// Copyright 2016 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 "src/builtins/builtins-constructor.h"
#include "src/builtins/builtins-utils.h"
#include "src/builtins/builtins.h"
#include "src/code-factory.h"
#include "src/code-stub-assembler.h"
#include "src/regexp/jsregexp.h"
#include "src/regexp/regexp-utils.h"
#include "src/string-builder.h"

namespace v8 {
namespace internal {

typedef compiler::Node Node;
typedef CodeStubAssembler::ParameterMode ParameterMode;
typedef compiler::CodeAssemblerState CodeAssemblerState;

class RegExpBuiltinsAssembler : public CodeStubAssembler {
 public:
  explicit RegExpBuiltinsAssembler(CodeAssemblerState* state)
      : CodeStubAssembler(state) {}

 protected:
  Node* FastLoadLastIndex(Node* regexp);
  Node* SlowLoadLastIndex(Node* context, Node* regexp);
  Node* LoadLastIndex(Node* context, Node* regexp, bool is_fastpath);

  void FastStoreLastIndex(Node* regexp, Node* value);
  void SlowStoreLastIndex(Node* context, Node* regexp, Node* value);
  void StoreLastIndex(Node* context, Node* regexp, Node* value,
                      bool is_fastpath);

  Node* ConstructNewResultFromMatchInfo(Node* const context, Node* const regexp,
                                        Node* const match_info,
                                        Node* const string);

  Node* RegExpPrototypeExecBodyWithoutResult(Node* const context,
                                             Node* const regexp,
                                             Node* const string,
                                             Label* if_didnotmatch,
                                             const bool is_fastpath);
  Node* RegExpPrototypeExecBody(Node* const context, Node* const regexp,
                                Node* const string, const bool is_fastpath);

  Node* ThrowIfNotJSReceiver(Node* context, Node* maybe_receiver,
                             MessageTemplate::Template msg_template,
                             char const* method_name);

  Node* IsInitialRegExpMap(Node* context, Node* map);
  void BranchIfFastRegExp(Node* context, Node* map, Label* if_isunmodified,
                          Label* if_ismodified);
  void BranchIfFastRegExpResult(Node* context, Node* map,
                                Label* if_isunmodified, Label* if_ismodified);

  Node* FlagsGetter(Node* const context, Node* const regexp, bool is_fastpath);

  Node* FastFlagGetter(Node* const regexp, JSRegExp::Flag flag);
  Node* SlowFlagGetter(Node* const context, Node* const regexp,
                       JSRegExp::Flag flag);
  Node* FlagGetter(Node* const context, Node* const regexp, JSRegExp::Flag flag,
                   bool is_fastpath);
  void FlagGetter(JSRegExp::Flag flag, v8::Isolate::UseCounterFeature counter,
                  const char* method_name);

  Node* IsRegExp(Node* const context, Node* const maybe_receiver);
  Node* RegExpInitialize(Node* const context, Node* const regexp,
                         Node* const maybe_pattern, Node* const maybe_flags);

  Node* RegExpExec(Node* context, Node* regexp, Node* string);

  Node* AdvanceStringIndex(Node* const string, Node* const index,
                           Node* const is_unicode);

  void RegExpPrototypeMatchBody(Node* const context, Node* const regexp,
                                Node* const string, const bool is_fastpath);

  void RegExpPrototypeSearchBodyFast(Node* const context, Node* const regexp,
                                     Node* const string);
  void RegExpPrototypeSearchBodySlow(Node* const context, Node* const regexp,
                                     Node* const string);

  void RegExpPrototypeSplitBody(Node* const context, Node* const regexp,
                                Node* const string, Node* const limit);

  Node* ReplaceGlobalCallableFastPath(Node* context, Node* regexp, Node* string,
                                      Node* replace_callable);
  Node* ReplaceSimpleStringFastPath(Node* context, Node* regexp, Node* string,
                                    Node* replace_string);
};

// -----------------------------------------------------------------------------
// ES6 section 21.2 RegExp Objects

Node* RegExpBuiltinsAssembler::FastLoadLastIndex(Node* regexp) {
  // Load the in-object field.
  static const int field_offset =
      JSRegExp::kSize + JSRegExp::kLastIndexFieldIndex * kPointerSize;
  return LoadObjectField(regexp, field_offset);
}

Node* RegExpBuiltinsAssembler::SlowLoadLastIndex(Node* context, Node* regexp) {
  // Load through the GetProperty stub.
  Node* const name = HeapConstant(isolate()->factory()->lastIndex_string());
  Callable getproperty_callable = CodeFactory::GetProperty(isolate());
  return CallStub(getproperty_callable, context, regexp, name);
}

Node* RegExpBuiltinsAssembler::LoadLastIndex(Node* context, Node* regexp,
                                             bool is_fastpath) {
  return is_fastpath ? FastLoadLastIndex(regexp)
                     : SlowLoadLastIndex(context, regexp);
}

// The fast-path of StoreLastIndex when regexp is guaranteed to be an unmodified
// JSRegExp instance.
void RegExpBuiltinsAssembler::FastStoreLastIndex(Node* regexp, Node* value) {
  // Store the in-object field.
  static const int field_offset =
      JSRegExp::kSize + JSRegExp::kLastIndexFieldIndex * kPointerSize;
  StoreObjectField(regexp, field_offset, value);
}

void RegExpBuiltinsAssembler::SlowStoreLastIndex(Node* context, Node* regexp,
                                                 Node* value) {
  // Store through runtime.
  // TODO(ishell): Use SetPropertyStub here once available.
  Node* const name = HeapConstant(isolate()->factory()->lastIndex_string());
  Node* const language_mode = SmiConstant(Smi::FromInt(STRICT));
  CallRuntime(Runtime::kSetProperty, context, regexp, name, value,
              language_mode);
}

void RegExpBuiltinsAssembler::StoreLastIndex(Node* context, Node* regexp,
                                             Node* value, bool is_fastpath) {
  if (is_fastpath) {
    FastStoreLastIndex(regexp, value);
  } else {
    SlowStoreLastIndex(context, regexp, value);
  }
}

Node* RegExpBuiltinsAssembler::ConstructNewResultFromMatchInfo(
    Node* const context, Node* const regexp, Node* const match_info,
    Node* const string) {
  Label named_captures(this), out(this);

  Node* const num_indices = SmiUntag(LoadFixedArrayElement(
      match_info, RegExpMatchInfo::kNumberOfCapturesIndex));
  Node* const num_results = SmiTag(WordShr(num_indices, 1));
  Node* const start =
      LoadFixedArrayElement(match_info, RegExpMatchInfo::kFirstCaptureIndex);
  Node* const end = LoadFixedArrayElement(
      match_info, RegExpMatchInfo::kFirstCaptureIndex + 1);

  // Calculate the substring of the first match before creating the result array
  // to avoid an unnecessary write barrier storing the first result.
  Node* const first = SubString(context, string, start, end);

  Node* const result =
      AllocateRegExpResult(context, num_results, start, string);
  Node* const result_elements = LoadElements(result);

  StoreFixedArrayElement(result_elements, 0, first, SKIP_WRITE_BARRIER);

  // If no captures exist we can skip named capture handling as well.
  GotoIf(SmiEqual(num_results, SmiConstant(1)), &out);

  // Store all remaining captures.
  Node* const limit = IntPtrAdd(
      IntPtrConstant(RegExpMatchInfo::kFirstCaptureIndex), num_indices);

  Variable var_from_cursor(
      this, MachineType::PointerRepresentation(),
      IntPtrConstant(RegExpMatchInfo::kFirstCaptureIndex + 2));
  Variable var_to_cursor(this, MachineType::PointerRepresentation(),
                         IntPtrConstant(1));

  Variable* vars[] = {&var_from_cursor, &var_to_cursor};
  Label loop(this, 2, vars);

