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(block, instr) {
 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(block, instr) {
 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(block, instr) {
 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       nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 286       nir_phi_src *src = ralloc(phi, nir_phi_src);
 287       src->pred = pred;
 288       src->src.parent_instr = &phi->instr;
 289       src->src.is_ssa = true;
 290       src->src.ssa = &undef->def;
 291
 292       list_addtail(&src->src.use_link, &undef->def.uses);
 293
 294       exec_list_push_tail(&phi->srcs, &src->node);
 295    }
 296 }
 297
 298 /**
 299  * Moves the successors of source to the successors of dest, leaving both
 300  * successors of source NULL.
 301  */
 302
 303 static void
 304 move_successors(nir_block *source, nir_block *dest)
 305 {
 306    nir_block *succ1 = source->successors[0];
 307    nir_block *succ2 = source->successors[1];
 308
 309    if (succ1) {
 310       unlink_blocks(source, succ1);
 311       rewrite_phi_preds(succ1, source, dest);
 312    }
 313
 314    if (succ2) {
 315       unlink_blocks(source, succ2);
 316       rewrite_phi_preds(succ2, source, dest);
 317    }
 318
 319    unlink_block_successors(dest);
 320    link_blocks(dest, succ1, succ2);
 321 }
 322
 323 /* Given a basic block with no successors that has been inserted into the
 324  * control flow tree, gives it the successors it would normally have assuming
 325  * it doesn't end in a jump instruction. Also inserts phi sources with undefs
 326  * if necessary.
 327  */
 328 static void
 329 block_add_normal_succs(nir_block *block)
 330 {
 331    if (exec_node_is_tail_sentinel(block->cf_node.node.next)) {
 332       nir_cf_node *parent = block->cf_node.parent;
 333       if (parent->type == nir_cf_node_if) {
 334          nir_cf_node *next = nir_cf_node_next(parent);
 335          assert(next->type == nir_cf_node_block);
 336          nir_block *next_block = nir_cf_node_as_block(next);
 337
 338          link_blocks(block, next_block, NULL);
 339       } else if (parent->type == nir_cf_node_loop) {
 340          nir_loop *loop = nir_cf_node_as_loop(parent);
 341
 342          nir_cf_node *head = nir_loop_first_cf_node(loop);
 343          assert(head->type == nir_cf_node_block);
 344          nir_block *head_block = nir_cf_node_as_block(head);
 345
 346          link_blocks(block, head_block, NULL);
 347          insert_phi_undef(head_block, block);
 348       } else {
 349          assert(parent->type == nir_cf_node_function);
 350          nir_function_impl *impl = nir_cf_node_as_function(parent);
 351          link_blocks(block, impl->end_block, NULL);
 352       }
 353    } else {
 354       nir_cf_node *next = nir_cf_node_next(&block->cf_node);
 355       if (next->type == nir_cf_node_if) {
 356          nir_if *next_if = nir_cf_node_as_if(next);
 357
 358          nir_cf_node *first_then = nir_if_first_then_node(next_if);
 359          assert(first_then->type == nir_cf_node_block);
 360          nir_block *first_then_block = nir_cf_node_as_block(first_then);
 361
 362          nir_cf_node *first_else = nir_if_first_else_node(next_if);
 363          assert(first_else->type == nir_cf_node_block);
 364          nir_block *first_else_block = nir_cf_node_as_block(first_else);
 365
 366          link_blocks(block, first_then_block, first_else_block);
 367       } else {
 368          assert(next->type == nir_cf_node_loop);
 369          nir_loop *next_loop = nir_cf_node_as_loop(next);
 370
 371          nir_cf_node *first = nir_loop_first_cf_node(next_loop);
 372          assert(first->type == nir_cf_node_block);
 373          nir_block *first_block = nir_cf_node_as_block(first);
 374
 375          link_blocks(block, first_block, NULL);
 376          insert_phi_undef(first_block, block);
 377       }
 378    }
 379 }
 380
 381 static nir_block *
 382 split_block_end(nir_block *block)
 383 {
 384    nir_block *new_block = nir_block_create(ralloc_parent(block));
 385    new_block->cf_node.parent = block->cf_node.parent;
 386    exec_node_insert_after(&block->cf_node.node, &new_block->cf_node.node);
 387
 388    if (block_ends_in_jump(block)) {
 389       /* Figure out what successor block would've had if it didn't have a jump
 390        * instruction, and make new_block have that successor.
