sdk/runtime/vm/regexp/regexp-compiler.cc

// Copyright 2019 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "vm/regexp/regexp-compiler.h"

#include <algorithm>
#include <limits>
#include <memory>
#include <optional>
#include <utility>

#include "vm/regexp/regexp-macro-assembler.h"
#include "vm/regexp/unibrow.h"
#include "vm/regexp/zone-list-inl.h"

#ifdef V8_INTL_SUPPORT
#include "unicode/locid.h"
#include "unicode/uniset.h"
#include "unicode/utypes.h"
#include "vm/regexp/special-case.h"
#endif  // V8_INTL_SUPPORT

namespace dart {

using namespace regexp_compiler_constants;  // NOLINT(build/namespaces)

#ifdef V8_ENABLE_REGEXP_DIAGNOSTICS
#define TRACE_COMPILER(compiler, msg)                                          \
  do {                                                                         \
    if (UNLIKELY(v8_flags.trace_regexp_compiler)) {                            \
      compiler->diagnostics()->os() << msg << std::endl;                       \
    }                                                                          \
  } while (false)
#define TRACE(msg) TRACE_COMPILER(compiler, msg)
#define TRACE_WITH_NODE(compiler, msg, node)                                   \
  do {                                                                         \
    if (UNLIKELY(v8_flags.trace_regexp_compiler)) {                            \
      RegExpGraphPrinter* printer = compiler->diagnostics()->graph_printer();  \
      std::ostream& os = compiler->diagnostics()->os();                        \
      os << msg;                                                               \
      printer->PrintNode(node);                                                \
    }                                                                          \
  } while (false)
#define TRACE_WITH_NODE_AND_TRACE(compiler, msg, node, trace)                  \
  do {                                                                         \
    if (UNLIKELY(v8_flags.trace_regexp_compiler)) {                            \
      RegExpGraphPrinter* printer = compiler->diagnostics()->graph_printer();  \
      std::ostream& os = compiler->diagnostics()->os();                        \
      os << msg;                                                               \
      printer->PrintNodeNoNewline(node);                                       \
      if (trace != nullptr) {                                                  \
        os << "  ";                                                            \
        printer->PrintTrace(trace);                                            \
      }                                                                        \
      os << std::endl;                                                         \
    }                                                                          \
  } while (false)
#define TRACE_EMIT(name)                                                       \
  TRACE_WITH_NODE_AND_TRACE(compiler, "* Assembling " << name << ": ", this,   \
                            trace)
#define TRACE_GRAPH(msg)                                                       \
  do {                                                                         \
    if (UNLIKELY(v8_flags.trace_regexp_graph_building)) {                      \
      diagnostics()->os() << msg << std::endl;                                 \
    }                                                                          \
  } while (false)
#define TRACE_GRAPH_WITH_NODE(msg, node)                                       \
  do {                                                                         \
    if (UNLIKELY(v8_flags.trace_regexp_graph_building)) {                      \
      std::ostream& os = diagnostics()->trace_tree_scope()->os();              \
      os << msg;                                                               \
      diagnostics()->ast_printer()->Print(node);                               \
      os << std::endl;                                                         \
    }                                                                          \
  } while (false)
#define REGISTER_NODE(node)                                                    \
  do {                                                                         \
    if (UNLIKELY(!!diagnostics() && diagnostics()->has_graph_labeller())) {    \
      diagnostics()->graph_labeller()->RegisterNode(node);                     \
    }                                                                          \
    if (UNLIKELY(v8_flags.trace_regexp_graph_building)) {                      \
      diagnostics()->trace_tree_scope()->os() << "+ ";                         \
      diagnostics()->graph_printer()->PrintNode(node);                         \
    }                                                                          \
  } while (false)
#else
#define TRACE_COMPILER(compiler, msg) (void(0))
#define TRACE(x) (void(0))
#define TRACE_WITH_NODE(compiler, msg, node) (void(0))
#define TRACE_WITH_NODE_AND_TRACE(compiler, msg, node, trace) (void(0))
#define TRACE_EMIT(name) (void(0))
#define TRACE_GRAPH(msg) (void(0))
#define TRACE_GRAPH_WITH_NODE(msg, node) (void(0))
#define REGISTER_NODE(node) (void(0))
#endif

// -------------------------------------------------------------------
// Implementation of the Irregexp regular expression engine.
//
// The Irregexp regular expression engine is intended to be a complete
// implementation of ECMAScript regular expressions.  It generates either
// bytecodes or native code.

//   The Irregexp regexp engine is structured in three steps.
//   1) The parser generates an abstract syntax tree.  See ast.cc.
//   2) From the AST a node network is created.  The nodes are all
//      subclasses of RegExpNode.  The nodes represent states when
//      executing a regular expression.  Several optimizations are
//      performed on the node network.
//   3) From the nodes we generate either byte codes or native code
//      that can actually execute the regular expression (perform
//      the search).  The code generation step is described in more
//      detail below.

// Code generation.
//
//   The nodes are divided into four main categories.
//   * Choice nodes
//        These represent places where the regular expression can
//        match in more than one way.  For example on entry to an
//        alternation (foo|bar) or a repetition (*, +, ? or {}).
//   * Action nodes
//        These represent places where some action should be
//        performed.  Examples include recording the current position
//        in the input string to a register (in order to implement
//        captures) or other actions on register for example in order
//        to implement the counters needed for {} repetitions.
//   * Matching nodes
//        These attempt to match some element part of the input string.
//        Examples of elements include character classes, plain strings
//        or back references.
//   * End nodes
//        These are used to implement the actions required on finding
//        a successful match or failing to find a match.
//
//   The code generated (whether as byte codes or native code) maintains
//   some state as it runs.  This consists of the following elements:
//
//   * The capture registers.  Used for string captures.
//   * Other registers.  Used for counters etc.
//   * The current position.
//   * The stack of backtracking information.  Used when a matching node
//     fails to find a match and needs to try an alternative.
//
// Conceptual regular expression execution model:
//
//   There is a simple conceptual model of regular expression execution
//   which will be presented first.  The actual code generated is a more
//   efficient simulation of the simple conceptual model:
//
//   * Choice nodes are implemented as follows:
//     For each choice except the last {
//       push current position
//       push backtrack code location
//       <generate code to test for choice>
//       backtrack code location:
//       pop current position
//     }
//     <generate code to test for last choice>
//
//   * Actions nodes are generated as follows
//     <push affected registers on backtrack stack>
//     <generate code to perform action>
//     push backtrack code location
//     <generate code to test for following nodes>
//     backtrack code location:
//     <pop affected registers to restore their state>
//     <pop backtrack location from stack and go to it>
//
//   * Matching nodes are generated as follows:
//     if input string matches at current position
//       update current position
//       <generate code to test for following nodes>
//     else
//       <pop backtrack location from stack and go to it>
//
//   Thus it can be seen that the current position is saved and restored
//   by the choice nodes, whereas the registers are saved and restored by
//   by the action nodes that manipulate them.
//
//   The other interesting aspect of this model is that nodes are generated
//   at the point where they are needed by a recursive call to Emit().  If
//   the node has already been code generated then the Emit() call will
//   generate a jump to the previously generated code instead.  In order to
//   limit recursion it is possible for the Emit() function to put the node
//   on a work list for later generation and instead generate a jump.  The
//   destination of the jump is resolved later when the code is generated.
//
// Actual regular expression code generation.
//
//   Code generation is actually more complicated than the above.  In order to
//   improve the efficiency of the generated code some optimizations are
//   performed
//
//   * Choice nodes have 1-character lookahead.
//     A choice node looks at the following character and eliminates some of
//     the choices immediately based on that character.  This is not yet
//     implemented.
//   * Simple greedy loops store reduced backtracking information.  We call
//     these fixed length loops
//     A quantifier like /.*foo/m will greedily match the whole input.  It will
//     then need to backtrack to a point where it can match "foo".  The naive
//     implementation of this would push each character position onto the
//     backtracking stack, then pop them off one by one.  This would use space
//     proportional to the length of the input string.  However since the "."
//     can only match in one way and always has a constant length (in this case
//     of 1) it suffices to store the current position on the top of the stack
//     once.  Matching now becomes merely incrementing the current position and
//     backtracking becomes decrementing the current position and checking the
//     result against the stored current position.  This is faster and saves
//     space.
//   * The current state is virtualized.
//     This is used to defer expensive operations until it is clear that they
//     are needed and to generate code for a node more than once, allowing
//     specialized an efficient versions of the code to be created. This is
//     explained in the section below.
//
// Execution state virtualization.
//
//   Instead of emitting code, nodes that manipulate the state can record their
//   manipulation in an object called the Trace.  The Trace object can record a
//   current position offset, an optional backtrack code location on the top of
//   the virtualized backtrack stack and some register changes.  When a node is
//   to be emitted it can flush the Trace or update it.  Flushing the Trace
//   will emit code to bring the actual state into line with the virtual state.
//   Avoiding flushing the state can postpone some work (e.g. updates of capture
//   registers).  Postponing work can save time when executing the regular
//   expression since it may be found that the work never has to be done as a
//   failure to match can occur.  In addition it is much faster to jump to a
//   known backtrack code location than it is to pop an unknown backtrack
//   location from the stack and jump there.
//
//   The virtual state found in the Trace affects code generation.  For example
//   the virtual state contains the difference between the actual current
//   position and the virtual current position, and matching code needs to use
//   this offset to attempt a match in the correct location of the input
//   string.  Therefore code generated for a non-trivial trace is specialized
//   to that trace.  The code generator therefore has the ability to generate
//   code for each node several times.  In order to limit the size of the
//   generated code there is an arbitrary limit on how many specialized sets of
//   code may be generated for a given node.  If the limit is reached, the
//   trace is flushed and a generic version of the code for a node is emitted.
//   This is subsequently used for that node.  The code emitted for non-generic
//   trace is not recorded in the node and so it cannot currently be reused in
//   the event that code generation is requested for an identical trace.

namespace {

constexpr uint32_t MaxCodeUnit(const bool one_byte) {
  static_assert(String::kMaxOneByteCharCodeU <=
                std::numeric_limits<uint16_t>::max());
  static_assert(String::kMaxUtf16CodeUnitU <=
                std::numeric_limits<uint16_t>::max());
  return one_byte ? String::kMaxOneByteCharCodeU : String::kMaxUtf16CodeUnitU;
}

constexpr uint32_t CharMask(const bool one_byte) {
  static_assert(Utils::IsPowerOfTwo(String::kMaxOneByteCharCodeU + 1));
  static_assert(Utils::IsPowerOfTwo(String::kMaxUtf16CodeUnitU + 1));
  return MaxCodeUnit(one_byte);
}

}  // namespace

void RegExpTree::AppendToText(RegExpText* text, Zone* zone) {
  UNREACHABLE();
}

void RegExpAtom::AppendToText(RegExpText* text, Zone* zone) {
  text->AddElement(TextElement::Atom(this), zone);
}

void RegExpClassRanges::AppendToText(RegExpText* text, Zone* zone) {
  text->AddElement(TextElement::ClassRanges(this), zone);
}

void RegExpText::AppendToText(RegExpText* text, Zone* zone) {
  for (int i = 0; i < elements()->length(); i++)
    text->AddElement(elements()->at(i), zone);
}

TextElement TextElement::Atom(RegExpAtom* atom) {
  return TextElement(ATOM, atom);
}

TextElement TextElement::ClassRanges(RegExpClassRanges* class_ranges) {
  return TextElement(CLASS_RANGES, class_ranges);
}

int TextElement::length() const {
  switch (text_type()) {
    case ATOM:
      return atom()->length();

    case CLASS_RANGES:
      return 1;
  }
  UNREACHABLE();
}

class RecursionCheck {
 public:
  explicit RecursionCheck(RegExpCompiler* compiler) : compiler_(compiler) {
    compiler->IncrementRecursionDepth();
  }
  ~RecursionCheck() { compiler_->DecrementRecursionDepth(); }

 private:
  RegExpCompiler* compiler_;
};

// Attempts to compile the regexp using an Irregexp code generator.  Returns
// a fixed array or a null handle depending on whether it succeeded.
RegExpCompiler::RegExpCompiler(Isolate* isolate,
                               Zone* zone,
                               int capture_count,
                               RegExpFlags flags,
                               bool one_byte)
    : next_register_(JSRegExp::RegistersForCaptureCount(capture_count)),
      unicode_lookaround_stack_register_(kNoRegister),
      unicode_lookaround_position_register_(kNoRegister),
      work_list_(nullptr),
      recursion_depth_(0),
      flags_(flags),
      one_byte_(one_byte),
      reg_exp_too_big_(false),
      limiting_recursion_(false),
      optimize_(FLAG_regexp_optimization),
      read_backward_(false),
      current_expansion_factor_(1),
      frequency_collator_(),
      isolate_(isolate),
      zone_(zone) {
  accept_ = zone->New<EndNode>(EndNode::ACCEPT, zone);
  DCHECK_GE(RegExpMacroAssembler::kMaxRegister, next_register_ - 1);
}

RegExpCompiler::CompilationResult RegExpCompiler::Assemble(
    Isolate* isolate,
    RegExpMacroAssembler* macro_assembler,
    RegExpNode* start,
    int capture_count,
    const String& pattern) {
  macro_assembler_ = macro_assembler;

  auto ReportError = [this]() {
    if (FLAG_correctness_fuzzer_suppressions) {
      FATAL("Aborting on excess zone allocation");
    }
    macro_assembler_->AbortedCodeGeneration();
    return CompilationResult::RegExpTooBig();
  };

  ZoneVector<RegExpNode*> work_list(zone());
  work_list_ = &work_list;
  V8Label fail;
  macro_assembler_->PushBacktrack(&fail);
  Trace new_trace;
  if (start->Emit(this, &new_trace).IsError()) {
    return ReportError();
  }
  macro_assembler_->BindJumpTarget(&fail);
  macro_assembler_->Fail();
  while (!work_list.empty()) {
    RegExpNode* node = work_list.back();
    TRACE_WITH_NODE(this, "Popping from worklist ", node);
    work_list.pop_back();
    node->set_on_work_list(false);
    if (!node->label()->is_bound()) {
      if (node->Emit(this, &new_trace).IsError()) {
        return ReportError();
      }
    }
  }
  if (IsRegExpTooBig()) return ReportError();

  ObjectPtr code = macro_assembler_->GetCode(pattern, flags_);
  work_list_ = nullptr;

  return {&Object::Handle(code), next_register_};
}

bool Trace::mentions_reg(int reg) const {
  for (auto trace : *this) {
    if (trace->has_action() && trace->action()->Mentions(reg)) return true;
  }
  return false;
}

bool Trace::GetStoredPosition(int reg, int* cp_offset) const {
  DCHECK_EQ(0, *cp_offset);
  for (auto trace : *this) {
    if (trace->has_action() && trace->action()->Mentions(reg)) {
      if (trace->action_->action_type() == ActionNode::STORE_POSITION ||
          trace->action_->action_type() == ActionNode::RESTORE_POSITION) {
        *cp_offset = trace->next_->cp_offset();
        return true;
      } else {
        return false;
      }
    }
  }
  return false;
}

// A (dynamically-sized) set of unsigned integers that behaves especially well
// on small integers (< kFirstLimit). May do zone-allocation.
class DynamicBitSet : public ZoneObject {
 public:
  bool Get(unsigned value) const {
    if (value < kFirstLimit) {
      return (first_ & (1 << value)) != 0;
    } else if (remaining_ == nullptr) {
      return false;
    } else {
      return remaining_->Contains(value);
    }
  }

  // Destructively set a value in this set.
  void Set(unsigned value, Zone* zone) {
    if (value < kFirstLimit) {
      first_ |= (1 << value);
    } else {
      if (remaining_ == nullptr)
        remaining_ = zone->New<ZoneList<unsigned>>(1, zone);
      if (remaining_->is_empty() || !remaining_->Contains(value))
        remaining_->Add(value, zone);
    }
  }

 private:
  static constexpr unsigned kFirstLimit = 32;

  uint32_t first_ = 0;
  ZoneList<unsigned>* remaining_ = nullptr;
};

int Trace::FindAffectedRegisters(DynamicBitSet* affected_registers,
                                 Zone* zone) {
  int max_register = RegExpCompiler::kNoRegister;
  for (auto trace : *this) {
    if (ActionNode* action = trace->action_) {
      int to = action->register_to();
      for (int i = action->register_from(); i <= to; i++) {
        affected_registers->Set(i, zone);
      }
      if (to > max_register) max_register = to;
    }
  }
  return max_register;
}

void Trace::RestoreAffectedRegisters(RegExpMacroAssembler* assembler,
                                     int max_register,
                                     const DynamicBitSet& registers_to_pop,
                                     const DynamicBitSet& registers_to_clear) {
  for (int reg = max_register; reg >= 0; reg--) {
    if (registers_to_pop.Get(reg)) {
      assembler->PopRegister(reg);
    } else if (registers_to_clear.Get(reg)) {
      int clear_to = reg;
      while (reg > 0 && registers_to_clear.Get(reg - 1)) {
        reg--;
      }
      assembler->ClearRegisters(reg, clear_to);
    }
  }
}

// Scans back through the deferred actions to find, for a given register, what
// needs to be done to effectuate the deferred actions.  Also tells us what
// needs to be undone on backtrack.
void Trace::ScanDeferredActions(Trace* top, int reg, RegisterFlushInfo* info) {
  // The chronologically first deferred action in the trace
  // is used to infer the action needed to restore a register
  // to its previous state (or not, if it's safe to ignore it).

