DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Implementation

Mercurial (b6d82b1a6b02)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef jit_MIRGraph_h
#define jit_MIRGraph_h

// This file declares the data structures used to build a control-flow graph
// containing MIR.

#include "jit/FixedList.h"
#include "jit/JitAllocPolicy.h"
#include "jit/MIR.h"

namespace js {
namespace jit {

class BytecodeAnalysis;
class MBasicBlock;
class MIRGraph;
class MStart;

class MDefinitionIterator;

typedef InlineListIterator<MInstruction> MInstructionIterator;
typedef InlineListReverseIterator<MInstruction> MInstructionReverseIterator;
typedef InlineListIterator<MPhi> MPhiIterator;

#ifdef DEBUG
typedef InlineForwardListIterator<MResumePoint> MResumePointIterator;
#endif

class LBlock;

class MBasicBlock : public TempObject, public InlineListNode<MBasicBlock> {
 public:
  enum Kind { NORMAL, PENDING_LOOP_HEADER, LOOP_HEADER, SPLIT_EDGE, DEAD };

 private:
  MBasicBlock(MIRGraph& graph, const CompileInfo& info, BytecodeSite* site,
              Kind kind);
  MOZ_MUST_USE bool init();
  void copySlots(MBasicBlock* from);
  MOZ_MUST_USE bool inherit(TempAllocator& alloc, size_t stackDepth,
                            MBasicBlock* maybePred, uint32_t popped,
                            unsigned stackPhiCount = 0);
  MOZ_MUST_USE bool inheritResumePoint(MBasicBlock* pred);
  void assertUsesAreNotWithin(MUseIterator use, MUseIterator end);

  // This block cannot be reached by any means.
  bool unreachable_;

  // Keeps track if the phis has been type specialized already.
  bool specialized_;

  // Pushes a copy of a local variable or argument.
  void pushVariable(uint32_t slot) { push(slots_[slot]); }

  // Sets a variable slot to the top of the stack, correctly creating copies
  // as needed.
  void setVariable(uint32_t slot) {
    MOZ_ASSERT(stackPosition_ > info_.firstStackSlot());
    setSlot(slot, slots_[stackPosition_ - 1]);
  }

  enum ReferencesType {
    RefType_None = 0,

    // Assert that the instruction is unused.
    RefType_AssertNoUses = 1 << 0,

    // Discard the operands of the resume point / instructions if the
    // following flag are given too.
    RefType_DiscardOperands = 1 << 1,
    RefType_DiscardResumePoint = 1 << 2,
    RefType_DiscardInstruction = 1 << 3,

    // Discard operands of the instruction and its resume point.
    RefType_DefaultNoAssert = RefType_DiscardOperands |
                              RefType_DiscardResumePoint |
                              RefType_DiscardInstruction,

    // Discard everything and assert that the instruction is not used.
    RefType_Default = RefType_AssertNoUses | RefType_DefaultNoAssert,

    // Discard resume point operands only, without discarding the operands
    // of the current instruction.  Asserts that the instruction is unused.
    RefType_IgnoreOperands = RefType_AssertNoUses | RefType_DiscardOperands |
                             RefType_DiscardResumePoint
  };

  void discardResumePoint(MResumePoint* rp,
                          ReferencesType refType = RefType_Default);

  // Remove all references to an instruction such that it can be removed from
  // the list of instruction, without keeping any dangling pointer to it. This
  // includes the operands of the instruction, and the resume point if
  // present.
  void prepareForDiscard(MInstruction* ins,
                         ReferencesType refType = RefType_Default);

 public:
  ///////////////////////////////////////////////////////
  ////////// BEGIN GRAPH BUILDING INSTRUCTIONS //////////
  ///////////////////////////////////////////////////////

  // Creates a new basic block for a MIR generator. If |pred| is not nullptr,
  // its slots and stack depth are initialized from |pred|.
  static MBasicBlock* New(MIRGraph& graph, size_t stackDepth,
                          const CompileInfo& info, MBasicBlock* maybePred,
                          BytecodeSite* site, Kind kind);
  static MBasicBlock* New(MIRGraph& graph, const CompileInfo& info,
                          MBasicBlock* pred, Kind kind);
  static MBasicBlock* NewPopN(MIRGraph& graph, const CompileInfo& info,
                              MBasicBlock* pred, BytecodeSite* site, Kind kind,
                              uint32_t popn);
  static MBasicBlock* NewWithResumePoint(MIRGraph& graph,
                                         const CompileInfo& info,
                                         MBasicBlock* pred, BytecodeSite* site,
                                         MResumePoint* resumePoint);
  static MBasicBlock* NewPendingLoopHeader(MIRGraph& graph,
                                           const CompileInfo& info,
                                           MBasicBlock* pred,
                                           BytecodeSite* site,
                                           unsigned loopStateSlots);
  static MBasicBlock* NewSplitEdge(MIRGraph& graph, MBasicBlock* pred,
                                   size_t predEdgeIdx, MBasicBlock* succ);

