir_phi_instr *phi = nir_instr_as_phi(instr);
 261       nir_ssa_undef_instr *undef =
 262          nir_ssa_undef_instr_create(ralloc_parent(phi),
 263                                     phi->dest.ssa.num_components,
 264                                     phi->dest.ssa.bit_size);
 265       nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 266       nir_phi_src *src = ralloc(phi, nir_phi_src);
 267       src->pred = pred;
 268       src->src.parent_instr = &phi->instr;
 269       src->src.is_ssa = true;
 270       src->src.ssa = &undef->def;
 271
 272       list_addtail(&src->src.use_link, &undef->def.uses);
 273
 274       exec_list_push_tail(&phi->srcs, &src->node);
 275    }
 276 }
 277
 278 /**
 279  * Moves the successors of source to the successors of dest, leaving both
 280  * successors of source NULL.
 281  */
 282
 283 static void
 284 move_successors(nir_block *source, nir_block *dest)
 285 {
 286    nir_block *succ1 = source->successors[0];
 287    nir_block *succ2 = source->successors[1];
 288
 289    if (succ1) {
 290       unlink_blocks(source, succ1);
 291       rewrite_phi_preds(succ1, source, dest);
 292    }
 293
 294    if (succ2) {
 295       unlink_blocks(source, succ2);
 296       rewrite_phi_preds(succ2, source, dest);
 297    }
 298
 299    unlink_block_successors(dest);
 300    link_blocks(dest, succ1, succ2);
 301 }
 302
 303 /* Given a basic block with no successors that has been inserted into the
 304  * control flow tree, gives it the successors it would normally have assuming
 305  * it doesn't end in a jump instruction. Also inserts phi sources with undefs
 306  * if necessary.
 307  */
 308 static void
 309 block_add_normal_succs(nir_block *block)
 310 {
 311    if (exec_node_is_tail_sentinel(block->cf_node.node.next)) {
 312       nir_cf_node *parent = block->cf_node.parent;
 313       if (parent->type == nir_cf_node_if) {
 314          nir_cf_node *next = nir_cf_node_next(parent);
 315          assert(next->type == nir_cf_node_block);
 316          nir_block *next_block = nir_cf_node_as_block(next);
 317
 318          link_blocks(block, next_block, NULL);
 319       } else if (parent->type == nir_cf_node_loop) {
 320          nir_loop *loop = nir_cf_node_as_loop(parent);
 321
 322          nir_cf_node *head = nir_loop_first_cf_node(loop);
 323          assert(head->type == nir_cf_node_block);
 324          nir_block *head_block = nir_cf_node_as_block(head);
 325
 326          link_blocks(block, head_block, NULL);
 327          insert_phi_undef(head_block, block);
 328       } else {
 329          assert(parent->type == nir_cf_node_function);
 330          nir_function_impl *impl = nir_cf_node_as_function(parent);
 331          link_blocks(block, impl->end_block, NULL);
 332       }
 333    } else {
 334       nir_cf_node *next = nir_cf_node_next(&block->cf_node);
 335       if (next->type == nir_cf_node_if) {
 336          nir_if *next_if = nir_cf_node_as_if(next);
 337
 338          nir_cf_node *first_then = nir_if_first_then_node(next_if);
 339          assert(first_then->type == nir_cf_node_block);
 340          nir_block *first_then_block = nir_cf_node_as_block(first_then);
 341
 342          nir_cf_node *first_else = nir_if_first_else_node(next_if);
 343          assert(first_else->type == nir_cf_node_block);
 344          nir_block *first_else_block = nir_cf_node_as_block(first_else);
 345
 346          link_blocks(block, first_then_block, first_else_block);
 347       } else {
 348          assert(next->type == nir_cf_node_loop);
 349          nir_loop *next_loop = nir_cf_node_as_loop(next);
 350
 351          nir_cf_node *first = nir_loop_first_cf_node(next_loop);
 352          assert(first->type == nir_cf_node_block);
 353          nir_block *first_block = nir_cf_node_as_block(first);
 354
 355          link_blocks(block, first_block, NULL);
 356          insert_phi_undef(first_block, block);
 357       }
 358    }
 359 }
 360
 361 static nir_block *
 362 split_block_end(nir_block *block)
 363 {
 364    nir_block *new_block = nir_block_create(ralloc_parent(block));
 365    new_block->cf_node.parent = block->cf_node.parent;
 366    exec_node_insert_after(&block->cf_node.node, &new_block->cf_node.node);
 367
 368    if (block_ends_in_jump(block)) {
 369       /* Figure out what successor block would've had if it didn't have a jump
 370        * instruction, and make new_block have that successor.
