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  * 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 inline void
  64 block_remove_pred(nir_block *block, nir_block *pred)
  65 {
  66    struct set_entry *entry = _mesa_set_search(block->predecessors, pred);
  67
  68    assert(entry);
  69
  70    _mesa_set_remove(block->predecessors, entry);
  71 }
  72
  73 static void
  74 link_blocks(nir_block *pred, nir_block *succ1, nir_block *succ2)
  75 {
  76    pred->successors[0] = succ1;
  77    if (succ1 != NULL)
  78       block_add_pred(succ1, pred);
  79
  80    pred->successors[1] = succ2;
  81    if (succ2 != NULL)
  82       block_add_pred(succ2, pred);
  83 }
  84
  85 static void
  86 unlink_blocks(nir_block *pred, nir_block *succ)
  87 {
  88    if (pred->successors[0] == succ) {
  89       pred->successors[0] = pred->successors[1];
  90       pred->successors[1] = NULL;
  91    } else {
  92       assert(pred->successors[1] == succ);
  93       pred->successors[1] = NULL;
  94    }
  95
  96    block_remove_pred(succ, pred);
  97 }
  98
  99 static void
 100 unlink_block_successors(nir_block *block)
 101 {
 102    if (block->successors[1] != NULL)
 103       unlink_blocks(block, block->successors[1]);
 104    if (block->successors[0] != NULL)
 105       unlink_blocks(block, block->successors[0]);
 106 }
 107
 108 static void
 109 link_non_block_to_block(nir_cf_node *node, nir_block *block)
 110 {
 111    if (node->type == nir_cf_node_if) {
 112       /*
 113        * We're trying to link an if to a block after it; this just means linking
 114        * the last block of the then and else branches.
 115        */
 116
 117       nir_if *if_stmt = nir_cf_node_as_if(node);
 118
 119       nir_cf_node *last_then = nir_if_last_then_node(if_stmt);
 120       assert(last_then->type == nir_cf_node_block);
 121       nir_block *last_then_block = nir_cf_node_as_block(last_then);
 122
 123       nir_cf_node *last_else = nir_if_last_else_node(if_stmt);
 124       assert(last_else->type == nir_cf_node_block);
 125       nir_block *last_else_block = nir_cf_node_as_block(last_else);
 126
 127       if (!block_ends_in_jump(last_then_block)) {
 128          unlink_block_successors(last_then_block);
 129          link_blocks(last_then_block, block, NULL);
 130       }
 131
 132       if (!block_ends_in_jump(last_else_block)) {
 133          unlink_block_successors(last_else_block);
 134          link_blocks(last_else_block, block, NULL);
 135       }
 136    } else {
 137       assert(node->type == nir_cf_node_loop);
 138
 139       /*
 140        * We can only get to this codepath if we're inserting a new loop, or
 141        * at least a loop with no break statements; we can't insert break
 142        * statements into a loop when we haven't inserted it into the CFG
 143        * because we wouldn't know which block comes after the loop
 144        * and therefore, which block should be the successor of the block with
 145        * the break). Therefore, we need to insert a fake edge (see invariant
 146        * #5).
 147        */
 148
 149       nir_loop *loop = nir_cf_node_as_loop(node);
 150
 151       nir_cf_node *last = nir_loop_last_cf_node(loop);
 152       assert(last->type == nir_cf_node_block);
 153       nir_block *last_block =  nir_cf_node_as_block(last);
 154
 155       last_block->successors[1] = block;
 156       block_add_pred(block, last_block);
 157    }
 158 }
 159
 160 static void
 161 link_block_to_non_block(nir_block *block, nir_cf_node *node)
 162 {
 163    if (node->type == nir_cf_node_if) {
 164       /*
 165        * We're trying to link a block to an if after it; this just means linking
 166        * the block to the first block of the then and else branches.