 391        */
 392       block_add_normal_succs(new_block);
 393    } else {
 394       move_successors(block, new_block);
 395    }
 396
 397    return new_block;
 398 }
 399
 400 static nir_block *
 401 split_block_before_instr(nir_instr *instr)
 402 {
 403    assert(instr->type != nir_instr_type_phi);
 404    nir_block *new_block = split_block_beginning(instr->block);
 405
 406    nir_foreach_instr_safe(instr->block, cur_instr) {
 407       if (cur_instr == instr)
 408          break;
 409
 410       exec_node_remove(&cur_instr->node);
 411       cur_instr->block = new_block;
 412       exec_list_push_tail(&new_block->instr_list, &cur_instr->node);
 413    }
 414
 415    return new_block;
 416 }
 417
 418 /* Splits a basic block at the point specified by the cursor. The "before" and
 419  * "after" arguments are filled out with the blocks resulting from the split
 420  * if non-NULL. Note that the "beginning" of the block is actually interpreted
 421  * as before the first non-phi instruction, and it's illegal to split a block
 422  * before a phi instruction.
 423  */
 424
 425 static void
 426 split_block_cursor(nir_cursor cursor,
 427                    nir_block **_before, nir_block **_after)
 428 {
 429    nir_block *before, *after;
 430    switch (cursor.option) {
 431    case nir_cursor_before_block:
 432       after = cursor.block;
 433       before = split_block_beginning(cursor.block);
 434       break;
 435
 436    case nir_cursor_after_block:
 437       before = cursor.block;
 438       after = split_block_end(cursor.block);
 439       break;
 440
 441    case nir_cursor_before_instr:
 442       after = cursor.instr->block;
 443       before = split_block_before_instr(cursor.instr);
 444       break;
 445
 446    case nir_cursor_after_instr:
 447       /* We lower this to split_block_before_instr() so that we can keep the
 448        * after-a-jump-instr case contained to split_block_end().
 449        */
 450       if (nir_instr_is_last(cursor.instr)) {
 451          before = cursor.instr->block;
 452          after = split_block_end(cursor.instr->block);
 453       } else {
 454          after = cursor.instr->block;
 455          before = split_block_before_instr(nir_instr_next(cursor.instr));
 456       }
 457       break;
 458
 459    default:
 460       unreachable("not reached");
 461    }
 462
 463    if (_before)
 464       *_before = before;
 465    if (_after)
 466       *_after = after;
 467 }
 468
 469 /**
 470  * Inserts a non-basic block between two basic blocks and links them together.