  bool dominates(const MBasicBlock* other) const {
    return other->domIndex() - domIndex() < numDominated();
  }

  void setId(uint32_t id) { id_ = id; }

  // Mark this block (and only this block) as unreachable.
  void setUnreachable() {
    MOZ_ASSERT(!unreachable_);
    setUnreachableUnchecked();
  }
  void setUnreachableUnchecked() { unreachable_ = true; }
  bool unreachable() const { return unreachable_; }
  // Move the definition to the top of the stack.
  void pick(int32_t depth);

  // Move the top of the stack definition under the depth-th stack value.
  void unpick(int32_t depth);

  // Exchange 2 stack slots at the defined depth
  void swapAt(int32_t depth);

  // Note: most of the methods below are hot. Do not un-inline them without
  // measuring the impact.

  // Gets the instruction associated with various slot types.
  MDefinition* peek(int32_t depth) {
    MOZ_ASSERT(depth < 0);
    MOZ_ASSERT(stackPosition_ + depth >= info_.firstStackSlot());
    return getSlot(stackPosition_ + depth);
  }

  MDefinition* environmentChain();
  MDefinition* argumentsObject();

  // Increase the number of slots available
  MOZ_MUST_USE bool increaseSlots(size_t num);
  MOZ_MUST_USE bool ensureHasSlots(size_t num);

  // Initializes a slot value; must not be called for normal stack
  // operations, as it will not create new SSA names for copies.
  void initSlot(uint32_t slot, MDefinition* ins) {
    slots_[slot] = ins;
    if (entryResumePoint()) {
      entryResumePoint()->initOperand(slot, ins);
    }
  }

  // Discard the slot at the given depth, lowering all slots above.
  void shimmySlots(int discardDepth);

  // In an OSR block, set all MOsrValues to use the MResumePoint attached to
  // the MStart.
  MOZ_MUST_USE bool linkOsrValues(MStart* start);

  // Sets the instruction associated with various slot types. The
  // instruction must lie at the top of the stack.
  void setLocal(uint32_t local) { setVariable(info_.localSlot(local)); }
  void setArg(uint32_t arg) { setVariable(info_.argSlot(arg)); }
  void setSlot(uint32_t slot, MDefinition* ins) { slots_[slot] = ins; }

  // Rewrites a slot directly, bypassing the stack transition. This should
  // not be used under most circumstances.
  void rewriteSlot(uint32_t slot, MDefinition* ins) { setSlot(slot, ins); }

  // Rewrites a slot based on its depth (same as argument to peek()).
  void rewriteAtDepth(int32_t depth, MDefinition* ins);

  // Tracks an instruction as being pushed onto the operand stack.
  void push(MDefinition* ins) {
    MOZ_ASSERT(stackPosition_ < nslots());
    slots_[stackPosition_++] = ins;
  }
  void pushArg(uint32_t arg) { pushVariable(info_.argSlot(arg)); }
  void pushLocal(uint32_t local) { pushVariable(info_.localSlot(local)); }
  void pushSlot(uint32_t slot) { pushVariable(slot); }
  void setEnvironmentChain(MDefinition* ins);
  void setArgumentsObject(MDefinition* ins);

  // Returns the top of the stack, then decrements the virtual stack pointer.
  MDefinition* pop() {
    MOZ_ASSERT(stackPosition_ > info_.firstStackSlot());
    return slots_[--stackPosition_];
  }
  void popn(uint32_t n) {
    MOZ_ASSERT(stackPosition_ - n >= info_.firstStackSlot());
    MOZ_ASSERT(stackPosition_ >= stackPosition_ - n);
    stackPosition_ -= n;
  }

  // Adds an instruction to this block's instruction list.
  inline void add(MInstruction* ins);

  // Marks the last instruction of the block; no further instructions
  // can be added.
  void end(MControlInstruction* ins) {
    MOZ_ASSERT(!hasLastIns());  // Existing control instructions should be
                                // removed first.
    MOZ_ASSERT(ins);
    add(ins);
  }