  // This is a little tricky because we are scanning the actions in reverse
  // historical order (newest first).
  for (auto trace : *top) {
    ActionNode* action = trace->action_;
    if (!action) continue;
    if (action->Mentions(reg)) {
      switch (action->action_type()) {
        case ActionNode::SET_REGISTER_FOR_LOOP: {
          if (!info->absolute) {
            info->value += action->value();
            info->absolute = true;
          }
          // SET_REGISTER_FOR_LOOP is only used for newly introduced loop
          // counters. They can have a significant previous value if they
          // occur in a loop. TODO(lrn): Propagate this information, so
          // we can set undo_action to IGNORE_ if we know there is no value to
          // restore.
          info->undo_action = RESTORE;
          DCHECK_EQ(info->store_position, kNoStore);
          DCHECK(!info->clear);
          break;
        }
        case ActionNode::INCREMENT_REGISTER:
          if (!info->absolute) {
            info->value++;
          }
          DCHECK_EQ(info->store_position, kNoStore);
          DCHECK(!info->clear);
          info->undo_action = RESTORE;
          break;
        case ActionNode::STORE_POSITION:
        case ActionNode::RESTORE_POSITION: {
          if (!info->clear && info->store_position == kNoStore) {
            info->store_position = trace->next()->cp_offset();
          }

          // For captures we know that stores and clears alternate.
          // Other register, are never cleared, and if the occur
          // inside a loop, they might be assigned more than once.
          if (reg <= 1) {
            // Registers zero and one, aka "capture zero", is
            // always set correctly if we succeed. There is no
            // need to undo a setting on backtrack, because we
            // will set it again or fail.
            info->undo_action = IGNORE_;
          } else {
            if (action->action_type() == ActionNode::STORE_POSITION) {
              info->undo_action = CLEAR;
            } else {
              info->undo_action = RESTORE;
            }
          }
          DCHECK(!info->absolute);
          DCHECK_EQ(info->value, 0);
          break;
        }
        case ActionNode::CLEAR_CAPTURES: {
          // Since we're scanning in reverse order, if we've already
          // set the position we have to ignore historically earlier
          // clearing operations.
          if (info->store_position == kNoStore) {
            info->clear = true;
          }
          info->undo_action = RESTORE;
          DCHECK(!info->absolute);
          DCHECK_EQ(info->value, 0);
          break;
        }
        default:
          UNREACHABLE();
      }
    }
  }
}

void Trace::PerformDeferredActions(RegExpMacroAssembler* assembler,
                                   int max_register,
                                   const DynamicBitSet& affected_registers,
                                   DynamicBitSet* registers_to_pop,
                                   DynamicBitSet* registers_to_clear,
                                   Zone* zone) {
  // Count pushes performed to force a stack limit check occasionally.
  int pushes = 0;

  for (int reg = 0; reg <= max_register; reg++) {
    if (!affected_registers.Get(reg)) continue;

    RegisterFlushInfo info;
    ScanDeferredActions(this, reg, &info);

    // Prepare for the undo-action (e.g., push if it's going to be popped).
    if (info.undo_action == RESTORE) {
      pushes++;
      RegExpMacroAssembler::StackCheckFlag stack_check =
          RegExpMacroAssembler::StackCheckFlag::kNoStackLimitCheck;
      DCHECK_GT(assembler->stack_limit_slack_slot_count(), 0);
      if (pushes == assembler->stack_limit_slack_slot_count()) {
        stack_check = RegExpMacroAssembler::StackCheckFlag::kCheckStackLimit;
        pushes = 0;
      }

      assembler->PushRegister(reg, stack_check);
      registers_to_pop->Set(reg, zone);
    } else if (info.undo_action == CLEAR) {
      registers_to_clear->Set(reg, zone);
    }
    // Perform the chronologically last action (or accumulated increment)
    // for the register.
    if (info.store_position != kNoStore) {
      assembler->WriteCurrentPositionToRegister(reg, info.store_position);
    } else if (info.clear) {
      assembler->ClearRegisters(reg, reg);
    } else if (info.absolute) {
      assembler->SetRegister(reg, info.value);
    } else if (info.value != 0) {
      assembler->AdvanceRegister(reg, info.value);
    }
  }
}

// This is called as we come into a loop choice node and some other tricky
// nodes.  It normalizes the state of the code generator to ensure we can
// generate generic code.  If the mode indicates that we are in a success
// situation then don't push anything, because the stack is about to be
// discarded, and also don't update the current position.
EmitResult Trace::Flush(RegExpCompiler* compiler,
                        RegExpNode* successor,
                        Trace::FlushMode mode) {
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
#ifdef V8_ENABLE_REGEXP_DIAGNOSTICS
  if (UNLIKELY(v8_flags.trace_regexp_compiler)) {
    RegExpGraphPrinter* printer = compiler->diagnostics()->graph_printer();
    std::ostream& os = compiler->diagnostics()->os();
    os << "* Flushing Trace (";
    switch (mode) {
      case Trace::FlushMode::kFlushFull:
        os << "Full";
        break;
      case Trace::FlushMode::kFlushSuccess:
        os << "Success";
        break;
    }
    os << "): ";
    printer->PrintTrace(this);
    os << std::endl;
  }
#endif

  DCHECK(!is_trivial());

  // Normally we don't need to update the current position register if we are
  // about to stop because we had a successful match, but the global mode
  // requires the current position register to be updated so it can start the
  // next match.  TODO(erikcorry): Perhaps it should use capture register 1
  // instead.
  bool update_current_position =
      cp_offset_ != 0 && (mode != kFlushSuccess || assembler->global());

  if (!has_any_actions() && (backtrack() == nullptr || mode == kFlushSuccess)) {
    // Here we just have some deferred cp advances to fix and we are back to
    // a normal situation.  We may also have to forget some information gained
    // through a quick check that was already performed.
    if (update_current_position) assembler->AdvanceCurrentPosition(cp_offset_);
    // Create a new trivial state and generate the node with that.
    Trace new_state;
    return successor->Emit(compiler, &new_state);
  }

  // Generate deferred actions here along with code to undo them again.
  DynamicBitSet affected_registers;

  if (backtrack() != nullptr && mode != kFlushSuccess) {
    // Here we have a concrete backtrack location.  These are set up by choice
    // nodes and so they indicate that we have a deferred save of the current
    // position which we may need to emit here.
    assembler->PushCurrentPosition();
  }

  int max_register =
      FindAffectedRegisters(&affected_registers, compiler->zone());
  DynamicBitSet registers_to_pop;
  DynamicBitSet registers_to_clear;
  PerformDeferredActions(assembler, max_register, affected_registers,
                         &registers_to_pop, &registers_to_clear,
                         compiler->zone());
  if (update_current_position) assembler->AdvanceCurrentPosition(cp_offset_);

  if (mode == kFlushSuccess) {
    Trace new_state;
    return successor->Emit(compiler, &new_state);
  }

  // Create a new trivial state and generate the node with that.
  V8Label undo;
  assembler->PushBacktrack(&undo);
  if (successor->KeepRecursing(compiler)) {
    Trace new_state;
    EmitResult r = successor->Emit(compiler, &new_state);
    if (UNLIKELY(r.IsError())) {
      // TODO(jgruber): If this pattern emerges elsewhere, let's wrap affected
      // labels in a scope object and add a convenience macro.
      undo.UnuseNear();
      undo.Unuse();
      return r;
    }
  } else {
    compiler->AddWork(successor);
    assembler->GoTo(successor->label());
  }

  // On backtrack we need to restore state.
  assembler->BindJumpTarget(&undo);
  RestoreAffectedRegisters(assembler, max_register, registers_to_pop,
                           registers_to_clear);
  if (backtrack() == nullptr) {
    assembler->Backtrack();
  } else {
    assembler->PopCurrentPosition();
    assembler->GoTo(backtrack());
  }
  return EmitResult::Success();
}

EmitResult NegativeSubmatchSuccess::Emit(RegExpCompiler* compiler,
                                         Trace* trace) {
  TRACE_EMIT("NegativeSubmatchSuccess");
  RegExpMacroAssembler* assembler = compiler->macro_assembler();

  // Omit flushing the trace. We discard the entire stack frame anyway.

  if (!label()->is_bound()) {
    // We are completely independent of the trace, since we ignore it,
    // so this code can be used as the generic version.
    assembler->Bind(label());
  }

  // Throw away everything on the backtrack stack since the start
  // of the negative submatch and restore the character position.
  assembler->ReadCurrentPositionFromRegister(current_position_register_);
  assembler->ReadStackPointerFromRegister(stack_pointer_register_);
  if (clear_capture_count_ > 0) {
    // Clear any captures that might have been performed during the success
    // of the body of the negative look-ahead.
    int clear_capture_end = clear_capture_start_ + clear_capture_count_ - 1;
    assembler->ClearRegisters(clear_capture_start_, clear_capture_end);
  }
  // Now that we have unwound the stack we find at the top of the stack the
  // backtrack that the BeginNegativeSubmatch node got.
  assembler->Backtrack();

  return EmitResult::Success();
}

EmitResult EndNode::Emit(RegExpCompiler* compiler, Trace* trace) {
  TRACE_EMIT("EndNode");
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  if (action_ == BACKTRACK) {
    // This node always backtracks, and we can do that immediately without
    // flushing first.  In practice many of these nodes have been eliminated
    // already during the ToNode phase, so it should not happen often.
    if (trace->is_trivial() && !label()->is_bound()) {
      // We only need this if the node was pushed on the work list with
      // AddWork, which can only happen with a stack overflow (KeepRecursing
      // returns false).
      assembler->Bind(label());
    }
    assembler->GoTo(trace->backtrack());
    return EmitResult::Success();
  }
  // The BACKTRACK case was handled above the NEGATIVE_SUBMATCH_SUCCESS is
  // handled in a different virtual method.
  CHECK_EQ(ACCEPT, action_);
  if (!trace->is_trivial()) {
    return trace->Flush(compiler, this, Trace::kFlushSuccess);
  }
  if (!label()->is_bound()) {
    assembler->Bind(label());
  }
  assembler->Succeed();
  return EmitResult::Success();
}

void GuardedAlternative::AddGuard(Guard* guard, Zone* zone) {
  if (guards_ == nullptr) guards_ = zone->New<ZoneList<Guard*>>(1, zone);
  guards_->Add(guard, zone);
}

ActionNode* ActionNode::SetRegisterForLoop(int reg,
                                           int val,
                                           RegExpNode* on_success) {
  return on_success->zone()->New<ActionNode>(SET_REGISTER_FOR_LOOP, on_success,
                                             reg, reg, val);
}

ActionNode* ActionNode::IncrementRegister(int reg, RegExpNode* on_success) {
  return on_success->zone()->New<ActionNode>(INCREMENT_REGISTER, on_success,
                                             reg);
}

ActionNode* ActionNode::StorePosition(int reg, RegExpNode* on_success) {
  return on_success->zone()->New<ActionNode>(STORE_POSITION, on_success, reg);
}

ActionNode* ActionNode::RestorePosition(int reg, RegExpNode* on_success) {
  return on_success->zone()->New<ActionNode>(RESTORE_POSITION, on_success, reg);
}

ActionNode* ActionNode::ClearCaptures(Interval range, RegExpNode* on_success) {
  return on_success->zone()->New<ActionNode>(CLEAR_CAPTURES, on_success,
                                             range.from(), range.to());
}

ActionNode* ActionNode::BeginPositiveSubmatch(int stack_reg,
                                              int position_reg,
                                              RegExpNode* body,
                                              ActionNode* success_node) {
  ActionNode* result =
      body->zone()->New<ActionNode>(BEGIN_POSITIVE_SUBMATCH, body);
  result->data_.u_submatch.stack_pointer_register = stack_reg;
  result->data_.u_submatch.current_position_register = position_reg;
  result->data_.u_submatch.success_node = success_node;
  return result;
}

ActionNode* ActionNode::BeginNegativeSubmatch(int stack_reg,
                                              int position_reg,
                                              RegExpNode* on_success) {
  ActionNode* result =
      on_success->zone()->New<ActionNode>(BEGIN_NEGATIVE_SUBMATCH, on_success);
  result->data_.u_submatch.stack_pointer_register = stack_reg;
  result->data_.u_submatch.current_position_register = position_reg;
  return result;
}

ActionNode* ActionNode::PositiveSubmatchSuccess(int stack_reg,
                                                int position_reg,
                                                int clear_register_count,
                                                int clear_register_from,
                                                RegExpNode* on_success) {
  ActionNode* result = on_success->zone()->New<ActionNode>(
      POSITIVE_SUBMATCH_SUCCESS, on_success);
  result->data_.u_submatch.stack_pointer_register = stack_reg;
  result->data_.u_submatch.current_position_register = position_reg;
  result->data_.u_submatch.clear_register_count = clear_register_count;
  result->data_.u_submatch.clear_register_from = clear_register_from;
  return result;
}

ActionNode* ActionNode::EmptyMatchCheck(int start_register,
                                        int repetition_register,
                                        int repetition_limit,
                                        RegExpNode* on_success) {
  ActionNode* result =
      on_success->zone()->New<ActionNode>(EMPTY_MATCH_CHECK, on_success);
  result->data_.u_empty_match_check.start_register = start_register;
  result->data_.u_empty_match_check.repetition_register = repetition_register;
  result->data_.u_empty_match_check.repetition_limit = repetition_limit;
  return result;
}

ActionNode* ActionNode::ModifyFlags(RegExpFlags flags, RegExpNode* on_success) {
  ActionNode* result =
      on_success->zone()->New<ActionNode>(MODIFY_FLAGS, on_success);
  result->data_.u_modify_flags.flags = flags;
  return result;
}

ActionNode* ActionNode::EatsAtLeast(int characters, RegExpNode* on_success) {
  ActionNode* result =
      on_success->zone()->New<ActionNode>(EATS_AT_LEAST, on_success);
  result->data_.u_eats_at_least.characters = characters;
  return result;
}

#define DEFINE_ACCEPT(Type)                                                    \
  void Type##Node::Accept(NodeVisitor* visitor) {                              \
    visitor->Visit##Type(this);                                                \
  }
FOR_EACH_NODE_TYPE(DEFINE_ACCEPT)
#undef DEFINE_ACCEPT

// -------------------------------------------------------------------
// Emit code.

void ChoiceNode::GenerateGuard(RegExpMacroAssembler* macro_assembler,
                               Guard* guard,
                               Trace* trace) {
  switch (guard->op()) {
    case Guard::LT:
      DCHECK(!trace->mentions_reg(guard->reg()));
      macro_assembler->IfRegisterGE(guard->reg(), guard->value(),
                                    trace->backtrack());
      break;
    case Guard::GEQ:
      DCHECK(!trace->mentions_reg(guard->reg()));
      macro_assembler->IfRegisterLT(guard->reg(), guard->value(),
                                    trace->backtrack());
      break;
  }
}

namespace {

#ifdef DEBUG
bool ContainsOnlyUtf16CodeUnits(unibrow::uchar* chars, int length) {
  static_assert(sizeof(unibrow::uchar) == 4);
  for (int i = 0; i < length; i++) {
    if (chars[i] > String::kMaxUtf16CodeUnit) return false;
  }
  return true;
}
#endif  // DEBUG

// Returns the number of characters in the equivalence class, omitting those
// that cannot occur in the source string because it is Latin1.  This is called
// both for unicode modes /ui and /vi, and also for legacy case independent
// mode /i.  In the case of Unicode modes we handled surrogate pair expansions
// earlier so at this point it's all about single-code-unit expansions.
int GetCaseIndependentLetters(Isolate* isolate,
                              uint16_t character,
                              RegExpCompiler* compiler,
                              unibrow::uchar* letters,
                              int letter_length) {
  bool one_byte_subject = compiler->one_byte();
  bool unicode = IsEitherUnicode(compiler->flags());
  static const uint16_t kMaxAscii = 0x7f;
  if (!unicode && character <= kMaxAscii) {
    // Fast case for common characters.
    uint16_t upper = character & ~0x20;
    if ('A' <= upper && upper <= 'Z') {
      letters[0] = upper;
      letters[1] = upper | 0x20;
      return 2;
    }
    letters[0] = character;
    return 1;
  }
#ifdef V8_INTL_SUPPORT

  if (!unicode && RegExpCaseFolding::IgnoreSet().contains(character)) {
    if (one_byte_subject && character > String::kMaxOneByteCharCode) {
      // This function promises not to return a character that is impossible
      // for the subject encoding.
      return 0;
    }
    letters[0] = character;
    DCHECK(ContainsOnlyUtf16CodeUnits(letters, 1));
    return 1;
  }
  bool in_special_add_set =
      RegExpCaseFolding::SpecialAddSet().contains(character);

  icu::UnicodeSet set;
  set.add(character);
  set = set.closeOver(unicode ? USET_SIMPLE_CASE_INSENSITIVE
                              : USET_CASE_INSENSITIVE);

  UChar32 canon = 0;
  if (in_special_add_set && !unicode) {
    canon = RegExpCaseFolding::Canonicalize(character);
  }

  int32_t range_count = set.getRangeCount();
  int items = 0;
  for (int32_t i = 0; i < range_count; i++) {
    UChar32 start = set.getRangeStart(i);
    UChar32 end = set.getRangeEnd(i);
    CHECK(end - start + items <= letter_length);
    for (UChar32 cu = start; cu <= end; cu++) {
      if (one_byte_subject && cu > String::kMaxOneByteCharCode) continue;
      if (!unicode && in_special_add_set &&
          RegExpCaseFolding::Canonicalize(cu) != canon) {
        continue;
      }
      letters[items++] = static_cast<unibrow::uchar>(cu);
    }
  }
  DCHECK(ContainsOnlyUtf16CodeUnits(letters, items));
  return items;
#else
  int length =
      isolate->jsregexp_uncanonicalize()->get(character, '\0', letters);
  // Unibrow returns 0 or 1 for characters where case independence is
  // trivial.
  if (length == 0) {
    letters[0] = character;
    length = 1;
  }

  if (one_byte_subject) {
    int new_length = 0;
    for (int i = 0; i < length; i++) {
      if (letters[i] <= String::kMaxOneByteCharCode) {
        letters[new_length++] = letters[i];
      }
    }
    length = new_length;
  }

  DCHECK(ContainsOnlyUtf16CodeUnits(letters, length));
  return length;
#endif  // V8_INTL_SUPPORT
}

inline bool EmitSimpleCharacter(Isolate* isolate,
                                RegExpCompiler* compiler,
                                uint16_t c,
                                V8Label* on_failure,
                                int cp_offset,
                                bool check,
                                bool preloaded) {
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  bool bound_checked = false;
  if (!preloaded) {
    assembler->LoadCurrentCharacter(cp_offset, on_failure, check);
    bound_checked = true;
  }
  assembler->CheckNotCharacter(c, on_failure);
  return bound_checked;
}

// Only emits non-letters (things that don't have case).  Only used for case
// independent matches.
inline bool EmitAtomNonLetter(Isolate* isolate,
                              RegExpCompiler* compiler,
                              uint16_t c,
                              V8Label* on_failure,
                              int cp_offset,
                              bool check,
                              bool preloaded) {
  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  bool one_byte = compiler->one_byte();
  unibrow::uchar chars[4];
  int length = GetCaseIndependentLetters(isolate, c, compiler, chars, 4);
  if (length < 1) {
    // This can't match.  Must be an one-byte subject and a non-one-byte
    // character.  We do not need to do anything since the one-byte pass
    // already handled this.
    CHECK(one_byte);
    return false;  // Bounds not checked.
  }
  bool checked = false;
  // We handle the length > 1 case in a later pass.
  if (length == 1) {
    // GetCaseIndependentLetters promises not to return characters that can't
    // match because of the subject encoding.  This case is already handled by
    // the one-byte pass.
    CHECK_IMPLIES(one_byte, chars[0] <= String::kMaxOneByteCharCodeU);
    if (!preloaded) {
      macro_assembler->LoadCurrentCharacter(cp_offset, on_failure, check);
      checked = check;
    }
    macro_assembler->CheckNotCharacter(chars[0], on_failure);
  }
  return checked;
}

bool ShortCutEmitCharacterPair(RegExpMacroAssembler* macro_assembler,
                               bool one_byte,
                               uint16_t c1,
                               uint16_t c2,
                               V8Label* on_failure) {
  const uint32_t char_mask = CharMask(one_byte);
  uint16_t exor = c1 ^ c2;
  // Check whether exor has only one bit set.
  if (((exor - 1) & exor) == 0) {
    // If c1 and c2 differ only by one bit.
    // Ecma262UnCanonicalize always gives the highest number last.
    DCHECK(c2 > c1);
    uint16_t mask = char_mask ^ exor;
    macro_assembler->CheckNotCharacterAfterAnd(c1, mask, on_failure);
    return true;
  }
  DCHECK(c2 > c1);
  uint16_t diff = c2 - c1;
  if (((diff - 1) & diff) == 0 && c1 >= diff) {
    // If the characters differ by 2^n but don't differ by one bit then
    // subtract the difference from the found character, then do the or
    // trick.  We avoid the theoretical case where negative numbers are
    // involved in order to simplify code generation.
    uint16_t mask = char_mask ^ diff;
    macro_assembler->CheckNotCharacterAfterMinusAnd(c1 - diff, diff, mask,
                                                    on_failure);
    return true;
  }
  return false;
}

// Only emits letters (things that have case).  Only used for case independent
// matches.
inline bool EmitAtomLetter(Isolate* isolate,
                           RegExpCompiler* compiler,
                           uint16_t c,
                           V8Label* on_failure,
                           int cp_offset,
                           bool check,
                           bool preloaded) {
  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  bool one_byte = compiler->one_byte();
  unibrow::uchar chars[4];
  int length = GetCaseIndependentLetters(isolate, c, compiler, chars, 4);
  // The 0 and 1 case are handled by earlier passes.
  if (length <= 1) return false;
  // We may not need to check against the end of the input string
  // if this character lies before a character that matched.
  if (!preloaded) {
    macro_assembler->LoadCurrentCharacter(cp_offset, on_failure, check);
  }
  V8Label ok;
  switch (length) {
    case 2: {
      if (ShortCutEmitCharacterPair(macro_assembler, one_byte, chars[0],
                                    chars[1], on_failure)) {
      } else {
        macro_assembler->CheckCharacter(chars[0], &ok);
        macro_assembler->CheckNotCharacter(chars[1], on_failure);
        macro_assembler->Bind(&ok);
      }
      break;
    }
    case 4:
      macro_assembler->CheckCharacter(chars[3], &ok);
      [[fallthrough]];
    case 3:
      macro_assembler->CheckCharacter(chars[0], &ok);
      macro_assembler->CheckCharacter(chars[1], &ok);
      macro_assembler->CheckNotCharacter(chars[2], on_failure);
      macro_assembler->Bind(&ok);
      break;
    default:
      UNREACHABLE();
  }
  return true;
}

void EmitBoundaryTest(RegExpMacroAssembler* masm,
                      int border,
                      V8Label* fall_through,
                      V8Label* above_or_equal,
                      V8Label* below) {
  if (below != fall_through) {
    masm->CheckCharacterLT(border, below);
    if (above_or_equal != fall_through) masm->GoTo(above_or_equal);
  } else {
    masm->CheckCharacterGT(border - 1, above_or_equal);
  }
}

void EmitDoubleBoundaryTest(RegExpMacroAssembler* masm,
                            int first,
                            int last,
                            V8Label* fall_through,
                            V8Label* in_range,
                            V8Label* out_of_range) {
  if (in_range == fall_through) {
    if (first == last) {
      masm->CheckNotCharacter(first, out_of_range);
    } else {
      masm->CheckCharacterNotInRange(first, last, out_of_range);
    }
  } else {
    if (first == last) {
      masm->CheckCharacter(first, in_range);
    } else {
      masm->CheckCharacterInRange(first, last, in_range);
    }
    if (out_of_range != fall_through) masm->GoTo(out_of_range);
  }
}