 471  */
 472
 473 static void
 474 insert_non_block(nir_block *before, nir_cf_node *node, nir_block *after)
 475 {
 476    node->parent = before->cf_node.parent;
 477    exec_node_insert_after(&before->cf_node.node, &node->node);
 478    link_block_to_non_block(before, node);
 479    link_non_block_to_block(node, after);
 480 }
 481
 482 /* walk up the control flow tree to find the innermost enclosed loop */
 483 static nir_loop *
 484 nearest_loop(nir_cf_node *node)
 485 {
 486    while (node->type != nir_cf_node_loop) {
 487       node = node->parent;
 488    }
 489
 490    return nir_cf_node_as_loop(node);
 491 }
 492
 493 /*
 494  * update the CFG after a jump instruction has been added to the end of a block
 495  */
 496
 497 void
 498 nir_handle_add_jump(nir_block *block)
 499 {
 500    nir_instr *instr = nir_block_last_instr(block);
 501    nir_jump_instr *jump_instr = nir_instr_as_jump(instr);
 502
 503    unlink_block_successors(block);
 504
 505    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 506    nir_metadata_preserve(impl, nir_metadata_none);
 507
 508    if (jump_instr->type == nir_jump_break ||
 509        jump_instr->type == nir_jump_continue) {
 510       nir_loop *loop = nearest_loop(&block->cf_node);
 511
 512       if (jump_instr->type == nir_jump_continue) {
 513          nir_cf_node *first_node = nir_loop_first_cf_node(loop);
 514          assert(first_node->type == nir_cf_node_block);
 515          nir_block *first_block = nir_cf_node_as_block(first_node);
 516          link_blocks(block, first_block, NULL);
 517       } else {
 518          nir_cf_node *after = nir_cf_node_next(&loop->cf_node);
 519          assert(after->type == nir_cf_node_block);
 520          nir_block *after_block = nir_cf_node_as_block(after);
 521          link_blocks(block, after_block, NULL);
 522
 523          /* If we inserted a fake link, remove it */
 524          nir_cf_node *last = nir_loop_last_cf_node(loop);
 525          assert(last->type == nir_cf_node_block);
 526          nir_block *last_block =  nir_cf_node_as_block(last);
 527          if (last_block->successors[1] != NULL)
 528             unlink_blocks(last_block, after_block);
 529       }
 530    } else {
 531       assert(jump_instr->type == nir_jump_return);
 532       link_blocks(block, impl->end_block, NULL);
 533    }
 534 }
 535
 536 static void
 537 remove_phi_src(nir_block *block, nir_block *pred)
 538 {
 539    nir_foreach_instr(block, instr) {
 540       if (instr->type != nir_instr_type_phi)
 541          break;
 542
 543       nir_phi_instr *phi = nir_instr_as_phi(instr);
 544       nir_foreach_phi_src_safe(phi, src) {
 545          if (src->pred == pred) {
 546             list_del(&src->src.use_link);
 547             exec_node_remove(&src->node);
 548          }
 549       }
 550    }
 551 }
 552
 553 /* Removes the successor of a block with a jump, and inserts a fake edge for
 554  * infinite loops. Note that the jump to be eliminated may be free-floating.
 555  */
 556
 557 static void
 558 unlink_jump(nir_block *block, nir_jump_type type, bool add_normal_successors)
 559 {
 560    nir_block *next = block->successors[0];
 561
 562    if (block->successors[0])
 563       remove_phi_src(block->successors[0], block);
 564    if (block->successors[1])
 565       remove_phi_src(block->successors[1], block);
 566
 567    unlink_block_successors(block);
 568    if (add_normal_successors)
 569       block_add_normal_succs(block);
 570
 571    /* If we've just removed a break, and the block we were jumping to (after
 572     * the loop) now has zero predecessors, we've created a new infinite loop.
 573     *
 574     * NIR doesn't allow blocks (other than the start block) to have zero
 575     * predecessors.  In particular, dominance assumes all blocks are reachable.
 576     * So, we insert a "fake link" by making successors[1] point after the loop.
 577     *
 578     * Note that we have to do this after unlinking/recreating the block's
 579     * successors.  If we removed a "break" at the end of the loop, then
 580     * block == last_block, so block->successors[0] would already be "next",
 581     * and adding a fake link would create two identical successors.  Doing
 582     * this afterward works, as we'll have changed block->successors[0] to
 583     * be the top of the loop.