 167        */
 168
 169       nir_if *if_stmt = nir_cf_node_as_if(node);
 170
 171       nir_cf_node *first_then = nir_if_first_then_node(if_stmt);
 172       assert(first_then->type == nir_cf_node_block);
 173       nir_block *first_then_block = nir_cf_node_as_block(first_then);
 174
 175       nir_cf_node *first_else = nir_if_first_else_node(if_stmt);
 176       assert(first_else->type == nir_cf_node_block);
 177       nir_block *first_else_block = nir_cf_node_as_block(first_else);
 178
 179       unlink_block_successors(block);
 180       link_blocks(block, first_then_block, first_else_block);
 181    } else {
 182       /*
 183        * For similar reasons as the corresponding case in
 184        * link_non_block_to_block(), don't worry about if the loop header has
 185        * any predecessors that need to be unlinked.
 186        */
 187
 188       assert(node->type == nir_cf_node_loop);
 189
 190       nir_loop *loop = nir_cf_node_as_loop(node);
 191
 192       nir_cf_node *loop_header = nir_loop_first_cf_node(loop);
 193       assert(loop_header->type == nir_cf_node_block);
 194       nir_block *loop_header_block = nir_cf_node_as_block(loop_header);
 195
 196       unlink_block_successors(block);
 197       link_blocks(block, loop_header_block, NULL);
 198    }
 199
 200 }
 201
 202 /**
 203  * Replace a block's successor with a different one.
 204  */
 205 static void
 206 replace_successor(nir_block *block, nir_block *old_succ, nir_block *new_succ)
 207 {
 208    if (block->successors[0] == old_succ) {
 209       block->successors[0] = new_succ;
 210    } else {
 211       assert(block->successors[1] == old_succ);
 212       block->successors[1] = new_succ;
 213    }
 214
 215    block_remove_pred(old_succ, block);
 216    block_add_pred(new_succ, block);
 217 }
 218
 219 /**
 220  * Takes a basic block and inserts a new empty basic block before it, making its
 221  * predecessors point to the new block. This essentially splits the block into
 222  * an empty header and a body so that another non-block CF node can be inserted
 223  * between the two. Note that this does *not* link the two basic blocks, so
 224  * some kind of cleanup *must* be performed after this call.
 225  */
 226
 227 static nir_block *
 228 split_block_beginning(nir_block *block)
 229 {
 230    nir_block *new_block = nir_block_create(ralloc_parent(block));
 231    new_block->cf_node.parent = block->cf_node.parent;
 232    exec_node_insert_node_before(&block->cf_node.node, &new_block->cf_node.node);
 233
 234    struct set_entry *entry;
 235    set_foreach(block->predecessors, entry) {
 236       nir_block *pred = (nir_block *) entry->key;
 237       replace_successor(pred, block, new_block);
 238    }
 239
 240    /* Any phi nodes must stay part of the new block, or else their
 241     * sourcse will be messed up. This will reverse the order of the phi's, but
 242     * order shouldn't matter.
 243     */
 244    nir_foreach_instr_safe(instr, block) {
 245       if (instr->type != nir_instr_type_phi)
 246          break;
 247
 248       exec_node_remove(&instr->node);
 249       instr->block = new_block;
 250       exec_list_push_head(&new_block->instr_list, &instr->node);
 251    }
 252
 253    return new_block;
 254 }
 255
 256 static void
 257 rewrite_phi_preds(nir_block *block, nir_block *old_pred, nir_block *new_pred)
 258 {
 259    nir_foreach_instr_safe(instr, block) {
 260       if (instr->type != nir_instr_type_phi)
 261          break;
 262
 263       nir_phi_instr *phi = nir_instr_as_phi(instr);
 264       nir_foreach_phi_src(phi, src) {
 265          if (src->pred == old_pred) {
 266             src->pred = new_pred;
 267             break;
 268          }
 269       }
 270    }
 271 }
 272
 273 static void
 274 insert_phi_undef(nir_block *block, nir_block *pred)
 275 {
 276    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 277    nir_foreach_instr(instr, block) {
 278       if (instr->type != nir_instr_type_phi)
 279          break;
 280
 281       nir_phi_instr *phi = nir_instr_as_phi(instr);
 282       nir_ssa_undef_instr *undef =
 283          nir_ssa_undef_instr_create(ralloc_parent(phi),
 284                                     phi->dest.ssa.num_components,
 285                                     phi->dest.ssa.bit_size);
 286       nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 287       nir_phi_src *src = ralloc(phi, nir_phi_src);
 288       src->pred = pred;
 289       src->src.parent_instr = &phi->instr;
 290       src->src.is_ssa = true;
 291       src->src.ssa = &undef->def;
 292
 293       list_addtail(&src->src.use_link, &undef->def.uses);
 294
 295       exec_list_push_tail(&phi->srcs, &src->node);
 296    }
 297 }
 298
 299 /**
 300  * Moves the successors of source to the successors of dest, leaving both
 301  * successors of source NULL.
