src/gallium/drivers/nv50/nv50_pc.c

   1 /*
   2  * Copyright 2010 Christoph Bumiller
   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 shall be included in
  12  * all copies or substantial portions of the Software.
  13  *
  14  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  15  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  17  * THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  18  * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
  19  * OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  20  * SOFTWARE.
  21  */
  22
  23 /* #define NV50PC_DEBUG */
  24
  25 #include "nv50_pc.h"
  26 #include "nv50_program.h"
  27
  28 #include <stdio.h>
  29
  30 /* returns TRUE if operands 0 and 1 can be swapped */
  31 boolean
  32 nv_op_commutative(uint opcode)
  33 {
  34    switch (opcode) {
  35    case NV_OP_ADD:
  36    case NV_OP_MUL:
  37    case NV_OP_MAD:
  38    case NV_OP_AND:
  39    case NV_OP_OR:
  40    case NV_OP_XOR:
  41    case NV_OP_MIN:
  42    case NV_OP_MAX:
  43    case NV_OP_SAD:
  44      return TRUE;
  45    default:
  46      return FALSE;
  47    }
  48 }
  49
  50 /* return operand to which the address register applies */
  51 int
  52 nv50_indirect_opnd(struct nv_instruction *i)
  53 {
  54    if (!i->src[4])
  55       return -1;
  56
  57    switch (i->opcode) {
  58    case NV_OP_MOV:
  59    case NV_OP_LDA:
  60       return 0;
  61    default:
  62       return 1;
  63    }
  64 }
  65
  66 boolean
  67 nv50_nvi_can_use_imm(struct nv_instruction *nvi, int s)
  68 {
  69    if (nvi->flags_src || nvi->flags_def)
  70       return FALSE;
  71
  72    switch (nvi->opcode) {
  73    case NV_OP_ADD:
  74    case NV_OP_MUL:
  75    case NV_OP_AND:
  76    case NV_OP_OR:
  77    case NV_OP_XOR:
  78    case NV_OP_SHL:
  79    case NV_OP_SHR:
  80       return (s == 1) && (nvi->src[0]->value->reg.file == NV_FILE_GPR) &&
  81          (nvi->def[0]->reg.file == NV_FILE_GPR);
  82    case NV_OP_MOV:
  83       assert(s == 0);
  84       return (nvi->def[0]->reg.file == NV_FILE_GPR);
  85    default:
  86       return FALSE;
  87    }
  88 }
  89
  90 boolean
  91 nv50_nvi_can_load(struct nv_instruction *nvi, int s, struct nv_value *value)
  92 {
  93    int i;
  94
  95    for (i = 0; i < 3 && nvi->src[i]; ++i)
  96       if (nvi->src[i]->value->reg.file == NV_FILE_IMM)
  97          return FALSE;
  98
  99    switch (nvi->opcode) {
 100    case NV_OP_ABS:
 101    case NV_OP_ADD:
 102    case NV_OP_CEIL:
 103    case NV_OP_FLOOR:
 104    case NV_OP_TRUNC:
 105    case NV_OP_CVT:
 106    case NV_OP_MAD:
 107    case NV_OP_MUL:
 108    case NV_OP_SAT:
 109    case NV_OP_SUB:
 110    case NV_OP_MAX:
 111    case NV_OP_MIN:
 112       if (s == 0 && (value->reg.file == NV_FILE_MEM_S ||
 113                      value->reg.file == NV_FILE_MEM_P))
 114          return TRUE;
 115       if (value->reg.file < NV_FILE_MEM_C(0) ||
 116           value->reg.file > NV_FILE_MEM_C(15))
 117          return FALSE;
 118       return (s == 1) ||
 119          ((s == 2) && (nvi->src[1]->value->reg.file == NV_FILE_GPR));
 120    case NV_OP_MOV:
 121       assert(s == 0);
 122       return /* TRUE */ FALSE; /* don't turn MOVs into loads */
 123    default:
 124       return FALSE;
 125    }
 126 }
 127
 128 /* Return whether this instruction can be executed conditionally. */
 129 boolean