 584     */
 585    if (type == nir_jump_break && next->predecessors->entries == 0) {
 586       nir_loop *loop =
 587          nir_cf_node_as_loop(nir_cf_node_prev(&next->cf_node));
 588
 589       /* insert fake link */
 590       nir_cf_node *last = nir_loop_last_cf_node(loop);
 591       assert(last->type == nir_cf_node_block);
 592       nir_block *last_block = nir_cf_node_as_block(last);
 593
 594       last_block->successors[1] = next;
 595       block_add_pred(next, last_block);
 596    }
 597 }
 598
 599 void
 600 nir_handle_remove_jump(nir_block *block, nir_jump_type type)
 601 {
 602    unlink_jump(block, type, true);
 603
 604    nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
 605    nir_metadata_preserve(impl, nir_metadata_none);
 606 }
 607
 608 static void
 609 update_if_uses(nir_cf_node *node)
 610 {
 611    if (node->type != nir_cf_node_if)
 612       return;
 613
 614    nir_if *if_stmt = nir_cf_node_as_if(node);
 615
 616    if_stmt->condition.parent_if = if_stmt;
 617    if (if_stmt->condition.is_ssa) {
 618       list_addtail(&if_stmt->condition.use_link,
 619                    &if_stmt->condition.ssa->if_uses);
 620    } else {
 621       list_addtail(&if_stmt->condition.use_link,
 622                    &if_stmt->condition.reg.reg->if_uses);
 623    }
 624 }
 625
 626 /**
 627  * Stitch two basic blocks together into one. The aggregate must have the same
 628  * predecessors as the first and the same successors as the second.
 629  */
 630
 631 static void
 632 stitch_blocks(nir_block *before, nir_block *after)
 633 {
 634    /*
 635     * We move after into before, so we have to deal with up to 2 successors vs.
 636     * possibly a large number of predecessors.
 637     *
 638     * TODO: special case when before is empty and after isn't?
 639     */
 640
 641    if (block_ends_in_jump(before)) {
 642       assert(exec_list_is_empty(&after->instr_list));
 643       if (after->successors[0])
 644          remove_phi_src(after->successors[0], after);
 645       if (after->successors[1])
 646          remove_phi_src(after->successors[1], after);
 647       unlink_block_successors(after);
 648       exec_node_remove(&after->cf_node.node);
 649    } else {
 650       move_successors(after, before);
 651
 652       foreach_list_typed(nir_instr, instr, node, &after->instr_list) {
 653          instr->block = before;
 654       }
 655
 656       exec_list_append(&before->instr_list, &after->instr_list);
 657       exec_node_remove(&after->cf_node.node);
 658    }
 659 }
 660
 661 void
 662 nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node)
 663 {
 664    nir_block *before, *after;
 665
 666    split_block_cursor(cursor, &before, &after);
 667
 668    if (node->type == nir_cf_node_block) {
 669       nir_block *block = nir_cf_node_as_block(node);
 670       exec_node_insert_after(&before->cf_node.node, &block->cf_node.node);
 671       block->cf_node.parent = before->cf_node.parent;
 672       /* stitch_blocks() assumes that any block that ends with a jump has
 673        * already been setup with the correct successors, so we need to set
 674        * up jumps here as the block is being inserted.
 675        */
 676       if (block_ends_in_jump(block))
 677          nir_handle_add_jump(block);
 678
 679       stitch_blocks(block, after);
 680       stitch_blocks(before, block);
 681    } else {
 682       update_if_uses(node);
 683       insert_non_block(before, node, after);
 684    }
 685 }
 686
 687 static bool
 688 replace_ssa_def_uses(nir_ssa_def *def, void *void_impl)
 689 {
 690    nir_function_impl *impl = void_impl;
 691    void *mem_ctx = ralloc_parent(impl);
 692
 693    nir_ssa_undef_instr *undef =
 694       nir_ssa_undef_instr_create(mem_ctx, def->num_components);
 695    nir_instr_insert_before_cf_list(&impl->body, &undef->instr);
 696    nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(&undef->def));
 697    return true;
 698 }
 699
 700 static void
 701 cleanup_cf_node(nir_cf_node *node, nir_function_impl *impl)
 702 {
 703    switch (node->type) {
 704    case nir_cf_node_block: {
 705       nir_block *block = nir_cf_node_as_block(node);