// even_label is for ranges[i] to ranges[i + 1] where i - start_index is even.
// odd_label is for ranges[i] to ranges[i + 1] where i - start_index is odd.
void EmitUseLookupTable(RegExpMacroAssembler* masm,
                        ZoneList<uint32_t>* ranges,
                        uint32_t start_index,
                        uint32_t end_index,
                        uint32_t min_char,
                        V8Label* fall_through,
                        V8Label* even_label,
                        V8Label* odd_label) {
  static const uint32_t kSize = RegExpMacroAssembler::kTableSize;
  static const uint32_t kMask = RegExpMacroAssembler::kTableMask;

  uint32_t base = (min_char & ~kMask);
  USE(base);

  // Assert that everything is on one kTableSize page.
  for (uint32_t i = start_index; i <= end_index; i++) {
    DCHECK_EQ(ranges->at(i) & ~kMask, base);
  }
  DCHECK(start_index == 0 || (ranges->at(start_index - 1) & ~kMask) <= base);

  char templ[kSize];
  V8Label* on_bit_set;
  V8Label* on_bit_clear;
  int bit;
  if (even_label == fall_through) {
    on_bit_set = odd_label;
    on_bit_clear = even_label;
    bit = 1;
  } else {
    on_bit_set = even_label;
    on_bit_clear = odd_label;
    bit = 0;
  }
  for (uint32_t i = 0; i < (ranges->at(start_index) & kMask) && i < kSize;
       i++) {
    templ[i] = bit;
  }
  uint32_t j = 0;
  bit ^= 1;
  for (uint32_t i = start_index; i < end_index; i++) {
    for (j = (ranges->at(i) & kMask); j < (ranges->at(i + 1) & kMask); j++) {
      templ[j] = bit;
    }
    bit ^= 1;
  }
  for (uint32_t i = j; i < kSize; i++) {
    templ[i] = bit;
  }
  // TODO(erikcorry): Cache these.
  TypedData& ba =
      TypedData::Handle(TypedData::New(kTypedDataUint8ArrayCid, kSize));
  for (uint32_t i = 0; i < kSize; i++) {
    ba.SetUint8(i, templ[i]);
  }
  masm->CheckBitInTable(ba, on_bit_set);
  if (on_bit_clear != fall_through) masm->GoTo(on_bit_clear);
}

void CutOutRange(RegExpMacroAssembler* masm,
                 ZoneList<uint32_t>* ranges,
                 uint32_t start_index,
                 uint32_t end_index,
                 uint32_t cut_index,
                 V8Label* even_label,
                 V8Label* odd_label) {
  bool odd = (((cut_index - start_index) & 1) == 1);
  V8Label* in_range_label = odd ? odd_label : even_label;
  V8Label dummy;
  EmitDoubleBoundaryTest(masm, ranges->at(cut_index),
                         ranges->at(cut_index + 1) - 1, &dummy, in_range_label,
                         &dummy);
  DCHECK(!dummy.is_linked());
  // Cut out the single range by rewriting the array.  This creates a new
  // range that is a merger of the two ranges on either side of the one we
  // are cutting out.  The oddity of the labels is preserved.
  for (uint32_t j = cut_index; j > start_index; j--) {
    ranges->at(j) = ranges->at(j - 1);
  }
  for (uint32_t j = cut_index + 1; j < end_index; j++) {
    ranges->at(j) = ranges->at(j + 1);
  }
}

// Unicode case.  Split the search space into kSize spaces that are handled
// with recursion.
void SplitSearchSpace(ZoneList<uint32_t>* ranges,
                      uint32_t start_index,
                      uint32_t end_index,
                      uint32_t* new_start_index,
                      uint32_t* new_end_index,
                      uint32_t* border) {
  static const uint32_t kSize = RegExpMacroAssembler::kTableSize;
  static const uint32_t kMask = RegExpMacroAssembler::kTableMask;

  uint32_t first = ranges->at(start_index);
  uint32_t last = ranges->at(end_index) - 1;

  *new_start_index = start_index;
  *border = (ranges->at(start_index) & ~kMask) + kSize;
  while (*new_start_index < end_index) {
    if (ranges->at(*new_start_index) > *border) break;
    (*new_start_index)++;
  }
  // new_start_index is the index of the first edge that is beyond the
  // current kSize space.

  // For very large search spaces we do a binary chop search of the non-Latin1
  // space instead of just going to the end of the current kSize space.  The
  // heuristics are complicated a little by the fact that any 128-character
  // encoding space can be quickly tested with a table lookup, so we don't
  // wish to do binary chop search at a smaller granularity than that.  A
  // 128-character space can take up a lot of space in the ranges array if,
  // for example, we only want to match every second character (eg. the lower
  // case characters on some Unicode pages).
  uint32_t binary_chop_index = (end_index + start_index) / 2;
  // The first test ensures that we get to the code that handles the Latin1
  // range with a single not-taken branch, speeding up this important
  // character range (even non-Latin1 charset-based text has spaces and
  // punctuation).
  if (*border - 1 > String::kMaxOneByteCharCode &&  // Latin1 case.
      end_index - start_index > (*new_start_index - start_index) * 2 &&
      last - first > kSize * 2 && binary_chop_index > *new_start_index &&
      ranges->at(binary_chop_index) >= first + 2 * kSize) {
    uint32_t scan_forward_for_section_border = binary_chop_index;
    uint32_t new_border = (ranges->at(binary_chop_index) | kMask) + 1;

    while (scan_forward_for_section_border < end_index) {
      if (ranges->at(scan_forward_for_section_border) > new_border) {
        *new_start_index = scan_forward_for_section_border;
        *border = new_border;
        break;
      }
      scan_forward_for_section_border++;
    }
  }

  DCHECK(*new_start_index > start_index);
  *new_end_index = *new_start_index - 1;
  if (ranges->at(*new_end_index) == *border) {
    (*new_end_index)--;
  }
  if (*border >= ranges->at(end_index)) {
    *border = ranges->at(end_index);
    *new_start_index = end_index;  // Won't be used.
    *new_end_index = end_index - 1;
  }
}

// Gets a series of segment boundaries representing a character class.  If the
// character is in the range between an even and an odd boundary (counting from
// start_index) then go to even_label, otherwise go to odd_label.  We already
// know that the character is in the range of min_char to max_char inclusive.
// Either label can be nullptr indicating backtracking.  Either label can also
// be equal to the fall_through label.
void GenerateBranches(RegExpMacroAssembler* masm,
                      ZoneList<uint32_t>* ranges,
                      uint32_t start_index,
                      uint32_t end_index,
                      uint32_t min_char,
                      uint32_t max_char,
                      V8Label* fall_through,
                      V8Label* even_label,
                      V8Label* odd_label) {
  DCHECK_LE(min_char, String::kMaxUtf16CodeUnit);
  DCHECK_LE(max_char, String::kMaxUtf16CodeUnit);

  uint32_t first = ranges->at(start_index);
  uint32_t last = ranges->at(end_index) - 1;

  DCHECK_LT(min_char, first);

  // Just need to test if the character is before or on-or-after
  // a particular character.
  if (start_index == end_index) {
    EmitBoundaryTest(masm, first, fall_through, even_label, odd_label);
    return;
  }

  // Another almost trivial case:  There is one interval in the middle that is
  // different from the end intervals.
  if (start_index + 1 == end_index) {
    EmitDoubleBoundaryTest(masm, first, last, fall_through, even_label,
                           odd_label);
    return;
  }

  // It's not worth using table lookup if there are very few intervals in the
  // character class.
  if (end_index - start_index <= 6) {
    // It is faster to test for individual characters, so we look for those
    // first, then try arbitrary ranges in the second round.
    static uint32_t kNoCutIndex = -1;
    uint32_t cut = kNoCutIndex;
    for (uint32_t i = start_index; i < end_index; i++) {
      if (ranges->at(i) == ranges->at(i + 1) - 1) {
        cut = i;
        break;
      }
    }
    if (cut == kNoCutIndex) cut = start_index;
    CutOutRange(masm, ranges, start_index, end_index, cut, even_label,
                odd_label);
    DCHECK_GE(end_index - start_index, 2);
    GenerateBranches(masm, ranges, start_index + 1, end_index - 1, min_char,
                     max_char, fall_through, even_label, odd_label);
    return;
  }

  // If there are a lot of intervals in the regexp, then we will use tables to
  // determine whether the character is inside or outside the character class.
  static const int kBits = RegExpMacroAssembler::kTableSizeBits;

  if ((max_char >> kBits) == (min_char >> kBits)) {
    EmitUseLookupTable(masm, ranges, start_index, end_index, min_char,
                       fall_through, even_label, odd_label);
    return;
  }

  if ((min_char >> kBits) != first >> kBits) {
    masm->CheckCharacterLT(first, odd_label);
    GenerateBranches(masm, ranges, start_index + 1, end_index, first, max_char,
                     fall_through, odd_label, even_label);
    return;
  }

  uint32_t new_start_index = 0;
  uint32_t new_end_index = 0;
  uint32_t border = 0;

  SplitSearchSpace(ranges, start_index, end_index, &new_start_index,
                   &new_end_index, &border);

  V8Label handle_rest;
  V8Label* above = &handle_rest;
  if (border == last + 1) {
    // We didn't find any section that started after the limit, so everything
    // above the border is one of the terminal labels.
    above = (end_index & 1) != (start_index & 1) ? odd_label : even_label;
    DCHECK(new_end_index == end_index - 1);
  }

  DCHECK_LE(start_index, new_end_index);
  DCHECK_LE(new_start_index, end_index);
  DCHECK_LT(start_index, new_start_index);
  DCHECK_LT(new_end_index, end_index);
  DCHECK(new_end_index + 1 == new_start_index ||
         (new_end_index + 2 == new_start_index &&
          border == ranges->at(new_end_index + 1)));
  DCHECK_LT(min_char, border - 1);
  DCHECK_LT(border, max_char);
  DCHECK_LT(ranges->at(new_end_index), border);
  DCHECK(border < ranges->at(new_start_index) ||
         (border == ranges->at(new_start_index) &&
          new_start_index == end_index && new_end_index == end_index - 1 &&
          border == last + 1));
  DCHECK(new_start_index == 0 || border >= ranges->at(new_start_index - 1));

  masm->CheckCharacterGT(border - 1, above);
  V8Label dummy;
  GenerateBranches(masm, ranges, start_index, new_end_index, min_char,
                   border - 1, &dummy, even_label, odd_label);
  if (handle_rest.is_linked()) {
    masm->Bind(&handle_rest);
    bool flip = (new_start_index & 1) != (start_index & 1);
    GenerateBranches(masm, ranges, new_start_index, end_index, border, max_char,
                     &dummy, flip ? odd_label : even_label,
                     flip ? even_label : odd_label);
  }
}

void EmitClassRanges(RegExpMacroAssembler* macro_assembler,
                     RegExpClassRanges* cr,
                     bool one_byte,
                     V8Label* on_failure,
                     int cp_offset,
                     bool check_offset,
                     bool preloaded,
                     Zone* zone) {
  ZoneList<CharacterRange>* ranges = cr->ranges(zone);
  CharacterRange::Canonicalize(ranges);

  // Now that all processing (like case-insensitivity) is done, clamp the
  // ranges to the set of ranges that may actually occur in the subject string.
  if (one_byte) CharacterRange::ClampToOneByte(ranges);

  const int ranges_length = ranges->length();
  if (ranges_length == 0) {
    if (!cr->is_negated()) {
      macro_assembler->GoTo(on_failure);
    }
    if (check_offset) {
      macro_assembler->CheckPosition(cp_offset, on_failure);
    }
    return;
  }

  const uint32_t max_char = MaxCodeUnit(one_byte);
  if (ranges_length == 1 && ranges->at(0).IsEverything(max_char)) {
    if (cr->is_negated()) {
      macro_assembler->GoTo(on_failure);
    } else {
      // This is a common case hit by non-anchored expressions.
      if (check_offset) {
        macro_assembler->CheckPosition(cp_offset, on_failure);
      }
    }
    return;
  }

  if (!preloaded) {
    macro_assembler->LoadCurrentCharacter(cp_offset, on_failure, check_offset);
  }

  if (cr->is_standard(zone) &&
      macro_assembler->CanOptimizeSpecialClassRanges(cr->standard_type())) {
    macro_assembler->CheckSpecialClassRanges(cr->standard_type(), on_failure);
    return;
  }

  static constexpr int kMaxRangesForInlineBranchGeneration = 16;
  if (ranges_length > kMaxRangesForInlineBranchGeneration) {
    // For large range sets, emit a more compact instruction sequence to avoid
    // a potentially problematic increase in code size.
    // Note the flipped logic below (we check InRange if negated, NotInRange if
    // not negated); this is necessary since the method falls through on
    // failure whereas we want to fall through on success.
    if (cr->is_negated()) {
      if (macro_assembler->CheckCharacterInRangeArray(ranges, on_failure)) {
        return;
      }
    } else {
      if (macro_assembler->CheckCharacterNotInRangeArray(ranges, on_failure)) {
        return;
      }
    }
  }

  // Generate a flat list of range boundaries for consumption by
  // GenerateBranches. See the comment on that function for how the list should
  // be structured
  ZoneList<uint32_t>* range_boundaries =
      zone->New<ZoneList<uint32_t>>(ranges_length * 2, zone);

  bool zeroth_entry_is_failure = !cr->is_negated();

  for (int i = 0; i < ranges_length; i++) {
    CharacterRange& range = ranges->at(i);
    if (range.from() == 0) {
      DCHECK_EQ(i, 0);
      zeroth_entry_is_failure = !zeroth_entry_is_failure;
    } else {
      range_boundaries->Add(range.from(), zone);
    }
    // `+ 1` to convert from inclusive to exclusive `to`.
    // [from, to] == [from, to+1[.
    range_boundaries->Add(range.to() + 1, zone);
  }
  int end_index = range_boundaries->length() - 1;
  if (range_boundaries->at(end_index) > max_char) {
    end_index--;
  }

  V8Label fall_through;
  GenerateBranches(macro_assembler, range_boundaries,
                   0,  // start_index.
                   end_index,
                   0,  // min_char.
                   max_char, &fall_through,
                   zeroth_entry_is_failure ? &fall_through : on_failure,
                   zeroth_entry_is_failure ? on_failure : &fall_through);
  macro_assembler->Bind(&fall_through);
}

}  // namespace

RegExpNode::~RegExpNode() = default;

RegExpNode::LimitResult RegExpNode::LimitVersions(RegExpCompiler* compiler,
                                                  Trace* trace) {
  // If we are generating a fixed length loop then don't stop and don't reuse
  // code.
  if (trace->special_loop_state() != nullptr) {
    return CONTINUE;
  }

  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  if (trace->is_trivial()) {
    if (label_.is_bound() || on_work_list() || !KeepRecursing(compiler)) {
      TRACE("* Limit Versions: Generic version available");
      // If a generic version is already scheduled to be generated or we have
      // recursed too deeply then just generate a jump to that code.
      macro_assembler->GoTo(&label_);
      // This will queue it up for generation of a generic version if it hasn't
      // already been queued.
      compiler->AddWork(this);
      return DONE;
    }
    // Generate generic version of the node and bind the label for later use.
    macro_assembler->Bind(&label_);
    return CONTINUE;
  }

  // We are being asked to make a non-generic version.  Keep track of how many
  // non-generic versions we generate so as not to overdo it.
  trace_count_++;
  if (KeepRecursing(compiler) && compiler->optimize() &&
      trace_count_ < kMaxCopiesCodeGenerated) {
    return CONTINUE;
  }

  // If we get here code has been generated for this node too many times or
  // recursion is too deep.  Time to switch to a generic version.  The code for
  // generic versions above can handle deep recursion properly.
  TRACE("* Limit Versions: Switch to generic version");
  bool was_limiting = compiler->limiting_recursion();
  compiler->set_limiting_recursion(true);
  trace->Flush(compiler, this);
  compiler->set_limiting_recursion(was_limiting);
  return DONE;
}

bool RegExpNode::KeepRecursing(RegExpCompiler* compiler) {
  return !compiler->limiting_recursion() &&
         compiler->recursion_depth() <= RegExpCompiler::kMaxRecursion;
}

void ActionNode::FillInBMInfo(Isolate* isolate,
                              int offset,
                              int budget,
                              BoyerMooreLookahead* bm,
                              bool not_at_start) {
  std::optional<RegExpFlags> old_flags;
  if (action_type_ == MODIFY_FLAGS) {
    // It is not guaranteed that we hit the resetting modify flags node, due to
    // recursion budget limitation for filling in BMInfo. Therefore we reset the
    // flags manually to the previous state after recursing.
    old_flags = bm->compiler()->flags();
    bm->compiler()->set_flags(flags());
  }
  if (action_type_ == BEGIN_POSITIVE_SUBMATCH) {
    // We use the node after the lookaround to fill in the eats_at_least info
    // so we have to use the same node to fill in the Boyer-Moore info.
    success_node()->on_success()->FillInBMInfo(isolate, offset, budget - 1, bm,
                                               not_at_start);
  } else if (action_type_ != POSITIVE_SUBMATCH_SUCCESS) {
    // We don't use the node after a positive submatch success because it
    // rewinds the position.  Since we returned 0 as the eats_at_least value for
    // this node, we don't need to fill in any data.
    on_success()->FillInBMInfo(isolate, offset, budget - 1, bm, not_at_start);
  }
  SaveBMInfo(bm, not_at_start, offset);
  if (old_flags.has_value()) {
    bm->compiler()->set_flags(*old_flags);
  }
}

void ActionNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                      RegExpCompiler* compiler,
                                      int filled_in,
                                      bool not_at_start,
                                      int budget) {
  if (action_type_ == BEGIN_POSITIVE_SUBMATCH) {
    // We use the node after the lookaround to fill in the eats_at_least info
    // so we have to use the same node to fill in the QuickCheck info.
    success_node()->on_success()->GetQuickCheckDetails(
        details, compiler, filled_in, not_at_start, budget - 1);
  } else if (action_type() != POSITIVE_SUBMATCH_SUCCESS) {
    // We don't use the node after a positive submatch success because it
    // rewinds the position.  Since we returned 0 as the eats_at_least value
    // for this node, we don't need to fill in any data.
    std::optional<RegExpFlags> old_flags;
    if (action_type() == MODIFY_FLAGS) {
      // It is not guaranteed that we hit the resetting modify flags node, as
      // GetQuickCheckDetails doesn't travers the whole graph. Therefore we
      // reset the flags manually to the previous state after recursing.
      old_flags = compiler->flags();
      compiler->set_flags(flags());
    }
    on_success()->GetQuickCheckDetails(details, compiler, filled_in,
                                       not_at_start, budget - 1);
    if (old_flags.has_value()) {
      compiler->set_flags(*old_flags);
    }
  }
}

void AssertionNode::FillInBMInfo(Isolate* isolate,
                                 int offset,
                                 int budget,
                                 BoyerMooreLookahead* bm,
                                 bool not_at_start) {
  // Match the behaviour of EatsAtLeast on this node.
  if (assertion_type() == AT_START && not_at_start) return;
  on_success()->FillInBMInfo(isolate, offset, budget - 1, bm, not_at_start);
  SaveBMInfo(bm, not_at_start, offset);
}

void NegativeLookaroundChoiceNode::GetQuickCheckDetails(
    QuickCheckDetails* details,
    RegExpCompiler* compiler,
    int filled_in,
    bool not_at_start,
    int budget) {
  RegExpNode* node = continue_node();
  return node->GetQuickCheckDetails(details, compiler, filled_in, not_at_start,
                                    budget - 1);
}

namespace {

// Takes the left-most 1-bit and smears it out, setting all bits to its right.
inline uint32_t SmearBitsRight(uint32_t v) {
  v |= v >> 1;
  v |= v >> 2;
  v |= v >> 4;
  v |= v >> 8;
  v |= v >> 16;
  return v;
}

