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    set_foreach(block->predecessors, entry) {
 193       nir_block *pred = (nir_block *) entry->key;
 194       replace_successor(pred, block, new_block);
 195    }
 196
 197    /* Any phi nodes must stay part of the new block, or else their
 198     * sourcse will be messed up. This will reverse the order of the phis, but
 199     * order shouldn't matter.
 200     */
 201    nir_foreach_instr_safe(instr, block) {
 202       if (instr->type != nir_instr_type_phi)
 203          break;
 204
 205       exec_node_remove(&instr->node);
 206       instr->block = new_block;
 207       exec_list_push_head(&new_block->instr_list, &instr->node);
 208    }
 209
 210    return new_block;
 211 }
 212
 213 static void
 214 rewrite_phi_preds(nir_block *block, nir_block *old_pred, nir_block *new_pred)
 215 {
 216    nir_foreach_instr_safe(instr, block) {
 217       if (instr->type != nir_instr_type_phi)
 218          break;
 219
 220       nir_phi_instr *phi = nir_instr_as_phi(instr);
 221       nir_foreach_phi_src(src, phi) {
 222          if (src->pred == old_pred) {
 223             src->pred = new_pred;
 224             break;
 225          }
 226       }
 227    }
 228 }
 229
 230 static void
 231 insert_phi_undef(nir_block *block, nir_block *pred)
 232 {
 233    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 234    nir_foreach_instr(instr, block) {
 235       if (instr->type != nir_instr_type_phi)
 236          break;
 237
 238       nir_phi_instr *phi = nir_instr_as_phi(instr);
 239       nir_ssa_undef_instr *undef =
 240          nir_ssa_undef_instr_create(ralloc_parent(phi),
 241                                     phi->dest.ssa.num_components,
 242                                     phi->dest.ssa.bit_size);
 243       nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 244       nir_phi_src *src = ralloc(phi, nir_phi_src);
 245       src->pred = pred;
 246       src->src.parent_instr = &phi->instr;
 247       src->src.is_ssa = true;
 248       src->src.ssa = &undef->def;
 249
 250       list_addtail(&src->src.use_link, &undef->def.uses);
 251
 252       exec_list_push_tail(&phi->srcs, &src->node);
 253    }
 254 }
 255
 256 /**
 257  * Moves the successors of source to the successors of dest, leaving both
 258  * successors of source NULL.
 259  */
 260
 261 static void
 262 move_successors(nir_block *source, nir_block *dest)
 263 {
 264    nir_block *succ1 = source->successors[0];
 265    nir_block *succ2 = source->successors[1];
 266
 267    if (succ1) {
 268       unlink_blocks(source, succ1);
 269       rewrite_phi_preds(succ1, source, dest);
 270    }
 271
 272    if (succ2) {
 273       unlink_blocks(source, succ2);
 274       rewrite_phi_preds(succ2, source, dest);
 275    }
 276
 277    unlink_block_successors(dest);
 278    link_blocks(dest, succ1, succ2);
 279 }
 280
 281 /* Given a basic block with no successors that has been inserted into the
 282  * control flow tree, gives it the successors it would normally have assuming
 283  * it doesn't end in a jump instruction. Also inserts phi sources with undefs
 284  * if necessary.
 285  */
 286 static void
 287 block_add_normal_succs(nir_block *block)
 288 {
 289    if (exec_node_is_tail_sentinel(block->cf_node.node.next)) {
 290       nir_cf_node *parent = block->cf_node.parent;
 291       if (parent->type == nir_cf_node_if) {
 292          nir_cf_node *next = nir_cf_node_next(parent);
 293          nir_block *next_block = nir_cf_node_as_block(next);
 294
 295          link_blocks(block, next_block, NULL);
 296       } else if (parent->type == nir_cf_node_loop) {
 297          nir_loop *loop = nir_cf_node_as_loop(parent);
 298
 299          nir_block *head_block = nir_loop_first_block(loop);
 300
 301          link_blocks(block, head_block, NULL);
 302          insert_phi_undef(head_block, block);
 303       } else {
 304          nir_function_impl *impl = nir_cf_node_as_function(parent);
 305          link_blocks(block, impl->end_block, NULL);
 306       }
 307    } else {
 308       nir_cf_node *next = nir_cf_node_next(&block->cf_node);
 309       if (next->type == nir_cf_node_if) {
 310          nir_if *next_if = nir_cf_node_as_if(next);
 311
 312          nir_block *first_then_block = nir_if_first_then_block(next_if);
 313          nir_block *first_else_block = nir_if_first_else_block(next_if);
 314
 315          link_blocks(block, first_then_block, first_else_block);
 316       } else {
 317          nir_loop *next_loop = nir_cf_node_as_loop(next);
 318
 319          nir_block *first_block = nir_loop_first_block(next_loop);
 320
 321          link_blocks(block, first_block, NULL);
 322          insert_phi_undef(first_block, block);
 323       }
 324    }
 325 }
 326
 327 static nir_block *
 328 split_block_end(nir_block *block)
 329 {
 330    nir_block *new_block = nir_block_create(ralloc_parent(block));
 331    new_block->cf_node.parent = block->cf_node.parent;
 332    exec_node_insert_after(&block->cf_node.node, &new_block->cf_node.node);
 333
 334    if (nir_block_ends_in_jump(block)) {
 335       /* Figure out what successor block would've had if it didn't have a jump
 336        * instruction, and make new_block have that successor.