 130 nv50_nvi_can_predicate(struct nv_instruction *nvi)
 131 {
 132    int i;
 133
 134    if (nvi->flags_src)
 135       return FALSE;
 136    for (i = 0; i < 4 && nvi->src[i]; ++i)
 137       if (nvi->src[i]->value->reg.file == NV_FILE_IMM)
 138          return FALSE;
 139    return TRUE;
 140 }
 141
 142 ubyte
 143 nv50_supported_src_mods(uint opcode, int s)
 144 {
 145    switch (opcode) {
 146    case NV_OP_ABS:
 147       return NV_MOD_NEG | NV_MOD_ABS; /* obviously */
 148    case NV_OP_ADD:
 149    case NV_OP_MUL:
 150    case NV_OP_MAD:
 151       return NV_MOD_NEG;
 152    case NV_OP_DFDX:
 153    case NV_OP_DFDY:
 154       assert(s == 0);
 155       return NV_MOD_NEG;
 156    case NV_OP_MAX:
 157    case NV_OP_MIN:
 158       return NV_MOD_ABS;
 159    case NV_OP_CVT:
 160    case NV_OP_LG2:
 161    case NV_OP_NEG:
 162    case NV_OP_PREEX2:
 163    case NV_OP_PRESIN:
 164    case NV_OP_RCP:
 165    case NV_OP_RSQ:
 166       return NV_MOD_ABS | NV_MOD_NEG;
 167    default:
 168       return 0;
 169    }
 170 }
 171
 172 int
 173 nv_nvi_refcount(struct nv_instruction *nvi)
 174 {
 175    int i, rc;
 176
 177    rc = nvi->flags_def ? nvi->flags_def->refc : 0;
 178
 179    for (i = 0; i < 4; ++i) {
 180       if (!nvi->def[i])
 181          return rc;
 182       rc += nvi->def[i]->refc;
 183    }
 184    return rc;
 185 }
 186
 187 int
 188 nvcg_replace_value(struct nv_pc *pc, struct nv_value *old_val,
 189                    struct nv_value *new_val)
 190 {
 191    int i, n;
 192
 193    if (old_val == new_val)
 194       return old_val->refc;
 195
 196    for (i = 0, n = 0; i < pc->num_refs; ++i) {
 197       if (pc->refs[i]->value == old_val) {
 198          ++n;
 199          nv_reference(pc, &pc->refs[i], new_val);
 200       }
 201    }
 202    return n;
 203 }
 204
 205 struct nv_value *
 206 nvcg_find_constant(struct nv_ref *ref)
 207 {
 208    struct nv_value *src;
 209
 210    if (!ref)
 211       return NULL;
 212
 213    src = ref->value;
 214    while (src->insn && src->insn->opcode == NV_OP_MOV) {
 215       assert(!src->insn->src[0]->mod);
 216       src = src->insn->src[0]->value;
 217    }
 218    if ((src->reg.file == NV_FILE_IMM) ||
 219        (src->insn && src->insn->opcode == NV_OP_LDA &&
 220         src->insn->src[0]->value->reg.file >= NV_FILE_MEM_C(0) &&
 221         src->insn->src[0]->value->reg.file <= NV_FILE_MEM_C(15)))
 222       return src;
 223    return NULL;
 224 }
 225
 226 struct nv_value *
 227 nvcg_find_immediate(struct nv_ref *ref)
 228 {
 229    struct nv_value *src = nvcg_find_constant(ref);
 230
 231    return (src && src->reg.file == NV_FILE_IMM) ? src : NULL;
 232 }
 233
 234 static void
 235 nv_pc_free_refs(struct nv_pc *pc)
 236 {
 237    int i;
 238    for (i = 0; i < pc->num_refs; i += 64)
 239       FREE(pc->refs[i]);
 240 }
 241
 242 static const char *
 243 edge_name(ubyte type)
 244 {
 245    switch (type) {
 246    case CFG_EDGE_FORWARD: return "forward";
 247    case CFG_EDGE_BACK: return "back";
 248    case CFG_EDGE_LOOP_ENTER: return "loop";
 249    case CFG_EDGE_LOOP_LEAVE: return "break";
 250    case CFG_EDGE_FAKE: return "fake";
 251    default:
 252       return "?";
 253    }
 254 }
 255
 256 void
 257 nv_pc_pass_in_order(struct nv_basic_block *root, nv_pc_pass_func f, void *priv)
 258 {
 259    struct nv_basic_block *bb[64], *bbb[16], *b;
 260    int j, p, pp;
 261
 262    bb[0] = root;