  Goto(&loop);
  Bind(&loop);
  {
    Node* const from_cursor = var_from_cursor.value();
    Node* const to_cursor = var_to_cursor.value();
    Node* const start = LoadFixedArrayElement(match_info, from_cursor);

    Label next_iter(this);
    GotoIf(SmiEqual(start, SmiConstant(-1)), &next_iter);

    Node* const from_cursor_plus1 = IntPtrAdd(from_cursor, IntPtrConstant(1));
    Node* const end = LoadFixedArrayElement(match_info, from_cursor_plus1);

    Node* const capture = SubString(context, string, start, end);
    StoreFixedArrayElement(result_elements, to_cursor, capture);
    Goto(&next_iter);

    Bind(&next_iter);
    var_from_cursor.Bind(IntPtrAdd(from_cursor, IntPtrConstant(2)));
    var_to_cursor.Bind(IntPtrAdd(to_cursor, IntPtrConstant(1)));
    Branch(UintPtrLessThan(var_from_cursor.value(), limit), &loop,
           &named_captures);
  }

  Bind(&named_captures);
  {
    // We reach this point only if captures exist, implying that this is an
    // IRREGEXP JSRegExp.

    CSA_ASSERT(this, HasInstanceType(regexp, JS_REGEXP_TYPE));
    CSA_ASSERT(this, SmiGreaterThan(num_results, SmiConstant(1)));

    // Preparations for named capture properties. Exit early if the result does
    // not have any named captures to minimize performance impact.

    Node* const data = LoadObjectField(regexp, JSRegExp::kDataOffset);
    CSA_ASSERT(this, SmiEqual(LoadFixedArrayElement(data, JSRegExp::kTagIndex),
                              SmiConstant(JSRegExp::IRREGEXP)));

    // The names fixed array associates names at even indices with a capture
    // index at odd indices.
    Node* const names =
        LoadFixedArrayElement(data, JSRegExp::kIrregexpCaptureNameMapIndex);
    GotoIf(SmiEqual(names, SmiConstant(0)), &out);

    // Allocate a new object to store the named capture properties.
    // TODO(jgruber): Could be optimized by adding the object map to the heap
    // root list.

    Node* const native_context = LoadNativeContext(context);
    Node* const map = LoadContextElement(
        native_context, Context::SLOW_OBJECT_WITH_NULL_PROTOTYPE_MAP);
    Node* const properties =
        AllocateNameDictionary(NameDictionary::kInitialCapacity);

    Node* const group_object = AllocateJSObjectFromMap(map, properties);

    // Store it on the result as a 'group' property.

    {
      Node* const name = HeapConstant(isolate()->factory()->group_string());
      CallRuntime(Runtime::kCreateDataProperty, context, result, name,
                  group_object);
    }

    // One or more named captures exist, add a property for each one.

    CSA_ASSERT(this, HasInstanceType(names, FIXED_ARRAY_TYPE));
    Node* const names_length = LoadAndUntagFixedArrayBaseLength(names);
    CSA_ASSERT(this, IntPtrGreaterThan(names_length, IntPtrConstant(0)));

    Variable var_i(this, MachineType::PointerRepresentation());
    var_i.Bind(IntPtrConstant(0));

    Variable* vars[] = {&var_i};
    const int vars_count = sizeof(vars) / sizeof(vars[0]);
    Label loop(this, vars_count, vars);

    Goto(&loop);
    Bind(&loop);
    {
      Node* const i = var_i.value();
      Node* const i_plus_1 = IntPtrAdd(i, IntPtrConstant(1));
      Node* const i_plus_2 = IntPtrAdd(i_plus_1, IntPtrConstant(1));

      Node* const name = LoadFixedArrayElement(names, i);
      Node* const index = LoadFixedArrayElement(names, i_plus_1);
      Node* const capture =
          LoadFixedArrayElement(result_elements, SmiUntag(index));

      CallRuntime(Runtime::kCreateDataProperty, context, group_object, name,
                  capture);

      var_i.Bind(i_plus_2);
      Branch(IntPtrGreaterThanOrEqual(var_i.value(), names_length), &out,
             &loop);
    }
  }

  Bind(&out);
  return result;
}

// ES#sec-regexp.prototype.exec
// RegExp.prototype.exec ( string )
// Implements the core of RegExp.prototype.exec but without actually
// constructing the JSRegExpResult. Returns either null (if the RegExp did not
// match) or a fixed array containing match indices as returned by
// RegExpExecStub.
Node* RegExpBuiltinsAssembler::RegExpPrototypeExecBodyWithoutResult(
    Node* const context, Node* const regexp, Node* const string,
    Label* if_didnotmatch, const bool is_fastpath) {
  Isolate* const isolate = this->isolate();

  Node* const null = NullConstant();
  Node* const int_zero = IntPtrConstant(0);
  Node* const smi_zero = SmiConstant(Smi::kZero);

  if (!is_fastpath) {
    ThrowIfNotInstanceType(context, regexp, JS_REGEXP_TYPE,
                           "RegExp.prototype.exec");
  }

  CSA_ASSERT(this, IsStringInstanceType(LoadInstanceType(string)));
  CSA_ASSERT(this, HasInstanceType(regexp, JS_REGEXP_TYPE));

  Variable var_result(this, MachineRepresentation::kTagged);
  Label out(this);

  Node* const native_context = LoadNativeContext(context);
  Node* const string_length = LoadStringLength(string);

  // Check whether the regexp is global or sticky, which determines whether we
  // update last index later on.
  Node* const flags = LoadObjectField(regexp, JSRegExp::kFlagsOffset);
  Node* const is_global_or_sticky = WordAnd(
      SmiUntag(flags), IntPtrConstant(JSRegExp::kGlobal | JSRegExp::kSticky));
  Node* const should_update_last_index =
      WordNotEqual(is_global_or_sticky, int_zero);

  // Grab and possibly update last index.
  Label run_exec(this);
  Variable var_lastindex(this, MachineRepresentation::kTagged);
  {
    Label if_doupdate(this), if_dontupdate(this);
    Branch(should_update_last_index, &if_doupdate, &if_dontupdate);

    Bind(&if_doupdate);
    {
      Node* const regexp_lastindex =
          LoadLastIndex(context, regexp, is_fastpath);
      var_lastindex.Bind(regexp_lastindex);

      // Omit ToLength if lastindex is a non-negative smi.
      {
        Label call_tolength(this, Label::kDeferred), next(this);
        Branch(TaggedIsPositiveSmi(regexp_lastindex), &next, &call_tolength);

        Bind(&call_tolength);
        {
          Callable tolength_callable = CodeFactory::ToLength(isolate);
          var_lastindex.Bind(
              CallStub(tolength_callable, context, regexp_lastindex));
          Goto(&next);
        }

        Bind(&next);
      }

      Node* const lastindex = var_lastindex.value();

      Label if_isoob(this, Label::kDeferred);
      GotoUnless(TaggedIsSmi(lastindex), &if_isoob);
      GotoUnless(SmiLessThanOrEqual(lastindex, string_length), &if_isoob);
      Goto(&run_exec);

      Bind(&if_isoob);
      {
        StoreLastIndex(context, regexp, smi_zero, is_fastpath);
        var_result.Bind(null);
        Goto(if_didnotmatch);
      }
    }

    Bind(&if_dontupdate);
    {
      var_lastindex.Bind(smi_zero);
      Goto(&run_exec);
    }
  }

  Node* match_indices;
  Label successful_match(this);
  Bind(&run_exec);
  {
    // Get last match info from the context.
    Node* const last_match_info = LoadContextElement(
        native_context, Context::REGEXP_LAST_MATCH_INFO_INDEX);