 302  */
 303
 304 static void
 305 move_successors(nir_block *source, nir_block *dest)
 306 {
 307    nir_block *succ1 = source->successors[0];
 308    nir_block *succ2 = source->successors[1];
 309
 310    if (succ1) {
 311       unlink_blocks(source, succ1);
 312       rewrite_phi_preds(succ1, source, dest);
 313    }
 314
 315    if (succ2) {
 316       unlink_blocks(source, succ2);
 317       rewrite_phi_preds(succ2, source, dest);
 318    }
 319
 320    unlink_block_successors(dest);
 321    link_blocks(dest, succ1, succ2);
 322 }
 323
 324 /* Given a basic block with no successors that has been inserted into the
 325  * control flow tree, gives it the successors it would normally have assuming
 326  * it doesn't end in a jump instruction. Also inserts phi sources with undefs
 327  * if necessary.
 328  */
 329 static void
 330 block_add_normal_succs(nir_block *block)
 331 {
 332    if (exec_node_is_tail_sentinel(block->cf_node.node.next)) {
 333       nir_cf_node *parent = block->cf_node.parent;
 334       if (parent->type == nir_cf_node_if) {
 335          nir_cf_node *next = nir_cf_node_next(parent);
 336          assert(next->type == nir_cf_node_block);
 337          nir_block *next_block = nir_cf_node_as_block(next);
 338
 339          link_blocks(block, next_block, NULL);
 340       } else if (parent->type == nir_cf_node_loop) {
 341          nir_loop *loop = nir_cf_node_as_loop(parent);
 342
 343          nir_cf_node *head = nir_loop_first_cf_node(loop);
 344          assert(head->type == nir_cf_node_block);
 345          nir_block *head_block = nir_cf_node_as_block(head);
 346
 347          link_blocks(block, head_block, NULL);
 348          insert_phi_undef(head_block, block);
 349       } else {
 350          assert(parent->type == nir_cf_node_function);
 351          nir_function_impl *impl = nir_cf_node_as_function(parent);
 352          link_blocks(block, impl->end_block, NULL);
 353       }
 354    } else {
 355       nir_cf_node *next = nir_cf_node_next(&block->cf_node);
 356       if (next->type == nir_cf_node_if) {
 357          nir_if *next_if = nir_cf_node_as_if(next);
 358
 359          nir_cf_node *first_then = nir_if_first_then_node(next_if);
 360          assert(first_then->type == nir_cf_node_block);
 361          nir_block *first_then_block = nir_cf_node_as_block(first_then);
 362
 363          nir_cf_node *first_else = nir_if_first_else_node(next_if);
 364          assert(first_else->type == nir_cf_node_block);
 365          nir_block *first_else_block = nir_cf_node_as_block(first_else);
 366
 367          link_blocks(block, first_then_block, first_else_block);
 368       } else {
 369          assert(next->type == nir_cf_node_loop);
 370          nir_loop *next_loop = nir_cf_node_as_loop(next);
 371
 372          nir_cf_node *first = nir_loop_first_cf_node(next_loop);
 373          assert(first->type == nir_cf_node_block);
 374          nir_block *first_block = nir_cf_node_as_block(first);
 375
 376          link_blocks(block, first_block, NULL);
 377          insert_phi_undef(first_block, block);
 378       }
 379    }
 380 }
 381
 382 static nir_block *
 383 split_block_end(nir_block *block)
 384 {
 385    nir_block *new_block = nir_block_create(ralloc_parent(block));
 386    new_block->cf_node.parent = block->cf_node.parent;
 387    exec_node_insert_after(&block->cf_node.node, &new_block->cf_node.node);
 388
 389    if (block_ends_in_jump(block)) {
 390       /* Figure out what successor block would've had if it didn't have a jump
 391        * instruction, and make new_block have that successor.
