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