}  // namespace

bool QuickCheckDetails::Rationalize(bool asc) {
  bool found_useful_op = false;
  const uint32_t char_mask = CharMask(asc);
  mask_ = 0;
  value_ = 0;
  int char_shift = 0;
  for (int i = 0; i < characters_; i++) {
    Position* pos = &positions_[i];
    if ((pos->mask & String::kMaxOneByteCharCode) != 0) {
      found_useful_op = true;
    }
    mask_ |= (pos->mask & char_mask) << char_shift;
    value_ |= (pos->value & char_mask) << char_shift;
    char_shift += asc ? 8 : 16;
  }
  return found_useful_op;
}

uint32_t RegExpNode::EatsAtLeast(bool not_at_start) {
  return not_at_start ? eats_at_least_.from_not_start
                      : eats_at_least_.from_possibly_start;
}

bool RegExpNode::EmitQuickCheck(RegExpCompiler* compiler,
                                Trace* bounds_check_trace,
                                Trace* trace,
                                bool preload_has_checked_bounds,
                                V8Label* on_possible_success,
                                QuickCheckDetails* details,
                                bool fall_through_on_failure,
                                ChoiceNode* predecessor) {
  DCHECK_NOT_NULL(predecessor);
  if (details->characters() == 0) {
    TRACE("* No QuickCheck characters found");
    return false;
  }
  GetQuickCheckDetails(details, compiler, 0,
                       trace->at_start() == Trace::FALSE_VALUE,
                       kRecursionBudget);
  if (details->cannot_match()) {
    TRACE("* QuickCheck cannot match");
    return false;
  }
  if (!details->Rationalize(compiler->one_byte())) {
    TRACE("* QuickCheck didn't find a useful operation");
    return false;
  }
  DCHECK(details->characters() == 1 ||
         compiler->macro_assembler()->CanReadUnaligned());
  uint32_t mask = details->mask();
  uint32_t value = details->value();

  RegExpMacroAssembler* assembler = compiler->macro_assembler();

  TRACE("* Emit QuickCheck");
  if (trace->characters_preloaded() != details->characters()) {
    DCHECK(trace->cp_offset() == bounds_check_trace->cp_offset());
    // The bounds check is performed using the minimum number of characters
    // any choice would eat, so if the bounds check fails, then none of the
    // choices can succeed, so we can just immediately backtrack, rather
    // than go to the next choice. The number of characters preloaded may be
    // less than the number used for the bounds check.
    int eats_at_least = predecessor->EatsAtLeast(
        bounds_check_trace->at_start() == Trace::FALSE_VALUE);
    DCHECK_GE(eats_at_least, details->characters());
    assembler->LoadCurrentCharacter(
        trace->cp_offset(), bounds_check_trace->backtrack(),
        !preload_has_checked_bounds, details->characters(), eats_at_least);
  }

  bool need_mask = true;

  if (details->characters() == 1) {
    // If number of characters preloaded is 1 then we used a byte or 16 bit
    // load so the value is already masked down.
    const uint32_t char_mask = CharMask(compiler->one_byte());
    if ((mask & char_mask) == char_mask) need_mask = false;
    mask &= char_mask;
  } else {
    // For 2-character preloads in one-byte mode or 1-character preloads in
    // two-byte mode we also use a 16 bit load with zero extend.
    static const uint32_t kTwoByteMask = 0xFFFF;
    static const uint32_t kFourByteMask = 0xFFFFFFFF;
    if (details->characters() == 2 && compiler->one_byte()) {
      if ((mask & kTwoByteMask) == kTwoByteMask) need_mask = false;
    } else if (details->characters() == 1 && !compiler->one_byte()) {
      if ((mask & kTwoByteMask) == kTwoByteMask) need_mask = false;
    } else {
      if (mask == kFourByteMask) need_mask = false;
    }
  }

  if (fall_through_on_failure) {
    if (need_mask) {
      assembler->CheckCharacterAfterAnd(value, mask, on_possible_success);
    } else {
      assembler->CheckCharacter(value, on_possible_success);
    }
  } else {
    if (need_mask) {
      assembler->CheckNotCharacterAfterAnd(value, mask, trace->backtrack());
    } else {
      assembler->CheckNotCharacter(value, trace->backtrack());
    }
  }
  return true;
}

// Here is the meat of GetQuickCheckDetails (see also the comment on the
// super-class in the .h file).
//
// We iterate along the text object, building up for each character a
// mask and value that can be used to test for a quick failure to match.
// The masks and values for the positions will be combined into a single
// machine word for the current character width in order to be used in
// generating a quick check.
void TextNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                    RegExpCompiler* compiler,
                                    int characters_filled_in,
                                    bool not_at_start,
                                    int budget) {
  // Do not collect any quick check details if the text node reads backward,
  // since it reads in the opposite direction than we use for quick checks.
  if (read_backward()) return;
  Isolate* isolate = compiler->macro_assembler()->isolate();
  DCHECK(characters_filled_in < details->characters());
  int characters = details->characters();
  const uint32_t char_mask = CharMask(compiler->one_byte());
  for (int k = 0; k < elements()->length(); k++) {
    TextElement elm = elements()->at(k);
    if (elm.text_type() == TextElement::ATOM) {
      base::Vector<const uint16_t> quarks = elm.atom()->data();
      for (int i = 0; i < characters && i < quarks.length(); i++) {
        QuickCheckDetails::Position* pos =
            details->positions(characters_filled_in);
        uint16_t c = quarks[i];
        if (IsIgnoreCase(compiler->flags())) {
          unibrow::uchar chars[4];
          int length =
              GetCaseIndependentLetters(isolate, c, compiler, chars, 4);
          if (length == 0) {
            // This can happen because all case variants are non-Latin1, but we
            // know the input is Latin1.
            details->set_cannot_match_from(characters_filled_in);
            pos->determines_perfectly = false;
            return;
          }
          if (length == 1) {
            // This letter has no case equivalents, so it's nice and simple
            // and the mask-compare will determine definitely whether we have
            // a match at this character position.
            pos->mask = char_mask;
            pos->value = chars[0];
            pos->determines_perfectly = true;
          } else {
            uint32_t common_bits = char_mask;
            uint32_t bits = chars[0];
            for (int j = 1; j < length; j++) {
              uint32_t differing_bits = ((chars[j] & common_bits) ^ bits);
              common_bits ^= differing_bits;
              bits &= common_bits;
            }
            // If length is 2 and common bits has only one zero in it then
            // our mask and compare instruction will determine definitely
            // whether we have a match at this character position.  Otherwise
            // it can only be an approximate check.
            uint32_t one_zero = (common_bits | ~char_mask);
            if (length == 2 && ((~one_zero) & ((~one_zero) - 1)) == 0) {
              pos->determines_perfectly = true;
            }
            pos->mask = common_bits;
            pos->value = bits;
          }
        } else {
          // Don't ignore case.  Nice simple case where the mask-compare will
          // determine definitely whether we have a match at this character
          // position.
          if (c > char_mask) {
            details->set_cannot_match_from(characters_filled_in);
            pos->determines_perfectly = false;
            return;
          }
          pos->mask = char_mask;
          pos->value = c;
          pos->determines_perfectly = true;
        }
        characters_filled_in++;
        DCHECK(characters_filled_in <= details->characters());
        if (characters_filled_in == details->characters()) {
          return;
        }
      }
    } else {
      QuickCheckDetails::Position* pos =
          details->positions(characters_filled_in);
      RegExpClassRanges* tree = elm.class_ranges();
      ZoneList<CharacterRange>* ranges = tree->ranges(zone());
      if (tree->is_negated() || ranges->is_empty()) {
        // A quick check uses multi-character mask and compare.  There is no
        // useful way to incorporate a negative char class into this scheme
        // so we just conservatively create a mask and value that will always
        // succeed.
        // Likewise for empty ranges (empty ranges can occur e.g. when
        // compiling for one-byte subjects and impossible (non-one-byte) ranges
        // have been removed).
        pos->mask = 0;
        pos->value = 0;
      } else {
        int first_range = 0;
        while (ranges->at(first_range).from() > char_mask) {
          first_range++;
          if (first_range == ranges->length()) {
            details->set_cannot_match_from(characters_filled_in);
            pos->determines_perfectly = false;
            return;
          }
        }
        CharacterRange range = ranges->at(first_range);
        const uint32_t first_from = range.from();
        const uint32_t first_to =
            (range.to() > char_mask) ? char_mask : range.to();
        const uint32_t differing_bits = (first_from ^ first_to);
        // A mask and compare is only perfect if the differing bits form a
        // number like 00011111 with one single block of trailing 1s.
        if ((differing_bits & (differing_bits + 1)) == 0 &&
            first_from + differing_bits == first_to) {
          pos->determines_perfectly = true;
        }
        uint32_t common_bits = ~SmearBitsRight(differing_bits);
        uint32_t bits = (first_from & common_bits);
        for (int i = first_range + 1; i < ranges->length(); i++) {
          range = ranges->at(i);
          const uint32_t from = range.from();
          if (from > char_mask) continue;
          const uint32_t to = (range.to() > char_mask) ? char_mask : range.to();
          // Here we are combining more ranges into the mask and compare
          // value.  With each new range the mask becomes more sparse and
          // so the chances of a false positive rise.  A character class
          // with multiple ranges is assumed never to be equivalent to a
          // mask and compare operation.
          pos->determines_perfectly = false;
          uint32_t new_common_bits = (from ^ to);
          new_common_bits = ~SmearBitsRight(new_common_bits);
          common_bits &= new_common_bits;
          bits &= new_common_bits;
          uint32_t new_differing_bits = (from & common_bits) ^ bits;
          common_bits ^= new_differing_bits;
          bits &= common_bits;
        }
        pos->mask = common_bits;
        pos->value = bits;
      }
      characters_filled_in++;
      DCHECK(characters_filled_in <= details->characters());
      if (characters_filled_in == details->characters()) return;
    }
  }
  DCHECK(characters_filled_in != details->characters());
  if (!details->cannot_match()) {
    on_success()->GetQuickCheckDetails(details, compiler, characters_filled_in,
                                       true, budget - 1);
  }
}

void QuickCheckDetails::Clear() {
  for (int i = 0; i < characters_; i++) {
    positions_[i].Clear();
  }
  characters_ = 0;
}

void QuickCheckDetails::Advance(int by, bool one_byte) {
  if (by >= characters_ || by < 0) {
    DCHECK_IMPLIES(by < 0, characters_ == 0);
    Clear();
    return;
  }
  DCHECK_LE(characters_ - by, 4);
  DCHECK_LE(characters_, 4);
  for (int i = 0; i < characters_ - by; i++) {
    positions_[i] = positions_[by + i];
  }
  for (int i = characters_ - by; i < characters_; i++) {
    positions_[i].Clear();
  }
  characters_ -= by;
  // We could change mask_ and value_ here but we would never advance unless
  // they had already been used in a check and they won't be used again because
  // it would gain us nothing.  So there's no point.
}

void QuickCheckDetails::Merge(QuickCheckDetails* other, int from_index) {
  DCHECK(characters_ == other->characters_);
  for (int i = from_index; i < characters_; i++) {
    QuickCheckDetails::Position* pos = positions(i);
    QuickCheckDetails::Position* other_pos = other->positions(i);
    if (pos->cannot_match) {
      *pos = *other_pos;
    } else if (!other_pos->cannot_match) {
      if (pos->mask != other_pos->mask || pos->value != other_pos->value ||
          !other_pos->determines_perfectly) {
        // Our mask-compare operation will be approximate unless we have the
        // exact same operation on both sides of the alternation.
        pos->determines_perfectly = false;
      }
      pos->mask &= other_pos->mask;
      pos->value &= pos->mask;
      other_pos->value &= pos->mask;
      uint32_t differing_bits = (pos->value ^ other_pos->value);
      pos->mask &= ~differing_bits;
      pos->value &= pos->mask;
    }
  }
}

class VisitMarker {
 public:
  explicit VisitMarker(NodeInfo* info) : info_(info) {
    DCHECK(!info->visited);
    info->visited = true;
  }
  ~VisitMarker() { info_->visited = false; }

 private:
  NodeInfo* info_;
};

// We need to check for the following characters: 0x39C 0x3BC 0x178.
bool RangeContainsLatin1Equivalents(CharacterRange range) {
  // TODO(dcarney): this could be a lot more efficient.
  return range.Contains(0x039C) || range.Contains(0x03BC) ||
         range.Contains(0x0178);
}

namespace {

bool RangesContainLatin1Equivalents(ZoneList<CharacterRange>* ranges) {
  for (int i = 0; i < ranges->length(); i++) {
    // TODO(dcarney): this could be a lot more efficient.
    if (RangeContainsLatin1Equivalents(ranges->at(i))) return true;
  }
  return false;
}

}  // namespace

bool TextNode::CanMatchLatin1(RegExpCompiler* compiler) {
  RegExpFlags flags = compiler->flags();
  int element_count = elements()->length();
  for (int i = 0; i < element_count; i++) {
    TextElement elm = elements()->at(i);
    if (elm.text_type() == TextElement::ATOM) {
      base::Vector<const uint16_t> quarks = elm.atom()->data();
      for (int j = 0; j < quarks.length(); j++) {
        uint16_t c = quarks[j];
        if (!IsIgnoreCase(flags)) {
          if (c > String::kMaxOneByteCharCode) return false;
        } else {
          unibrow::uchar chars[4];
          int length = GetCaseIndependentLetters(compiler->isolate(), c,
                                                 compiler, chars, 4);
          if (length == 0 || chars[0] > String::kMaxOneByteCharCode) {
            return false;
          }
        }
      }
    } else {
      // A character class can also be impossible to match in one-byte mode.
      DCHECK(elm.text_type() == TextElement::CLASS_RANGES);
      RegExpClassRanges* cr = elm.class_ranges();
      ZoneList<CharacterRange>* ranges = cr->ranges(zone());
      CharacterRange::Canonicalize(ranges);
      // Now they are in order so we only need to look at the first.
      // If we are in non-Unicode case independent mode then we need
      // to be a bit careful here, because the character classes have
      // not been case-desugared yet, but there are characters and ranges
      // that can become Latin-1 when case is considered.
      int range_count = ranges->length();
      if (cr->is_negated()) {
        if (range_count != 0 && ranges->at(0).from() == 0 &&
            ranges->at(0).to() >= String::kMaxOneByteCharCode) {
          bool case_complications = !IsEitherUnicode(flags) &&
                                    IsIgnoreCase(flags) &&
                                    RangesContainLatin1Equivalents(ranges);
          if (!case_complications) {
            return false;
          }
        }
      } else {
        if (range_count == 0 ||
            ranges->at(0).from() > String::kMaxOneByteCharCode) {
          bool case_complications = !IsEitherUnicode(flags) &&
                                    IsIgnoreCase(flags) &&
                                    RangesContainLatin1Equivalents(ranges);
          if (!case_complications) {
            return false;
          }
        }
      }
    }
  }
  return true;  // It might match Latin1 input, we can't eliminate this node.
}

void LoopChoiceNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                          RegExpCompiler* compiler,
                                          int characters_filled_in,
                                          bool not_at_start,
                                          int budget) {
  if (body_can_be_zero_length_ || budget <= 0) return;
  not_at_start = not_at_start || this->not_at_start();
  DCHECK_EQ(alternatives_->length(), 2);  // There's just loop and continue.
  ChoiceNode::GetQuickCheckDetails(details, compiler, characters_filled_in,
                                   not_at_start, budget);
}

void LoopChoiceNode::FillInBMInfo(Isolate* isolate,
                                  int offset,
                                  int budget,
                                  BoyerMooreLookahead* bm,
                                  bool not_at_start) {
  if (body_can_be_zero_length_ || budget <= 0) {
    bm->SetRest(offset);
    SaveBMInfo(bm, not_at_start, offset);
    return;
  }
  ChoiceNode::FillInBMInfo(isolate, offset, budget - 1, bm, not_at_start);
  SaveBMInfo(bm, not_at_start, offset);
}

void ChoiceNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                      RegExpCompiler* compiler,
                                      int characters_filled_in,
                                      bool not_at_start,
                                      int budget) {
  not_at_start = (not_at_start || not_at_start_);
  int choice_count = alternatives_->length();
  DCHECK_LT(0, choice_count);
  budget /= choice_count;
  alternatives_->at(0).node()->GetQuickCheckDetails(
      details, compiler, characters_filled_in, not_at_start, budget);
  for (int i = 1; i < choice_count; i++) {
    QuickCheckDetails new_details(details->characters());
    RegExpNode* node = alternatives_->at(i).node();
    node->GetQuickCheckDetails(&new_details, compiler, characters_filled_in,
                               not_at_start, budget);
    // Here we merge the quick match details of the two branches.
    details->Merge(&new_details, characters_filled_in);
  }
}

namespace {

// Check for [0-9A-Z_a-z].
void EmitWordCheck(RegExpMacroAssembler* assembler,
                   V8Label* word,
                   V8Label* non_word,
                   bool fall_through_on_word) {
  StandardCharacterSet character_set = fall_through_on_word
                                           ? StandardCharacterSet::kWord
                                           : StandardCharacterSet::kNotWord;
  // \w and \W is supported on all platforms.
  DCHECK(assembler->CanOptimizeSpecialClassRanges(character_set));
  assembler->CheckSpecialClassRanges(character_set,
                                     fall_through_on_word ? non_word : word);
}

// Emit the code to check for a ^ in multiline mode (1-character lookbehind
// that matches newline or the start of input).
EmitResult EmitHat(RegExpCompiler* compiler,
                   RegExpNode* on_success,
                   Trace* trace) {
  RegExpMacroAssembler* assembler = compiler->macro_assembler();

  // We will load the previous character into the current character register.
  Trace new_trace(*trace);
  new_trace.InvalidateCurrentCharacter();

  // A positive (> 0) cp_offset means we've already successfully matched a
  // non-empty-width part of the pattern, and thus cannot be at or before the
  // start of the subject string. We can thus skip both at-start and
  // bounds-checks when loading the one-character lookbehind.
  const bool may_be_at_or_before_subject_string_start =
      new_trace.cp_offset() <= 0;

  V8Label ok;
  if (may_be_at_or_before_subject_string_start) {
    // The start of input counts as a newline in this context, so skip to ok if
    // we are at the start.
    assembler->CheckAtStart(new_trace.cp_offset(), &ok);
  }

  // If we've already checked that we are not at the start of input, it's okay
  // to load the previous character without bounds checks.
  const bool can_skip_bounds_check = !may_be_at_or_before_subject_string_start;
  assembler->LoadCurrentCharacter(new_trace.cp_offset() - 1,
                                  new_trace.backtrack(), can_skip_bounds_check);
  // Line Terminator is supported on all platforms.
  DCHECK(assembler->CanOptimizeSpecialClassRanges(
      StandardCharacterSet::kLineTerminator));
  assembler->CheckSpecialClassRanges(StandardCharacterSet::kLineTerminator,
                                     new_trace.backtrack());
  assembler->Bind(&ok);
  return on_success->Emit(compiler, &new_trace);
}