 371        */
 372       block_add_normal_succs(new_block);
 373    } else {
 374       move_successors(block, new_block);
 375    }
 376
 377    return new_block;
 378 }
 379
 380 static nir_block *
 381 split_block_before_instr(nir_instr *instr)
 382 {
 383    assert(instr->type != nir_instr_type_phi);
 384    nir_block *new_block = split_block_beginning(instr->block);
 385
 386    nir_foreach_instr_safe(cur_instr, instr->block) {
 387       if (cur_instr == instr)
 388          break;
 389
 390       exec_node_remove(&cur_instr->node);
 391       cur_instr->block = new_block;
 392       exec_list_push_tail(&new_block->instr_list, &cur_instr->node);
 393    }
 394
 395    return new_block;
 396 }
 397
 398 /* Splits a basic block at the point specified by the cursor. The "before" and
 399  * "after" arguments are filled out with the blocks resulting from the split
 400  * if non-NULL. Note that the "beginning" of the block is actually interpreted
 401  * as before the first non-phi instruction, and it's illegal to split a block
 402  * before a phi instruction.
 403  */
 404
 405 static void
 406 split_block_cursor(nir_cursor cursor,
 407                    nir_block **_before, nir_block **_after)
 408 {
 409    nir_block *before, *after;
 410    switch (cursor.option) {
 411    case nir_cursor_before_block:
 412       after = cursor.block;
 413       before = split_block_beginning(cursor.block);
 414       break;
 415
 416    case nir_cursor_after_block:
 417       before = cursor.block;
 418       after = split_block_end(cursor.block);
 419       break;
 420
 421    case nir_cursor_before_instr:
 422       after = cursor.instr->block;
 423       before = split_block_before_instr(cursor.instr);
 424       break;
 425
 426    case nir_cursor_after_instr:
 427       /* We lower this to split_block_before_instr() so that we can keep the
 428        * after-a-jump-instr case contained to split_block_end().
 429        */
 430       if (nir_instr_is_last(cursor.instr)) {
 431          before = cursor.instr->block;
 432          after = split_block_end(cursor.instr->block);
 433       } else {
 434          after = cursor.instr->block;
 435          before = split_block_before_instr(nir_instr_next(cursor.instr));
 436       }
 437       break;
 438
 439    default:
 440       unreachable("not reached");
 441    }
 442
 443    if (_before)
 444       *_before = before;
 445    if (_after)
 446       *_after = after;
 447 }
 448
 449 /**
 450  * Inserts a non-basic block between two basic blocks and links them together.
 451  */
 452
 453 static void
 454 insert_non_block(nir_block *before, nir_cf_node *node, nir_block *after)
 455 {
 456    node->parent = before->cf_node.parent;
 457    exec_node_insert_after(&before->cf_node.node, &node->node);
 458    link_block_to_non_block(before, node);
 459    link_non_block_to_block(node, after);
 460 }
 461
 462 /* walk up the control flow tree to find the innermost enclosed loop */
 463 static nir_loop *
 464 nearest_loop(nir_cf_node *node)
 465 {
 466    while (node->type != nir_cf_node_loop) {
 467       node = node->parent;
 468    }
 469
 470    return nir_cf_node_as_loop(node);
 471 }
 472
 473 /*
 474  * update the CFG after a jump instruction has been added to the end of a block
 475  */
 476
 477 void
 478 nir_handle_add_jump(nir_block *block)
 479 {
 480    nir_instr *instr = nir_block_last_instr(block);
 481    nir_jump_instr *jump_instr = nir_instr_as_jump(instr);
 482
 483    unlink_block_successors(block);
 484
 485    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 486    nir_metadata_preserve(impl, nir_metadata_none);
 487
 488    if (jump_instr->type == nir_jump_break ||
 489        jump_instr->type == nir_jump_continue) {
 490       nir_loop *loop = nearest_loop(&block->cf_node);
 491
 492       if (jump_instr->type == nir_jump_continue) {
 493          nir_cf_node *first_node = nir_loop_first_cf_node(loop);
 494          assert(first_node->type == nir_cf_node_block);
 495          nir_block *first_block = nir_cf_node_as_block(first_node);
 496          link_blocks(block, first_block, NULL);
 497       } else {
 498          nir_cf_node *after = nir_cf_node_next(&loop->cf_node);
 499          assert(after->type == nir_cf_node_block);
 500          nir_block *after_block = nir_cf_node_as_block(after);
 501          link_blocks(block, after_block, NULL);
 502       }
 503    } else {
 504       assert(jump_instr->type == nir_jump_return);
 505       link_blocks(block, impl->end_block, NULL);
 506    }
 507 }
 508
 509 static void
 510 remove_phi_src(nir_block *block, nir_block *pred)
 511 {
 512    nir_foreach_instr(instr, block) {
 513       if (instr->type != nir_instr_type_phi)
 514          break;
 515
 516       nir_phi_instr *phi = nir_instr_as_phi(instr);
 517       nir_foreach_phi_src_safe(src, phi) {
 518          if (src->pred == pred) {
 519             list_del(&src->src.use_link);
 520             exec_node_remove(&src->node);
 521          }
 522       }
 523    }
 524 }
 525
 526 /* Removes the successor of a block with a jump. Note that the jump to be
 527  * eliminated may be free-floating.