 392        */
 393       block_add_normal_succs(new_block);
 394    } else {
 395       move_successors(block, new_block);
 396    }
 397
 398    return new_block;
 399 }
 400
 401 static nir_block *
 402 split_block_before_instr(nir_instr *instr)
 403 {
 404    assert(instr->type != nir_instr_type_phi);
 405    nir_block *new_block = split_block_beginning(instr->block);
 406
 407    nir_foreach_instr_safe(cur_instr, instr->block) {
 408       if (cur_instr == instr)
 409          break;
 410
 411       exec_node_remove(&cur_instr->node);
 412       cur_instr->block = new_block;
 413       exec_list_push_tail(&new_block->instr_list, &cur_instr->node);
 414    }
 415
 416    return new_block;
 417 }
 418
 419 /* Splits a basic block at the point specified by the cursor. The "before" and
 420  * "after" arguments are filled out with the blocks resulting from the split
 421  * if non-NULL. Note that the "beginning" of the block is actually interpreted
 422  * as before the first non-phi instruction, and it's illegal to split a block
 423  * before a phi instruction.
 424  */
 425
 426 static void
 427 split_block_cursor(nir_cursor cursor,
 428                    nir_block **_before, nir_block **_after)
 429 {
 430    nir_block *before, *after;
 431    switch (cursor.option) {
 432    case nir_cursor_before_block:
 433       after = cursor.block;
 434       before = split_block_beginning(cursor.block);
 435       break;
 436
 437    case nir_cursor_after_block:
 438       before = cursor.block;
 439       after = split_block_end(cursor.block);
 440       break;
 441
 442    case nir_cursor_before_instr:
 443       after = cursor.instr->block;
 444       before = split_block_before_instr(cursor.instr);
 445       break;
 446
 447    case nir_cursor_after_instr:
 448       /* We lower this to split_block_before_instr() so that we can keep the
 449        * after-a-jump-instr case contained to split_block_end().
 450        */
 451       if (nir_instr_is_last(cursor.instr)) {
 452          before = cursor.instr->block;
 453          after = split_block_end(cursor.instr->block);
 454       } else {
 455          after = cursor.instr->block;
 456          before = split_block_before_instr(nir_instr_next(cursor.instr));
 457       }
 458       break;
 459
 460    default:
 461       unreachable("not reached");
 462    }
 463
 464    if (_before)
 465       *_before = before;
 466    if (_after)
 467       *_after = after;
 468 }
 469
 470 /**
 471  * Inserts a non-basic block between two basic blocks and links them together.
