src/glsl/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  * 5. The CFG must always be connected - this means that we must insert a fake
  43  *    CFG edge for loops with no break statement.
  44  *
  45  * The purpose of the second one is so that we have places to insert code during
  46  * GCM, as well as eliminating the possibility of critical edges.
  47  */
  48 /*@{*/
  49
  50 static bool
  51 block_ends_in_jump(nir_block *block)
  52 {
  53    return !exec_list_is_empty(&block->instr_list) &&
  54           nir_block_last_instr(block)->type == nir_instr_type_jump;
  55 }
  56
  57 static inline void
  58 block_add_pred(nir_block *block, nir_block *pred)
  59 {
  60    _mesa_set_add(block->predecessors, pred);
  61 }
  62
  63 static void
  64 link_blocks(nir_block *pred, nir_block *succ1, nir_block *succ2)
  65 {
  66    pred->successors[0] = succ1;
  67    if (succ1 != NULL)
  68       block_add_pred(succ1, pred);
  69
  70    pred->successors[1] = succ2;
  71    if (succ2 != NULL)
  72       block_add_pred(succ2, pred);
  73 }
  74
  75 static void
  76 unlink_blocks(nir_block *pred, nir_block *succ)
  77 {
  78    if (pred->successors[0] == succ) {
  79       pred->successors[0] = pred->successors[1];
  80       pred->successors[1] = NULL;
  81    } else {
  82       assert(pred->successors[1] == succ);
  83       pred->successors[1] = NULL;
  84    }
  85
  86    struct set_entry *entry = _mesa_set_search(succ->predecessors, pred);
  87
  88    assert(entry);
  89
  90    _mesa_set_remove(succ->predecessors, entry);
  91 }
  92
  93 static void
  94 unlink_block_successors(nir_block *block)
  95 {
  96    if (block->successors[0] != NULL)
  97       unlink_blocks(block, block->successors[0]);
  98    if (block->successors[1] != NULL)
  99       unlink_blocks(block, block->successors[1]);
 100 }
 101
 102 static void
 103 link_non_block_to_block(nir_cf_node *node, nir_block *block)
 104 {
 105    if (node->type == nir_cf_node_if) {
 106       /*
 107        * We're trying to link an if to a block after it; this just means linking
 108        * the last block of the then and else branches.
 109        */
 110
 111       nir_if *if_stmt = nir_cf_node_as_if(node);
 112
 113       nir_cf_node *last_then = nir_if_last_then_node(if_stmt);
 114       assert(last_then->type == nir_cf_node_block);
 115       nir_block *last_then_block = nir_cf_node_as_block(last_then);
 116
 117       nir_cf_node *last_else = nir_if_last_else_node(if_stmt);
 118       assert(last_else->type == nir_cf_node_block);
 119       nir_block *last_else_block = nir_cf_node_as_block(last_else);
 120
 121       if (!block_ends_in_jump(last_then_block)) {
 122          unlink_block_successors(last_then_block);
 123          link_blocks(last_then_block, block, NULL);
 124       }
 125
 126       if (!block_ends_in_jump(last_else_block)) {
 127          unlink_block_successors(last_else_block);
 128          link_blocks(last_else_block, block, NULL);
 129       }
 130    } else {
 131       assert(node->type == nir_cf_node_loop);
 132
 133       /*
 134        * We can only get to this codepath if we're inserting a new loop, or
 135        * at least a loop with no break statements; we can't insert break
 136        * statements into a loop when we haven't inserted it into the CFG
 137        * because we wouldn't know which block comes after the loop
 138        * and therefore, which block should be the successor of the block with
 139        * the break). Therefore, we need to insert a fake edge (see invariant
 140        * #5).
 141        */
 142
 143       nir_loop *loop = nir_cf_node_as_loop(node);
 144
 145       nir_cf_node *last = nir_loop_last_cf_node(loop);
 146       assert(last->type == nir_cf_node_block);
 147       nir_block *last_block =  nir_cf_node_as_block(last);
 148
 149       last_block->successors[1] = block;
 150       block_add_pred(block, last_block);
 151    }
 152 }
 153
 154 static void
 155 link_block_to_non_block(nir_block *block, nir_cf_node *node)
 156 {
 157    if (node->type == nir_cf_node_if) {
 158       /*
 159        * We're trying to link a block to an if after it; this just means linking
 160        * the block to the first block of the then and else branches.