    // Call the exec stub.
    Callable exec_callable = CodeFactory::RegExpExec(isolate);
    match_indices = CallStub(exec_callable, context, regexp, string,
                             var_lastindex.value(), last_match_info);
    var_result.Bind(match_indices);

    // {match_indices} is either null or the RegExpMatchInfo array.
    // Return early if exec failed, possibly updating last index.
    GotoUnless(WordEqual(match_indices, null), &successful_match);

    GotoUnless(should_update_last_index, if_didnotmatch);

    StoreLastIndex(context, regexp, smi_zero, is_fastpath);
    Goto(if_didnotmatch);
  }

  Bind(&successful_match);
  {
    GotoUnless(should_update_last_index, &out);

    // Update the new last index from {match_indices}.
    Node* const new_lastindex = LoadFixedArrayElement(
        match_indices, RegExpMatchInfo::kFirstCaptureIndex + 1);

    StoreLastIndex(context, regexp, new_lastindex, is_fastpath);
    Goto(&out);
  }

  Bind(&out);
  return var_result.value();
}

// ES#sec-regexp.prototype.exec
// RegExp.prototype.exec ( string )
Node* RegExpBuiltinsAssembler::RegExpPrototypeExecBody(Node* const context,
                                                       Node* const regexp,
                                                       Node* const string,
                                                       const bool is_fastpath) {
  Node* const null = NullConstant();

  Variable var_result(this, MachineRepresentation::kTagged);

  Label if_didnotmatch(this), out(this);
  Node* const indices_or_null = RegExpPrototypeExecBodyWithoutResult(
      context, regexp, string, &if_didnotmatch, is_fastpath);

  // Successful match.
  {
    Node* const match_indices = indices_or_null;
    Node* const result =
        ConstructNewResultFromMatchInfo(context, regexp, match_indices, string);
    var_result.Bind(result);
    Goto(&out);
  }

  Bind(&if_didnotmatch);
  {
    var_result.Bind(null);
    Goto(&out);
  }

  Bind(&out);
  return var_result.value();
}

Node* RegExpBuiltinsAssembler::ThrowIfNotJSReceiver(
    Node* context, Node* maybe_receiver, MessageTemplate::Template msg_template,
    char const* method_name) {
  Label out(this), throw_exception(this, Label::kDeferred);
  Variable var_value_map(this, MachineRepresentation::kTagged);

  GotoIf(TaggedIsSmi(maybe_receiver), &throw_exception);

  // Load the instance type of the {value}.
  var_value_map.Bind(LoadMap(maybe_receiver));
  Node* const value_instance_type = LoadMapInstanceType(var_value_map.value());

  Branch(IsJSReceiverInstanceType(value_instance_type), &out, &throw_exception);

  // The {value} is not a compatible receiver for this method.
  Bind(&throw_exception);
  {
    Node* const message_id = SmiConstant(Smi::FromInt(msg_template));
    Node* const method_name_str = HeapConstant(
        isolate()->factory()->NewStringFromAsciiChecked(method_name, TENURED));

    Callable callable = CodeFactory::ToString(isolate());
    Node* const value_str = CallStub(callable, context, maybe_receiver);

    CallRuntime(Runtime::kThrowTypeError, context, message_id, method_name_str,
                value_str);
    var_value_map.Bind(UndefinedConstant());
    Goto(&out);  // Never reached.
  }

  Bind(&out);
  return var_value_map.value();
}

Node* RegExpBuiltinsAssembler::IsInitialRegExpMap(Node* context, Node* map) {
  Node* const native_context = LoadNativeContext(context);
  Node* const regexp_fun =
      LoadContextElement(native_context, Context::REGEXP_FUNCTION_INDEX);
  Node* const initial_map =
      LoadObjectField(regexp_fun, JSFunction::kPrototypeOrInitialMapOffset);
  Node* const has_initialmap = WordEqual(map, initial_map);

  return has_initialmap;
}

// RegExp fast path implementations rely on unmodified JSRegExp instances.
// We use a fairly coarse granularity for this and simply check whether both
// the regexp itself is unmodified (i.e. its map has not changed) and its
// prototype is unmodified.
void RegExpBuiltinsAssembler::BranchIfFastRegExp(Node* context, Node* map,
                                                 Label* if_isunmodified,
                                                 Label* if_ismodified) {
  Node* const native_context = LoadNativeContext(context);
  Node* const regexp_fun =
      LoadContextElement(native_context, Context::REGEXP_FUNCTION_INDEX);
  Node* const initial_map =
      LoadObjectField(regexp_fun, JSFunction::kPrototypeOrInitialMapOffset);
  Node* const has_initialmap = WordEqual(map, initial_map);

  GotoUnless(has_initialmap, if_ismodified);

  Node* const initial_proto_initial_map =
      LoadContextElement(native_context, Context::REGEXP_PROTOTYPE_MAP_INDEX);
  Node* const proto_map = LoadMap(LoadMapPrototype(map));
  Node* const proto_has_initialmap =
      WordEqual(proto_map, initial_proto_initial_map);

  // TODO(ishell): Update this check once map changes for constant field
  // tracking are landing.

  Branch(proto_has_initialmap, if_isunmodified, if_ismodified);
}

void RegExpBuiltinsAssembler::BranchIfFastRegExpResult(Node* context, Node* map,
                                                       Label* if_isunmodified,
                                                       Label* if_ismodified) {
  Node* const native_context = LoadNativeContext(context);
  Node* const initial_regexp_result_map =
      LoadContextElement(native_context, Context::REGEXP_RESULT_MAP_INDEX);

  Branch(WordEqual(map, initial_regexp_result_map), if_isunmodified,
         if_ismodified);
}

// ES#sec-regexp.prototype.exec
// RegExp.prototype.exec ( string )
TF_BUILTIN(RegExpPrototypeExec, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const maybe_string = Parameter(1);
  Node* const context = Parameter(4);

  // Ensure {maybe_receiver} is a JSRegExp.
  Node* const regexp_map = ThrowIfNotInstanceType(
      context, maybe_receiver, JS_REGEXP_TYPE, "RegExp.prototype.exec");
  Node* const receiver = maybe_receiver;

  // Convert {maybe_string} to a String.
  Node* const string = ToString(context, maybe_string);

  Label if_isfastpath(this), if_isslowpath(this);
  Branch(IsInitialRegExpMap(context, regexp_map), &if_isfastpath,
         &if_isslowpath);

  Bind(&if_isfastpath);
  {
    Node* const result =
        RegExpPrototypeExecBody(context, receiver, string, true);
    Return(result);
  }

  Bind(&if_isslowpath);
  {
    Node* const result =
        RegExpPrototypeExecBody(context, receiver, string, false);
    Return(result);
  }
}

Node* RegExpBuiltinsAssembler::FlagsGetter(Node* const context,
                                           Node* const regexp,
                                           bool is_fastpath) {
  Isolate* isolate = this->isolate();

  Node* const int_zero = IntPtrConstant(0);
  Node* const int_one = IntPtrConstant(1);
  Variable var_length(this, MachineType::PointerRepresentation(), int_zero);
  Variable var_flags(this, MachineType::PointerRepresentation());

  // First, count the number of characters we will need and check which flags
  // are set.

  if (is_fastpath) {
    // Refer to JSRegExp's flag property on the fast-path.
    Node* const flags_smi = LoadObjectField(regexp, JSRegExp::kFlagsOffset);
    Node* const flags_intptr = SmiUntag(flags_smi);
    var_flags.Bind(flags_intptr);

#define CASE_FOR_FLAG(FLAG)                                  \
  do {                                                       \
    Label next(this);                                        \
    GotoUnless(IsSetWord(flags_intptr, FLAG), &next);        \
    var_length.Bind(IntPtrAdd(var_length.value(), int_one)); \
    Goto(&next);                                             \
    Bind(&next);                                             \
  } while (false)