}  // namespace

// Emit the code to handle \b and \B (word-boundary or non-word-boundary).
EmitResult AssertionNode::EmitBoundaryCheck(RegExpCompiler* compiler,
                                            Trace* trace) {
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  Isolate* isolate = assembler->isolate();
  Trace::TriBool next_is_word_character = Trace::UNKNOWN;
  bool not_at_start = (trace->at_start() == Trace::FALSE_VALUE);
  BoyerMooreLookahead* lookahead = bm_info(not_at_start);
  if (lookahead == nullptr) {
    int eats_at_least =
        std::min(kMaxLookaheadForBoyerMoore, EatsAtLeast(not_at_start));
    if (eats_at_least >= 1) {
      BoyerMooreLookahead* bm =
          zone()->New<BoyerMooreLookahead>(eats_at_least, compiler, zone());
      FillInBMInfo(isolate, 0, kRecursionBudget, bm, not_at_start);
      if (bm->at(0)->is_non_word()) next_is_word_character = Trace::FALSE_VALUE;
      if (bm->at(0)->is_word()) next_is_word_character = Trace::TRUE_VALUE;
    }
  } else {
    if (lookahead->at(0)->is_non_word())
      next_is_word_character = Trace::FALSE_VALUE;
    if (lookahead->at(0)->is_word()) next_is_word_character = Trace::TRUE_VALUE;
  }
  bool at_boundary = (assertion_type_ == AssertionNode::AT_BOUNDARY);
  if (next_is_word_character == Trace::UNKNOWN) {
    V8Label before_non_word;
    V8Label before_word;
    if (trace->characters_preloaded() != 1) {
      assembler->LoadCurrentCharacter(trace->cp_offset(), &before_non_word);
    }
    // Fall through on non-word.
    EmitWordCheck(assembler, &before_word, &before_non_word, false);
    // Next character is not a word character.
    assembler->Bind(&before_non_word);
    V8Label ok;
    RETURN_IF_ERROR(BacktrackIfPrevious(compiler, trace,
                                        at_boundary ? kIsNonWord : kIsWord));
    assembler->GoTo(&ok);

    assembler->Bind(&before_word);
    RETURN_IF_ERROR(BacktrackIfPrevious(compiler, trace,
                                        at_boundary ? kIsWord : kIsNonWord));
    assembler->Bind(&ok);
  } else if (next_is_word_character == Trace::TRUE_VALUE) {
    RETURN_IF_ERROR(BacktrackIfPrevious(compiler, trace,
                                        at_boundary ? kIsWord : kIsNonWord));
  } else {
    DCHECK(next_is_word_character == Trace::FALSE_VALUE);
    RETURN_IF_ERROR(BacktrackIfPrevious(compiler, trace,
                                        at_boundary ? kIsNonWord : kIsWord));
  }
  return EmitResult::Success();
}

EmitResult AssertionNode::BacktrackIfPrevious(
    RegExpCompiler* compiler,
    Trace* trace,
    AssertionNode::IfPrevious backtrack_if_previous) {
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  Trace new_trace(*trace);
  new_trace.InvalidateCurrentCharacter();

  V8Label fall_through;
  V8Label* non_word = backtrack_if_previous == kIsNonWord
                          ? new_trace.backtrack()
                          : &fall_through;
  V8Label* word = backtrack_if_previous == kIsNonWord ? &fall_through
                                                      : new_trace.backtrack();

  // A positive (> 0) cp_offset means we've already successfully matched a
  // non-empty-width part of the pattern, and thus cannot be at or before the
  // start of the subject string. We can thus skip both at-start and
  // bounds-checks when loading the one-character lookbehind.
  const bool may_be_at_or_before_subject_string_start =
      new_trace.cp_offset() <= 0;

  if (may_be_at_or_before_subject_string_start) {
    // The start of input counts as a non-word character, so the question is
    // decided if we are at the start.
    assembler->CheckAtStart(new_trace.cp_offset(), non_word);
  }

  // If we've already checked that we are not at the start of input, it's okay
  // to load the previous character without bounds checks.
  const bool can_skip_bounds_check = !may_be_at_or_before_subject_string_start;
  static_assert(Trace::kCPOffsetSlack == 1);
  assembler->LoadCurrentCharacter(new_trace.cp_offset() - 1, non_word,
                                  can_skip_bounds_check);
  EmitWordCheck(assembler, word, non_word, backtrack_if_previous == kIsNonWord);

  assembler->Bind(&fall_through);
  return on_success()->Emit(compiler, &new_trace);
}

void AssertionNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                         RegExpCompiler* compiler,
                                         int filled_in,
                                         bool not_at_start,
                                         int budget) {
  if (assertion_type_ == AT_START && not_at_start) {
    details->set_cannot_match_from(filled_in);
    return;
  }
  if (assertion_type_ == AT_END) {
    details->set_cannot_match_from(filled_in);
    return;
  }
  return on_success()->GetQuickCheckDetails(details, compiler, filled_in,
                                            not_at_start, budget - 1);
}

void EndNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                   RegExpCompiler* compiler,
                                   int characters_filled_in,
                                   bool not_at_start,
                                   int budget) {
  details->set_cannot_match_from(characters_filled_in);
}

EmitResult AssertionNode::Emit(RegExpCompiler* compiler, Trace* trace) {
  TRACE_EMIT("AssertionNode");
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  switch (assertion_type_) {
    case AT_END: {
      V8Label ok;
      assembler->CheckPosition(trace->cp_offset(), &ok);
      assembler->GoTo(trace->backtrack());
      assembler->Bind(&ok);
      break;
    }
    case AT_START: {
      if (trace->at_start() == Trace::FALSE_VALUE) {
        assembler->GoTo(trace->backtrack());
        return EmitResult::Success();
      }
      if (trace->at_start() == Trace::UNKNOWN) {
        assembler->CheckNotAtStart(trace->cp_offset(), trace->backtrack());
        Trace at_start_trace = *trace;
        at_start_trace.set_at_start(Trace::TRUE_VALUE);
        return on_success()->Emit(compiler, &at_start_trace);
      }
    } break;
    case AFTER_NEWLINE:
      return EmitHat(compiler, on_success(), trace);
    case AT_BOUNDARY:
    case AT_NON_BOUNDARY: {
      return EmitBoundaryCheck(compiler, trace);
    }
  }
  return on_success()->Emit(compiler, trace);
}

namespace {

bool DeterminedAlready(const QuickCheckDetails* quick_check, int offset) {
  if (quick_check == nullptr) return false;
  if (offset >= quick_check->characters()) return false;
  return quick_check->positions(offset)->determines_perfectly;
}

void UpdateBoundsCheck(int index, int* checked_up_to) {
  if (index > *checked_up_to) {
    *checked_up_to = index;
  }
}

}  // namespace

// We call this repeatedly to generate code for each pass over the text node.
// The passes are in increasing order of difficulty because we hope one
// of the first passes will fail in which case we are saved the work of the
// later passes.  for example for the case independent regexp /%[asdfghjkl]a/
// we will check the '%' in the first pass, the case independent 'a' in the
// second pass and the character class in the last pass.
//
// The passes are done from right to left, so for example to test for /bar/
// we will first test for an 'r' with offset 2, then an 'a' with offset 1
// and then a 'b' with offset 0.  This means we can avoid the end-of-input
// bounds check most of the time.  In the example we only need to check for
// end-of-input when loading the putative 'r'.
//
// A slight complication involves the fact that the first character may already
// be fetched into a register by the previous node.  In this case we want to
// do the test for that character first.  We do this in separate passes.  The
// 'preloaded' argument indicates that we are doing such a 'pass'.  If such a
// pass has been performed then subsequent passes will have true in
// first_element_checked to indicate that that character does not need to be
// checked again.
//
// In addition to all this we are passed a Trace, which can
// contain an AlternativeGeneration object.  In this AlternativeGeneration
// object we can see details of any quick check that was already passed in
// order to get to the code we are now generating.  The quick check can involve
// loading characters, which means we do not need to recheck the bounds
// up to the limit the quick check already checked.  In addition the quick
// check can have involved a mask and compare operation which may simplify
// or obviate the need for further checks at some character positions.
void TextNode::TextEmitPass(RegExpCompiler* compiler,
                            TextEmitPassType pass,
                            bool preloaded,
                            Trace* trace,
                            bool first_element_checked,
                            int* checked_up_to) {
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  Isolate* isolate = assembler->isolate();
  bool one_byte = compiler->one_byte();
  V8Label* backtrack = trace->backtrack();
  const QuickCheckDetails* quick_check = trace->quick_check_performed();
  int element_count = elements()->length();
  int backward_offset = read_backward() ? -Length() : 0;
  for (int i = preloaded ? 0 : element_count - 1; i >= 0; i--) {
    TextElement elm = elements()->at(i);
    int cp_offset = trace->cp_offset() + elm.cp_offset() + backward_offset;
    if (elm.text_type() == TextElement::ATOM) {
      base::Vector<const uint16_t> quarks = elm.atom()->data();
      for (int j = preloaded ? 0 : quarks.length() - 1; j >= 0; j--) {
        if (first_element_checked && i == 0 && j == 0) continue;
        if (DeterminedAlready(quick_check, elm.cp_offset() + j)) continue;
        uint16_t quark = quarks[j];
        bool needs_bounds_check =
            *checked_up_to < cp_offset + j || read_backward();
        bool bounds_checked = false;
        switch (pass) {
          case NON_LATIN1_MATCH: {
            DCHECK(one_byte);  // This pass is only done in one-byte mode.
            if (IsIgnoreCase(compiler->flags())) {
              // We are compiling for a one-byte subject, case independent mode.
              // We have to check whether any of the case alternatives are in
              // the one-byte range.
              unibrow::uchar chars[4];
              // Only returns characters that are in the one-byte range.
              int length =
                  GetCaseIndependentLetters(isolate, quark, compiler, chars, 4);
              if (length == 0) {
                assembler->GoTo(backtrack);
                return;
              }
            } else {
              // Case-dependent mode.
              if (quark > String::kMaxOneByteCharCode) {
                assembler->GoTo(backtrack);
                return;
              }
            }
            break;
          }
          case NON_LETTER_CHARACTER_MATCH:
            bounds_checked =
                EmitAtomNonLetter(isolate, compiler, quark, backtrack,
                                  cp_offset + j, needs_bounds_check, preloaded);
            break;
          case SIMPLE_CHARACTER_MATCH:
            bounds_checked = EmitSimpleCharacter(isolate, compiler, quark,
                                                 backtrack, cp_offset + j,
                                                 needs_bounds_check, preloaded);
            break;
          case CASE_CHARACTER_MATCH:
            bounds_checked =
                EmitAtomLetter(isolate, compiler, quark, backtrack,
                               cp_offset + j, needs_bounds_check, preloaded);
            break;
          default:
            break;
        }
        if (bounds_checked) UpdateBoundsCheck(cp_offset + j, checked_up_to);
      }
    } else {
      DCHECK_EQ(TextElement::CLASS_RANGES, elm.text_type());
      if (pass == CHARACTER_CLASS_MATCH) {
        if (first_element_checked && i == 0) continue;
        if (DeterminedAlready(quick_check, elm.cp_offset())) continue;
        RegExpClassRanges* cr = elm.class_ranges();
        bool bounds_check = *checked_up_to < cp_offset || read_backward();
        EmitClassRanges(assembler, cr, one_byte, backtrack, cp_offset,
                        bounds_check, preloaded, zone());
        UpdateBoundsCheck(cp_offset, checked_up_to);
      }
    }
  }
}

int TextNode::Length() {
  TextElement elm = elements()->last();
  DCHECK_LE(0, elm.cp_offset());
  return elm.cp_offset() + elm.length();
}

TextNode* TextNode::CreateForCharacterRanges(Zone* zone,
                                             ZoneList<CharacterRange>* ranges,
                                             bool read_backward,
                                             RegExpNode* on_success) {
  DCHECK_NOT_NULL(ranges);
  // TODO(jgruber): There's no fundamental need to create this
  // RegExpClassRanges; we could refactor to avoid the allocation.
  return zone->New<TextNode>(zone->New<RegExpClassRanges>(zone, ranges),
                             read_backward, on_success);
}

TextNode* TextNode::CreateForSurrogatePair(
    Zone* zone,
    CharacterRange lead,
    ZoneList<CharacterRange>* trail_ranges,
    bool read_backward,
    RegExpNode* on_success) {
  ZoneList<TextElement>* elms = zone->New<ZoneList<TextElement>>(2, zone);
  if (lead.from() == lead.to()) {
    ZoneList<uint16_t> lead_surrogate(1, zone);
    lead_surrogate.Add(lead.from(), zone);
    RegExpAtom* atom = zone->New<RegExpAtom>(lead_surrogate.ToConstVector());
    elms->Add(TextElement::Atom(atom), zone);
  } else {
    ZoneList<CharacterRange>* lead_ranges = CharacterRange::List(zone, lead);
    elms->Add(TextElement::ClassRanges(
                  zone->New<RegExpClassRanges>(zone, lead_ranges)),
              zone);
  }
  elms->Add(TextElement::ClassRanges(
                zone->New<RegExpClassRanges>(zone, trail_ranges)),
            zone);
  return zone->New<TextNode>(elms, read_backward, on_success);
}

TextNode* TextNode::CreateForSurrogatePair(
    Zone* zone,
    ZoneList<CharacterRange>* lead_ranges,
    CharacterRange trail,
    bool read_backward,
    RegExpNode* on_success) {
  ZoneList<CharacterRange>* trail_ranges = CharacterRange::List(zone, trail);
  ZoneList<TextElement>* elms = zone->New<ZoneList<TextElement>>(2, zone);
  elms->Add(
      TextElement::ClassRanges(zone->New<RegExpClassRanges>(zone, lead_ranges)),
      zone);
  elms->Add(TextElement::ClassRanges(
                zone->New<RegExpClassRanges>(zone, trail_ranges)),
            zone);
  return zone->New<TextNode>(elms, read_backward, on_success);
}

// This generates the code to match a text node.  A text node can contain
// straight character sequences (possibly to be matched in a case-independent
// way) and character classes.  For efficiency we do not do this in a single
// pass from left to right.  Instead we pass over the text node several times,
// emitting code for some character positions every time.  See the comment on
// TextEmitPass for details.
EmitResult TextNode::Emit(RegExpCompiler* compiler, Trace* trace) {
  TRACE_EMIT("TextNode");
  LimitResult limit_result = LimitVersions(compiler, trace);
  if (limit_result == DONE) return EmitResult::Success();
  DCHECK(limit_result == CONTINUE);

  if (trace->cp_offset() + Length() > RegExpMacroAssembler::kMaxCPOffset) {
    compiler->SetRegExpTooBig();
    return EmitResult::Error();
  }

#ifdef V8_ENABLE_REGEXP_DIAGNOSTICS
  if (UNLIKELY(v8_flags.trace_regexp_compiler)) {
    const QuickCheckDetails* quick_check = trace->quick_check_performed();
    if (quick_check != nullptr) {
      for (int i = 0; i < quick_check->characters(); ++i) {
        if (quick_check->positions(i)->determines_perfectly) {
          TRACE("  Character at position "
                << i << " already determined by QuickCheck");
        }
      }
    }
  }
#endif

  if (compiler->one_byte()) {
    int dummy = 0;
    TextEmitPass(compiler, NON_LATIN1_MATCH, false, trace, false, &dummy);
  }

  bool first_elt_done = false;
  static_assert(Trace::kCPOffsetSlack == 1);
  int bound_checked_to = trace->cp_offset() - 1;
  bound_checked_to += trace->bound_checked_up_to();

  // If a character is preloaded into the current character register then
  // check that first to save reloading it.
  for (int twice = 0; twice < 2; twice++) {
    bool is_preloaded_pass = twice == 0;
    if (is_preloaded_pass && trace->characters_preloaded() != 1) continue;
    if (IsIgnoreCase(compiler->flags())) {
      TextEmitPass(compiler, NON_LETTER_CHARACTER_MATCH, is_preloaded_pass,
                   trace, first_elt_done, &bound_checked_to);
      TextEmitPass(compiler, CASE_CHARACTER_MATCH, is_preloaded_pass, trace,
                   first_elt_done, &bound_checked_to);
    } else {
      TextEmitPass(compiler, SIMPLE_CHARACTER_MATCH, is_preloaded_pass, trace,
                   first_elt_done, &bound_checked_to);
    }
    TextEmitPass(compiler, CHARACTER_CLASS_MATCH, is_preloaded_pass, trace,
                 first_elt_done, &bound_checked_to);
    first_elt_done = true;
  }

  Trace successor_trace(*trace);
  // If we advance backward, we may end up at the start.
  RETURN_IF_ERROR(successor_trace.AdvanceCurrentPositionInTrace(
      read_backward() ? -Length() : Length(), compiler));
  successor_trace.set_at_start(read_backward() ? Trace::UNKNOWN
                                               : Trace::FALSE_VALUE);
  RecursionCheck rc(compiler);
  return on_success()->Emit(compiler, &successor_trace);
}

void Trace::InvalidateCurrentCharacter() {
  characters_preloaded_ = 0;
}

EmitResult Trace::AdvanceCurrentPositionInTrace(int by,
                                                RegExpCompiler* compiler) {
  // We don't have an instruction for shifting the current character register
  // down or for using a shifted value for anything so lets just forget that
  // we preloaded any characters into it.
  characters_preloaded_ = 0;
  // Adjust the offsets of the quick check performed information.  This
  // information is used to find out what we already determined about the
  // characters by means of mask and compare.
  quick_check_performed_.Advance(by, compiler->one_byte());
  cp_offset_ += by;
  bound_checked_up_to_ = std::max(0, bound_checked_up_to_ - by);
  static_assert(RegExpMacroAssembler::kMaxCPOffset ==
                -RegExpMacroAssembler::kMinCPOffset);
  if (std::abs(cp_offset_) + kCPOffsetSlack >
      RegExpMacroAssembler::kMaxCPOffset) {
    compiler->SetRegExpTooBig();
    cp_offset_ = 0;
    return EmitResult::Error();
  }
  return EmitResult::Success();
}

void TextNode::MakeCaseIndependent(Isolate* isolate,
                                   bool is_one_byte,
                                   RegExpFlags flags) {
  if (!IsIgnoreCase(flags)) return;
#ifdef V8_INTL_SUPPORT
  // This is done in an earlier step when generating the nodes from the AST
  // because we may have to split up into separate nodes.
  if (NeedsUnicodeCaseEquivalents(flags)) return;
#endif

  int element_count = elements()->length();
  for (int i = 0; i < element_count; i++) {
    TextElement elm = elements()->at(i);
    if (elm.text_type() == TextElement::CLASS_RANGES) {
      RegExpClassRanges* cr = elm.class_ranges();
      // None of the standard character classes is different in the case
      // independent case and it slows us down if we don't know that.
      if (cr->is_standard(zone())) continue;
      ZoneList<CharacterRange>* ranges = cr->ranges(zone());
      CharacterRange::AddCaseEquivalents(isolate, zone(), ranges, is_one_byte);
    }
  }
}

int TextNode::FixedLengthLoopLength() {
  return Length();
}

RegExpNode* TextNode::GetSuccessorOfOmnivorousTextNode(
    RegExpCompiler* compiler) {
  if (read_backward()) return nullptr;
  if (elements()->length() != 1) return nullptr;
  TextElement elm = elements()->at(0);
  if (elm.text_type() != TextElement::CLASS_RANGES) return nullptr;
  RegExpClassRanges* node = elm.class_ranges();
  ZoneList<CharacterRange>* ranges = node->ranges(zone());
  CharacterRange::Canonicalize(ranges);
  if (node->is_negated()) {
    return ranges->length() == 0 ? on_success() : nullptr;
  }
  if (ranges->length() != 1) return nullptr;
  const uint32_t max_char = MaxCodeUnit(compiler->one_byte());
  return ranges->at(0).IsEverything(max_char) ? on_success() : nullptr;
}

// Finds the fixed match length of a sequence of nodes that goes from
// this alternative and back to this choice node.  If there are variable
// length nodes or other complications in the way then return a sentinel
// value indicating that a fixed length loop cannot be constructed.
int ChoiceNode::FixedLengthLoopLengthForAlternative(
    GuardedAlternative* alternative) {
  int length = 0;
  RegExpNode* node = alternative->node();
  // Later we will generate code for all these text nodes using recursion
  // so we have to limit the max number.
  int recursion_depth = 0;
  while (node != this) {
    if (recursion_depth++ > RegExpCompiler::kMaxRecursion) {
      return kNodeIsTooComplexForFixedLengthLoops;
    }
    int node_length = node->FixedLengthLoopLength();
    if (node_length == kNodeIsTooComplexForFixedLengthLoops) {
      return kNodeIsTooComplexForFixedLengthLoops;
    }
    length += node_length;
    node = node->AsSeqRegExpNode()->on_success();
  }
  if (read_backward()) {
    length = -length;
  }
  // Check that we can jump by the whole text length. If not, return sentinel
  // to indicate the we can't construct a fixed length loop.
  if (length < RegExpMacroAssembler::kMinCPOffset ||
      length > RegExpMacroAssembler::kMaxCPOffset) {
    return kNodeIsTooComplexForFixedLengthLoops;
  }
  return length;
}

void LoopChoiceNode::AddLoopAlternative(GuardedAlternative alt) {
  DCHECK_NULL(loop_node_);
  AddAlternative(alt);
  loop_node_ = alt.node();
}

void LoopChoiceNode::AddContinueAlternative(GuardedAlternative alt) {
  DCHECK_NULL(continue_node_);
  AddAlternative(alt);
  continue_node_ = alt.node();
}