 263    p = 1;
 264    pp = 0;
 265
 266    while (p > 0) {
 267       b = bb[--p];
 268       b->priv = 0;
 269
 270       for (j = 1; j >= 0; --j) {
 271          if (!b->out[j])
 272             continue;
 273
 274          switch (b->out_kind[j]) {
 275          case CFG_EDGE_BACK:
 276             continue;
 277          case CFG_EDGE_FORWARD:
 278          case CFG_EDGE_FAKE:
 279             if (++b->out[j]->priv == b->out[j]->num_in)
 280                bb[p++] = b->out[j];
 281             break;
 282          case CFG_EDGE_LOOP_ENTER:
 283             bb[p++] = b->out[j];
 284             break;
 285          case CFG_EDGE_LOOP_LEAVE:
 286             bbb[pp++] = b->out[j];
 287             break;
 288          default:
 289             assert(0);
 290             break;
 291          }
 292       }
 293
 294       f(priv, b);
 295
 296       if (!p) {
 297          p = pp;
 298          for (; pp > 0; --pp)
 299             bb[pp - 1] = bbb[pp - 1];
 300       }
 301    }
 302 }
 303
 304 static void
 305 nv_do_print_function(void *priv, struct nv_basic_block *b)
 306 {
 307    struct nv_instruction *i = b->phi;
 308
 309    debug_printf("=== BB %i ", b->id);
 310    if (b->out[0])
 311       debug_printf("[%s -> %i] ", edge_name(b->out_kind[0]), b->out[0]->id);
 312    if (b->out[1])
 313       debug_printf("[%s -> %i] ", edge_name(b->out_kind[1]), b->out[1]->id);
 314    debug_printf("===\n");
 315
 316    i = b->phi;
 317    if (!i)
 318       i = b->entry;
 319    for (; i; i = i->next)
 320       nv_print_instruction(i);
 321 }
 322
 323 void
 324 nv_print_function(struct nv_basic_block *root)
 325 {
 326    if (root->subroutine)
 327       debug_printf("SUBROUTINE %i\n", root->subroutine);
 328    else
 329       debug_printf("MAIN\n");
 330
 331    nv_pc_pass_in_order(root, nv_do_print_function, root);
 332 }
 333
 334 void
 335 nv_print_program(struct nv_pc *pc)
 336 {
 337    int i;
 338    for (i = 0; i < pc->num_subroutines + 1; ++i)
 339       if (pc->root[i])
 340          nv_print_function(pc->root[i]);
 341 }
 342
 343 #ifdef NV50_PC_DEBUG
 344 static void
 345 nv_do_print_cfgraph(struct nv_pc *pc, FILE *f, struct nv_basic_block *b)
 346 {
 347    int i;
 348
 349    b->pass_seq = pc->pass_seq;
 350
 351    fprintf(f, "\t%i [shape=box]\n", b->id);
 352
 353    for (i = 0; i < 2; ++i) {
 354       if (!b->out[i])
 355          continue;
 356       switch (b->out_kind[i]) {
 357       case CFG_EDGE_FORWARD:
 358          fprintf(f, "\t%i -> %i;\n", b->id, b->out[i]->id);
 359          break;
 360       case CFG_EDGE_LOOP_ENTER:
 361          fprintf(f, "\t%i -> %i [color=green];\n", b->id, b->out[i]->id);
 362          break;
 363       case CFG_EDGE_LOOP_LEAVE:
 364          fprintf(f, "\t%i -> %i [color=red];\n", b->id, b->out[i]->id);
 365          break;
 366       case CFG_EDGE_BACK:
 367          fprintf(f, "\t%i -> %i;\n", b->id, b->out[i]->id);
 368          continue;
 369       case CFG_EDGE_FAKE:
 370          fprintf(f, "\t%i -> %i [style=dotted];\n", b->id, b->out[i]->id);
 371          break;
 372       default:
 373          assert(0);
 374          break;
 375       }
 376       if (b->out[i]->pass_seq < pc->pass_seq)
 377          nv_do_print_cfgraph(pc, f, b->out[i]);
 378    }
 379 }
 380
 381 /* Print the control flow graph of subroutine @subr (0 == MAIN) to a file. */
 382 static void