    CASE_FOR_FLAG(JSRegExp::kGlobal);
    CASE_FOR_FLAG(JSRegExp::kIgnoreCase);
    CASE_FOR_FLAG(JSRegExp::kMultiline);
    CASE_FOR_FLAG(JSRegExp::kUnicode);
    CASE_FOR_FLAG(JSRegExp::kSticky);
#undef CASE_FOR_FLAG
  } else {
    DCHECK(!is_fastpath);

    // Fall back to GetProperty stub on the slow-path.
    var_flags.Bind(int_zero);

    Callable getproperty_callable = CodeFactory::GetProperty(isolate);

#define CASE_FOR_FLAG(NAME, FLAG)                                             \
  do {                                                                        \
    Label next(this);                                                         \
    Node* const name =                                                        \
        HeapConstant(isolate->factory()->InternalizeUtf8String(NAME));        \
    Node* const flag = CallStub(getproperty_callable, context, regexp, name); \
    Label if_isflagset(this);                                                 \
    BranchIfToBooleanIsTrue(flag, &if_isflagset, &next);                      \
    Bind(&if_isflagset);                                                      \
    var_length.Bind(IntPtrAdd(var_length.value(), int_one));                  \
    var_flags.Bind(WordOr(var_flags.value(), IntPtrConstant(FLAG)));          \
    Goto(&next);                                                              \
    Bind(&next);                                                              \
  } while (false)

    CASE_FOR_FLAG("global", JSRegExp::kGlobal);
    CASE_FOR_FLAG("ignoreCase", JSRegExp::kIgnoreCase);
    CASE_FOR_FLAG("multiline", JSRegExp::kMultiline);
    CASE_FOR_FLAG("unicode", JSRegExp::kUnicode);
    CASE_FOR_FLAG("sticky", JSRegExp::kSticky);
#undef CASE_FOR_FLAG
  }

  // Allocate a string of the required length and fill it with the corresponding
  // char for each set flag.

  {
    Node* const result = AllocateSeqOneByteString(context, var_length.value());
    Node* const flags_intptr = var_flags.value();

    Variable var_offset(
        this, MachineType::PointerRepresentation(),
        IntPtrConstant(SeqOneByteString::kHeaderSize - kHeapObjectTag));

#define CASE_FOR_FLAG(FLAG, CHAR)                              \
  do {                                                         \
    Label next(this);                                          \
    GotoUnless(IsSetWord(flags_intptr, FLAG), &next);          \
    Node* const value = Int32Constant(CHAR);                   \
    StoreNoWriteBarrier(MachineRepresentation::kWord8, result, \
                        var_offset.value(), value);            \
    var_offset.Bind(IntPtrAdd(var_offset.value(), int_one));   \
    Goto(&next);                                               \
    Bind(&next);                                               \
  } while (false)

    CASE_FOR_FLAG(JSRegExp::kGlobal, 'g');
    CASE_FOR_FLAG(JSRegExp::kIgnoreCase, 'i');
    CASE_FOR_FLAG(JSRegExp::kMultiline, 'm');
    CASE_FOR_FLAG(JSRegExp::kUnicode, 'u');
    CASE_FOR_FLAG(JSRegExp::kSticky, 'y');
#undef CASE_FOR_FLAG

    return result;
  }
}

// ES#sec-isregexp IsRegExp ( argument )
Node* RegExpBuiltinsAssembler::IsRegExp(Node* const context,
                                        Node* const maybe_receiver) {
  Label out(this), if_isregexp(this);

  Variable var_result(this, MachineRepresentation::kWord32, Int32Constant(0));

  GotoIf(TaggedIsSmi(maybe_receiver), &out);
  GotoUnless(IsJSReceiver(maybe_receiver), &out);

  Node* const receiver = maybe_receiver;

  // Check @@match.
  {
    Callable getproperty_callable = CodeFactory::GetProperty(isolate());
    Node* const name = HeapConstant(isolate()->factory()->match_symbol());
    Node* const value = CallStub(getproperty_callable, context, receiver, name);

    Label match_isundefined(this), match_isnotundefined(this);
    Branch(IsUndefined(value), &match_isundefined, &match_isnotundefined);

    Bind(&match_isundefined);
    Branch(HasInstanceType(receiver, JS_REGEXP_TYPE), &if_isregexp, &out);

    Bind(&match_isnotundefined);
    BranchIfToBooleanIsTrue(value, &if_isregexp, &out);
  }

  Bind(&if_isregexp);
  var_result.Bind(Int32Constant(1));
  Goto(&out);

  Bind(&out);
  return var_result.value();
}

// ES#sec-regexpinitialize
// Runtime Semantics: RegExpInitialize ( obj, pattern, flags )
Node* RegExpBuiltinsAssembler::RegExpInitialize(Node* const context,
                                                Node* const regexp,
                                                Node* const maybe_pattern,
                                                Node* const maybe_flags) {
  // Normalize pattern.
  Node* const pattern =
      Select(IsUndefined(maybe_pattern), [=] { return EmptyStringConstant(); },
             [=] { return ToString(context, maybe_pattern); },
             MachineRepresentation::kTagged);

  // Normalize flags.
  Node* const flags =
      Select(IsUndefined(maybe_flags), [=] { return EmptyStringConstant(); },
             [=] { return ToString(context, maybe_flags); },
             MachineRepresentation::kTagged);

  // Initialize.

  return CallRuntime(Runtime::kRegExpInitializeAndCompile, context, regexp,
                     pattern, flags);
}

TF_BUILTIN(RegExpPrototypeFlagsGetter, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const context = Parameter(3);

  Node* const map = ThrowIfNotJSReceiver(context, maybe_receiver,
                                         MessageTemplate::kRegExpNonObject,
                                         "RegExp.prototype.flags");
  Node* const receiver = maybe_receiver;

  Label if_isfastpath(this), if_isslowpath(this, Label::kDeferred);
  Branch(IsInitialRegExpMap(context, map), &if_isfastpath, &if_isslowpath);

  Bind(&if_isfastpath);
  Return(FlagsGetter(context, receiver, true));

  Bind(&if_isslowpath);
  Return(FlagsGetter(context, receiver, false));
}

// ES#sec-regexp-pattern-flags
// RegExp ( pattern, flags )
TF_BUILTIN(RegExpConstructor, RegExpBuiltinsAssembler) {
  Node* const pattern = Parameter(1);
  Node* const flags = Parameter(2);
  Node* const new_target = Parameter(3);
  Node* const context = Parameter(5);

  Isolate* isolate = this->isolate();

  Variable var_flags(this, MachineRepresentation::kTagged, flags);
  Variable var_pattern(this, MachineRepresentation::kTagged, pattern);
  Variable var_new_target(this, MachineRepresentation::kTagged, new_target);

  Node* const native_context = LoadNativeContext(context);
  Node* const regexp_function =
      LoadContextElement(native_context, Context::REGEXP_FUNCTION_INDEX);

  Node* const pattern_is_regexp = IsRegExp(context, pattern);

  {
    Label next(this);

    GotoUnless(IsUndefined(new_target), &next);
    var_new_target.Bind(regexp_function);

    GotoUnless(pattern_is_regexp, &next);
    GotoUnless(IsUndefined(flags), &next);

    Callable getproperty_callable = CodeFactory::GetProperty(isolate);
    Node* const name = HeapConstant(isolate->factory()->constructor_string());
    Node* const value = CallStub(getproperty_callable, context, pattern, name);

    GotoUnless(WordEqual(value, regexp_function), &next);
    Return(pattern);

    Bind(&next);
  }

  {
    Label next(this), if_patternisfastregexp(this),
        if_patternisslowregexp(this);
    GotoIf(TaggedIsSmi(pattern), &next);