  // Adds a phi instruction, but does not set successorWithPhis.
  void addPhi(MPhi* phi);

  // Adds a resume point to this block.
  void addResumePoint(MResumePoint* resume) {
#ifdef DEBUG
    resumePoints_.pushFront(resume);
#endif
  }

  // Discard pre-allocated resume point.
  void discardPreAllocatedResumePoint(MResumePoint* resume) {
    MOZ_ASSERT(!resume->instruction());
    discardResumePoint(resume);
  }

  // Adds a predecessor. Every predecessor must have the same exit stack
  // depth as the entry state to this block. Adding a predecessor
  // automatically creates phi nodes and rewrites uses as needed.
  MOZ_MUST_USE bool addPredecessor(TempAllocator& alloc, MBasicBlock* pred);
  MOZ_MUST_USE bool addPredecessorPopN(TempAllocator& alloc, MBasicBlock* pred,
                                       uint32_t popped);

  // Add a predecessor which won't introduce any new phis to this block.
  // This may be called after the contents of this block have been built.
  MOZ_MUST_USE bool addPredecessorSameInputsAs(MBasicBlock* pred,
                                               MBasicBlock* existingPred);

  // Stranger utilities used for inlining.
  MOZ_MUST_USE bool addPredecessorWithoutPhis(MBasicBlock* pred);
  void inheritSlots(MBasicBlock* parent);
  MOZ_MUST_USE bool initEntrySlots(TempAllocator& alloc);

  // Replaces an edge for a given block with a new block. This is
  // used for critical edge splitting.
  //
  // Note: If successorWithPhis is set, you must not be replacing it.
  void replacePredecessor(MBasicBlock* old, MBasicBlock* split);
  void replaceSuccessor(size_t pos, MBasicBlock* split);

  // Removes `pred` from the predecessor list. If this block defines phis,
  // removes the entry for `pred` and updates the indices of later entries.
  // This may introduce redundant phis if the new block has fewer
  // than two predecessors.
  void removePredecessor(MBasicBlock* pred);

  // A version of removePredecessor which expects that phi operands to
  // |pred| have already been removed.
  void removePredecessorWithoutPhiOperands(MBasicBlock* pred, size_t predIndex);

  // Resets all the dominator info so that it can be recomputed.
  void clearDominatorInfo();

  // Sets a back edge. This places phi nodes and rewrites instructions within
  // the current loop as necessary. If the backedge introduces new types for
  // phis at the loop header, returns a disabling abort.
  MOZ_MUST_USE AbortReason setBackedge(TempAllocator& alloc,
                                       MBasicBlock* block);
  MOZ_MUST_USE bool setBackedgeWasm(MBasicBlock* block);

  // Resets a LOOP_HEADER block to a NORMAL block.  This is needed when
  // optimizations remove the backedge.
  void clearLoopHeader();

  // Sets a block to a LOOP_HEADER block, with newBackedge as its backedge.
  // This is needed when optimizations remove the normal entry to a loop
  // with multiple entries.
  void setLoopHeader(MBasicBlock* newBackedge);

  // Propagates phis placed in a loop header down to this successor block.
  void inheritPhis(MBasicBlock* header);

  // Propagates backedge slots into phis operands of the loop header.
  MOZ_MUST_USE bool inheritPhisFromBackedge(TempAllocator& alloc,
                                            MBasicBlock* backedge,
                                            bool* hadTypeChange);

  // Compute the types for phis in this block according to their inputs.
  MOZ_MUST_USE bool specializePhis(TempAllocator& alloc);

  void insertBefore(MInstruction* at, MInstruction* ins);
  void insertAfter(MInstruction* at, MInstruction* ins);

  void insertAtEnd(MInstruction* ins);

  // Add an instruction to this block, from elsewhere in the graph.
  void addFromElsewhere(MInstruction* ins);

  // Move an instruction. Movement may cross block boundaries.
  void moveBefore(MInstruction* at, MInstruction* ins);

  enum IgnoreTop { IgnoreNone = 0, IgnoreRecover = 1 << 0 };

  // Locate the top of the |block|, where it is safe to insert a new
  // instruction.
  MInstruction* safeInsertTop(MDefinition* ins = nullptr,
                              IgnoreTop ignore = IgnoreNone);

  // Removes an instruction with the intention to discard it.
  void discard(MInstruction* ins);
  void discardLastIns();
  void discardDef(MDefinition* def);
  void discardAllInstructions();
  void discardAllInstructionsStartingAt(MInstructionIterator iter);
  void discardAllPhiOperands();
  void discardAllPhis();
  void discardAllResumePoints(bool discardEntry = true);
  void clear();