 472  */
 473
 474 static void
 475 insert_non_block(nir_block *before, nir_cf_node *node, nir_block *after)
 476 {
 477    node->parent = before->cf_node.parent;
 478    exec_node_insert_after(&before->cf_node.node, &node->node);
 479    link_block_to_non_block(before, node);
 480    link_non_block_to_block(node, after);
 481 }
 482
 483 /* walk up the control flow tree to find the innermost enclosed loop */
 484 static nir_loop *
 485 nearest_loop(nir_cf_node *node)
 486 {
 487    while (node->type != nir_cf_node_loop) {
 488       node = node->parent;
 489    }
 490
 491    return nir_cf_node_as_loop(node);
 492 }
 493
 494 /*
 495  * update the CFG after a jump instruction has been added to the end of a block
 496  */
 497
 498 void
 499 nir_handle_add_jump(nir_block *block)
 500 {
 501    nir_instr *instr = nir_block_last_instr(block);
 502    nir_jump_instr *jump_instr = nir_instr_as_jump(instr);
 503
 504    unlink_block_successors(block);
 505
 506    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 507    nir_metadata_preserve(impl, nir_metadata_none);
 508
 509    if (jump_instr->type == nir_jump_break ||
 510        jump_instr->type == nir_jump_continue) {
 511       nir_loop *loop = nearest_loop(&block->cf_node);
 512
 513       if (jump_instr->type == nir_jump_continue) {
 514          nir_cf_node *first_node = nir_loop_first_cf_node(loop);
 515          assert(first_node->type == nir_cf_node_block);
 516          nir_block *first_block = nir_cf_node_as_block(first_node);
 517          link_blocks(block, first_block, NULL);
 518       } else {
 519          nir_cf_node *after = nir_cf_node_next(&loop->cf_node);
 520          assert(after->type == nir_cf_node_block);
 521          nir_block *after_block = nir_cf_node_as_block(after);
 522          link_blocks(block, after_block, NULL);
 523
 524          /* If we inserted a fake link, remove it */
 525          nir_cf_node *last = nir_loop_last_cf_node(loop);
 526          assert(last->type == nir_cf_node_block);
 527          nir_block *last_block =  nir_cf_node_as_block(last);
 528          if (last_block->successors[1] != NULL)
 529             unlink_blocks(last_block, after_block);
 530       }
 531    } else {
 532       assert(jump_instr->type == nir_jump_return);
 533       link_blocks(block, impl->end_block, NULL);
 534    }
 535 }
 536
 537 static void
 538 remove_phi_src(nir_block *block, nir_block *pred)
 539 {
 540    nir_foreach_instr(instr, block) {
 541       if (instr->type != nir_instr_type_phi)
 542          break;
 543
 544       nir_phi_instr *phi = nir_instr_as_phi(instr);
 545       nir_foreach_phi_src_safe(phi, src) {
 546          if (src->pred == pred) {
 547             list_del(&src->src.use_link);
 548             exec_node_remove(&src->node);
 549          }
 550       }
 551    }
 552 }
 553
 554 /* Removes the successor of a block with a jump, and inserts a fake edge for
 555  * infinite loops. Note that the jump to be eliminated may be free-floating.
 556  */
 557
 558 static void
 559 unlink_jump(nir_block *block, nir_jump_type type, bool add_normal_successors)
 560 {
 561    nir_block *next = block->successors[0];
 562
 563    if (block->successors[0])
 564       remove_phi_src(block->successors[0], block);
 565    if (block->successors[1])
 566       remove_phi_src(block->successors[1], block);
 567
 568    unlink_block_successors(block);
 569    if (add_normal_successors)
 570       block_add_normal_succs(block);
 571
 572    /* If we've just removed a break, and the block we were jumping to (after
 573     * the loop) now has zero predecessors, we've created a new infinite loop.
 574     *
 575     * NIR doesn't allow blocks (other than the start block) to have zero
 576     * predecessors.  In particular, dominance assumes all blocks are reachable.
 577     * So, we insert a "fake link" by making successors[1] point after the loop.
 578     *
 579     * Note that we have to do this after unlinking/recreating the block's
 580     * successors.  If we removed a "break" at the end of the loop, then
 581     * block == last_block, so block->successors[0] would already be "next",
 582     * and adding a fake link would create two identical successors.  Doing
 583     * this afterward works, as we'll have changed block->successors[0] to
 584     * be the top of the loop.
