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