    GotoIf(HasInstanceType(pattern, JS_REGEXP_TYPE), &if_patternisfastregexp);

    Branch(pattern_is_regexp, &if_patternisslowregexp, &next);

    Bind(&if_patternisfastregexp);
    {
      Node* const source = LoadObjectField(pattern, JSRegExp::kSourceOffset);
      var_pattern.Bind(source);

      {
        Label inner_next(this);
        GotoUnless(IsUndefined(flags), &inner_next);

        Node* const value = FlagsGetter(context, pattern, true);
        var_flags.Bind(value);
        Goto(&inner_next);

        Bind(&inner_next);
      }

      Goto(&next);
    }

    Bind(&if_patternisslowregexp);
    {
      Callable getproperty_callable = CodeFactory::GetProperty(isolate);

      {
        Node* const name = HeapConstant(isolate->factory()->source_string());
        Node* const value =
            CallStub(getproperty_callable, context, pattern, name);
        var_pattern.Bind(value);
      }

      {
        Label inner_next(this);
        GotoUnless(IsUndefined(flags), &inner_next);

        Node* const name = HeapConstant(isolate->factory()->flags_string());
        Node* const value =
            CallStub(getproperty_callable, context, pattern, name);
        var_flags.Bind(value);
        Goto(&inner_next);

        Bind(&inner_next);
      }

      Goto(&next);
    }

    Bind(&next);
  }

  // Allocate.

  Variable var_regexp(this, MachineRepresentation::kTagged);
  {
    Label allocate_jsregexp(this), allocate_generic(this, Label::kDeferred),
        next(this);
    Branch(WordEqual(var_new_target.value(), regexp_function),
           &allocate_jsregexp, &allocate_generic);

    Bind(&allocate_jsregexp);
    {
      Node* const initial_map = LoadObjectField(
          regexp_function, JSFunction::kPrototypeOrInitialMapOffset);
      Node* const regexp = AllocateJSObjectFromMap(initial_map);
      var_regexp.Bind(regexp);
      Goto(&next);
    }

    Bind(&allocate_generic);
    {
      ConstructorBuiltinsAssembler constructor_assembler(this->state());
      Node* const regexp = constructor_assembler.EmitFastNewObject(
          context, regexp_function, var_new_target.value());
      var_regexp.Bind(regexp);
      Goto(&next);
    }

    Bind(&next);
  }

  Node* const result = RegExpInitialize(context, var_regexp.value(),
                                        var_pattern.value(), var_flags.value());
  Return(result);
}

// ES#sec-regexp.prototype.compile
// RegExp.prototype.compile ( pattern, flags )
TF_BUILTIN(RegExpPrototypeCompile, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const maybe_pattern = Parameter(1);
  Node* const maybe_flags = Parameter(2);
  Node* const context = Parameter(5);

  ThrowIfNotInstanceType(context, maybe_receiver, JS_REGEXP_TYPE,
                         "RegExp.prototype.compile");
  Node* const receiver = maybe_receiver;

  Variable var_flags(this, MachineRepresentation::kTagged, maybe_flags);
  Variable var_pattern(this, MachineRepresentation::kTagged, maybe_pattern);

  // Handle a JSRegExp pattern.
  {
    Label next(this);

    GotoIf(TaggedIsSmi(maybe_pattern), &next);
    GotoUnless(HasInstanceType(maybe_pattern, JS_REGEXP_TYPE), &next);

    Node* const pattern = maybe_pattern;

    // {maybe_flags} must be undefined in this case, otherwise throw.
    {
      Label next(this);
      GotoIf(IsUndefined(maybe_flags), &next);

      Node* const message_id = SmiConstant(MessageTemplate::kRegExpFlags);
      TailCallRuntime(Runtime::kThrowTypeError, context, message_id);

      Bind(&next);
    }

    Node* const new_flags = FlagsGetter(context, pattern, true);
    Node* const new_pattern = LoadObjectField(pattern, JSRegExp::kSourceOffset);

    var_flags.Bind(new_flags);
    var_pattern.Bind(new_pattern);

    Goto(&next);
    Bind(&next);
  }

  Node* const result = RegExpInitialize(context, receiver, var_pattern.value(),
                                        var_flags.value());
  Return(result);
}

// ES6 21.2.5.10.
TF_BUILTIN(RegExpPrototypeSourceGetter, RegExpBuiltinsAssembler) {
  Node* const receiver = Parameter(0);
  Node* const context = Parameter(3);

  // Check whether we have an unmodified regexp instance.
  Label if_isjsregexp(this), if_isnotjsregexp(this, Label::kDeferred);

  GotoIf(TaggedIsSmi(receiver), &if_isnotjsregexp);
  Branch(HasInstanceType(receiver, JS_REGEXP_TYPE), &if_isjsregexp,
         &if_isnotjsregexp);

  Bind(&if_isjsregexp);
  {
    Node* const source = LoadObjectField(receiver, JSRegExp::kSourceOffset);
    Return(source);
  }

  Bind(&if_isnotjsregexp);
  {
    Isolate* isolate = this->isolate();
    Node* const native_context = LoadNativeContext(context);
    Node* const regexp_fun =
        LoadContextElement(native_context, Context::REGEXP_FUNCTION_INDEX);
    Node* const initial_map =
        LoadObjectField(regexp_fun, JSFunction::kPrototypeOrInitialMapOffset);
    Node* const initial_prototype = LoadMapPrototype(initial_map);

    Label if_isprototype(this), if_isnotprototype(this);
    Branch(WordEqual(receiver, initial_prototype), &if_isprototype,
           &if_isnotprototype);

    Bind(&if_isprototype);
    {
      const int counter = v8::Isolate::kRegExpPrototypeSourceGetter;
      Node* const counter_smi = SmiConstant(counter);
      CallRuntime(Runtime::kIncrementUseCounter, context, counter_smi);

      Node* const result =
          HeapConstant(isolate->factory()->NewStringFromAsciiChecked("(?:)"));
      Return(result);
    }

    Bind(&if_isnotprototype);
    {
      Node* const message_id =
          SmiConstant(Smi::FromInt(MessageTemplate::kRegExpNonRegExp));
      Node* const method_name_str =
          HeapConstant(isolate->factory()->NewStringFromAsciiChecked(
              "RegExp.prototype.source"));
      TailCallRuntime(Runtime::kThrowTypeError, context, message_id,
                      method_name_str);
    }
  }
}

BUILTIN(RegExpPrototypeToString) {
  HandleScope scope(isolate);
  CHECK_RECEIVER(JSReceiver, recv, "RegExp.prototype.toString");

  if (*recv == isolate->regexp_function()->prototype()) {
    isolate->CountUsage(v8::Isolate::kRegExpPrototypeToString);
  }

  IncrementalStringBuilder builder(isolate);

  builder.AppendCharacter('/');
  {
    Handle<Object> source;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
        isolate, source,
        JSReceiver::GetProperty(recv, isolate->factory()->source_string()));
    Handle<String> source_str;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, source_str,
                                       Object::ToString(isolate, source));
    builder.AppendString(source_str);
  }

  builder.AppendCharacter('/');
  {
    Handle<Object> flags;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
        isolate, flags,
        JSReceiver::GetProperty(recv, isolate->factory()->flags_string()));
    Handle<String> flags_str;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, flags_str,
                                       Object::ToString(isolate, flags));
    builder.AppendString(flags_str);
  }