 337        */
 338       block_add_normal_succs(new_block);
 339    } else {
 340       move_successors(block, new_block);
 341    }
 342
 343    return new_block;
 344 }
 345
 346 static nir_block *
 347 split_block_before_instr(nir_instr *instr)
 348 {
 349    assert(instr->type != nir_instr_type_phi);
 350    nir_block *new_block = split_block_beginning(instr->block);
 351
 352    nir_foreach_instr_safe(cur_instr, instr->block) {
 353       if (cur_instr == instr)
 354          break;
 355
 356       exec_node_remove(&cur_instr->node);
 357       cur_instr->block = new_block;
 358       exec_list_push_tail(&new_block->instr_list, &cur_instr->node);
 359    }
 360
 361    return new_block;
 362 }
 363
 364 /* Splits a basic block at the point specified by the cursor. The "before" and
 365  * "after" arguments are filled out with the blocks resulting from the split
 366  * if non-NULL. Note that the "beginning" of the block is actually interpreted
 367  * as before the first non-phi instruction, and it's illegal to split a block
 368  * before a phi instruction.
 369  */
 370
 371 static void
 372 split_block_cursor(nir_cursor cursor,
 373                    nir_block **_before, nir_block **_after)
 374 {
 375    nir_block *before, *after;
 376    switch (cursor.option) {
 377    case nir_cursor_before_block:
 378       after = cursor.block;
 379       before = split_block_beginning(cursor.block);
 380       break;
 381
 382    case nir_cursor_after_block:
 383       before = cursor.block;
 384       after = split_block_end(cursor.block);
 385       break;
 386
 387    case nir_cursor_before_instr:
 388       after = cursor.instr->block;
 389       before = split_block_before_instr(cursor.instr);
 390       break;
 391
 392    case nir_cursor_after_instr:
 393       /* We lower this to split_block_before_instr() so that we can keep the
 394        * after-a-jump-instr case contained to split_block_end().
 395        */
 396       if (nir_instr_is_last(cursor.instr)) {
 397          before = cursor.instr->block;
 398          after = split_block_end(cursor.instr->block);
 399       } else {
 400          after = cursor.instr->block;
 401          before = split_block_before_instr(nir_instr_next(cursor.instr));
 402       }
 403       break;
 404
 405    default:
 406       unreachable("not reached");
 407    }
 408
 409    if (_before)
 410       *_before = before;
 411    if (_after)
 412       *_after = after;
 413 }
 414
 415 /**
 416  * Inserts a non-basic block between two basic blocks and links them together.
 417  */
 418
 419 static void
 420 insert_non_block(nir_block *before, nir_cf_node *node, nir_block *after)
 421 {
 422    node->parent = before->cf_node.parent;
 423    exec_node_insert_after(&before->cf_node.node, &node->node);
 424    link_block_to_non_block(before, node);
 425    link_non_block_to_block(node, after);
 426 }
 427
 428 /* walk up the control flow tree to find the innermost enclosed loop */
 429 static nir_loop *
 430 nearest_loop(nir_cf_node *node)
 431 {
 432    while (node->type != nir_cf_node_loop) {
 433       node = node->parent;
 434    }
 435
 436    return nir_cf_node_as_loop(node);
 437 }
 438
 439 static void
 440 remove_phi_src(nir_block *block, nir_block *pred)
 441 {
 442    nir_foreach_instr(instr, block) {
 443       if (instr->type != nir_instr_type_phi)
 444          break;
 445
 446       nir_phi_instr *phi = nir_instr_as_phi(instr);
 447       nir_foreach_phi_src_safe(src, phi) {
 448          if (src->pred == pred) {
 449             list_del(&src->src.use_link);
 450             exec_node_remove(&src->node);
 451          }
 452       }
 453    }
 454 }
 455
 456 /*
 457  * update the CFG after a jump instruction has been added to the end of a block
 458  */
 459
 460 void
 461 nir_handle_add_jump(nir_block *block)
 462 {
 463    nir_instr *instr = nir_block_last_instr(block);
 464    nir_jump_instr *jump_instr = nir_instr_as_jump(instr);
 465
 466    if (block->successors[0])
 467       remove_phi_src(block->successors[0], block);
 468    if (block->successors[1])
 469       remove_phi_src(block->successors[1], block);
 470    unlink_block_successors(block);
 471
 472    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 473    nir_metadata_preserve(impl, nir_metadata_none);
 474
 475    if (jump_instr->type == nir_jump_break ||
 476        jump_instr->type == nir_jump_continue) {
 477       nir_loop *loop = nearest_loop(&block->cf_node);
 478
 479       if (jump_instr->type == nir_jump_continue) {
 480          nir_block *first_block = nir_loop_first_block(loop);
 481          link_blocks(block, first_block, NULL);
 482       } else {
 483          nir_cf_node *after = nir_cf_node_next(&loop->cf_node);
 484          nir_block *after_block = nir_cf_node_as_block(after);
 485          link_blocks(block, after_block, NULL);
 486       }
 487    } else {
 488       assert(jump_instr->type == nir_jump_return);
 489       link_blocks(block, impl->end_block, NULL);
 490    }
 491 }
 492
 493 /* Removes the successor of a block with a jump. Note that the jump to be
 494  * eliminated may be free-floating.