 706       /* We need to walk the instructions and clean up defs/uses */
 707       nir_foreach_instr_safe(block, instr) {
 708          if (instr->type == nir_instr_type_jump) {
 709             nir_jump_type jump_type = nir_instr_as_jump(instr)->type;
 710             unlink_jump(block, jump_type, false);
 711          } else {
 712             nir_foreach_ssa_def(instr, replace_ssa_def_uses, impl);
 713             nir_instr_remove(instr);
 714          }
 715       }
 716       break;
 717    }
 718
 719    case nir_cf_node_if: {
 720       nir_if *if_stmt = nir_cf_node_as_if(node);
 721       foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list)
 722          cleanup_cf_node(child, impl);
 723       foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list)
 724          cleanup_cf_node(child, impl);
 725
 726       list_del(&if_stmt->condition.use_link);
 727       break;
 728    }
 729
 730    case nir_cf_node_loop: {
 731       nir_loop *loop = nir_cf_node_as_loop(node);
 732       foreach_list_typed(nir_cf_node, child, node, &loop->body)
 733          cleanup_cf_node(child, impl);
 734       break;
 735    }
 736    case nir_cf_node_function: {
 737       nir_function_impl *impl = nir_cf_node_as_function(node);
 738       foreach_list_typed(nir_cf_node, child, node, &impl->body)
 739          cleanup_cf_node(child, impl);
 740       break;
 741    }
 742    default:
 743       unreachable("Invalid CF node type");
 744    }
 745 }
 746
 747 void
 748 nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end)
 749 {
 750    nir_block *block_begin, *block_end, *block_before, *block_after;
 751
 752    if (nir_cursors_equal(begin, end)) {
 753       exec_list_make_empty(&extracted->list);
 754       extracted->impl = NULL; /* we shouldn't need this */
 755       return;
 756    }
 757
 758    /* In the case where begin points to an instruction in some basic block and
 759     * end points to the end of the same basic block, we rely on the fact that
 760     * splitting on an instruction moves earlier instructions into a new basic
 761     * block. If the later instructions were moved instead, then the end cursor
 762     * would be pointing to the same place that begin used to point to, which
 763     * is obviously not what we want.
 764     */
 765    split_block_cursor(begin, &block_before, &block_begin);
 766    split_block_cursor(end, &block_end, &block_after);
 767
 768    extracted->impl = nir_cf_node_get_function(&block_begin->cf_node);
 769    exec_list_make_empty(&extracted->list);
 770
 771    /* Dominance and other block-related information is toast. */
 772    nir_metadata_preserve(extracted->impl, nir_metadata_none);
 773
 774    nir_cf_node *cf_node = &block_begin->cf_node;
 775    nir_cf_node *cf_node_end = &block_end->cf_node;
 776    while (true) {
 777       nir_cf_node *next = nir_cf_node_next(cf_node);
 778
 779       exec_node_remove(&cf_node->node);
 780       cf_node->parent = NULL;
 781       exec_list_push_tail(&extracted->list, &cf_node->node);
 782
 783       if (cf_node == cf_node_end)
 784          break;
 785
 786       cf_node = next;
 787    }
 788
 789    stitch_blocks(block_before, block_after);
 790 }
 791
 792 void
 793 nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor)
 794 {
 795    nir_block *before, *after;
 796
 797    if (exec_list_is_empty(&cf_list->list))
 798       return;
 799
 800    split_block_cursor(cursor, &before, &after);
 801
 802    foreach_list_typed_safe(nir_cf_node, node, node, &cf_list->list) {
 803       exec_node_remove(&node->node);
 804       node->parent = before->cf_node.parent;
 805       exec_node_insert_node_before(&after->cf_node.node, &node->node);
 806    }
 807
 808    stitch_blocks(before,
 809                  nir_cf_node_as_block(nir_cf_node_next(&before->cf_node)));
 810    stitch_blocks(nir_cf_node_as_block(nir_cf_node_prev(&after->cf_node)),
 811                  after);
 812 }
 813
 814 void
 815 nir_cf_delete(nir_cf_list *cf_list)
 816 {
 817    foreach_list_typed(nir_cf_node, node, node, &cf_list->list) {
 818       cleanup_cf_node(node, cf_list->impl);
 819    }
 820 }