 383 nv_print_cfgraph(struct nv_pc *pc, const char *filepath, int subr)
 384 {
 385    FILE *f;
 386
 387    f = fopen(filepath, "a");
 388    if (!f)
 389       return;
 390
 391    fprintf(f, "digraph G {\n");
 392
 393    ++pc->pass_seq;
 394
 395    nv_do_print_cfgraph(pc, f, pc->root[subr]);
 396
 397    fprintf(f, "}\n");
 398
 399    fclose(f);
 400 }
 401 #endif
 402
 403 static INLINE void
 404 nvcg_show_bincode(struct nv_pc *pc)
 405 {
 406    int i;
 407
 408    for (i = 0; i < pc->bin_size / 4; ++i)
 409       debug_printf("0x%08x ", pc->emit[i]);
 410    debug_printf("\n");
 411 }
 412
 413 static int
 414 nv50_emit_program(struct nv_pc *pc)
 415 {
 416    uint32_t *code = pc->emit;
 417    int n;
 418
 419    NV50_DBGMSG("emitting program: size = %u\n", pc->bin_size);
 420
 421    for (n = 0; n < pc->num_blocks; ++n) {
 422       struct nv_instruction *i;
 423       struct nv_basic_block *b = pc->bb_list[n];
 424
 425       for (i = b->entry; i; i = i->next) {
 426          nv50_emit_instruction(pc, i);
 427
 428          pc->bin_pos += 1 + (pc->emit[0] & 1);
 429          pc->emit += 1 + (pc->emit[0] & 1);
 430       }
 431    }
 432    assert(pc->emit == &code[pc->bin_size / 4]);
 433
 434    /* XXX: we can do better than this ... */
 435    if (!(pc->emit[-2] & 1) || (pc->emit[-2] & 2) || (pc->emit[-1] & 3)) {
 436       pc->emit[0] = 0xf0000001;
 437       pc->emit[1] = 0xe0000000;
 438       pc->bin_size += 8;
 439    }
 440
 441    pc->emit = code;
 442    code[pc->bin_size / 4 - 1] |= 1;
 443
 444 #ifdef NV50PC_DEBUG
 445    nvcg_show_bincode(pc);
 446 #endif
 447
 448    return 0;
 449 }
 450
 451 int
 452 nv50_generate_code(struct nv50_translation_info *ti)
 453 {
 454    struct nv_pc *pc;
 455    int ret;
 456    int i;
 457
 458    pc = CALLOC_STRUCT(nv_pc);
 459    if (!pc)
 460       return 1;
 461
 462    pc->root = CALLOC(ti->subr_nr + 1, sizeof(pc->root[0]));
 463    if (!pc->root) {
 464       FREE(pc);
 465       return 1;
 466    }
 467    pc->num_subroutines = ti->subr_nr;
 468
 469    ret = nv50_tgsi_to_nc(pc, ti);
 470    if (ret)
 471       goto out;
 472 #ifdef NV50PC_DEBUG
 473    nv_print_program(pc);
 474 #endif
 475
 476    pc->opt_reload_elim = ti->store_to_memory ? FALSE : TRUE;
 477
 478    /* optimization */
 479    ret = nv_pc_exec_pass0(pc);
 480    if (ret)
 481       goto out;
 482 #ifdef NV50PC_DEBUG
 483    nv_print_program(pc);
 484 #endif
 485
 486    /* register allocation */
 487    ret = nv_pc_exec_pass1(pc);
 488    if (ret)
 489       goto out;
 490 #ifdef NV50PC_DEBUG
 491    nv_print_program(pc);
 492    nv_print_cfgraph(pc, "nv50_shader_cfgraph.dot", 0);
 493 #endif
 494
 495    /* prepare for emission */
 496    ret = nv_pc_exec_pass2(pc);
 497    if (ret)
 498       goto out;
 499
 500    pc->emit = CALLOC(pc->bin_size / 4 + 2, 4);
 501    if (!pc->emit) {
 502       ret = 3;
 503       goto out;
 504    }
 505    ret = nv50_emit_program(pc);
 506    if (ret)
 507       goto out;
 508
 509    ti->p->code_size = pc->bin_size;
 510    ti->p->code = pc->emit;
 511
 512    ti->p->immd_size = pc->immd_count * 4;
 513    ti->p->immd = pc->immd_buf;
 514
 515    /* highest 16 bit reg to num of 32 bit regs */
 516    ti->p->max_gpr = (pc->max_reg[NV_FILE_GPR] >> 1) + 1;
 517
 518    ti->p->fixups = pc->fixups;
 519    ti->p->num_fixups = pc->num_fixups;
 520
 521    NV50_DBGMSG("SHADER TRANSLATION - %s\n", ret ? "failure" : "success");