 161        */
 162
 163       nir_if *if_stmt = nir_cf_node_as_if(node);
 164
 165       nir_cf_node *first_then = nir_if_first_then_node(if_stmt);
 166       assert(first_then->type == nir_cf_node_block);
 167       nir_block *first_then_block = nir_cf_node_as_block(first_then);
 168
 169       nir_cf_node *first_else = nir_if_first_else_node(if_stmt);
 170       assert(first_else->type == nir_cf_node_block);
 171       nir_block *first_else_block = nir_cf_node_as_block(first_else);
 172
 173       unlink_block_successors(block);
 174       link_blocks(block, first_then_block, first_else_block);
 175    } else {
 176       /*
 177        * For similar reasons as the corresponding case in
 178        * link_non_block_to_block(), don't worry about if the loop header has
 179        * any predecessors that need to be unlinked.
 180        */
 181
 182       assert(node->type == nir_cf_node_loop);
 183
 184       nir_loop *loop = nir_cf_node_as_loop(node);
 185
 186       nir_cf_node *loop_header = nir_loop_first_cf_node(loop);
 187       assert(loop_header->type == nir_cf_node_block);
 188       nir_block *loop_header_block = nir_cf_node_as_block(loop_header);
 189
 190       unlink_block_successors(block);
 191       link_blocks(block, loop_header_block, NULL);
 192    }
 193
 194 }
 195
 196 /**
 197  * Takes a basic block and inserts a new empty basic block before it, making its
 198  * predecessors point to the new block. This essentially splits the block into
 199  * an empty header and a body so that another non-block CF node can be inserted
 200  * between the two. Note that this does *not* link the two basic blocks, so
 201  * some kind of cleanup *must* be performed after this call.
 202  */
 203
 204 static nir_block *
 205 split_block_beginning(nir_block *block)
 206 {
 207    nir_block *new_block = nir_block_create(ralloc_parent(block));
 208    new_block->cf_node.parent = block->cf_node.parent;
 209    exec_node_insert_node_before(&block->cf_node.node, &new_block->cf_node.node);
 210
 211    struct set_entry *entry;
 212    set_foreach(block->predecessors, entry) {
 213       nir_block *pred = (nir_block *) entry->key;
 214
 215       unlink_blocks(pred, block);
 216       link_blocks(pred, new_block, NULL);
 217    }
 218
 219    /* Any phi nodes must stay part of the new block, or else their
 220     * sourcse will be messed up. This will reverse the order of the phi's, but
 221     * order shouldn't matter.
 222     */
 223    nir_foreach_instr_safe(block, instr) {
 224       if (instr->type != nir_instr_type_phi)
 225          break;
 226
 227       exec_node_remove(&instr->node);
 228       instr->block = new_block;
 229       exec_list_push_head(&new_block->instr_list, &instr->node);
 230    }
 231
 232    return new_block;
 233 }
 234
 235 static void
 236 rewrite_phi_preds(nir_block *block, nir_block *old_pred, nir_block *new_pred)
 237 {
 238    nir_foreach_instr_safe(block, instr) {
 239       if (instr->type != nir_instr_type_phi)
 240          break;
 241
 242       nir_phi_instr *phi = nir_instr_as_phi(instr);
 243       nir_foreach_phi_src(phi, src) {
 244          if (src->pred == old_pred) {
 245             src->pred = new_pred;
 246             break;
 247          }
 248       }
 249    }
 250 }
 251
 252 static void
 253 insert_phi_undef(nir_block *block, nir_block *pred)
 254 {
 255    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 256    nir_foreach_instr(block, instr) {
 257       if (instr->type != nir_instr_type_phi)
 258          break;
 259
 260       nir_phi_instr *phi = nir_instr_as_phi(instr);
 261       nir_ssa_undef_instr *undef =
 262          nir_ssa_undef_instr_create(ralloc_parent(phi),
 263                                     phi->dest.ssa.num_components);
 264       nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 265       nir_phi_src *src = ralloc(phi, nir_phi_src);
 266       src->pred = pred;
 267       src->src.parent_instr = &phi->instr;
 268       src->src.is_ssa = true;
 269       src->src.ssa = &undef->def;
 270
 271       list_addtail(&src->src.use_link, &undef->def.uses);
 272
 273       exec_list_push_tail(&phi->srcs, &src->node);
 274    }
 275 }
 276
 277 /**
 278  * Moves the successors of source to the successors of dest, leaving both
 279  * successors of source NULL.