  // Same as |void discard(MInstruction* ins)| but assuming that
  // all operands are already discarded.
  void discardIgnoreOperands(MInstruction* ins);

  // Discards a phi instruction and updates predecessor successorWithPhis.
  void discardPhi(MPhi* phi);

  // Some instruction which are guarding against some MIRType value, or
  // against a type expectation should be considered as removing a potenatial
  // branch where the guard does not hold.  We need to register such
  // instructions in order to do destructive optimizations correctly, such as
  // Range Analysis.
  void flagOperandsOfPrunedBranches(MInstruction* ins);

  // Mark this block as having been removed from the graph.
  void markAsDead() {
    MOZ_ASSERT(kind_ != DEAD);
    kind_ = DEAD;
  }

  ///////////////////////////////////////////////////////
  /////////// END GRAPH BUILDING INSTRUCTIONS ///////////
  ///////////////////////////////////////////////////////

  MIRGraph& graph() { return graph_; }
  const CompileInfo& info() const { return info_; }
  jsbytecode* pc() const { return pc_; }
  uint32_t nslots() const { return slots_.length(); }
  uint32_t id() const { return id_; }
  uint32_t numPredecessors() const { return predecessors_.length(); }

  uint32_t domIndex() const {
    MOZ_ASSERT(!isDead());
    return domIndex_;
  }
  void setDomIndex(uint32_t d) { domIndex_ = d; }

  MBasicBlock* getPredecessor(uint32_t i) const { return predecessors_[i]; }
  size_t indexForPredecessor(MBasicBlock* block) const {
    // This should only be called before critical edge splitting.
    MOZ_ASSERT(!block->successorWithPhis());

    for (size_t i = 0; i < predecessors_.length(); i++) {
      if (predecessors_[i] == block) {
        return i;
      }
    }
    MOZ_CRASH();
  }
  bool hasAnyIns() const { return !instructions_.empty(); }
  bool hasLastIns() const {
    return hasAnyIns() && instructions_.rbegin()->isControlInstruction();
  }
  MControlInstruction* lastIns() const {
    MOZ_ASSERT(hasLastIns());
    return instructions_.rbegin()->toControlInstruction();
  }
  // Find or allocate an optimized out constant.
  MConstant* optimizedOutConstant(TempAllocator& alloc);
  MPhiIterator phisBegin() const { return phis_.begin(); }
  MPhiIterator phisBegin(MPhi* at) const { return phis_.begin(at); }
  MPhiIterator phisEnd() const { return phis_.end(); }
  bool phisEmpty() const { return phis_.empty(); }
#ifdef DEBUG
  MResumePointIterator resumePointsBegin() const {
    return resumePoints_.begin();
  }
  MResumePointIterator resumePointsEnd() const { return resumePoints_.end(); }
  bool resumePointsEmpty() const { return resumePoints_.empty(); }
#endif
  MInstructionIterator begin() { return instructions_.begin(); }
  MInstructionIterator begin(MInstruction* at) {
    MOZ_ASSERT(at->block() == this);
    return instructions_.begin(at);
  }
  MInstructionIterator end() { return instructions_.end(); }
  MInstructionReverseIterator rbegin() { return instructions_.rbegin(); }
  MInstructionReverseIterator rbegin(MInstruction* at) {
    MOZ_ASSERT(at->block() == this);
    return instructions_.rbegin(at);
  }
  MInstructionReverseIterator rend() { return instructions_.rend(); }
  bool isLoopHeader() const { return kind_ == LOOP_HEADER; }
  bool hasUniqueBackedge() const {
    MOZ_ASSERT(isLoopHeader());
    MOZ_ASSERT(numPredecessors() >= 2);
    if (numPredecessors() == 2) {
      return true;
    }
    if (numPredecessors() == 3) {  // fixup block added by ValueNumbering phase.
      return getPredecessor(1)->numPredecessors() == 0;
    }
    return false;
  }
  MBasicBlock* backedge() const {
    MOZ_ASSERT(hasUniqueBackedge());
    return getPredecessor(numPredecessors() - 1);
  }
  MBasicBlock* loopHeaderOfBackedge() const {
    MOZ_ASSERT(isLoopBackedge());
    return getSuccessor(numSuccessors() - 1);
  }
  MBasicBlock* loopPredecessor() const {
    MOZ_ASSERT(isLoopHeader());
    return getPredecessor(0);
  }
  bool isLoopBackedge() const {
    if (!numSuccessors()) {
      return false;
    }
    MBasicBlock* lastSuccessor = getSuccessor(numSuccessors() - 1);
    return lastSuccessor->isLoopHeader() &&
           lastSuccessor->hasUniqueBackedge() &&
           lastSuccessor->backedge() == this;
  }
  bool isSplitEdge() const { return kind_ == SPLIT_EDGE; }
  bool isDead() const { return kind_ == DEAD; }