 522
 523 out:
 524    nv_pc_free_refs(pc);
 525
 526    for (i = 0; i < pc->num_blocks; ++i)
 527       FREE(pc->bb_list[i]);
 528
 529    if (ret) { /* on success, these will be referenced by nv50_program */
 530       if (pc->emit)
 531          FREE(pc->emit);
 532       if (pc->immd_buf)
 533          FREE(pc->immd_buf);
 534       if (pc->fixups)
 535          FREE(pc->fixups);
 536    }
 537    FREE(pc);
 538    return ret;
 539 }
 540
 541 static void
 542 nvbb_insert_phi(struct nv_basic_block *b, struct nv_instruction *i)
 543 {
 544    if (!b->phi) {
 545       i->prev = NULL;
 546       b->phi = i;
 547       i->next = b->entry;
 548       if (b->entry) {
 549          assert(!b->entry->prev && b->exit);
 550          b->entry->prev = i;
 551       } else {
 552          b->entry = i;
 553          b->exit = i;
 554       }
 555    } else {
 556       assert(b->entry);
 557       if (b->entry->opcode == NV_OP_PHI) { /* insert after entry */
 558          assert(b->entry == b->exit);
 559          b->entry->next = i;
 560          i->prev = b->entry;
 561          b->entry = i;
 562          b->exit = i;
 563       } else { /* insert before entry */
 564          assert(b->entry->prev && b->exit);
 565          i->next = b->entry;
 566          i->prev = b->entry->prev;
 567          b->entry->prev = i;
 568          i->prev->next = i;
 569       }
 570    }
 571 }
 572
 573 void
 574 nvbb_insert_tail(struct nv_basic_block *b, struct nv_instruction *i)
 575 {
 576    if (i->opcode == NV_OP_PHI) {
 577       nvbb_insert_phi(b, i);
 578    } else {
 579       i->prev = b->exit;
 580       if (b->exit)
 581          b->exit->next = i;
 582       b->exit = i;
 583       if (!b->entry)
 584          b->entry = i;
 585       else
 586       if (i->prev && i->prev->opcode == NV_OP_PHI)
 587          b->entry = i;
 588    }
 589
 590    i->bb = b;
 591    b->num_instructions++;
 592 }
 593
 594 void
 595 nvi_insert_after(struct nv_instruction *at, struct nv_instruction *ni)
 596 {
 597    if (!at->next) {
 598       nvbb_insert_tail(at->bb, ni);
 599       return;
 600    }
 601    ni->next = at->next;
 602    ni->prev = at;
 603    ni->next->prev = ni;
 604    ni->prev->next = ni;
 605 }
 606
 607 void
 608 nv_nvi_delete(struct nv_instruction *nvi)
 609 {
 610    struct nv_basic_block *b = nvi->bb;
 611    int j;
 612
 613    /* debug_printf("REM: "); nv_print_instruction(nvi); */
 614
 615    for (j = 0; j < 5; ++j)
 616       nv_reference(NULL, &nvi->src[j], NULL);
 617    nv_reference(NULL, &nvi->flags_src, NULL);
 618
 619    if (nvi->next)
 620       nvi->next->prev = nvi->prev;
 621    else {
 622       assert(nvi == b->exit);
 623       b->exit = nvi->prev;
 624    }
 625
 626    if (nvi->prev)
 627       nvi->prev->next = nvi->next;
 628
 629    if (nvi == b->entry) {
 630       /* PHIs don't get hooked to b->entry */
 631       b->entry = nvi->next;
 632       assert(!nvi->prev || nvi->prev->opcode == NV_OP_PHI);
 633    }
 634
 635    if (nvi == b->phi) {
 636       if (nvi->opcode != NV_OP_PHI)
 637          NV50_DBGMSG("NOTE: b->phi points to non-PHI instruction\n");
 638
 639       assert(!nvi->prev);
 640       if (!nvi->next || nvi->next->opcode != NV_OP_PHI)
 641          b->phi = NULL;
 642       else
 643          b->phi = nvi->next;
 644    }
 645 }
 646
 647 void