 280  */
 281
 282 static void
 283 move_successors(nir_block *source, nir_block *dest)
 284 {
 285    nir_block *succ1 = source->successors[0];
 286    nir_block *succ2 = source->successors[1];
 287
 288    if (succ1) {
 289       unlink_blocks(source, succ1);
 290       rewrite_phi_preds(succ1, source, dest);
 291    }
 292
 293    if (succ2) {
 294       unlink_blocks(source, succ2);
 295       rewrite_phi_preds(succ2, source, dest);
 296    }
 297
 298    unlink_block_successors(dest);
 299    link_blocks(dest, succ1, succ2);
 300 }
 301
 302 /* Given a basic block with no successors that has been inserted into the
 303  * control flow tree, gives it the successors it would normally have assuming
 304  * it doesn't end in a jump instruction. Also inserts phi sources with undefs
 305  * if necessary.
 306  */
 307 static void
 308 block_add_normal_succs(nir_block *block)
 309 {
 310    if (exec_node_is_tail_sentinel(block->cf_node.node.next)) {
 311       nir_cf_node *parent = block->cf_node.parent;
 312       if (parent->type == nir_cf_node_if) {
 313          nir_cf_node *next = nir_cf_node_next(parent);
 314          assert(next->type == nir_cf_node_block);
 315          nir_block *next_block = nir_cf_node_as_block(next);
 316
 317          link_blocks(block, next_block, NULL);
 318       } else {
 319          assert(parent->type == nir_cf_node_loop);
 320          nir_loop *loop = nir_cf_node_as_loop(parent);
 321
 322          nir_cf_node *head = nir_loop_first_cf_node(loop);
 323          assert(head->type == nir_cf_node_block);
 324          nir_block *head_block = nir_cf_node_as_block(head);
 325
 326          link_blocks(block, head_block, NULL);
 327          insert_phi_undef(head_block, block);
 328       }
 329    } else {
 330       nir_cf_node *next = nir_cf_node_next(&block->cf_node);
 331       if (next->type == nir_cf_node_if) {
 332          nir_if *next_if = nir_cf_node_as_if(next);
 333
 334          nir_cf_node *first_then = nir_if_first_then_node(next_if);
 335          assert(first_then->type == nir_cf_node_block);
 336          nir_block *first_then_block = nir_cf_node_as_block(first_then);
 337
 338          nir_cf_node *first_else = nir_if_first_else_node(next_if);
 339          assert(first_else->type == nir_cf_node_block);
 340          nir_block *first_else_block = nir_cf_node_as_block(first_else);
 341
 342          link_blocks(block, first_then_block, first_else_block);
 343       } else {
 344          assert(next->type == nir_cf_node_loop);
 345          nir_loop *next_loop = nir_cf_node_as_loop(next);
 346
 347          nir_cf_node *first = nir_loop_first_cf_node(next_loop);
 348          assert(first->type == nir_cf_node_block);
 349          nir_block *first_block = nir_cf_node_as_block(first);
 350
 351          link_blocks(block, first_block, NULL);
 352          insert_phi_undef(first_block, block);
 353       }
 354    }
 355 }
 356
 357 static nir_block *
 358 split_block_end(nir_block *block)
 359 {
 360    nir_block *new_block = nir_block_create(ralloc_parent(block));
 361    new_block->cf_node.parent = block->cf_node.parent;
 362    exec_node_insert_after(&block->cf_node.node, &new_block->cf_node.node);
 363
 364    if (block_ends_in_jump(block)) {
 365       /* Figure out what successor block would've had if it didn't have a jump
 366        * instruction, and make new_block have that successor.
 367        */
 368       block_add_normal_succs(new_block);
 369    } else {
 370       move_successors(block, new_block);
 371    }
 372
 373    return new_block;
 374 }
 375
 376 static nir_block *
 377 split_block_before_instr(nir_instr *instr)
 378 {
 379    assert(instr->type != nir_instr_type_phi);
 380    nir_block *new_block = split_block_beginning(instr->block);
 381
 382    nir_foreach_instr_safe(instr->block, cur_instr) {
 383       if (cur_instr == instr)
 384          break;
 385
 386       exec_node_remove(&cur_instr->node);
 387       cur_instr->block = new_block;
 388       exec_list_push_tail(&new_block->instr_list, &cur_instr->node);
 389    }
 390
 391    return new_block;
 392 }
 393
 394 /* Splits a basic block at the point specified by the cursor. The "before" and
 395  * "after" arguments are filled out with the blocks resulting from the split
 396  * if non-NULL. Note that the "beginning" of the block is actually interpreted
 397  * as before the first non-phi instruction, and it's illegal to split a block
 398  * before a phi instruction.