 495  */
 496
 497 static void
 498 unlink_jump(nir_block *block, nir_jump_type type, bool add_normal_successors)
 499 {
 500    if (block->successors[0])
 501       remove_phi_src(block->successors[0], block);
 502    if (block->successors[1])
 503       remove_phi_src(block->successors[1], block);
 504
 505    unlink_block_successors(block);
 506    if (add_normal_successors)
 507       block_add_normal_succs(block);
 508 }
 509
 510 void
 511 nir_handle_remove_jump(nir_block *block, nir_jump_type type)
 512 {
 513    unlink_jump(block, type, true);
 514
 515    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 516    nir_metadata_preserve(impl, nir_metadata_none);
 517 }
 518
 519 static void
 520 update_if_uses(nir_cf_node *node)
 521 {
 522    if (node->type != nir_cf_node_if)
 523       return;
 524
 525    nir_if *if_stmt = nir_cf_node_as_if(node);
 526
 527    if_stmt->condition.parent_if = if_stmt;
 528    if (if_stmt->condition.is_ssa) {
 529       list_addtail(&if_stmt->condition.use_link,
 530                    &if_stmt->condition.ssa->if_uses);
 531    } else {
 532       list_addtail(&if_stmt->condition.use_link,
 533                    &if_stmt->condition.reg.reg->if_uses);
 534    }
 535 }
 536
 537 /**
 538  * Stitch two basic blocks together into one. The aggregate must have the same
 539  * predecessors as the first and the same successors as the second.
 540  */
 541
 542 static void
 543 stitch_blocks(nir_block *before, nir_block *after)
 544 {
 545    /*
 546     * We move after into before, so we have to deal with up to 2 successors vs.
 547     * possibly a large number of predecessors.
 548     *
 549     * TODO: special case when before is empty and after isn't?
 550     */
 551
 552    if (nir_block_ends_in_jump(before)) {
 553       assert(exec_list_is_empty(&after->instr_list));
 554       if (after->successors[0])
 555          remove_phi_src(after->successors[0], after);
 556       if (after->successors[1])
 557          remove_phi_src(after->successors[1], after);
 558       unlink_block_successors(after);
 559       exec_node_remove(&after->cf_node.node);
 560    } else {
 561       move_successors(after, before);
 562
 563       foreach_list_typed(nir_instr, instr, node, &after->instr_list) {
 564          instr->block = before;
 565       }
 566
 567       exec_list_append(&before->instr_list, &after->instr_list);
 568       exec_node_remove(&after->cf_node.node);
 569    }
 570 }
 571
 572 void
 573 nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node)
 574 {
 575    nir_block *before, *after;
 576
 577    split_block_cursor(cursor, &before, &after);
 578
 579    if (node->type == nir_cf_node_block) {
 580       nir_block *block = nir_cf_node_as_block(node);
 581       exec_node_insert_after(&before->cf_node.node, &block->cf_node.node);
 582       block->cf_node.parent = before->cf_node.parent;
 583       /* stitch_blocks() assumes that any block that ends with a jump has
 584        * already been setup with the correct successors, so we need to set
 585        * up jumps here as the block is being inserted.