  RETURN_RESULT_OR_FAILURE(isolate, builder.Finish());
}

// Fast-path implementation for flag checks on an unmodified JSRegExp instance.
Node* RegExpBuiltinsAssembler::FastFlagGetter(Node* const regexp,
                                              JSRegExp::Flag flag) {
  Node* const smi_zero = SmiConstant(Smi::kZero);
  Node* const flags = LoadObjectField(regexp, JSRegExp::kFlagsOffset);
  Node* const mask = SmiConstant(Smi::FromInt(flag));
  Node* const is_flag_set = WordNotEqual(SmiAnd(flags, mask), smi_zero);

  return is_flag_set;
}

// Load through the GetProperty stub.
Node* RegExpBuiltinsAssembler::SlowFlagGetter(Node* const context,
                                              Node* const regexp,
                                              JSRegExp::Flag flag) {
  Factory* factory = isolate()->factory();

  Label out(this);
  Variable var_result(this, MachineRepresentation::kWord32);

  Node* name;

  switch (flag) {
    case JSRegExp::kGlobal:
      name = HeapConstant(factory->global_string());
      break;
    case JSRegExp::kIgnoreCase:
      name = HeapConstant(factory->ignoreCase_string());
      break;
    case JSRegExp::kMultiline:
      name = HeapConstant(factory->multiline_string());
      break;
    case JSRegExp::kSticky:
      name = HeapConstant(factory->sticky_string());
      break;
    case JSRegExp::kUnicode:
      name = HeapConstant(factory->unicode_string());
      break;
    default:
      UNREACHABLE();
  }

  Callable getproperty_callable = CodeFactory::GetProperty(isolate());
  Node* const value = CallStub(getproperty_callable, context, regexp, name);

  Label if_true(this), if_false(this);
  BranchIfToBooleanIsTrue(value, &if_true, &if_false);

  Bind(&if_true);
  {
    var_result.Bind(Int32Constant(1));
    Goto(&out);
  }

  Bind(&if_false);
  {
    var_result.Bind(Int32Constant(0));
    Goto(&out);
  }

  Bind(&out);
  return var_result.value();
}

Node* RegExpBuiltinsAssembler::FlagGetter(Node* const context,
                                          Node* const regexp,
                                          JSRegExp::Flag flag,
                                          bool is_fastpath) {
  return is_fastpath ? FastFlagGetter(regexp, flag)
                     : SlowFlagGetter(context, regexp, flag);
}

void RegExpBuiltinsAssembler::FlagGetter(JSRegExp::Flag flag,
                                         v8::Isolate::UseCounterFeature counter,
                                         const char* method_name) {
  Node* const receiver = Parameter(0);
  Node* const context = Parameter(3);

  Isolate* isolate = this->isolate();

  // Check whether we have an unmodified regexp instance.
  Label if_isunmodifiedjsregexp(this),
      if_isnotunmodifiedjsregexp(this, Label::kDeferred);

  GotoIf(TaggedIsSmi(receiver), &if_isnotunmodifiedjsregexp);

  Node* const receiver_map = LoadMap(receiver);
  Node* const instance_type = LoadMapInstanceType(receiver_map);

  Branch(Word32Equal(instance_type, Int32Constant(JS_REGEXP_TYPE)),
         &if_isunmodifiedjsregexp, &if_isnotunmodifiedjsregexp);

  Bind(&if_isunmodifiedjsregexp);
  {
    // Refer to JSRegExp's flag property on the fast-path.
    Node* const is_flag_set = FastFlagGetter(receiver, flag);
    Return(SelectBooleanConstant(is_flag_set));
  }

  Bind(&if_isnotunmodifiedjsregexp);
  {
    Node* const native_context = LoadNativeContext(context);
    Node* const regexp_fun =
        LoadContextElement(native_context, Context::REGEXP_FUNCTION_INDEX);
    Node* const initial_map =
        LoadObjectField(regexp_fun, JSFunction::kPrototypeOrInitialMapOffset);
    Node* const initial_prototype = LoadMapPrototype(initial_map);

    Label if_isprototype(this), if_isnotprototype(this);
    Branch(WordEqual(receiver, initial_prototype), &if_isprototype,
           &if_isnotprototype);

    Bind(&if_isprototype);
    {
      Node* const counter_smi = SmiConstant(Smi::FromInt(counter));
      CallRuntime(Runtime::kIncrementUseCounter, context, counter_smi);
      Return(UndefinedConstant());
    }

    Bind(&if_isnotprototype);
    {
      Node* const message_id =
          SmiConstant(Smi::FromInt(MessageTemplate::kRegExpNonRegExp));
      Node* const method_name_str = HeapConstant(
          isolate->factory()->NewStringFromAsciiChecked(method_name));
      CallRuntime(Runtime::kThrowTypeError, context, message_id,
                  method_name_str);
      Return(UndefinedConstant());  // Never reached.
    }
  }
}

// ES6 21.2.5.4.
TF_BUILTIN(RegExpPrototypeGlobalGetter, RegExpBuiltinsAssembler) {
  FlagGetter(JSRegExp::kGlobal, v8::Isolate::kRegExpPrototypeOldFlagGetter,
             "RegExp.prototype.global");
}

// ES6 21.2.5.5.
TF_BUILTIN(RegExpPrototypeIgnoreCaseGetter, RegExpBuiltinsAssembler) {
  FlagGetter(JSRegExp::kIgnoreCase, v8::Isolate::kRegExpPrototypeOldFlagGetter,
             "RegExp.prototype.ignoreCase");
}

// ES6 21.2.5.7.
TF_BUILTIN(RegExpPrototypeMultilineGetter, RegExpBuiltinsAssembler) {
  FlagGetter(JSRegExp::kMultiline, v8::Isolate::kRegExpPrototypeOldFlagGetter,
             "RegExp.prototype.multiline");
}

// ES6 21.2.5.12.
TF_BUILTIN(RegExpPrototypeStickyGetter, RegExpBuiltinsAssembler) {
  FlagGetter(JSRegExp::kSticky, v8::Isolate::kRegExpPrototypeStickyGetter,
             "RegExp.prototype.sticky");
}

// ES6 21.2.5.15.
TF_BUILTIN(RegExpPrototypeUnicodeGetter, RegExpBuiltinsAssembler) {
  FlagGetter(JSRegExp::kUnicode, v8::Isolate::kRegExpPrototypeUnicodeGetter,
             "RegExp.prototype.unicode");
}

// The properties $1..$9 are the first nine capturing substrings of the last
// successful match, or ''.  The function RegExpMakeCaptureGetter will be
// called with indices from 1 to 9.
#define DEFINE_CAPTURE_GETTER(i)                        \
  BUILTIN(RegExpCapture##i##Getter) {                   \
    HandleScope scope(isolate);                         \
    return *RegExpUtils::GenericCaptureGetter(          \
        isolate, isolate->regexp_last_match_info(), i); \
  }
DEFINE_CAPTURE_GETTER(1)
DEFINE_CAPTURE_GETTER(2)
DEFINE_CAPTURE_GETTER(3)
DEFINE_CAPTURE_GETTER(4)
DEFINE_CAPTURE_GETTER(5)
DEFINE_CAPTURE_GETTER(6)
DEFINE_CAPTURE_GETTER(7)
DEFINE_CAPTURE_GETTER(8)
DEFINE_CAPTURE_GETTER(9)
#undef DEFINE_CAPTURE_GETTER

// The properties `input` and `$_` are aliases for each other.  When this
// value is set, the value it is set to is coerced to a string.
// Getter and setter for the input.