 399  */
 400
 401 static void
 402 split_block_cursor(nir_cursor cursor,
 403                    nir_block **_before, nir_block **_after)
 404 {
 405    nir_block *before, *after;
 406    switch (cursor.option) {
 407    case nir_cursor_before_block:
 408       after = cursor.block;
 409       before = split_block_beginning(cursor.block);
 410       break;
 411
 412    case nir_cursor_after_block:
 413       before = cursor.block;
 414       after = split_block_end(cursor.block);
 415       break;
 416
 417    case nir_cursor_before_instr:
 418       after = cursor.instr->block;
 419       before = split_block_before_instr(cursor.instr);
 420       break;
 421
 422    case nir_cursor_after_instr:
 423       /* We lower this to split_block_before_instr() so that we can keep the
 424        * after-a-jump-instr case contained to split_block_end().
 425        */
 426       if (nir_instr_is_last(cursor.instr)) {
 427          before = cursor.instr->block;
 428          after = split_block_end(cursor.instr->block);
 429       } else {
 430          after = cursor.instr->block;
 431          before = split_block_before_instr(nir_instr_next(cursor.instr));
 432       }
 433       break;
 434    }
 435
 436    if (_before)
 437       *_before = before;
 438    if (_after)
 439       *_after = after;
 440 }
 441
 442 /**
 443  * Inserts a non-basic block between two basic blocks and links them together.
 444  */
 445
 446 static void
 447 insert_non_block(nir_block *before, nir_cf_node *node, nir_block *after)
 448 {
 449    node->parent = before->cf_node.parent;
 450    exec_node_insert_after(&before->cf_node.node, &node->node);
 451    link_block_to_non_block(before, node);
 452    link_non_block_to_block(node, after);
 453 }
 454
 455 /* walk up the control flow tree to find the innermost enclosed loop */
 456 static nir_loop *
 457 nearest_loop(nir_cf_node *node)
 458 {
 459    while (node->type != nir_cf_node_loop) {
 460       node = node->parent;
 461    }
 462
 463    return nir_cf_node_as_loop(node);
 464 }
 465
 466 /*
 467  * update the CFG after a jump instruction has been added to the end of a block
 468  */
 469
 470 void
 471 nir_handle_add_jump(nir_block *block)
 472 {
 473    nir_instr *instr = nir_block_last_instr(block);
 474    nir_jump_instr *jump_instr = nir_instr_as_jump(instr);
 475
 476    unlink_block_successors(block);
 477
 478    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 479    nir_metadata_preserve(impl, nir_metadata_none);
 480
 481    if (jump_instr->type == nir_jump_break ||
 482        jump_instr->type == nir_jump_continue) {
 483       nir_loop *loop = nearest_loop(&block->cf_node);
 484
 485       if (jump_instr->type == nir_jump_continue) {
 486          nir_cf_node *first_node = nir_loop_first_cf_node(loop);
 487          assert(first_node->type == nir_cf_node_block);
 488          nir_block *first_block = nir_cf_node_as_block(first_node);
 489          link_blocks(block, first_block, NULL);
 490       } else {
 491          nir_cf_node *after = nir_cf_node_next(&loop->cf_node);
 492          assert(after->type == nir_cf_node_block);
 493          nir_block *after_block = nir_cf_node_as_block(after);
 494          link_blocks(block, after_block, NULL);
 495
 496          /* If we inserted a fake link, remove it */
 497          nir_cf_node *last = nir_loop_last_cf_node(loop);
 498          assert(last->type == nir_cf_node_block);
 499          nir_block *last_block =  nir_cf_node_as_block(last);
 500          if (last_block->successors[1] != NULL)
 501             unlink_blocks(last_block, after_block);
 502       }
 503    } else {
 504       assert(jump_instr->type == nir_jump_return);
 505       link_blocks(block, impl->end_block, NULL);
 506    }
 507 }
 508
 509 static void
 510 remove_phi_src(nir_block *block, nir_block *pred)
 511 {
 512    nir_foreach_instr(block, instr) {
 513       if (instr->type != nir_instr_type_phi)
 514          break;
 515
 516       nir_phi_instr *phi = nir_instr_as_phi(instr);
 517       nir_foreach_phi_src_safe(phi, src) {
 518          if (src->pred == pred) {
 519             list_del(&src->src.use_link);
 520             exec_node_remove(&src->node);
 521          }
 522       }
 523    }
 524 }
 525
 526 /* Removes the successor of a block with a jump, and inserts a fake edge for
 527  * infinite loops. Note that the jump to be eliminated may be free-floating.