 586        */
 587       if (nir_block_ends_in_jump(block))
 588          nir_handle_add_jump(block);
 589
 590       stitch_blocks(block, after);
 591       stitch_blocks(before, block);
 592    } else {
 593       update_if_uses(node);
 594       insert_non_block(before, node, after);
 595    }
 596 }
 597
 598 static bool
 599 replace_ssa_def_uses(nir_ssa_def *def, void *void_impl)
 600 {
 601    nir_function_impl *impl = void_impl;
 602    void *mem_ctx = ralloc_parent(impl);
 603
 604    nir_ssa_undef_instr *undef =
 605       nir_ssa_undef_instr_create(mem_ctx, def->num_components,
 606                                  def->bit_size);
 607    nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 608    nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(&undef->def));
 609    return true;
 610 }
 611
 612 static void
 613 cleanup_cf_node(nir_cf_node *node, nir_function_impl *impl)
 614 {
 615    switch (node->type) {
 616    case nir_cf_node_block: {
 617       nir_block *block = nir_cf_node_as_block(node);
 618       /* We need to walk the instructions and clean up defs/uses */
 619       nir_foreach_instr_safe(instr, block) {
 620          if (instr->type == nir_instr_type_jump) {
 621             nir_jump_type jump_type = nir_instr_as_jump(instr)->type;
 622             unlink_jump(block, jump_type, false);
 623          } else {
 624             nir_foreach_ssa_def(instr, replace_ssa_def_uses, impl);
 625             nir_instr_remove(instr);
 626          }
 627       }
 628       break;
 629    }
 630
 631    case nir_cf_node_if: {
 632       nir_if *if_stmt = nir_cf_node_as_if(node);
 633       foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list)
 634          cleanup_cf_node(child, impl);
 635       foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list)
 636          cleanup_cf_node(child, impl);
 637
 638       list_del(&if_stmt->condition.use_link);
 639       break;
 640    }
 641
 642    case nir_cf_node_loop: {
 643       nir_loop *loop = nir_cf_node_as_loop(node);
 644       foreach_list_typed(nir_cf_node, child, node, &loop->body)
 645          cleanup_cf_node(child, impl);
 646       break;
 647    }
 648    case nir_cf_node_function: {
 649       nir_function_impl *impl = nir_cf_node_as_function(node);
 650       foreach_list_typed(nir_cf_node, child, node, &impl->body)
 651          cleanup_cf_node(child, impl);
 652       break;
 653    }
 654    default:
 655       unreachable("Invalid CF node type");
 656    }
 657 }
 658
 659 void
 660 nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end)
 661 {
 662    nir_block *block_begin, *block_end, *block_before, *block_after;
 663
 664    if (nir_cursors_equal(begin, end)) {
 665       exec_list_make_empty(&extracted->list);
 666       extracted->impl = NULL; /* we shouldn't need this */
 667       return;
 668    }
 669
 670    /* In the case where begin points to an instruction in some basic block and
 671     * end points to the end of the same basic block, we rely on the fact that
 672     * splitting on an instruction moves earlier instructions into a new basic
 673     * block. If the later instructions were moved instead, then the end cursor
 674     * would be pointing to the same place that begin used to point to, which
 675     * is obviously not what we want.
 676     */
 677    split_block_cursor(begin, &block_before, &block_begin);
 678    split_block_cursor(end, &block_end, &block_after);
 679
 680    extracted->impl = nir_cf_node_get_function(&block_begin->cf_node);
 681    exec_list_make_empty(&extracted->list);
 682
 683    /* Dominance and other block-related information is toast. */
 684    nir_metadata_preserve(extracted->impl, nir_metadata_none);
 685
 686    nir_cf_node *cf_node = &block_begin->cf_node;
 687    nir_cf_node *cf_node_end = &block_end->cf_node;
 688    while (true) {
 689       nir_cf_node *next = nir_cf_node_next(cf_node);
 690
 691       exec_node_remove(&cf_node->node);
 692       cf_node->parent = NULL;
 693       exec_list_push_tail(&extracted->list, &cf_node->node);
 694
 695       if (cf_node == cf_node_end)
 696          break;
 697
 698       cf_node = next;
 699    }
 700
 701    stitch_blocks(block_before, block_after);
 702 }
 703
 704 void
 705 nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor)
 706 {
 707    nir_block *before, *after;
 708
 709    if (exec_list_is_empty(&cf_list->list))
 710       return;
 711
 712    split_block_cursor(cursor, &before, &after);
 713
 714    foreach_list_typed_safe(nir_cf_node, node, node, &cf_list->list) {
 715       exec_node_remove(&node->node);
 716       node->parent = before->cf_node.parent;
 717       exec_node_insert_node_before(&after->cf_node.node, &node->node);
 718    }
 719
 720    stitch_blocks(before,
 721                  nir_cf_node_as_block(nir_cf_node_next(&before->cf_node)));
 722    stitch_blocks(nir_cf_node_as_block(nir_cf_node_prev(&after->cf_node)),
 723                  after);
 724 }
 725
 726 void
 727 nir_cf_delete(nir_cf_list *cf_list)
 728 {
 729    foreach_list_typed(nir_cf_node, node, node, &cf_list->list) {
 730       cleanup_cf_node(node, cf_list->impl);
 731    }
 732 }