EmitResult LoopChoiceNode::Emit(RegExpCompiler* compiler, Trace* trace) {
  TRACE_EMIT("LoopChoice");
  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  if (trace->special_loop_state() != nullptr &&
      trace->special_loop_state()->loop_choice_node() == this) {
    // Back edge of fixed length optimized loop node graph.
    int text_length =
        FixedLengthLoopLengthForAlternative(&(alternatives_->at(0)));
    DCHECK_NE(kNodeIsTooComplexForFixedLengthLoops, text_length);
    // Update the counter-based backtracking info on the stack.  This is an
    // optimization for fixed length loops (see below).
    DCHECK(trace->cp_offset() == text_length);
    macro_assembler->AdvanceCurrentPosition(text_length);
    trace->special_loop_state()->GoToLoopTopLabel(macro_assembler);
    return EmitResult::Success();
  }
  DCHECK_NULL(trace->special_loop_state());
  if (!trace->is_trivial()) {
    return trace->Flush(compiler, this);
  }
  return ChoiceNode::Emit(compiler, trace);
}

int ChoiceNode::CalculatePreloadCharacters(RegExpCompiler* compiler,
                                           int eats_at_least) {
  int preload_characters = std::min(4, eats_at_least);
  DCHECK_LE(preload_characters, 4);
  if (compiler->macro_assembler()->CanReadUnaligned()) {
    bool one_byte = compiler->one_byte();
    if (one_byte) {
      // We can't preload 3 characters because there is no machine instruction
      // to do that.  We can't just load 4 because we could be reading
      // beyond the end of the string, which could cause a memory fault.
      if (preload_characters == 3) preload_characters = 2;
    } else {
      if (preload_characters > 2) preload_characters = 2;
    }
  } else {
    if (preload_characters > 1) preload_characters = 1;
  }
  return preload_characters;
}

// This class is used when generating the alternatives in a choice node.  It
// records the way the alternative is being code generated.
class AlternativeGeneration /*: public Malloced*/ {
 public:
  AlternativeGeneration()
      : possible_success(),
        expects_preload(false),
        after(),
        quick_check_details() {}
  V8Label possible_success;
  bool expects_preload;
  V8Label after;
  QuickCheckDetails quick_check_details;
};

// Creates a list of AlternativeGenerations.  If the list has a reasonable
// size then it is on the stack, otherwise the excess is on the heap.
class AlternativeGenerationList {
 public:
  AlternativeGenerationList(int count, Zone* zone) : alt_gens_(count, zone) {
    for (int i = 0; i < count && i < kAFew; i++) {
      alt_gens_.Add(a_few_alt_gens_ + i, zone);
    }
    for (int i = kAFew; i < count; i++) {
      alt_gens_.Add(new AlternativeGeneration(), zone);
    }
  }
  ~AlternativeGenerationList() {
    for (int i = kAFew; i < alt_gens_.length(); i++) {
      delete alt_gens_[i];
      alt_gens_[i] = nullptr;
    }
  }

  AlternativeGeneration* at(int i) { return alt_gens_[i]; }

 private:
  static const int kAFew = 10;
  ZoneList<AlternativeGeneration*> alt_gens_;
  AlternativeGeneration a_few_alt_gens_[kAFew];
};

void BoyerMoorePositionInfo::Set(int character) {
  SetInterval(Interval(character, character));
}

namespace {

ContainedInLattice AddRange(ContainedInLattice containment,
                            const int* ranges,
                            int ranges_length,
                            Interval new_range) {
  DCHECK_EQ(1, ranges_length & 1);
  DCHECK_EQ(String::kMaxCodePoint + 1, ranges[ranges_length - 1]);
  if (containment == kLatticeUnknown) return containment;
  bool inside = false;
  int last = 0;
  for (int i = 0; i < ranges_length; inside = !inside, last = ranges[i], i++) {
    // Consider the range from last to ranges[i].
    // We haven't got to the new range yet.
    if (ranges[i] <= new_range.from()) continue;
    // New range is wholly inside last-ranges[i].  Note that new_range.to() is
    // inclusive, but the values in ranges are not.
    if (last <= new_range.from() && new_range.to() < ranges[i]) {
      return Combine(containment, inside ? kLatticeIn : kLatticeOut);
    }
    return kLatticeUnknown;
  }
  return containment;
}

int BitsetFirstSetBit(BoyerMoorePositionInfo::Bitset bitset) {
  static_assert(BoyerMoorePositionInfo::kMapSize ==
                2 * kInt64Size * kBitsPerByte);

  // Slight fiddling is needed here, since the bitset is of length 128 while
  // CountTrailingZeros requires an integral type and std::bitset can only
  // convert to unsigned long long. So we handle the most- and least-significant
  // bits separately.

  {
    static constexpr BoyerMoorePositionInfo::Bitset mask(~uint64_t{0});
    BoyerMoorePositionInfo::Bitset masked_bitset = bitset & mask;
    static_assert(kInt64Size >= sizeof(decltype(masked_bitset.to_ullong())));
    uint64_t lsb = masked_bitset.to_ullong();
    if (lsb != 0) return Utils::CountTrailingZeros64(lsb);
  }

  {
    BoyerMoorePositionInfo::Bitset masked_bitset = bitset >> 64;
    uint64_t msb = masked_bitset.to_ullong();
    if (msb != 0) return 64 + Utils::CountTrailingZeros64(msb);
  }

  return -1;
}

}  // namespace

void BoyerMoorePositionInfo::SetInterval(const Interval& interval) {
  w_ = AddRange(w_, kWordRanges, kWordRangeCount, interval);

  if (interval.size() >= kMapSize) {
    map_count_ = kMapSize;
    map_.set();
    return;
  }

  for (int i = interval.from(); i <= interval.to(); i++) {
    int mod_character = (i & kMask);
    if (!map_[mod_character]) {
      map_count_++;
      map_.set(mod_character);
    }
    if (map_count_ == kMapSize) return;
  }
}

void BoyerMoorePositionInfo::SetAll() {
  w_ = kLatticeUnknown;
  if (map_count_ != kMapSize) {
    map_count_ = kMapSize;
    map_.set();
  }
}

BoyerMooreLookahead::BoyerMooreLookahead(int length,
                                         RegExpCompiler* compiler,
                                         Zone* zone)
    : length_(length),
      compiler_(compiler),
      max_char_(MaxCodeUnit(compiler->one_byte())) {
  bitmaps_ = zone->New<ZoneList<BoyerMoorePositionInfo*>>(length, zone);
  for (int i = 0; i < length; i++) {
    bitmaps_->Add(zone->New<BoyerMoorePositionInfo>(), zone);
  }
}

// Find the longest range of lookahead that has the fewest number of different
// characters that can occur at a given position.  Since we are optimizing two
// different parameters at once this is a tradeoff.
bool BoyerMooreLookahead::FindWorthwhileInterval(int* from, int* to) {
  int biggest_points = 0;
  // If more than 32 characters out of 128 can occur it is unlikely that we can
  // be lucky enough to step forwards much of the time.
  const int kMaxMax = 32;
  for (int max_number_of_chars = 4; max_number_of_chars < kMaxMax;
       max_number_of_chars *= 2) {
    biggest_points =
        FindBestInterval(max_number_of_chars, biggest_points, from, to);
  }
  if (biggest_points == 0) return false;
  return true;
}

// Find the highest-points range between 0 and length_ where the character
// information is not too vague.  'Too vague' means that there are more than
// max_number_of_chars that can occur at this position.  Calculates the number
// of points as the product of width-of-the-range and
// probability-of-finding-one-of-the-characters, where the probability is
// calculated using the frequency distribution of the sample subject string.
int BoyerMooreLookahead::FindBestInterval(int max_number_of_chars,
                                          int old_biggest_points,
                                          int* from,
                                          int* to) {
  int biggest_points = old_biggest_points;
  static const int kSize = RegExpMacroAssembler::kTableSize;
  for (int i = 0; i < length_;) {
    while (i < length_ && Count(i) > max_number_of_chars)
      i++;
    if (i == length_) break;
    int remembered_from = i;

    BoyerMoorePositionInfo::Bitset union_bitset;
    for (; i < length_ && Count(i) <= max_number_of_chars; i++) {
      union_bitset |= bitmaps_->at(i)->raw_bitset();
    }

    int frequency = 0;

    // Iterate only over set bits.
    int j;
    while ((j = BitsetFirstSetBit(union_bitset)) != -1) {
      DCHECK(union_bitset[j]);  // Sanity check.
      // Add 1 to the frequency to give a small per-character boost for
      // the cases where our sampling is not good enough and many
      // characters have a frequency of zero.  This means the frequency
      // can theoretically be up to 2*kSize though we treat it mostly as
      // a fraction of kSize.
      frequency += compiler_->frequency_collator()->Frequency(j) + 1;
      union_bitset.reset(j);
    }

    // We use the probability of skipping times the distance we are skipping to
    // judge the effectiveness of this.  Actually we have a cut-off:  By
    // dividing by 2 we switch off the skipping if the probability of skipping
    // is less than 50%.  This is because the multibyte mask-and-compare
    // skipping in quickcheck is more likely to do well on this case.
    bool in_quickcheck_range =
        ((i - remembered_from < 4) ||
         (compiler_->one_byte() ? remembered_from <= 4 : remembered_from <= 2));
    // Called 'probability' but it is only a rough estimate and can actually
    // be outside the 0-kSize range.
    int probability = (in_quickcheck_range ? kSize / 2 : kSize) - frequency;
    int points = (i - remembered_from) * probability;
    TRACE_COMPILER(compiler_, "  Points for "
                                  << max_number_of_chars << " chars: " << points
                                  << " (start at " << remembered_from
                                  << "; probability: " << probability << ")");
    if (points > biggest_points) {
      *from = remembered_from;
      *to = i - 1;
      biggest_points = points;
    }
  }
  return biggest_points;
}

// Take all the characters that will not prevent a successful match if they
// occur in the subject string in the range between min_lookahead and
// max_lookahead (inclusive) measured from the current position.  If the
// character at max_lookahead offset is not one of these characters, then we
// can safely skip forwards by the number of characters in the range.
// For example for the pattern /..abcd.../ our range will be 2-5 inclusive
// (four characters) and the characters [abcd] will be in the allow-
// match set.  If we find a 'z' at offset 5 we know we can't match at the
// current position or at the next three, so we can skip forwards 4 positions.
//
// nibble_table is only used for SIMD variants and encodes the same information
// as boolean_skip_table but in only 128 bits. It contains 16 bytes where the
// index into the table represent low nibbles of a character, and the stored
// byte is a bitset representing matching high nibbles. E.g. to store the
// character 'b' (0x62) in the nibble table, we set the 6th bit in row 2.  We
// use it for the case where the range is only one character wide, eg the
// regexp /..[a-d]../.  In this case finding a letter in the e-z range means
// we can move forward one but we compensate for this by processing 16
// characters at a time.
int BoyerMooreLookahead::GetSkipTable(int min_lookahead,
                                      int max_lookahead,
                                      const TypedData& boolean_skip_table,
                                      const TypedData& nibble_table) {
  const int kSkipArrayEntry = 0;
  const int kDontSkipArrayEntry = 1;

  //std::memset(boolean_skip_table->begin(), kSkipArrayEntry,
  //            boolean_skip_table->length());
  for (intptr_t i = 0, n = boolean_skip_table.Length(); i < n; i++) {
    boolean_skip_table.SetUint8(i, kSkipArrayEntry);
  }
  const bool fill_nibble_table = !nibble_table.IsNull();
  if (fill_nibble_table) {
    //std::memset(nibble_table->begin(), 0, nibble_table->length());
    for (intptr_t i = 0, n = nibble_table.Length(); i < n; i++) {
      nibble_table.SetUint8(i, 0);
    }
  }

  for (int i = max_lookahead; i >= min_lookahead; i--) {
    BoyerMoorePositionInfo::Bitset bitset = bitmaps_->at(i)->raw_bitset();

    // Iterate only over set bits.
    int j;
    while ((j = BitsetFirstSetBit(bitset)) != -1) {
      DCHECK(bitset[j]);  // Sanity check.
      boolean_skip_table.SetUint8(j, kDontSkipArrayEntry);
      if (fill_nibble_table) {
        int lo_nibble = j & 0x0f;
        int hi_nibble = (j >> 4) & 0x07;
        int row = nibble_table.GetUint8(lo_nibble);
        row |= 1 << hi_nibble;
        nibble_table.SetUint8(lo_nibble, row);
      }
      bitset.reset(j);
    }
  }

  const int skip = max_lookahead + 1 - min_lookahead;
  return skip;
}

// See comment above on the implementation of GetSkipTable.
void BoyerMooreLookahead::EmitSkipInstructions(RegExpMacroAssembler* masm) {
  const int kSize = RegExpMacroAssembler::kTableSize;

  int min_lookahead = 0;
  int max_lookahead = 0;

  if (!FindWorthwhileInterval(&min_lookahead, &max_lookahead)) {
    TRACE_COMPILER(compiler_, "  No worthwhile interval found");
    return;
  }

  // Check if we only have a single non-empty position info, and that info
  // contains only one or two characters.
  bool found_single_position = false;
  constexpr uint32_t kNoChar = 0xffffffff;
  uint32_t char_one = kNoChar;
  uint32_t char_two = kNoChar;
  bool use_simd = masm->SkipUntilBitInTableUseSimd(1);
  for (int i = min_lookahead; i <= max_lookahead; i++) {
    BoyerMoorePositionInfo* map = bitmaps_->at(i);
    if (map->map_count() == 0) {
      // If we have a position where no characters can match then we just can't
      // match.
      masm->Fail();
      return;
    }

    if (found_single_position || map->map_count() > 2) {
      // We found a second position or there were more than two characters that
      // matched at this position.
      found_single_position = false;
      break;
    }

    BoyerMoorePositionInfo::Bitset bitset = map->raw_bitset();
    char_one = BitsetFirstSetBit(bitset);
    if (map->map_count() == 2) {
      bitset.reset(char_one);
      char_two = BitsetFirstSetBit(bitset);
    } else {
      char_two = char_one;  // Everything below here works for identical chars.
    }
    DCHECK(!found_single_position);
    if (Utils::CountOneBits(char_one ^ char_two) > 1) {
      // For case independent matches we often find two characters that differ
      // only at one bit positions, but in this case they differed more.  We
      // don't have a great bytecode for two characters that are too different.
      break;
    }

    DCHECK_LE(map->map_count(), 2);

    found_single_position = true;

    DCHECK_NE(char_one, kNoChar);
    DCHECK_NE(char_two, kNoChar);
  }

  DCHECK_IMPLIES(found_single_position, max_lookahead == min_lookahead);

  if (found_single_position && max_lookahead < 3) {
    // The mask-compare can probably handle this better.
    return;
  }

  if (found_single_position && !use_simd) {
    // TODO(pthier): Add vectorized version. At that point we will want
    // to remove the ' && !use_simd' above.
    DCHECK(max_char_ > kSize);  // This means we will have to do the 'and'.

    V8Label cont;
    uint16_t mask = RegExpMacroAssembler::kTableMask;
    mask &= ~(char_one ^ char_two);  // Mask out the bit where they differ.
    masm->SkipUntilCharAnd(max_lookahead, 1, char_one & mask, mask, length(),
                           &cont, &cont);

    masm->Bind(&cont);
    return;
  }

  TypedData& boolean_skip_table = TypedData::Handle(
      TypedData::New(kTypedDataUint8ArrayCid, kSize, Heap::kOld));
  TypedData& nibble_table = TypedData::Handle();
  const int skip_distance = max_lookahead + 1 - min_lookahead;
  if (masm->SkipUntilBitInTableUseSimd(skip_distance)) {
    // The current implementation is tailored specifically for 128-bit tables.
    static_assert(kSize == 128);
    nibble_table = TypedData::New(kTypedDataUint8ArrayCid, kSize / kBitsPerByte,
                                  Heap::kOld);
  }
  GetSkipTable(min_lookahead, max_lookahead, boolean_skip_table, nibble_table);
  DCHECK_NE(0, skip_distance);

  V8Label cont;
  masm->SkipUntilBitInTable(max_lookahead, boolean_skip_table, nibble_table,
                            skip_distance, &cont, &cont);
  masm->Bind(&cont);
}

/* Code generation for choice nodes.
 *
 * We generate quick checks that do a mask and compare to eliminate a
 * choice.  If the quick check succeeds then it jumps to the continuation to
 * do slow checks and check subsequent nodes.  If it fails (the common case)
 * it falls through to the next choice.
 *
 * Here is the desired flow graph.  Nodes directly below each other imply
 * fallthrough.  Alternatives 1 and 2 have quick checks.  Alternative
 * 3 doesn't have a quick check so we have to call the slow check.
 * Nodes are marked Qn for quick checks and Sn for slow checks.  The entire
 * regexp continuation is generated directly after the Sn node, up to the
 * next GoTo if we decide to reuse some already generated code.  Some
 * nodes expect preload_characters to be preloaded into the current
 * character register.  R nodes do this preloading.  Vertices are marked
 * F for failures and S for success (possible success in the case of quick
 * nodes).  L, V, < and > are used as arrow heads.
 *
 * ----------> R
 *             |
 *             V
 *            Q1 -----> S1
 *             |   S   /
 *            F|      /
 *             |    F/
 *             |    /
 *             |   R
 *             |  /
 *             V L
 *            Q2 -----> S2
 *             |   S   /
 *            F|      /
 *             |    F/
 *             |    /
 *             |   R
 *             |  /
 *             V L
 *            S3
 *             |
 *            F|
 *             |
 *             R
 *             |
 * backtrack   V
 * <----------Q4
 *   \    F    |
 *    \        |S
 *     \   F   V
 *      \-----S4
 *
 * For fixed length loops we push the current position, then generate the code
 * that eats the input specially in EmitFixedLengthLoop.  The other choice (the
 * continuation) is generated by the normal code in EmitChoices, and steps back
 * in the input to the starting position when it fails to match.  The loop code
 * looks like this (U is the unwind code that steps back in the fixed length
 * loop).
 *
 *              _____
 *             /     \
 *             V     |
 * ----------> S1    |
 *            /|     |
 *           / |S    |
 *         F/  \_____/
 *         /
 *        |<-----
 *        |      \
 *        V       |S
 *        Q2 ---> U----->backtrack
 *        |  F   /
 *       S|     /
 *        V  F /
 *        S2--/
 */

SpecialLoopState::SpecialLoopState(bool not_at_start,
                                   ChoiceNode* loop_choice_node)
    : loop_choice_node_(loop_choice_node) {
  backtrack_trace_.set_backtrack(&step_label_);
  if (not_at_start) backtrack_trace_.set_at_start(Trace::FALSE_VALUE);
}

void SpecialLoopState::BindStepLabel(RegExpMacroAssembler* macro_assembler) {
  macro_assembler->Bind(&step_label_);
}

void SpecialLoopState::BindLoopTopLabel(RegExpMacroAssembler* macro_assembler) {
  macro_assembler->Bind(&loop_top_label_);
}

void SpecialLoopState::GoToLoopTopLabel(RegExpMacroAssembler* macro_assembler) {
  macro_assembler->GoTo(&loop_top_label_);
}

void ChoiceNode::AssertGuardsMentionRegisters(Trace* trace) {
#ifdef DEBUG
  int choice_count = alternatives_->length();
  for (int i = 0; i < choice_count - 1; i++) {
    GuardedAlternative alternative = alternatives_->at(i);
    const ZoneList<Guard*>* guards = alternative.guards();
    int guard_count = (guards == nullptr) ? 0 : guards->length();
    for (int j = 0; j < guard_count; j++) {
      DCHECK(!trace->mentions_reg(guards->at(j)->reg()));
    }
  }
#endif
}

void ChoiceNode::SetUpPreLoad(RegExpCompiler* compiler,
                              Trace* current_trace,
                              PreloadState* state) {
  if (state->eats_at_least_ == PreloadState::kEatsAtLeastNotYetInitialized) {
    // Save some time by looking at most one machine word ahead.
    state->eats_at_least_ =
        EatsAtLeast(current_trace->at_start() == Trace::FALSE_VALUE);
  }
  state->preload_characters_ =
      CalculatePreloadCharacters(compiler, state->eats_at_least_);

  state->preload_is_current_ =
      (current_trace->characters_preloaded() == state->preload_characters_);
  state->preload_has_checked_bounds_ = state->preload_is_current_;
}