BUILTIN(RegExpInputGetter) {
  HandleScope scope(isolate);
  Handle<Object> obj(isolate->regexp_last_match_info()->LastInput(), isolate);
  return obj->IsUndefined(isolate) ? isolate->heap()->empty_string()
                                   : String::cast(*obj);
}

BUILTIN(RegExpInputSetter) {
  HandleScope scope(isolate);
  Handle<Object> value = args.atOrUndefined(isolate, 1);
  Handle<String> str;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, str,
                                     Object::ToString(isolate, value));
  isolate->regexp_last_match_info()->SetLastInput(*str);
  return isolate->heap()->undefined_value();
}

// Getters for the static properties lastMatch, lastParen, leftContext, and
// rightContext of the RegExp constructor.  The properties are computed based
// on the captures array of the last successful match and the subject string
// of the last successful match.
BUILTIN(RegExpLastMatchGetter) {
  HandleScope scope(isolate);
  return *RegExpUtils::GenericCaptureGetter(
      isolate, isolate->regexp_last_match_info(), 0);
}

BUILTIN(RegExpLastParenGetter) {
  HandleScope scope(isolate);
  Handle<RegExpMatchInfo> match_info = isolate->regexp_last_match_info();
  const int length = match_info->NumberOfCaptureRegisters();
  if (length <= 2) return isolate->heap()->empty_string();  // No captures.

  DCHECK_EQ(0, length % 2);
  const int last_capture = (length / 2) - 1;

  // We match the SpiderMonkey behavior: return the substring defined by the
  // last pair (after the first pair) of elements of the capture array even if
  // it is empty.
  return *RegExpUtils::GenericCaptureGetter(isolate, match_info, last_capture);
}

BUILTIN(RegExpLeftContextGetter) {
  HandleScope scope(isolate);
  Handle<RegExpMatchInfo> match_info = isolate->regexp_last_match_info();
  const int start_index = match_info->Capture(0);
  Handle<String> last_subject(match_info->LastSubject());
  return *isolate->factory()->NewSubString(last_subject, 0, start_index);
}

BUILTIN(RegExpRightContextGetter) {
  HandleScope scope(isolate);
  Handle<RegExpMatchInfo> match_info = isolate->regexp_last_match_info();
  const int start_index = match_info->Capture(1);
  Handle<String> last_subject(match_info->LastSubject());
  const int len = last_subject->length();
  return *isolate->factory()->NewSubString(last_subject, start_index, len);
}

// ES#sec-regexpexec Runtime Semantics: RegExpExec ( R, S )
Node* RegExpBuiltinsAssembler::RegExpExec(Node* context, Node* regexp,
                                          Node* string) {
  Isolate* isolate = this->isolate();

  Node* const null = NullConstant();

  Variable var_result(this, MachineRepresentation::kTagged);
  Label out(this), if_isfastpath(this), if_isslowpath(this);

  Node* const map = LoadMap(regexp);
  BranchIfFastRegExp(context, map, &if_isfastpath, &if_isslowpath);

  Bind(&if_isfastpath);
  {
    Node* const result = RegExpPrototypeExecBody(context, regexp, string, true);
    var_result.Bind(result);
    Goto(&out);
  }

  Bind(&if_isslowpath);
  {
    // Take the slow path of fetching the exec property, calling it, and
    // verifying its return value.

    // Get the exec property.
    Node* const name = HeapConstant(isolate->factory()->exec_string());
    Callable getproperty_callable = CodeFactory::GetProperty(isolate);
    Node* const exec = CallStub(getproperty_callable, context, regexp, name);

    // Is {exec} callable?
    Label if_iscallable(this), if_isnotcallable(this);

    GotoIf(TaggedIsSmi(exec), &if_isnotcallable);

    Node* const exec_map = LoadMap(exec);
    Branch(IsCallableMap(exec_map), &if_iscallable, &if_isnotcallable);

    Bind(&if_iscallable);
    {
      Callable call_callable = CodeFactory::Call(isolate);
      Node* const result = CallJS(call_callable, context, exec, regexp, string);

      var_result.Bind(result);
      GotoIf(WordEqual(result, null), &out);

      ThrowIfNotJSReceiver(context, result,
                           MessageTemplate::kInvalidRegExpExecResult, "unused");

      Goto(&out);
    }

    Bind(&if_isnotcallable);
    {
      ThrowIfNotInstanceType(context, regexp, JS_REGEXP_TYPE,
                             "RegExp.prototype.exec");

      Node* const result =
          RegExpPrototypeExecBody(context, regexp, string, false);
      var_result.Bind(result);
      Goto(&out);
    }
  }

  Bind(&out);
  return var_result.value();
}

// ES#sec-regexp.prototype.test
// RegExp.prototype.test ( S )
TF_BUILTIN(RegExpPrototypeTest, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const maybe_string = Parameter(1);
  Node* const context = Parameter(4);

  // Ensure {maybe_receiver} is a JSReceiver.
  Node* const map = ThrowIfNotJSReceiver(
      context, maybe_receiver, MessageTemplate::kIncompatibleMethodReceiver,
      "RegExp.prototype.test");
  Node* const receiver = maybe_receiver;

  // Convert {maybe_string} to a String.
  Node* const string = ToString(context, maybe_string);

  Label fast_path(this), slow_path(this);
  BranchIfFastRegExp(context, map, &fast_path, &slow_path);

  Bind(&fast_path);
  {
    Label if_didnotmatch(this);
    RegExpPrototypeExecBodyWithoutResult(context, receiver, string,
                                         &if_didnotmatch, true);
    Return(TrueConstant());

    Bind(&if_didnotmatch);
    Return(FalseConstant());
  }

  Bind(&slow_path);
  {
    // Call exec.
    Node* const match_indices = RegExpExec(context, receiver, string);

    // Return true iff exec matched successfully.
    Node* const result =
        SelectBooleanConstant(WordNotEqual(match_indices, NullConstant()));
    Return(result);
  }
}

Node* RegExpBuiltinsAssembler::AdvanceStringIndex(Node* const string,
                                                  Node* const index,
                                                  Node* const is_unicode) {
  // Default to last_index + 1.
  Node* const index_plus_one = SmiAdd(index, SmiConstant(1));
  Variable var_result(this, MachineRepresentation::kTagged, index_plus_one);

  Label if_isunicode(this), out(this);
  Branch(is_unicode, &if_isunicode, &out);

  Bind(&if_isunicode);
  {
    Node* const string_length = LoadStringLength(string);
    GotoUnless(SmiLessThan(index_plus_one, string_length), &out);

    Node* const lead = StringCharCodeAt(string, index);
    GotoUnless(Word32Equal(Word32And(lead, Int32Constant(0xFC00)),
                           Int32Constant(0xD800)),
               &out);

    Node* const trail = StringCharCodeAt(string, index_plus_one);
    GotoUnless(Word32Equal(Word32And(trail, Int32Constant(0xFC00)),
                           Int32Constant(0xDC00)),
               &out);

    // At a surrogate pair, return index + 2.
    Node* const index_plus_two = SmiAdd(index, SmiConstant(2));
    var_result.Bind(index_plus_two);

    Goto(&out);
  }

  Bind(&out);
  return var_result.value();
}

namespace {

// Utility class implementing a growable fixed array through CSA.
class GrowableFixedArray {
  typedef CodeStubAssembler::Label Label;
  typedef CodeStubAssembler::Variable Variable;

 public:
  explicit GrowableFixedArray(CodeStubAssembler* a)
      : assembler_(a),
        var_array_(a, MachineRepresentation::kTagged),
        var_length_(a, MachineType::PointerRepresentation()),
        var_capacity_(a, MachineType::PointerRepresentation()) {
    Initialize();
  }

  Node* length() const { return var_length_.value(); }

  Variable* var_array() { return &var_array_; }
  Variable* var_length() { return &var_length_; }
  Variable* var_capacity() { return &var_capacity_; }

  void Push(Node* const value) {
    CodeStubAssembler* a = assembler_;

    Node* const length = var_length_.value();
    Node* const capacity = var_capacity_.value();

    Label grow(a), store(a);
    a->Branch(a->IntPtrEqual(capacity, length), &grow, &store);

    a->Bind(&grow);
    {
      Node* const new_capacity = NewCapacity(a, capacity);
      Node* const new_array = ResizeFixedArray(length, new_capacity);

      var_capacity_.Bind(new_capacity);
      var_array_.Bind(new_array);
      a->Goto(&store);
    }

    a->Bind(&store);
    {
      Node* const array = var_array_.value();
      a->StoreFixedArrayElement(array, length, value);