 528  */
 529
 530 static
 531 void unlink_jump(nir_block *block, nir_jump_type type)
 532 {
 533    if (block->successors[0])
 534       remove_phi_src(block->successors[0], block);
 535    if (block->successors[1])
 536       remove_phi_src(block->successors[1], block);
 537
 538    if (type == nir_jump_break) {
 539       nir_block *next = block->successors[0];
 540
 541       if (next->predecessors->entries == 1) {
 542          nir_loop *loop =
 543             nir_cf_node_as_loop(nir_cf_node_prev(&next->cf_node));
 544
 545          /* insert fake link */
 546          nir_cf_node *last = nir_loop_last_cf_node(loop);
 547          assert(last->type == nir_cf_node_block);
 548          nir_block *last_block = nir_cf_node_as_block(last);
 549
 550          last_block->successors[1] = next;
 551          block_add_pred(next, last_block);
 552       }
 553    }
 554
 555    unlink_block_successors(block);
 556 }
 557
 558 void
 559 nir_handle_remove_jump(nir_block *block, nir_jump_type type)
 560 {
 561    unlink_jump(block, type);
 562
 563    block_add_normal_succs(block);
 564
 565    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 566    nir_metadata_preserve(impl, nir_metadata_none);
 567 }
 568
 569 static void
 570 update_if_uses(nir_cf_node *node)
 571 {
 572    if (node->type != nir_cf_node_if)
 573       return;
 574
 575    nir_if *if_stmt = nir_cf_node_as_if(node);
 576
 577    if_stmt->condition.parent_if = if_stmt;
 578    if (if_stmt->condition.is_ssa) {
 579       list_addtail(&if_stmt->condition.use_link,
 580                    &if_stmt->condition.ssa->if_uses);
 581    } else {
 582       list_addtail(&if_stmt->condition.use_link,
 583                    &if_stmt->condition.reg.reg->if_uses);
 584    }
 585 }
 586
 587 /**
 588  * Stitch two basic blocks together into one. The aggregate must have the same
 589  * predecessors as the first and the same successors as the second.
 590  */
 591
 592 static void
 593 stitch_blocks(nir_block *before, nir_block *after)
 594 {
 595    /*
 596     * We move after into before, so we have to deal with up to 2 successors vs.
 597     * possibly a large number of predecessors.
 598     *
 599     * TODO: special case when before is empty and after isn't?
 600     */
 601
 602    if (block_ends_in_jump(before)) {
 603       assert(exec_list_is_empty(&after->instr_list));
 604       if (after->successors[0])
 605          remove_phi_src(after->successors[0], after);
 606       if (after->successors[1])
 607          remove_phi_src(after->successors[1], after);
 608       unlink_block_successors(after);
 609       exec_node_remove(&after->cf_node.node);
 610    } else {
 611       move_successors(after, before);
 612
 613       foreach_list_typed(nir_instr, instr, node, &after->instr_list) {
 614          instr->block = before;
 615       }
 616
 617       exec_list_append(&before->instr_list, &after->instr_list);
 618       exec_node_remove(&after->cf_node.node);
 619    }
 620 }
 621
 622 void
 623 nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node)
 624 {
 625    nir_block *before, *after;
 626
 627    split_block_cursor(cursor, &before, &after);
 628
 629    if (node->type == nir_cf_node_block) {
 630       nir_block *block = nir_cf_node_as_block(node);
 631       exec_node_insert_after(&before->cf_node.node, &block->cf_node.node);
 632       block->cf_node.parent = before->cf_node.parent;
 633       /* stitch_blocks() assumes that any block that ends with a jump has
 634        * already been setup with the correct successors, so we need to set
 635        * up jumps here as the block is being inserted.