EmitResult ChoiceNode::Emit(RegExpCompiler* compiler, Trace* trace) {
  TRACE_EMIT("Choice");
  int choice_count = alternatives_->length();

  if (choice_count == 1 && alternatives_->at(0).guards() == nullptr) {
    return alternatives_->at(0).node()->Emit(compiler, trace);
  }

  AssertGuardsMentionRegisters(trace);

  LimitResult limit_result = LimitVersions(compiler, trace);
  if (limit_result == DONE) return EmitResult::Success();
  DCHECK(limit_result == CONTINUE);

  // For loop nodes we already flushed (see LoopChoiceNode::Emit), but for
  // other choice nodes we only flush if we are out of code size budget.
  if (trace->flush_budget() == 0 && trace->has_any_actions()) {
    return trace->Flush(compiler, this);
  }

  RecursionCheck rc(compiler);

  PreloadState preload;
  preload.init();
  // This must be outside the 'if' because the trace we use for what
  // comes after the special_loop is inside it and needs the lifetime.
  SpecialLoopState special_loop_state(not_at_start(), this);

  int text_length = FixedLengthLoopLengthForAlternative(&alternatives_->at(0));
  AlternativeGenerationList alt_gens(choice_count, zone());

  // Flags need to be reset to the state of the ChoiceNode at the beginning
  // of each alternative (in-line and out-of-line), as flags might be modified
  // when emitting an alternative.
  RegExpFlags flags = compiler->flags();
  if (choice_count > 1 && text_length != kNodeIsTooComplexForFixedLengthLoops) {
    trace = EmitFixedLengthLoop(compiler, trace, &alt_gens, &preload,
                                &special_loop_state, text_length, flags);
    if (trace == nullptr) return EmitResult::Error();
  } else {
    preload.eats_at_least_ =
        EmitOptimizedUnanchoredSearch(compiler, trace, &special_loop_state);

    RETURN_IF_ERROR(
        EmitChoices(compiler, &alt_gens, 0, trace, &preload, flags));
  }

  // At this point we need to generate slow checks for the alternatives where
  // the quick check was inlined.  We can recognize these because the associated
  // label was bound.
  int new_flush_budget = trace->flush_budget() / choice_count;
  for (int i = 0; i < choice_count; i++) {
    compiler->set_flags(flags);
    AlternativeGeneration* alt_gen = alt_gens.at(i);
    Trace new_trace(*trace);
    // If there are actions to be flushed we have to limit how many times
    // they are flushed.  Take the budget of the parent trace and distribute
    // it fairly amongst the children.
    if (new_trace.has_any_actions()) {
      new_trace.set_flush_budget(new_flush_budget);
    }
    bool next_expects_preload =
        i == choice_count - 1 ? false : alt_gens.at(i + 1)->expects_preload;
    RETURN_IF_ERROR(EmitOutOfLineContinuation(
        compiler, &new_trace, alternatives_->at(i), alt_gen,
        preload.preload_characters_, next_expects_preload));
  }

  return EmitResult::Success();
}

Trace* ChoiceNode::EmitFixedLengthLoop(
    RegExpCompiler* compiler,
    Trace* trace,
    AlternativeGenerationList* alt_gens,
    PreloadState* preload,
    SpecialLoopState* fixed_length_loop_state,
    int text_length,
    RegExpFlags flags) {
  TRACE("* Emit fixed length loop");
  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  // Here we have special handling for greedy loops containing only text nodes
  // and other simple nodes.  We call these fixed length loops.  These are
  // handled by pushing the current position on the stack and then incrementing
  // the current position each time around the switch.  On backtrack we
  // decrement the current position and check it against the pushed value.
  // This avoids pushing backtrack information for each iteration of the loop,
  // which could take up a lot of space.
  DCHECK(trace->special_loop_state() == nullptr);
  macro_assembler->PushCurrentPosition();
  // This is the label for trying to match what comes after the greedy
  // quantifier, either because the body of the quantifier failed, or because
  // we have stepped back to try again with one iteration fewer.
  V8Label after_body_match_attempt;
  Trace fixed_length_match_trace;
  if (not_at_start()) fixed_length_match_trace.set_at_start(Trace::FALSE_VALUE);
  fixed_length_match_trace.set_backtrack(&after_body_match_attempt);
  fixed_length_loop_state->BindLoopTopLabel(macro_assembler);
  fixed_length_match_trace.set_special_loop_state(fixed_length_loop_state);
  EmitResult result =
      alternatives_->at(0).node()->Emit(compiler, &fixed_length_match_trace);
  macro_assembler->Bind(&after_body_match_attempt);
  if (result.IsError()) return nullptr;

  Trace* new_trace = fixed_length_loop_state->backtrack_trace();

  // In a fixed length loop there is only one other choice, which is what
  // comes after the greedy quantifer.  Try to match that now.
  result = EmitChoices(compiler, alt_gens, 1, new_trace, preload, flags);
  if (result.IsError()) return nullptr;

  fixed_length_loop_state->BindStepLabel(macro_assembler);
  // If we have unwound to the bottom then backtrack.
  macro_assembler->CheckFixedLengthLoop(trace->backtrack());
  // Otherwise try the second priority at an earlier position.
  macro_assembler->AdvanceCurrentPosition(-text_length);
  macro_assembler->GoTo(&after_body_match_attempt);
  return new_trace;
}

int ChoiceNode::EmitOptimizedUnanchoredSearch(
    RegExpCompiler* compiler,
    Trace* trace,
    SpecialLoopState* search_loop_state) {
  int eats_at_least = PreloadState::kEatsAtLeastNotYetInitialized;
  if (alternatives_->length() != 2) return eats_at_least;

  GuardedAlternative alt1 = alternatives_->at(1);
  if (alt1.guards() != nullptr && alt1.guards()->length() != 0) {
    TRACE(
        "  Alternatives with guards -> Can't emit optimized unanchored search");
    return eats_at_least;
  }
  RegExpNode* eats_anything_node = alt1.node();
  if (eats_anything_node->GetSuccessorOfOmnivorousTextNode(compiler) != this) {
    return eats_at_least;
  }

  // Really we should be creating a new trace when we execute this function,
  // but there is no need, because the code it generates cannot backtrack, and
  // we always arrive here with a trivial trace (since it's the entry to a
  // loop.  That also implies that there are no preloaded characters, which is
  // good, because it means we won't be violating any assumptions by
  // overwriting those characters with new load instructions.
  DCHECK(trace->is_trivial());

  TRACE("* Emit optimized unanchored search");
  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  Isolate* isolate = macro_assembler->isolate();
  // At this point we know that we are at a non-greedy loop that will eat
  // any character one at a time.  Any non-anchored regexp has such a
  // loop prepended to it in order to find where it starts.  We look for
  // a pattern of the form ...abc... where we can look 6 characters ahead
  // and step forwards 3 if the character is not one of abc.  Abc need
  // not be atoms, they can be any reasonably limited character class or
  // small alternation.
  BoyerMooreLookahead* bm = bm_info(false);
  // The --no-regexp-quick-check is for testing.  It disables the compiler's
  // clever optimizations that attempt to eliminate match positions. This
  // way the regular regexp machinery gets more exercise and test coverage.
  if (bm == nullptr && FLAG_regexp_quick_check) {
    eats_at_least = std::min(kMaxLookaheadForBoyerMoore, EatsAtLeast(false));
    if (eats_at_least >= 1) {
      bm = zone()->New<BoyerMooreLookahead>(eats_at_least, compiler, zone());
      GuardedAlternative alt0 = alternatives_->at(0);
      alt0.node()->FillInBMInfo(isolate, 0, kRecursionBudget, bm, false);
    }
  }
  if (bm != nullptr) {
#ifdef V8_ENABLE_REGEXP_DIAGNOSTICS
    if (UNLIKELY(v8_flags.trace_regexp_compiler)) {
      RegExpGraphPrinter* printer = compiler->diagnostics()->graph_printer();
      std::ostream& os = compiler->diagnostics()->os();
      os << "  ";
      printer->PrintBoyerMooreLookahead(bm);
    }
#endif
    bm->EmitSkipInstructions(macro_assembler);
  }
  return eats_at_least;
}

EmitResult ChoiceNode::EmitChoices(RegExpCompiler* compiler,
                                   AlternativeGenerationList* alt_gens,
                                   int first_choice,
                                   Trace* trace,
                                   PreloadState* preload,
                                   RegExpFlags flags) {
  TRACE("* Emit Choices");
  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  SetUpPreLoad(compiler, trace, preload);

  // For now we just call all choices one after the other.  The idea ultimately
  // is to use the Dispatch table to try only the relevant ones.
  int choice_count = alternatives_->length();

  int new_flush_budget = trace->flush_budget() / choice_count;

  bool quick_check_flags = FLAG_regexp_optimization && FLAG_regexp_quick_check;

  for (int i = first_choice; i < choice_count; i++) {
    compiler->set_flags(flags);
    bool is_last = i == choice_count - 1;
    bool fall_through_on_failure = !is_last;
    GuardedAlternative alternative = alternatives_->at(i);
    AlternativeGeneration* alt_gen = alt_gens->at(i);
    alt_gen->quick_check_details.set_characters(preload->preload_characters_);
    const ZoneList<Guard*>* guards = alternative.guards();
    int guard_count = (guards == nullptr) ? 0 : guards->length();
    Trace new_trace(*trace);
    new_trace.set_characters_preloaded(
        preload->preload_is_current_ ? preload->preload_characters_ : 0);
    if (preload->preload_has_checked_bounds_) {
      new_trace.set_bound_checked_up_to(preload->preload_characters_);
    }
    new_trace.quick_check_performed()->Clear();
    if (not_at_start_) new_trace.set_at_start(Trace::FALSE_VALUE);
    if (!is_last) {
      new_trace.set_backtrack(&alt_gen->after);
    }
    alt_gen->expects_preload = preload->preload_is_current_;
    bool generate_full_check_inline = false;
    TRACE_WITH_NODE_AND_TRACE(compiler, "  Choice " << i << " ",
                              alternative.node(), &new_trace);
    if (quick_check_flags && try_to_emit_quick_check_for_alternative(i == 0) &&
        alternative.node()->EmitQuickCheck(
            compiler, trace, &new_trace, preload->preload_has_checked_bounds_,
            &alt_gen->possible_success, &alt_gen->quick_check_details,
            fall_through_on_failure, this)) {
      // Quick check was generated for this choice.
      preload->preload_is_current_ = true;
      preload->preload_has_checked_bounds_ = true;
      // If we generated the quick check to fall through on possible success,
      // we now need to generate the full check inline.
      if (!fall_through_on_failure) {
        macro_assembler->Bind(&alt_gen->possible_success);
        new_trace.set_quick_check_performed(&alt_gen->quick_check_details);
        new_trace.set_characters_preloaded(preload->preload_characters_);
        new_trace.set_bound_checked_up_to(preload->preload_characters_);
        generate_full_check_inline = true;
      }
    } else if (alt_gen->quick_check_details.cannot_match()) {
      if (!fall_through_on_failure) {
        macro_assembler->GoTo(trace->backtrack());
      }
      continue;
    } else {
      // No quick check was generated.  Put the full code here.
      // If this is not the first choice then there could be slow checks from
      // previous cases that go here when they fail.  There's no reason to
      // insist that they preload characters since the slow check we are about
      // to generate probably can't use it.
      if (i != first_choice) {
        alt_gen->expects_preload = false;
        new_trace.InvalidateCurrentCharacter();
      }
      generate_full_check_inline = true;
    }
    if (generate_full_check_inline) {
      if (new_trace.has_any_actions()) {
        new_trace.set_flush_budget(new_flush_budget);
      }
      for (int j = 0; j < guard_count; j++) {
        GenerateGuard(macro_assembler, guards->at(j), &new_trace);
      }
      RETURN_IF_ERROR(alternative.node()->Emit(compiler, &new_trace));
      preload->preload_is_current_ = false;
    }
    macro_assembler->Bind(&alt_gen->after);
  }
  return EmitResult::Success();
}

EmitResult ChoiceNode::EmitOutOfLineContinuation(RegExpCompiler* compiler,
                                                 Trace* trace,
                                                 GuardedAlternative alternative,
                                                 AlternativeGeneration* alt_gen,
                                                 int preload_characters,
                                                 bool next_expects_preload) {
  if (!alt_gen->possible_success.is_linked()) return EmitResult::Success();
  TRACE_WITH_NODE_AND_TRACE(compiler, "* Emit Out-of-Line Continuation for ",
                            alternative.node(), trace);

  RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
  macro_assembler->Bind(&alt_gen->possible_success);
  Trace out_of_line_trace(*trace);
  out_of_line_trace.set_characters_preloaded(preload_characters);
  out_of_line_trace.set_quick_check_performed(&alt_gen->quick_check_details);
  if (not_at_start_) out_of_line_trace.set_at_start(Trace::FALSE_VALUE);
  const ZoneList<Guard*>* guards = alternative.guards();
  int guard_count = (guards == nullptr) ? 0 : guards->length();
  if (next_expects_preload) {
    V8Label reload_current_char;
    out_of_line_trace.set_backtrack(&reload_current_char);
    for (int j = 0; j < guard_count; j++) {
      GenerateGuard(macro_assembler, guards->at(j), &out_of_line_trace);
    }
    RETURN_IF_ERROR(alternative.node()->Emit(compiler, &out_of_line_trace));
    macro_assembler->Bind(&reload_current_char);
    // Reload the current character, since the next quick check expects that.
    // We don't need to check bounds here because we only get into this
    // code through a quick check which already did the checked load.
    macro_assembler->LoadCurrentCharacter(trace->cp_offset(), nullptr, false,
                                          preload_characters);
    macro_assembler->GoTo(&(alt_gen->after));
  } else {
    out_of_line_trace.set_backtrack(&(alt_gen->after));
    for (int j = 0; j < guard_count; j++) {
      GenerateGuard(macro_assembler, guards->at(j), &out_of_line_trace);
    }
    RETURN_IF_ERROR(alternative.node()->Emit(compiler, &out_of_line_trace));
  }
  return EmitResult::Success();
}

EmitResult ActionNode::Emit(RegExpCompiler* compiler, Trace* trace) {
  TRACE_EMIT("Action");
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  LimitResult limit_result = LimitVersions(compiler, trace);
  if (limit_result == DONE) return EmitResult::Success();
  DCHECK(limit_result == CONTINUE);

  RecursionCheck rc(compiler);

  switch (action_type_) {
    // Start with the actions we know how to defer. These are just recorded in
    // the new trace, no code is emitted right now.  (If we backtrack then we
    // don't have to perform and undo these actions.)
    case STORE_POSITION:
    case RESTORE_POSITION:
    case INCREMENT_REGISTER:
    case SET_REGISTER_FOR_LOOP:
    case CLEAR_CAPTURES: {
      Trace new_trace = *trace;
      new_trace.add_action(this);
      RETURN_IF_ERROR(on_success()->Emit(compiler, &new_trace));
      break;
    }
    case EATS_AT_LEAST:
      RETURN_IF_ERROR(on_success()->Emit(compiler, trace));
      break;  // Doesn't actually do anything.
    // We don't yet have the ability to defer these.
    case BEGIN_POSITIVE_SUBMATCH:
    case BEGIN_NEGATIVE_SUBMATCH:
      if (!trace->is_trivial()) {
        // Complex situation: Flush the trace state to the assembler and
        // generate a generic version of this action.  This call will
        // recurse back to the else clause here.
        trace->Flush(compiler, this);
      } else {
        assembler->WriteCurrentPositionToRegister(
            data_.u_submatch.current_position_register, 0);
        assembler->WriteStackPointerToRegister(
            data_.u_submatch.stack_pointer_register);
        RETURN_IF_ERROR(on_success()->Emit(compiler, trace));
      }
      break;
    case EMPTY_MATCH_CHECK: {
      int start_pos_reg = data_.u_empty_match_check.start_register;
      int stored_pos = 0;
      int rep_reg = data_.u_empty_match_check.repetition_register;
      bool has_minimum = (rep_reg != RegExpCompiler::kNoRegister);
      bool know_dist = trace->GetStoredPosition(start_pos_reg, &stored_pos);
      if (know_dist && !has_minimum && stored_pos == trace->cp_offset()) {
        // If we know we haven't advanced and there is no minimum we
        // can just backtrack immediately.
        assembler->GoTo(trace->backtrack());
      } else if (know_dist && stored_pos < trace->cp_offset()) {
        // If we know we've advanced we can generate the continuation
        // immediately.
        RETURN_IF_ERROR(on_success()->Emit(compiler, trace));
      } else if (!trace->is_trivial()) {
        trace->Flush(compiler, this);
      } else {
        V8Label skip_empty_check;
        // If we have a minimum number of repetitions we check the current
        // number first and skip the empty check if it's not enough.
        if (has_minimum) {
          int limit = data_.u_empty_match_check.repetition_limit;
          assembler->IfRegisterLT(rep_reg, limit, &skip_empty_check);
        }
        // If the match is empty we bail out, otherwise we fall through
        // to the on-success continuation.
        assembler->IfRegisterEqPos(start_pos_reg, trace->backtrack());
        assembler->Bind(&skip_empty_check);
        RETURN_IF_ERROR(on_success()->Emit(compiler, trace));
      }
      break;
    }
    case POSITIVE_SUBMATCH_SUCCESS: {
      if (!trace->is_trivial()) {
        return trace->Flush(compiler, this, Trace::kFlushSuccess);
      }
      assembler->ReadCurrentPositionFromRegister(
          data_.u_submatch.current_position_register);
      assembler->ReadStackPointerFromRegister(
          data_.u_submatch.stack_pointer_register);
      int clear_register_count = data_.u_submatch.clear_register_count;
      if (clear_register_count == 0) {
        return on_success()->Emit(compiler, trace);
      }
      int clear_registers_from = data_.u_submatch.clear_register_from;
      V8Label clear_registers_backtrack;
      Trace new_trace = *trace;
      new_trace.set_backtrack(&clear_registers_backtrack);
      RETURN_IF_ERROR(on_success()->Emit(compiler, &new_trace));

      assembler->Bind(&clear_registers_backtrack);
      int clear_registers_to = clear_registers_from + clear_register_count - 1;
      assembler->ClearRegisters(clear_registers_from, clear_registers_to);

      DCHECK(trace->backtrack() == nullptr);
      assembler->Backtrack();
      return EmitResult::Success();
    }
    case MODIFY_FLAGS: {
      compiler->set_flags(flags());
      RETURN_IF_ERROR(on_success()->Emit(compiler, trace));
      break;
    }
    default:
      UNREACHABLE();
  }
  return EmitResult::Success();
}

EmitResult BackReferenceNode::Emit(RegExpCompiler* compiler, Trace* trace) {
  TRACE_EMIT("BackReference");
  RegExpMacroAssembler* assembler = compiler->macro_assembler();
  if (!trace->is_trivial()) {
    return trace->Flush(compiler, this);
  }

  LimitResult limit_result = LimitVersions(compiler, trace);
  if (limit_result == DONE) return EmitResult::Success();
  DCHECK(limit_result == CONTINUE);

  RecursionCheck rc(compiler);