 528  */
 529
 530 static void
 531 unlink_jump(nir_block *block, nir_jump_type type, bool add_normal_successors)
 532 {
 533    nir_block *next = block->successors[0];
 534
 535    if (block->successors[0])
 536       remove_phi_src(block->successors[0], block);
 537    if (block->successors[1])
 538       remove_phi_src(block->successors[1], block);
 539
 540    unlink_block_successors(block);
 541    if (add_normal_successors)
 542       block_add_normal_succs(block);
 543 }
 544
 545 void
 546 nir_handle_remove_jump(nir_block *block, nir_jump_type type)
 547 {
 548    unlink_jump(block, type, true);
 549
 550    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 551    nir_metadata_preserve(impl, nir_metadata_none);
 552 }
 553
 554 static void
 555 update_if_uses(nir_cf_node *node)
 556 {
 557    if (node->type != nir_cf_node_if)
 558       return;
 559
 560    nir_if *if_stmt = nir_cf_node_as_if(node);
 561
 562    if_stmt->condition.parent_if = if_stmt;
 563    if (if_stmt->condition.is_ssa) {
 564       list_addtail(&if_stmt->condition.use_link,
 565                    &if_stmt->condition.ssa->if_uses);
 566    } else {
 567       list_addtail(&if_stmt->condition.use_link,
 568                    &if_stmt->condition.reg.reg->if_uses);
 569    }
 570 }
 571
 572 /**
 573  * Stitch two basic blocks together into one. The aggregate must have the same
 574  * predecessors as the first and the same successors as the second.
 575  */
 576
 577 static void
 578 stitch_blocks(nir_block *before, nir_block *after)
 579 {
 580    /*
 581     * We move after into before, so we have to deal with up to 2 successors vs.
 582     * possibly a large number of predecessors.
 583     *
 584     * TODO: special case when before is empty and after isn't?
 585     */
 586
 587    if (block_ends_in_jump(before)) {
 588       assert(exec_list_is_empty(&after->instr_list));
 589       if (after->successors[0])
 590          remove_phi_src(after->successors[0], after);
 591       if (after->successors[1])
 592          remove_phi_src(after->successors[1], after);
 593       unlink_block_successors(after);
 594       exec_node_remove(&after->cf_node.node);
 595    } else {
 596       move_successors(after, before);
 597
 598       foreach_list_typed(nir_instr, instr, node, &after->instr_list) {
 599          instr->block = before;
 600       }
 601
 602       exec_list_append(&before->instr_list, &after->instr_list);
 603       exec_node_remove(&after->cf_node.node);
 604    }
 605 }
 606
 607 void
 608 nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node)
 609 {
 610    nir_block *before, *after;
 611
 612    split_block_cursor(cursor, &before, &after);
 613
 614    if (node->type == nir_cf_node_block) {
 615       nir_block *block = nir_cf_node_as_block(node);
 616       exec_node_insert_after(&before->cf_node.node, &block->cf_node.node);
 617       block->cf_node.parent = before->cf_node.parent;
 618       /* stitch_blocks() assumes that any block that ends with a jump has
 619        * already been setup with the correct successors, so we need to set
 620        * up jumps here as the block is being inserted.