 648 nv_nvi_permute(struct nv_instruction *i1, struct nv_instruction *i2)
 649 {
 650    struct nv_basic_block *b = i1->bb;
 651
 652    assert(i1->opcode != NV_OP_PHI &&
 653           i2->opcode != NV_OP_PHI);
 654    assert(i1->next == i2);
 655
 656    if (b->exit == i2)
 657       b->exit = i1;
 658
 659    if (b->entry == i1)
 660       b->entry = i2;
 661
 662    i2->prev = i1->prev;
 663    i1->next = i2->next;
 664    i2->next = i1;
 665    i1->prev = i2;
 666
 667    if (i2->prev)
 668       i2->prev->next = i2;
 669    if (i1->next)
 670       i1->next->prev = i1;
 671 }
 672
 673 void
 674 nvbb_attach_block(struct nv_basic_block *parent,
 675                   struct nv_basic_block *b, ubyte edge_kind)
 676 {
 677    assert(b->num_in < 8);
 678
 679    if (parent->out[0]) {
 680       assert(!parent->out[1]);
 681       parent->out[1] = b;
 682       parent->out_kind[1] = edge_kind;
 683    } else {
 684       parent->out[0] = b;
 685       parent->out_kind[0] = edge_kind;
 686    }
 687
 688    b->in[b->num_in] = parent;
 689    b->in_kind[b->num_in++] = edge_kind;
 690 }
 691
 692 /* NOTE: all BRKs are treated as conditional, so there are 2 outgoing BBs */
 693
 694 boolean
 695 nvbb_dominated_by(struct nv_basic_block *b, struct nv_basic_block *d)
 696 {
 697    int j;
 698
 699    if (b == d)
 700       return TRUE;
 701
 702    for (j = 0; j < b->num_in; ++j)
 703       if ((b->in_kind[j] != CFG_EDGE_BACK) && !nvbb_dominated_by(b->in[j], d))
 704          return FALSE;
 705
 706    return j ? TRUE : FALSE;
 707 }
 708
 709 /* check if @bf (future) can be reached from @bp (past), stop at @bt */
 710 boolean
 711 nvbb_reachable_by(struct nv_basic_block *bf, struct nv_basic_block *bp,
 712                   struct nv_basic_block *bt)
 713 {
 714    struct nv_basic_block *q[NV_PC_MAX_BASIC_BLOCKS], *b;
 715    int i, p, n;
 716
 717    p = 0;
 718    n = 1;
 719    q[0] = bp;
 720
 721    while (p < n) {
 722       b = q[p++];
 723
 724       if (b == bf)
 725          break;
 726       if (b == bt)
 727          continue;
 728       assert(n <= (1024 - 2));
 729
 730       for (i = 0; i < 2; ++i) {
 731          if (b->out[i] && !IS_WALL_EDGE(b->out_kind[i]) && !b->out[i]->priv) {
 732             q[n] = b->out[i];
 733             q[n++]->priv = 1;
 734          }
 735       }
 736    }
 737    for (--n; n >= 0; --n)
 738       q[n]->priv = 0;
 739
 740    return (b == bf);
 741 }
 742
 743 static struct nv_basic_block *
 744 nvbb_find_dom_frontier(struct nv_basic_block *b, struct nv_basic_block *df)
 745 {
 746    struct nv_basic_block *out;
 747    int i;
 748
 749    if (!nvbb_dominated_by(df, b)) {
 750       for (i = 0; i < df->num_in; ++i) {
 751          if (df->in_kind[i] == CFG_EDGE_BACK)
 752             continue;
 753          if (nvbb_dominated_by(df->in[i], b))
 754             return df;
 755       }
 756    }
 757    for (i = 0; i < 2 && df->out[i]; ++i) {
 758       if (df->out_kind[i] == CFG_EDGE_BACK)
 759          continue;
 760       if ((out = nvbb_find_dom_frontier(b, df->out[i])))
 761          return out;
 762    }
 763    return NULL;
 764 }
 765
 766 struct nv_basic_block *
 767 nvbb_dom_frontier(struct nv_basic_block *b)
 768 {
 769    struct nv_basic_block *df;
 770    int i;
 771
 772    for (i = 0; i < 2 && b->out[i]; ++i)
 773       if ((df = nvbb_find_dom_frontier(b, b->out[i])))
 774          return df;
 775    return NULL;
 776 }