 636        */
 637       if (block_ends_in_jump(block))
 638          nir_handle_add_jump(block);
 639
 640       stitch_blocks(block, after);
 641       stitch_blocks(before, block);
 642    } else {
 643       update_if_uses(node);
 644       insert_non_block(before, node, after);
 645    }
 646 }
 647
 648 static bool
 649 replace_ssa_def_uses(nir_ssa_def *def, void *void_impl)
 650 {
 651    nir_function_impl *impl = void_impl;
 652    void *mem_ctx = ralloc_parent(impl);
 653
 654    nir_ssa_undef_instr *undef =
 655       nir_ssa_undef_instr_create(mem_ctx, def->num_components);
 656    nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 657    nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(&undef->def), mem_ctx);
 658    return true;
 659 }
 660
 661 static void
 662 cleanup_cf_node(nir_cf_node *node, nir_function_impl *impl)
 663 {
 664    switch (node->type) {
 665    case nir_cf_node_block: {
 666       nir_block *block = nir_cf_node_as_block(node);
 667       /* We need to walk the instructions and clean up defs/uses */
 668       nir_foreach_instr_safe(block, instr) {
 669          if (instr->type == nir_instr_type_jump) {
 670             nir_jump_type jump_type = nir_instr_as_jump(instr)->type;
 671             unlink_jump(block, jump_type);
 672          } else {
 673             nir_foreach_ssa_def(instr, replace_ssa_def_uses, impl);
 674             nir_instr_remove(instr);
 675          }
 676       }
 677       break;
 678    }
 679
 680    case nir_cf_node_if: {
 681       nir_if *if_stmt = nir_cf_node_as_if(node);
 682       foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list)
 683          cleanup_cf_node(child, impl);
 684       foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list)
 685          cleanup_cf_node(child, impl);
 686
 687       list_del(&if_stmt->condition.use_link);
 688       break;
 689    }
 690
 691    case nir_cf_node_loop: {
 692       nir_loop *loop = nir_cf_node_as_loop(node);
 693       foreach_list_typed(nir_cf_node, child, node, &loop->body)
 694          cleanup_cf_node(child, impl);
 695       break;
 696    }
 697    case nir_cf_node_function: {
 698       nir_function_impl *impl = nir_cf_node_as_function(node);
 699       foreach_list_typed(nir_cf_node, child, node, &impl->body)
 700          cleanup_cf_node(child, impl);
 701       break;
 702    }
 703    default:
 704       unreachable("Invalid CF node type");
 705    }
 706 }
 707
 708 void
 709 nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end)
 710 {
 711    nir_block *block_begin, *block_end, *block_before, *block_after;
 712
 713    /* In the case where begin points to an instruction in some basic block and
 714     * end points to the end of the same basic block, we rely on the fact that
 715     * splitting on an instruction moves earlier instructions into a new basic
 716     * block. If the later instructions were moved instead, then the end cursor
 717     * would be pointing to the same place that begin used to point to, which
 718     * is obviously not what we want.
 719     */
 720    split_block_cursor(begin, &block_before, &block_begin);
 721    split_block_cursor(end, &block_end, &block_after);
 722
 723    extracted->impl = nir_cf_node_get_function(&block_begin->cf_node);
 724    exec_list_make_empty(&extracted->list);
 725
 726    nir_cf_node *cf_node = &block_begin->cf_node;
 727    nir_cf_node *cf_node_end = &block_end->cf_node;
 728    while (true) {
 729       nir_cf_node *next = nir_cf_node_next(cf_node);
 730
 731       exec_node_remove(&cf_node->node);
 732       cf_node->parent = NULL;
 733       exec_list_push_tail(&extracted->list, &cf_node->node);
 734
 735       if (cf_node == cf_node_end)
 736          break;
 737
 738       cf_node = next;
 739    }
 740
 741    stitch_blocks(block_before, block_after);
 742 }
 743
 744 void
 745 nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor)
 746 {
 747    nir_block *before, *after;
 748
 749    split_block_cursor(cursor, &before, &after);
 750
 751    foreach_list_typed_safe(nir_cf_node, node, node, &cf_list->list) {
 752       exec_node_remove(&node->node);
 753       node->parent = before->cf_node.parent;
 754       exec_node_insert_node_before(&after->cf_node.node, &node->node);
 755    }
 756
 757    stitch_blocks(before,
 758                  nir_cf_node_as_block(nir_cf_node_next(&before->cf_node)));
 759    stitch_blocks(nir_cf_node_as_block(nir_cf_node_prev(&after->cf_node)),
 760                  after);
 761 }
 762
 763 void
 764 nir_cf_delete(nir_cf_list *cf_list)
 765 {
 766    foreach_list_typed(nir_cf_node, node, node, &cf_list->list) {
 767       cleanup_cf_node(node, cf_list->impl);
 768    }
 769 }