 621        */
 622       if (block_ends_in_jump(block))
 623          nir_handle_add_jump(block);
 624
 625       stitch_blocks(block, after);
 626       stitch_blocks(before, block);
 627    } else {
 628       update_if_uses(node);
 629       insert_non_block(before, node, after);
 630    }
 631 }
 632
 633 static bool
 634 replace_ssa_def_uses(nir_ssa_def *def, void *void_impl)
 635 {
 636    nir_function_impl *impl = void_impl;
 637    void *mem_ctx = ralloc_parent(impl);
 638
 639    nir_ssa_undef_instr *undef =
 640       nir_ssa_undef_instr_create(mem_ctx, def->num_components,
 641                                  def->bit_size);
 642    nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 643    nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(&undef->def));
 644    return true;
 645 }
 646
 647 static void
 648 cleanup_cf_node(nir_cf_node *node, nir_function_impl *impl)
 649 {
 650    switch (node->type) {
 651    case nir_cf_node_block: {
 652       nir_block *block = nir_cf_node_as_block(node);
 653       /* We need to walk the instructions and clean up defs/uses */
 654       nir_foreach_instr_safe(instr, block) {
 655          if (instr->type == nir_instr_type_jump) {
 656             nir_jump_type jump_type = nir_instr_as_jump(instr)->type;
 657             unlink_jump(block, jump_type, false);
 658          } else {
 659             nir_foreach_ssa_def(instr, replace_ssa_def_uses, impl);
 660             nir_instr_remove(instr);
 661          }
 662       }
 663       break;
 664    }
 665
 666    case nir_cf_node_if: {
 667       nir_if *if_stmt = nir_cf_node_as_if(node);
 668       foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list)
 669          cleanup_cf_node(child, impl);
 670       foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list)
 671          cleanup_cf_node(child, impl);
 672
 673       list_del(&if_stmt->condition.use_link);
 674       break;
 675    }
 676
 677    case nir_cf_node_loop: {
 678       nir_loop *loop = nir_cf_node_as_loop(node);
 679       foreach_list_typed(nir_cf_node, child, node, &loop->body)
 680          cleanup_cf_node(child, impl);
 681       break;
 682    }
 683    case nir_cf_node_function: {
 684       nir_function_impl *impl = nir_cf_node_as_function(node);
 685       foreach_list_typed(nir_cf_node, child, node, &impl->body)
 686          cleanup_cf_node(child, impl);
 687       break;
 688    }
 689    default:
 690       unreachable("Invalid CF node type");
 691    }
 692 }
 693
 694 void
 695 nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end)
 696 {
 697    nir_block *block_begin, *block_end, *block_before, *block_after;
 698
 699    if (nir_cursors_equal(begin, end)) {
 700       exec_list_make_empty(&extracted->list);
 701       extracted->impl = NULL; /* we shouldn't need this */
 702       return;
 703    }
 704
 705    /* In the case where begin points to an instruction in some basic block and
 706     * end points to the end of the same basic block, we rely on the fact that
 707     * splitting on an instruction moves earlier instructions into a new basic
 708     * block. If the later instructions were moved instead, then the end cursor
 709     * would be pointing to the same place that begin used to point to, which
 710     * is obviously not what we want.
 711     */
 712    split_block_cursor(begin, &block_before, &block_begin);
 713    split_block_cursor(end, &block_end, &block_after);
 714
 715    extracted->impl = nir_cf_node_get_function(&block_begin->cf_node);
 716    exec_list_make_empty(&extracted->list);
 717
 718    /* Dominance and other block-related information is toast. */
 719    nir_metadata_preserve(extracted->impl, nir_metadata_none);
 720
 721    nir_cf_node *cf_node = &block_begin->cf_node;
 722    nir_cf_node *cf_node_end = &block_end->cf_node;
 723    while (true) {
 724       nir_cf_node *next = nir_cf_node_next(cf_node);
 725
 726       exec_node_remove(&cf_node->node);
 727       cf_node->parent = NULL;
 728       exec_list_push_tail(&extracted->list, &cf_node->node);
 729
 730       if (cf_node == cf_node_end)
 731          break;
 732
 733       cf_node = next;
 734    }
 735
 736    stitch_blocks(block_before, block_after);
 737 }
 738
 739 void
 740 nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor)
 741 {
 742    nir_block *before, *after;
 743
 744    if (exec_list_is_empty(&cf_list->list))
 745       return;
 746
 747    split_block_cursor(cursor, &before, &after);
 748
 749    foreach_list_typed_safe(nir_cf_node, node, node, &cf_list->list) {
 750       exec_node_remove(&node->node);
 751       node->parent = before->cf_node.parent;
 752       exec_node_insert_node_before(&after->cf_node.node, &node->node);
 753    }
 754
 755    stitch_blocks(before,
 756                  nir_cf_node_as_block(nir_cf_node_next(&before->cf_node)));
 757    stitch_blocks(nir_cf_node_as_block(nir_cf_node_prev(&after->cf_node)),
 758                  after);
 759 }
 760
 761 void
 762 nir_cf_delete(nir_cf_list *cf_list)
 763 {
 764    foreach_list_typed(nir_cf_node, node, node, &cf_list->list) {
 765       cleanup_cf_node(node, cf_list->impl);
 766    }
 767 }