 585     */
 586    if (type == nir_jump_break && next->predecessors->entries == 0) {
 587       nir_loop *loop =
 588          nir_cf_node_as_loop(nir_cf_node_prev(&next->cf_node));
 589
 590       /* insert fake link */
 591       nir_cf_node *last = nir_loop_last_cf_node(loop);
 592       assert(last->type == nir_cf_node_block);
 593       nir_block *last_block = nir_cf_node_as_block(last);
 594
 595       last_block->successors[1] = next;
 596       block_add_pred(next, last_block);
 597    }
 598 }
 599
 600 void
 601 nir_handle_remove_jump(nir_block *block, nir_jump_type type)
 602 {
 603    unlink_jump(block, type, true);
 604
 605    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 606    nir_metadata_preserve(impl, nir_metadata_none);
 607 }
 608
 609 static void
 610 update_if_uses(nir_cf_node *node)
 611 {
 612    if (node->type != nir_cf_node_if)
 613       return;
 614
 615    nir_if *if_stmt = nir_cf_node_as_if(node);
 616
 617    if_stmt->condition.parent_if = if_stmt;
 618    if (if_stmt->condition.is_ssa) {
 619       list_addtail(&if_stmt->condition.use_link,
 620                    &if_stmt->condition.ssa->if_uses);
 621    } else {
 622       list_addtail(&if_stmt->condition.use_link,
 623                    &if_stmt->condition.reg.reg->if_uses);
 624    }
 625 }
 626
 627 /**
 628  * Stitch two basic blocks together into one. The aggregate must have the same
 629  * predecessors as the first and the same successors as the second.
 630  */
 631
 632 static void
 633 stitch_blocks(nir_block *before, nir_block *after)
 634 {
 635    /*
 636     * We move after into before, so we have to deal with up to 2 successors vs.
 637     * possibly a large number of predecessors.
 638     *
 639     * TODO: special case when before is empty and after isn't?
 640     */
 641
 642    if (block_ends_in_jump(before)) {
 643       assert(exec_list_is_empty(&after->instr_list));
 644       if (after->successors[0])
 645          remove_phi_src(after->successors[0], after);
 646       if (after->successors[1])
 647          remove_phi_src(after->successors[1], after);
 648       unlink_block_successors(after);
 649       exec_node_remove(&after->cf_node.node);
 650    } else {
 651       move_successors(after, before);
 652
 653       foreach_list_typed(nir_instr, instr, node, &after->instr_list) {
 654          instr->block = before;
 655       }
 656
 657       exec_list_append(&before->instr_list, &after->instr_list);
 658       exec_node_remove(&after->cf_node.node);
 659    }
 660 }
 661
 662 void
 663 nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node)
 664 {
 665    nir_block *before, *after;
 666
 667    split_block_cursor(cursor, &before, &after);
 668
 669    if (node->type == nir_cf_node_block) {
 670       nir_block *block = nir_cf_node_as_block(node);
 671       exec_node_insert_after(&before->cf_node.node, &block->cf_node.node);
 672       block->cf_node.parent = before->cf_node.parent;
 673       /* stitch_blocks() assumes that any block that ends with a jump has
 674        * already been setup with the correct successors, so we need to set
 675        * up jumps here as the block is being inserted.
 676        */
 677       if (block_ends_in_jump(block))
 678          nir_handle_add_jump(block);
 679
 680       stitch_blocks(block, after);
 681       stitch_blocks(before, block);
 682    } else {
 683       update_if_uses(node);
 684       insert_non_block(before, node, after);
 685    }
 686 }
 687
 688 static bool
 689 replace_ssa_def_uses(nir_ssa_def *def, void *void_impl)
 690 {
 691    nir_function_impl *impl = void_impl;
 692    void *mem_ctx = ralloc_parent(impl);
 693
 694    nir_ssa_undef_instr *undef =
 695       nir_ssa_undef_instr_create(mem_ctx, def->num_components,
 696                                  def->bit_size);
 697    nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 698    nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(&undef->def));
 699    return true;
 700 }
 701
 702 static void
 703 cleanup_cf_node(nir_cf_node *node, nir_function_impl *impl)
 704 {
 705    switch (node->type) {
 706    case nir_cf_node_block: {