  uint32_t stackDepth() const { return stackPosition_; }
  void setStackDepth(uint32_t depth) { stackPosition_ = depth; }
  bool isMarked() const { return mark_; }
  void mark() {
    MOZ_ASSERT(!mark_, "Marking already-marked block");
    markUnchecked();
  }
  void markUnchecked() { mark_ = true; }
  void unmark() {
    MOZ_ASSERT(mark_, "Unarking unmarked block");
    unmarkUnchecked();
  }
  void unmarkUnchecked() { mark_ = false; }

  MBasicBlock* immediateDominator() const { return immediateDominator_; }

  void setImmediateDominator(MBasicBlock* dom) { immediateDominator_ = dom; }

  MTest* immediateDominatorBranch(BranchDirection* pdirection);

  size_t numImmediatelyDominatedBlocks() const {
    return immediatelyDominated_.length();
  }

  MBasicBlock* getImmediatelyDominatedBlock(size_t i) const {
    return immediatelyDominated_[i];
  }

  MBasicBlock** immediatelyDominatedBlocksBegin() {
    return immediatelyDominated_.begin();
  }

  MBasicBlock** immediatelyDominatedBlocksEnd() {
    return immediatelyDominated_.end();
  }

  // Return the number of blocks dominated by this block. All blocks
  // dominate at least themselves, so this will always be non-zero.
  size_t numDominated() const {
    MOZ_ASSERT(numDominated_ != 0);
    return numDominated_;
  }

  void addNumDominated(size_t n) { numDominated_ += n; }

  // Add |child| to this block's immediately-dominated set.
  bool addImmediatelyDominatedBlock(MBasicBlock* child);

  // Remove |child| from this block's immediately-dominated set.
  void removeImmediatelyDominatedBlock(MBasicBlock* child);

  // This function retrieves the internal instruction associated with a
  // slot, and should not be used for normal stack operations. It is an
  // internal helper that is also used to enhance spew.
  MDefinition* getSlot(uint32_t index) {
    MOZ_ASSERT(index < stackPosition_);
    return slots_[index];
  }

  MResumePoint* entryResumePoint() const { return entryResumePoint_; }
  void setEntryResumePoint(MResumePoint* rp) { entryResumePoint_ = rp; }
  void clearEntryResumePoint() {
    discardResumePoint(entryResumePoint_);
    entryResumePoint_ = nullptr;
  }
  MResumePoint* outerResumePoint() const { return outerResumePoint_; }
  void setOuterResumePoint(MResumePoint* outer) {
    MOZ_ASSERT(!outerResumePoint_);
    outerResumePoint_ = outer;
  }
  void clearOuterResumePoint() {
    discardResumePoint(outerResumePoint_);
    outerResumePoint_ = nullptr;
  }
  MResumePoint* callerResumePoint() const { return callerResumePoint_; }
  void setCallerResumePoint(MResumePoint* caller) {
    callerResumePoint_ = caller;
  }
  size_t numEntrySlots() const { return entryResumePoint()->stackDepth(); }
  MDefinition* getEntrySlot(size_t i) const {
    MOZ_ASSERT(i < numEntrySlots());
    return entryResumePoint()->getOperand(i);
  }

  LBlock* lir() const { return lir_; }
  void assignLir(LBlock* lir) {
    MOZ_ASSERT(!lir_);
    lir_ = lir;
  }

