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