 707       nir_block *block = nir_cf_node_as_block(node);
 708       /* We need to walk the instructions and clean up defs/uses */
 709       nir_foreach_instr_safe(instr, block) {
 710          if (instr->type == nir_instr_type_jump) {
 711             nir_jump_type jump_type = nir_instr_as_jump(instr)->type;
 712             unlink_jump(block, jump_type, false);
 713          } else {
 714             nir_foreach_ssa_def(instr, replace_ssa_def_uses, impl);
 715             nir_instr_remove(instr);
 716          }
 717       }
 718       break;
 719    }
 720
 721    case nir_cf_node_if: {
 722       nir_if *if_stmt = nir_cf_node_as_if(node);
 723       foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list)
 724          cleanup_cf_node(child, impl);
 725       foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list)
 726          cleanup_cf_node(child, impl);
 727
 728       list_del(&if_stmt->condition.use_link);
 729       break;
 730    }
 731
 732    case nir_cf_node_loop: {
 733       nir_loop *loop = nir_cf_node_as_loop(node);
 734       foreach_list_typed(nir_cf_node, child, node, &loop->body)
 735          cleanup_cf_node(child, impl);
 736       break;
 737    }
 738    case nir_cf_node_function: {
 739       nir_function_impl *impl = nir_cf_node_as_function(node);
 740       foreach_list_typed(nir_cf_node, child, node, &impl->body)
 741          cleanup_cf_node(child, impl);
 742       break;
 743    }
 744    default:
 745       unreachable("Invalid CF node type");
 746    }
 747 }
 748
 749 void
 750 nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end)
 751 {
 752    nir_block *block_begin, *block_end, *block_before, *block_after;
 753
 754    if (nir_cursors_equal(begin, end)) {
 755       exec_list_make_empty(&extracted->list);
 756       extracted->impl = NULL; /* we shouldn't need this */
 757       return;
 758    }
 759
 760    /* In the case where begin points to an instruction in some basic block and
 761     * end points to the end of the same basic block, we rely on the fact that
 762     * splitting on an instruction moves earlier instructions into a new basic
 763     * block. If the later instructions were moved instead, then the end cursor
 764     * would be pointing to the same place that begin used to point to, which
 765     * is obviously not what we want.
 766     */
 767    split_block_cursor(begin, &block_before, &block_begin);
 768    split_block_cursor(end, &block_end, &block_after);
 769
 770    extracted->impl = nir_cf_node_get_function(&block_begin->cf_node);
 771    exec_list_make_empty(&extracted->list);
 772
 773    /* Dominance and other block-related information is toast. */
 774    nir_metadata_preserve(extracted->impl, nir_metadata_none);
 775
 776    nir_cf_node *cf_node = &block_begin->cf_node;
 777    nir_cf_node *cf_node_end = &block_end->cf_node;
 778    while (true) {
 779       nir_cf_node *next = nir_cf_node_next(cf_node);
 780
 781       exec_node_remove(&cf_node->node);
 782       cf_node->parent = NULL;
 783       exec_list_push_tail(&extracted->list, &cf_node->node);
 784
 785       if (cf_node == cf_node_end)
 786          break;
 787
 788       cf_node = next;
 789    }
 790
 791    stitch_blocks(block_before, block_after);
 792 }
 793
 794 void
 795 nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor)
 796 {
 797    nir_block *before, *after;
 798
 799    if (exec_list_is_empty(&cf_list->list))
 800       return;
 801
 802    split_block_cursor(cursor, &before, &after);
 803
 804    foreach_list_typed_safe(nir_cf_node, node, node, &cf_list->list) {
 805       exec_node_remove(&node->node);
 806       node->parent = before->cf_node.parent;
 807       exec_node_insert_node_before(&after->cf_node.node, &node->node);
 808    }
 809
 810    stitch_blocks(before,
 811                  nir_cf_node_as_block(nir_cf_node_next(&before->cf_node)));
 812    stitch_blocks(nir_cf_node_as_block(nir_cf_node_prev(&after->cf_node)),
 813                  after);
 814 }
 815
 816 void
 817 nir_cf_delete(nir_cf_list *cf_list)
 818 {
 819    foreach_list_typed(nir_cf_node, node, node, &cf_list->list) {
 820       cleanup_cf_node(node, cf_list->impl);
 821    }
 822 }