  MBasicBlock* successorWithPhis() const { return successorWithPhis_; }
  uint32_t positionInPhiSuccessor() const {
    MOZ_ASSERT(successorWithPhis());
    return positionInPhiSuccessor_;
  }
  void setSuccessorWithPhis(MBasicBlock* successor, uint32_t id) {
    successorWithPhis_ = successor;
    positionInPhiSuccessor_ = id;
  }
  void clearSuccessorWithPhis() { successorWithPhis_ = nullptr; }
  size_t numSuccessors() const {
    MOZ_ASSERT(lastIns());
    return lastIns()->numSuccessors();
  }
  MBasicBlock* getSuccessor(size_t index) const {
    MOZ_ASSERT(lastIns());
    return lastIns()->getSuccessor(index);
  }
  size_t getSuccessorIndex(MBasicBlock*) const;
  size_t getPredecessorIndex(MBasicBlock*) const;

  void setLoopDepth(uint32_t loopDepth) { loopDepth_ = loopDepth; }
  uint32_t loopDepth() const { return loopDepth_; }

  bool strict() const { return info_.script()->strict(); }

  void dumpStack(GenericPrinter& out);
  void dumpStack();

  void dump(GenericPrinter& out);
  void dump();

  // Hit count
  enum class HitState {
    // Not hit information is attached to this basic block.
    NotDefined,

    // The hit information is a raw counter. Note that due to inlining this
    // counter is not guaranteed to be consistent over the graph.
    Count,

    // The hit information is a frequency, which is a form of normalized
    // counter, where a hit-count can be compared against any previous block
    // in the graph.
    Frequency
  };
  HitState getHitState() const { return hitState_; }
  void setHitCount(uint64_t count) {
    hitCount_ = count;
    hitState_ = HitState::Count;
  }
  uint64_t getHitCount() const {
    MOZ_ASSERT(hitState_ == HitState::Count);
    return hitCount_;
  }

  // Track bailouts by storing the current pc in MIR instruction added at
  // this cycle. This is also used for tracking calls and optimizations when
  // profiling.
  void updateTrackedSite(BytecodeSite* site) {
    MOZ_ASSERT(site->tree() == trackedSite_->tree());
    trackedSite_ = site;
  }
  BytecodeSite* trackedSite() const { return trackedSite_; }
  jsbytecode* trackedPc() const {
    return trackedSite_ ? trackedSite_->pc() : nullptr;
  }
  InlineScriptTree* trackedTree() const {
    return trackedSite_ ? trackedSite_->tree() : nullptr;
  }

  // This class is used for reverting the graph within IonBuilder.
  class BackupPoint {
    friend MBasicBlock;

    MBasicBlock* current_;
    MInstruction* lastIns_;
    uint32_t stackPosition_;
    FixedList<MDefinition*> slots_;
#ifdef DEBUG
    // The following fields should remain identical during IonBuilder
    // construction, these are used for assertions.
    MPhi* lastPhi_;
    uintptr_t predecessorsCheckSum_;
    HashNumber instructionsCheckSum_;
    uint32_t id_;
    MResumePoint* callerResumePoint_;
    MResumePoint* entryResumePoint_;

    size_t computePredecessorsCheckSum(MBasicBlock* block);
    HashNumber computeInstructionsCheckSum(MBasicBlock* block);
#endif
   public:
    explicit BackupPoint(MBasicBlock* current);
    MOZ_MUST_USE bool init(TempAllocator& alloc);
    MBasicBlock* restore();
  };

  friend BackupPoint;

 private:
  MIRGraph& graph_;
  const CompileInfo& info_;  // Each block originates from a particular script.
  InlineList<MInstruction> instructions_;
  Vector<MBasicBlock*, 1, JitAllocPolicy> predecessors_;
  InlineList<MPhi> phis_;
  FixedList<MDefinition*> slots_;
  uint32_t stackPosition_;
  uint32_t id_;
  uint32_t domIndex_;  // Index in the dominator tree.
  uint32_t numDominated_;
  jsbytecode* pc_;
  LBlock* lir_;

  // Copy of a dominator block's outerResumePoint_ which holds the state of
  // caller frame at the time of the call. If not null, this implies that this
  // basic block corresponds to an inlined script.
  MResumePoint* callerResumePoint_;

  // Resume point holding baseline-like frame for the PC corresponding to the
  // entry of this basic block.
  MResumePoint* entryResumePoint_;

  // Resume point holding baseline-like frame for the PC corresponding to the
  // beginning of the call-site which is being inlined after this block.
  MResumePoint* outerResumePoint_;

#ifdef DEBUG
  // Unordered list used to verify that all the resume points which are
  // registered are correctly removed when a basic block is removed.
  InlineForwardList<MResumePoint> resumePoints_;
#endif

  MBasicBlock* successorWithPhis_;
  uint32_t positionInPhiSuccessor_;
  uint32_t loopDepth_;
  Kind kind_ : 8;

  // Utility mark for traversal algorithms.
  bool mark_;