  DCHECK_EQ(start_reg_ + 1, end_reg_);
  if (IsIgnoreCase(compiler->flags())) {
    bool unicode = IsEitherUnicode(compiler->flags());
    assembler->CheckNotBackReferenceIgnoreCase(start_reg_, read_backward(),
                                               unicode, trace->backtrack());
  } else {
    assembler->CheckNotBackReference(start_reg_, read_backward(),
                                     trace->backtrack());
  }
  // We are going to advance backward, so we may end up at the start.
  if (read_backward()) trace->set_at_start(Trace::UNKNOWN);

  // Check that the back reference does not end inside a surrogate pair.
  if (IsEitherUnicode(compiler->flags()) && !compiler->one_byte()) {
    assembler->CheckNotInSurrogatePair(trace->cp_offset(), trace->backtrack());
  }
  return on_success()->Emit(compiler, trace);
}

void TextNode::CalculateOffsets() {
  int element_count = elements()->length();
  // Set up the offsets of the elements relative to the start.  This is a fixed
  // quantity since a TextNode can only contain fixed-width things.
  int cp_offset = 0;
  for (int i = 0; i < element_count; i++) {
    TextElement& elm = elements()->at(i);
    elm.set_cp_offset(cp_offset);
    cp_offset += elm.length();
  }
}

namespace {

// Assertion propagation moves information about assertions such as
// \b to the affected nodes.  For instance, in /.\b./ information must
// be propagated to the first '.' that whatever follows needs to know
// if it matched a word or a non-word, and to the second '.' that it
// has to check if it succeeds a word or non-word.  In this case the
// result will be something like:
//
//   +-------+        +------------+
//   |   .   |        |      .     |
//   +-------+  --->  +------------+
//   | word? |        | check word |
//   +-------+        +------------+
class AssertionPropagator : public AllStatic {
 public:
  static void VisitText(TextNode* that) {}

  static void VisitAction(ActionNode* that) {
    // If the next node is interested in what it follows then this node
    // has to be interested too so it can pass the information on.
    that->info()->AddFromFollowing(that->on_success()->info());
  }

  static void VisitChoice(ChoiceNode* that, int i) {
    // Anything the following nodes need to know has to be known by
    // this node also, so it can pass it on.
    that->info()->AddFromFollowing(that->alternatives()->at(i).node()->info());
  }

  static void VisitLoopChoiceContinueNode(LoopChoiceNode* that) {
    that->info()->AddFromFollowing(that->continue_node()->info());
  }

  static void VisitLoopChoiceLoopNode(LoopChoiceNode* that) {
    that->info()->AddFromFollowing(that->loop_node()->info());
  }

  static void VisitNegativeLookaroundChoiceLookaroundNode(
      NegativeLookaroundChoiceNode* that) {
    VisitChoice(that, NegativeLookaroundChoiceNode::kLookaroundIndex);
  }

  static void VisitNegativeLookaroundChoiceContinueNode(
      NegativeLookaroundChoiceNode* that) {
    VisitChoice(that, NegativeLookaroundChoiceNode::kContinueIndex);
  }

  static void VisitBackReference(BackReferenceNode* that) {}

  static void VisitAssertion(AssertionNode* that) {}
};

// Propagates information about the minimum size of successful matches from
// successor nodes to their predecessors. Note that all eats_at_least values
// are initialized to zero before analysis.
class EatsAtLeastPropagator : public AllStatic {
 public:
  static void VisitText(TextNode* that) {
    // The eats_at_least value is not used if reading backward.
    if (!that->read_backward()) {
      // We are not at the start after this node, and thus we can use the
      // successor's from_not_start value.
      uint8_t eats_at_least = base::saturated_cast<uint8_t>(
          that->Length() +
          that->on_success()->eats_at_least_info()->from_not_start);
      that->set_eats_at_least_info(EatsAtLeastInfo(eats_at_least));
    }
  }

  static void VisitAction(ActionNode* that) {
    switch (that->action_type()) {
      case ActionNode::BEGIN_POSITIVE_SUBMATCH: {
        // For a begin positive submatch we propagate the eats_at_least
        // data from the successor of the success node, ignoring the body of
        // the lookahead, which eats nothing, since it is a zero-width
        // assertion.
        // TODO(chromium:42201836) This is better than discarding all
        // information when there is a positive lookahead, but it loses some
        // information that could be useful, since the body of the lookahead
        // could tell us something about how close to the end of the string we
        // are.
        that->set_eats_at_least_info(
            *that->success_node()->on_success()->eats_at_least_info());
        break;
      }
      case ActionNode::POSITIVE_SUBMATCH_SUCCESS:
        // We do not propagate eats_at_least data through positive submatch
        // success because it rewinds input.
        DCHECK(that->eats_at_least_info()->IsZero());
        break;
      case ActionNode::EATS_AT_LEAST: {
        EatsAtLeastInfo eats = *that->on_success()->eats_at_least_info();
        eats.SetMax(that->stored_eats_at_least());
        that->set_eats_at_least_info(eats);
        break;
      }
      default:
        // Otherwise, the current node eats at least as much as its successor.
        // Note: we can propagate eats_at_least data for BEGIN_NEGATIVE_SUBMATCH
        // because NegativeLookaroundChoiceNode ignores its lookaround successor
        // when computing eats-at-least and quick check information.
        that->set_eats_at_least_info(*that->on_success()->eats_at_least_info());
        break;
    }
  }

  static void VisitChoice(ChoiceNode* that, int i) {
    // The minimum possible match from a choice node is the minimum of its
    // successors.
    EatsAtLeastInfo eats_at_least =
        i == 0 ? EatsAtLeastInfo(UINT8_MAX) : *that->eats_at_least_info();
    eats_at_least.SetMin(
        *that->alternatives()->at(i).node()->eats_at_least_info());
    that->set_eats_at_least_info(eats_at_least);
  }

  static void VisitLoopChoiceContinueNode(LoopChoiceNode* that) {
    if (!that->read_backward()) {
      that->set_eats_at_least_info(
          *that->continue_node()->eats_at_least_info());
    }
  }

  static void VisitLoopChoiceLoopNode(LoopChoiceNode* that) {}

  static void VisitNegativeLookaroundChoiceLookaroundNode(
      NegativeLookaroundChoiceNode* that) {}

  static void VisitNegativeLookaroundChoiceContinueNode(
      NegativeLookaroundChoiceNode* that) {
    that->set_eats_at_least_info(*that->continue_node()->eats_at_least_info());
  }

  static void VisitBackReference(BackReferenceNode* that) {
    if (!that->read_backward()) {
      that->set_eats_at_least_info(*that->on_success()->eats_at_least_info());
    }
  }

  static void VisitAssertion(AssertionNode* that) {
    EatsAtLeastInfo eats_at_least = *that->on_success()->eats_at_least_info();
    if (that->assertion_type() == AssertionNode::AT_START) {
      // If we know we are not at the start and we are asked "how many
      // characters will you match if you succeed?" then we can answer anything
      // since false implies false.  So let's just set the max answer
      // (UINT8_MAX) since that won't prevent us from preloading a lot of
      // characters for the other branches in the node graph.
      eats_at_least.from_not_start = UINT8_MAX;
    }
    that->set_eats_at_least_info(eats_at_least);
  }
};

}  // namespace

// -------------------------------------------------------------------
// Analysis

// Iterates the node graph and provides the opportunity for propagators to set
// values that depend on successor nodes.
template <typename... Propagators>
class Analysis : public NodeVisitor {
 public:
  Analysis(Isolate* isolate, bool is_one_byte, RegExpFlags flags)
      : isolate_(isolate),
        is_one_byte_(is_one_byte),
        flags_(flags),
        error_(RegExpError::kNone) {}

  void EnsureAnalyzed(RegExpNode* that) {
    if (!OSThread::Current()->HasStackHeadroom()) {
      if (FLAG_correctness_fuzzer_suppressions) {
        FATAL("Analysis: Aborting on stack overflow");
      }
      fail(RegExpError::kAnalysisStackOverflow);
      return;
    }
    if (that->info()->been_analyzed || that->info()->being_analyzed) return;
    that->info()->being_analyzed = true;
    that->Accept(this);
    that->info()->being_analyzed = false;
    that->info()->been_analyzed = true;
  }

  bool has_failed() { return error_ != RegExpError::kNone; }
  RegExpError error() {
    DCHECK(error_ != RegExpError::kNone);
    return error_;
  }
  void fail(RegExpError error) { error_ = error; }

  Isolate* isolate() const { return isolate_; }

  void VisitEnd(EndNode* that) override {
    // nothing to do
  }

// Used to call the given static function on each propagator / variadic template
// argument.
#define STATIC_FOR_EACH(expr)                                                  \
  do {                                                                         \
    int dummy[] = {((expr), 0)...};                                            \
    USE(dummy);                                                                \
  } while (false)

  void VisitText(TextNode* that) override {
    that->MakeCaseIndependent(isolate(), is_one_byte_, flags());
    EnsureAnalyzed(that->on_success());
    if (has_failed()) return;
    that->CalculateOffsets();
    STATIC_FOR_EACH(Propagators::VisitText(that));
  }

  void VisitAction(ActionNode* that) override {
    if (that->action_type() == ActionNode::MODIFY_FLAGS) {
      set_flags(that->flags());
    }
    EnsureAnalyzed(that->on_success());
    if (has_failed()) return;
    STATIC_FOR_EACH(Propagators::VisitAction(that));
  }

  void VisitChoice(ChoiceNode* that) override {
    for (int i = 0; i < that->alternatives()->length(); i++) {
      EnsureAnalyzed(that->alternatives()->at(i).node());
      if (has_failed()) return;
      STATIC_FOR_EACH(Propagators::VisitChoice(that, i));
    }
  }

  void VisitLoopChoice(LoopChoiceNode* that) override {
    DCHECK_EQ(that->alternatives()->length(), 2);  // Just loop and continue.

    // First propagate all information from the continuation node.
    // Due to the unusual visitation order, we need to manage the flags manually
    // as if we were visiting the loop node before visiting the continuation.
    RegExpFlags orig_flags = flags();

    EnsureAnalyzed(that->continue_node());
    if (has_failed()) return;
    // Propagators don't access global state (including flags), so we don't need
    // to reset them here.
    STATIC_FOR_EACH(Propagators::VisitLoopChoiceContinueNode(that));

    RegExpFlags continuation_flags = flags();

    // Check the loop last since it may need the value of this node
    // to get a correct result.
    set_flags(orig_flags);
    EnsureAnalyzed(that->loop_node());
    if (has_failed()) return;
    // Propagators don't access global state (including flags), so we don't need
    // to reset them here.
    STATIC_FOR_EACH(Propagators::VisitLoopChoiceLoopNode(that));

    set_flags(continuation_flags);
  }

  void VisitNegativeLookaroundChoice(
      NegativeLookaroundChoiceNode* that) override {
    DCHECK_EQ(that->alternatives()->length(), 2);  // Lookaround and continue.

    EnsureAnalyzed(that->lookaround_node());
    if (has_failed()) return;
    STATIC_FOR_EACH(
        Propagators::VisitNegativeLookaroundChoiceLookaroundNode(that));

    EnsureAnalyzed(that->continue_node());
    if (has_failed()) return;
    STATIC_FOR_EACH(
        Propagators::VisitNegativeLookaroundChoiceContinueNode(that));
  }

  void VisitBackReference(BackReferenceNode* that) override {
    EnsureAnalyzed(that->on_success());
    if (has_failed()) return;
    STATIC_FOR_EACH(Propagators::VisitBackReference(that));
  }

  void VisitAssertion(AssertionNode* that) override {
    EnsureAnalyzed(that->on_success());
    if (has_failed()) return;
    STATIC_FOR_EACH(Propagators::VisitAssertion(that));
  }

#undef STATIC_FOR_EACH

 private:
  RegExpFlags flags() const { return flags_; }
  void set_flags(RegExpFlags flags) { flags_ = flags; }

  Isolate* isolate_;
  const bool is_one_byte_;
  RegExpFlags flags_;
  RegExpError error_;

  DISALLOW_IMPLICIT_CONSTRUCTORS(Analysis);
};

RegExpError AnalyzeRegExp(Isolate* isolate,
                          bool is_one_byte,
                          RegExpFlags flags,
                          RegExpNode* node) {
  Analysis<AssertionPropagator, EatsAtLeastPropagator> analysis(
      isolate, is_one_byte, flags);
  DCHECK_EQ(node->info()->been_analyzed, false);
  analysis.EnsureAnalyzed(node);
  DCHECK_IMPLIES(analysis.has_failed(), analysis.error() != RegExpError::kNone);
  return analysis.has_failed() ? analysis.error() : RegExpError::kNone;
}

void BackReferenceNode::FillInBMInfo(Isolate* isolate,
                                     int offset,
                                     int budget,
                                     BoyerMooreLookahead* bm,
                                     bool not_at_start) {
  // Working out the set of characters that a backreference can match is too
  // hard, so we just say that any character can match.
  bm->SetRest(offset);
  SaveBMInfo(bm, not_at_start, offset);
}

static_assert(BoyerMoorePositionInfo::kMapSize ==
              RegExpMacroAssembler::kTableSize);

void ChoiceNode::FillInBMInfo(Isolate* isolate,
                              int offset,
                              int budget,
                              BoyerMooreLookahead* bm,
                              bool not_at_start) {
  ZoneList<GuardedAlternative>* alts = alternatives();
  budget = (budget - 1) / alts->length();
  for (int i = 0; i < alts->length(); i++) {
    GuardedAlternative& alt = alts->at(i);
    if (alt.guards() != nullptr && alt.guards()->length() != 0) {
      bm->SetRest(offset);  // Give up trying to fill in info.
      SaveBMInfo(bm, not_at_start, offset);
      return;
    }
    alt.node()->FillInBMInfo(isolate, offset, budget, bm, not_at_start);
  }
  SaveBMInfo(bm, not_at_start, offset);
}

void TextNode::FillInBMInfo(Isolate* isolate,
                            int initial_offset,
                            int budget,
                            BoyerMooreLookahead* bm,
                            bool not_at_start) {
  TRACE_WITH_NODE(bm->compiler(), "* Fill BM Info for Text: ", this);
  if (initial_offset >= bm->length()) return;
  if (read_backward()) return;
  int offset = initial_offset;
  int max_char = bm->max_char();
  for (int i = 0; i < elements()->length(); i++) {
    if (offset >= bm->length()) {
      if (initial_offset == 0) set_bm_info(not_at_start, bm);
      return;
    }
    TextElement text = elements()->at(i);
    if (text.text_type() == TextElement::ATOM) {
      RegExpAtom* atom = text.atom();
      for (int j = 0; j < atom->length(); j++, offset++) {
        if (offset >= bm->length()) {
          if (initial_offset == 0) set_bm_info(not_at_start, bm);
          return;
        }
        uint16_t character = atom->data()[j];
        if (IsIgnoreCase(bm->compiler()->flags())) {
          unibrow::uchar chars[4];
          int length = GetCaseIndependentLetters(isolate, character,
                                                 bm->compiler(), chars, 4);
          for (int k = 0; k < length; k++) {
            bm->Set(offset, chars[k]);
          }
        } else {
          if (character <= max_char) bm->Set(offset, character);
        }
      }
    } else {
      DCHECK_EQ(TextElement::CLASS_RANGES, text.text_type());
      RegExpClassRanges* class_ranges = text.class_ranges();
      ZoneList<CharacterRange>* ranges = class_ranges->ranges(zone());
      if (class_ranges->is_negated()) {
        bm->SetAll(offset);
      } else {
        for (int k = 0; k < ranges->length(); k++) {
          CharacterRange& range = ranges->at(k);
          if (static_cast<int>(range.from()) > max_char) continue;
          int to = std::min(max_char, static_cast<int>(range.to()));
          bm->SetInterval(offset, Interval(range.from(), to));
        }
      }
      offset++;
    }
  }
  if (offset >= bm->length()) {
    if (initial_offset == 0) set_bm_info(not_at_start, bm);
    return;
  }
  on_success()->FillInBMInfo(isolate, offset, budget - 1, bm,
                             true);  // Not at start after a text node.
  if (initial_offset == 0) set_bm_info(not_at_start, bm);
}

RegExpNode* RegExpCompiler::OptionallyStepBackToLeadSurrogate(
    RegExpNode* on_success) {
  TRACE_COMPILER(this, "* Optionally step back to lead surrogate");
  DCHECK(!read_backward());
  ZoneList<CharacterRange>* lead_surrogates = CharacterRange::List(
      zone(), CharacterRange::Range(kLeadSurrogateStart, kLeadSurrogateEnd));
  ZoneList<CharacterRange>* trail_surrogates = CharacterRange::List(
      zone(), CharacterRange::Range(kTrailSurrogateStart, kTrailSurrogateEnd));

  ChoiceNode* optional_step_back = zone()->New<ChoiceNode>(2, zone());

  int stack_register = UnicodeLookaroundStackRegister();
  int position_register = UnicodeLookaroundPositionRegister();
  RegExpNode* step_back = TextNode::CreateForCharacterRanges(
      zone(), lead_surrogates, true, on_success);
  RegExpLookaround::Builder builder(true, step_back, this, stack_register,
                                    position_register);
  REGISTER_NODE(step_back);
  RegExpNode* match_trail = TextNode::CreateForCharacterRanges(
      zone(), trail_surrogates, false, builder.on_match_success());
  REGISTER_NODE(match_trail);

  optional_step_back->AddAlternative(
      GuardedAlternative(builder.ForMatch(this, match_trail)));
  optional_step_back->AddAlternative(GuardedAlternative(on_success));

  REGISTER_NODE(optional_step_back);
  return optional_step_back;
}

RegExpNode* RegExpCompiler::PreprocessRegExp(RegExpCompileData* data,
                                             bool is_one_byte) {
#ifdef V8_ENABLE_REGEXP_DIAGNOSTICS
  TraceRegExpTreeScope trace_tree_scope(diagnostics());
#endif
  TRACE_GRAPH_WITH_NODE("* Preprocess RegExp ", data->tree);
  REGISTER_NODE(accept());
  // Wrap the body of the regexp in capture #0.
  RegExpNode* captured_body =
      RegExpCapture::ToNode(data->tree, 0, this, accept());
  RegExpNode* node = captured_body;
  if (!data->tree->IsAnchoredAtStart() && !IsSticky(flags())) {
    // Add a .*? at the beginning, outside the body capture, unless
    // this expression is anchored at the beginning or sticky.
    TRACE_GRAPH("* Add .*? at beginning of unanchored, non-sticky RegExp");
    RegExpNode* loop_node = RegExpQuantifier::ToNode(
        0, RegExpTree::kInfinity, false,
        zone()->New<RegExpClassRanges>(StandardCharacterSet::kEverything), this,
        captured_body, data->contains_anchor);

    if (data->contains_anchor) {
      // Unroll loop once, to take care of the case that might start
      // at the start of input.
      TRACE_GRAPH("* Unroll loop once");
      ChoiceNode* first_step_node = zone()->New<ChoiceNode>(2, zone());
      first_step_node->AddAlternative(GuardedAlternative(captured_body));
      first_step_node->AddAlternative(GuardedAlternative(zone()->New<TextNode>(
          zone()->New<RegExpClassRanges>(StandardCharacterSet::kEverything),
          false, loop_node)));
      REGISTER_NODE(first_step_node);
      node = first_step_node;
    } else {
      node = loop_node;
    }
  }
  if (!is_one_byte && IsEitherUnicode(flags()) &&
      (IsGlobal(flags()) || IsSticky(flags()))) {
    node = OptionallyStepBackToLeadSurrogate(node);
  }

  // We can run out of registers during preprocessing, or we can recurse too
  // deep during ToNode. Indicate an error in either case.
  if (reg_exp_too_big_) {
    data->error = RegExpError::kTooLarge;
  }
  CHECK_NE(nullptr, node);
  return node;
}

void RegExpCompiler::ToNodeCheckForStackOverflow() {
  //if (StackLimitCheck{isolate()}.HasOverflowed()) {
  if (!OSThread::Current()->HasStackHeadroom()) {
    SetRegExpTooBig();
  }
}

#ifdef V8_ENABLE_REGEXP_DIAGNOSTICS
void RegExpCompiler::set_diagnostics(
    std::unique_ptr<RegExpDiagnostics> diagnostics) {
  diagnostics_ = std::move(diagnostics);
}
#endif

}  // namespace dart