  Vector<MBasicBlock*, 1, JitAllocPolicy> immediatelyDominated_;
  MBasicBlock* immediateDominator_;

  BytecodeSite* trackedSite_;

  // Record the number of times a block got visited. Note, due to inlined
  // scripts these numbers might not be continuous.
  uint64_t hitCount_;
  HitState hitState_;

#if defined(JS_ION_PERF) || defined(DEBUG)
  unsigned lineno_;
  unsigned columnIndex_;

 public:
  void setLineno(unsigned l) { lineno_ = l; }
  unsigned lineno() const { return lineno_; }
  void setColumnIndex(unsigned c) { columnIndex_ = c; }
  unsigned columnIndex() const { return columnIndex_; }
#endif
};

typedef InlineListIterator<MBasicBlock> MBasicBlockIterator;
typedef InlineListIterator<MBasicBlock> ReversePostorderIterator;
typedef InlineListReverseIterator<MBasicBlock> PostorderIterator;

typedef Vector<MBasicBlock*, 1, JitAllocPolicy> MIRGraphReturns;

class MIRGraph {
  InlineList<MBasicBlock> blocks_;
  TempAllocator* alloc_;
  MIRGraphReturns* returnAccumulator_;
  uint32_t blockIdGen_;
  uint32_t idGen_;
  MBasicBlock* osrBlock_;

  size_t numBlocks_;
  bool hasTryBlock_;

  InlineList<MPhi> phiFreeList_;
  size_t phiFreeListLength_;

 public:
  explicit MIRGraph(TempAllocator* alloc)
      : alloc_(alloc),
        returnAccumulator_(nullptr),
        blockIdGen_(0),
        idGen_(0),
        osrBlock_(nullptr),
        numBlocks_(0),
        hasTryBlock_(false),
        phiFreeListLength_(0) {}

  TempAllocator& alloc() const { return *alloc_; }

  void addBlock(MBasicBlock* block);
  void insertBlockAfter(MBasicBlock* at, MBasicBlock* block);
  void insertBlockBefore(MBasicBlock* at, MBasicBlock* block);

  void unmarkBlocks();

  void setReturnAccumulator(MIRGraphReturns* accum) {
    returnAccumulator_ = accum;
  }
  MIRGraphReturns* returnAccumulator() const { return returnAccumulator_; }

  MOZ_MUST_USE bool addReturn(MBasicBlock* returnBlock) {
    if (!returnAccumulator_) {
      return true;
    }

    return returnAccumulator_->append(returnBlock);
  }

  MBasicBlock* entryBlock() { return *blocks_.begin(); }
  MBasicBlockIterator begin() { return blocks_.begin(); }
  MBasicBlockIterator begin(MBasicBlock* at) { return blocks_.begin(at); }
  MBasicBlockIterator end() { return blocks_.end(); }
  PostorderIterator poBegin() { return blocks_.rbegin(); }
  PostorderIterator poBegin(MBasicBlock* at) { return blocks_.rbegin(at); }
  PostorderIterator poEnd() { return blocks_.rend(); }
  ReversePostorderIterator rpoBegin() { return blocks_.begin(); }
  ReversePostorderIterator rpoBegin(MBasicBlock* at) {
    return blocks_.begin(at);
  }
  ReversePostorderIterator rpoEnd() { return blocks_.end(); }
  MOZ_MUST_USE bool removeSuccessorBlocks(MBasicBlock* block);
  void removeBlock(MBasicBlock* block);
  void removeBlockIncludingPhis(MBasicBlock* block);
  void moveBlockToEnd(MBasicBlock* block) {
    blocks_.remove(block);
    MOZ_ASSERT_IF(!blocks_.empty(), block->id());
    blocks_.pushBack(block);
  }
  void moveBlockBefore(MBasicBlock* at, MBasicBlock* block) {
    MOZ_ASSERT(block->id());
    blocks_.remove(block);
    blocks_.insertBefore(at, block);
  }
  void removeBlockFromList(MBasicBlock* block) {
    blocks_.remove(block);
    numBlocks_--;
  }
  size_t numBlocks() const { return numBlocks_; }
  uint32_t numBlockIds() const { return blockIdGen_; }
  void allocDefinitionId(MDefinition* ins) { ins->setId(idGen_++); }
  uint32_t getNumInstructionIds() { return idGen_; }
  MResumePoint* entryResumePoint() { return entryBlock()->entryResumePoint(); }

  void setOsrBlock(MBasicBlock* osrBlock) {
    MOZ_ASSERT(!osrBlock_);
    osrBlock_ = osrBlock;
  }
  MBasicBlock* osrBlock() { return osrBlock_; }

  bool hasTryBlock() const { return hasTryBlock_; }
  void setHasTryBlock() { hasTryBlock_ = true; }

  void dump(GenericPrinter& out);
  void dump();

  void addPhiToFreeList(MPhi* phi) {
    phiFreeList_.pushBack(phi);
    phiFreeListLength_++;
  }
  size_t phiFreeListLength() const { return phiFreeListLength_; }
  MPhi* takePhiFromFreeList() {
    MOZ_ASSERT(phiFreeListLength_ > 0);
    phiFreeListLength_--;
    return phiFreeList_.popBack();
  }
};

class MDefinitionIterator {
  friend class MBasicBlock;
  friend class MNodeIterator;

 private:
  MBasicBlock* block_;
  MPhiIterator phiIter_;
  MInstructionIterator iter_;

  bool atPhi() const { return phiIter_ != block_->phisEnd(); }

  MDefinition* getIns() {
    if (atPhi()) {
      return *phiIter_;
    }
    return *iter_;
  }

  bool more() const { return atPhi() || (*iter_) != block_->lastIns(); }

 public:
  explicit MDefinitionIterator(MBasicBlock* block)
      : block_(block), phiIter_(block->phisBegin()), iter_(block->begin()) {}

  MDefinitionIterator operator++() {
    MOZ_ASSERT(more());
    if (atPhi()) {
      ++phiIter_;
    } else {
      ++iter_;
    }
    return *this;
  }

  MDefinitionIterator operator++(int) {
    MDefinitionIterator old(*this);
    operator++();
    return old;
  }

  explicit operator bool() const { return more(); }

  MDefinition* operator*() { return getIns(); }

  MDefinition* operator->() { return getIns(); }
};

// Iterates on all resume points, phis, and instructions of a MBasicBlock.
// Resume points are visited as long as the instruction which holds it is not
// discarded.
class MNodeIterator {
 private:
  // Last instruction which holds a resume point. To handle the entry point
  // resume point, it is set to the last instruction, assuming that the last
  // instruction is not discarded before we visit it.
  MInstruction* last_;

  // Definition iterator which is one step ahead when visiting resume points.
  // This is in order to avoid incrementing the iterator while it is settled
  // on a discarded instruction.
  MDefinitionIterator defIter_;

  MBasicBlock* block() const { return defIter_.block_; }

  bool atResumePoint() const { return last_ && !last_->isDiscarded(); }

  MNode* getNode() {
    if (!atResumePoint()) {
      return *defIter_;
    }

    // We use the last instruction as a sentinelle to iterate over the entry
    // resume point of the basic block, before even starting to iterate on
    // the instruction list.  Otherwise, the last_ corresponds to the
    // previous instruction.
    if (last_ != block()->lastIns()) {
      return last_->resumePoint();
    }
    return block()->entryResumePoint();
  }

  void next() {
    if (!atResumePoint()) {
      if (defIter_->isInstruction() &&
          defIter_->toInstruction()->resumePoint()) {
        // In theory, we could but in practice this does not happen.
        MOZ_ASSERT(*defIter_ != block()->lastIns());
        last_ = defIter_->toInstruction();
      }

      defIter_++;
    } else {
      last_ = nullptr;
    }
  }

  bool more() const { return defIter_ || atResumePoint(); }

 public:
  explicit MNodeIterator(MBasicBlock* block)
      : last_(block->entryResumePoint() ? block->lastIns() : nullptr),
        defIter_(block) {
    MOZ_ASSERT(bool(block->entryResumePoint()) == atResumePoint());

    // We use the last instruction to check for the entry resume point,
    // assert that no control instruction has any resume point.  If so, then
    // we need to handle this case in this iterator.
    MOZ_ASSERT(!block->lastIns()->resumePoint());
  }

  MNodeIterator operator++(int) {
    MNodeIterator old(*this);
    if (more()) {
      next();
    }
    return old;
  }

  explicit operator bool() const { return more(); }

  MNode* operator*() { return getNode(); }

  MNode* operator->() { return getNode(); }
};

void MBasicBlock::add(MInstruction* ins) {
  MOZ_ASSERT(!hasLastIns());
  ins->setBlock(this);
  graph().allocDefinitionId(ins);
  instructions_.pushBack(ins);
  ins->setTrackedSite(trackedSite_);
}

}  // namespace jit
}  // namespace js

#endif /* jit_MIRGraph_h */