      Node* const new_length = a->IntPtrAdd(length, a->IntPtrConstant(1));
      var_length_.Bind(new_length);
    }
  }

  Node* ToJSArray(Node* const context) {
    CodeStubAssembler* a = assembler_;

    const ElementsKind kind = FAST_ELEMENTS;

    Node* const native_context = a->LoadNativeContext(context);
    Node* const array_map = a->LoadJSArrayElementsMap(kind, native_context);

    // Shrink to fit if necessary.
    {
      Label next(a);

      Node* const length = var_length_.value();
      Node* const capacity = var_capacity_.value();

      a->GotoIf(a->WordEqual(length, capacity), &next);

      Node* const array = ResizeFixedArray(length, length);
      var_array_.Bind(array);
      var_capacity_.Bind(length);
      a->Goto(&next);

      a->Bind(&next);
    }

    Node* const result_length = a->SmiTag(length());
    Node* const result = a->AllocateUninitializedJSArrayWithoutElements(
        kind, array_map, result_length, nullptr);

    // Note: We do not currently shrink the fixed array.

    a->StoreObjectField(result, JSObject::kElementsOffset, var_array_.value());

    return result;
  }

 private:
  void Initialize() {
    CodeStubAssembler* a = assembler_;

    const ElementsKind kind = FAST_ELEMENTS;

    static const int kInitialArraySize = 8;
    Node* const capacity = a->IntPtrConstant(kInitialArraySize);
    Node* const array = a->AllocateFixedArray(kind, capacity);

    a->FillFixedArrayWithValue(kind, array, a->IntPtrConstant(0), capacity,
                               Heap::kTheHoleValueRootIndex);

    var_array_.Bind(array);
    var_capacity_.Bind(capacity);
    var_length_.Bind(a->IntPtrConstant(0));
  }

  Node* NewCapacity(CodeStubAssembler* a, Node* const current_capacity) {
    CSA_ASSERT(a, a->IntPtrGreaterThan(current_capacity, a->IntPtrConstant(0)));

    // Growth rate is analog to JSObject::NewElementsCapacity:
    // new_capacity = (current_capacity + (current_capacity >> 1)) + 16.

    Node* const new_capacity = a->IntPtrAdd(
        a->IntPtrAdd(current_capacity, a->WordShr(current_capacity, 1)),
        a->IntPtrConstant(16));

    return new_capacity;
  }

  // Creates a new array with {new_capacity} and copies the first
  // {element_count} elements from the current array.
  Node* ResizeFixedArray(Node* const element_count, Node* const new_capacity) {
    CodeStubAssembler* a = assembler_;

    CSA_ASSERT(a, a->IntPtrGreaterThan(element_count, a->IntPtrConstant(0)));
    CSA_ASSERT(a, a->IntPtrGreaterThan(new_capacity, a->IntPtrConstant(0)));
    CSA_ASSERT(a, a->IntPtrGreaterThanOrEqual(new_capacity, element_count));

    const ElementsKind kind = FAST_ELEMENTS;
    const WriteBarrierMode barrier_mode = UPDATE_WRITE_BARRIER;
    const ParameterMode mode = CodeStubAssembler::INTPTR_PARAMETERS;
    const CodeStubAssembler::AllocationFlags flags =
        CodeStubAssembler::kAllowLargeObjectAllocation;

    Node* const from_array = var_array_.value();
    Node* const to_array =
        a->AllocateFixedArray(kind, new_capacity, mode, flags);
    a->CopyFixedArrayElements(kind, from_array, kind, to_array, element_count,
                              new_capacity, barrier_mode, mode);

    return to_array;
  }

 private:
  CodeStubAssembler* const assembler_;
  Variable var_array_;
  Variable var_length_;
  Variable var_capacity_;
};

}  // namespace

void RegExpBuiltinsAssembler::RegExpPrototypeMatchBody(Node* const context,
                                                       Node* const regexp,
                                                       Node* const string,
                                                       const bool is_fastpath) {
  Isolate* const isolate = this->isolate();

  Node* const null = NullConstant();
  Node* const int_zero = IntPtrConstant(0);
  Node* const smi_zero = SmiConstant(Smi::kZero);

  Node* const is_global =
      FlagGetter(context, regexp, JSRegExp::kGlobal, is_fastpath);

  Label if_isglobal(this), if_isnotglobal(this);
  Branch(is_global, &if_isglobal, &if_isnotglobal);

  Bind(&if_isnotglobal);
  {
    Node* const result =
        is_fastpath ? RegExpPrototypeExecBody(context, regexp, string, true)
                    : RegExpExec(context, regexp, string);
    Return(result);
  }

  Bind(&if_isglobal);
  {
    Node* const is_unicode =
        FlagGetter(context, regexp, JSRegExp::kUnicode, is_fastpath);

    StoreLastIndex(context, regexp, smi_zero, is_fastpath);

    // Allocate an array to store the resulting match strings.

    GrowableFixedArray array(this);

    // Loop preparations. Within the loop, collect results from RegExpExec
    // and store match strings in the array.

    Variable* vars[] = {array.var_array(), array.var_length(),
                        array.var_capacity()};
    Label loop(this, 3, vars), out(this);
    Goto(&loop);

    Bind(&loop);
    {
      Variable var_match(this, MachineRepresentation::kTagged);

      Label if_didmatch(this), if_didnotmatch(this);
      if (is_fastpath) {
        // On the fast path, grab the matching string from the raw match index
        // array.
        Node* const match_indices = RegExpPrototypeExecBodyWithoutResult(
            context, regexp, string, &if_didnotmatch, true);

        Node* const match_from = LoadFixedArrayElement(
            match_indices, RegExpMatchInfo::kFirstCaptureIndex);
        Node* const match_to = LoadFixedArrayElement(
            match_indices, RegExpMatchInfo::kFirstCaptureIndex + 1);

        Node* match = SubString(context, string, match_from, match_to);
        var_match.Bind(match);

        Goto(&if_didmatch);
      } else {
        DCHECK(!is_fastpath);
        Node* const result = RegExpExec(context, regexp, string);

        Label load_match(this);
        Branch(WordEqual(result, null), &if_didnotmatch, &load_match);

        Bind(&load_match);
        {
          Label fast_result(this), slow_result(this);
          BranchIfFastRegExpResult(context, LoadMap(result), &fast_result,
                                   &slow_result);

          Bind(&fast_result);
          {
            Node* const result_fixed_array = LoadElements(result);
            Node* const match = LoadFixedArrayElement(result_fixed_array, 0);

            // The match is guaranteed to be a string on the fast path.
            CSA_ASSERT(this, IsStringInstanceType(LoadInstanceType(match)));

            var_match.Bind(match);
            Goto(&if_didmatch);
          }

          Bind(&slow_result);
          {
            // TODO(ishell): Use GetElement stub once it's available.
            Node* const name = smi_zero;
            Callable getproperty_callable = CodeFactory::GetProperty(isolate);
            Node* const match =
                CallStub(getproperty_callable, context, result, name);

            var_match.Bind(ToString(context, match));
            Goto(&if_didmatch);
          }
        }
      }

      Bind(&if_didnotmatch);
      {
        // Return null if there were no matches, otherwise just exit the loop.
        GotoUnless(IntPtrEqual(array.length(), int_zero), &out);
        Return(null);
      }

      Bind(&if_didmatch);
      {
        Node* match = var_match.value();

        // Store the match, growing the fixed array if needed.

        array.Push(match);

        // Advance last index if the match is the empty string.

        Node* const match_length = LoadStringLength(match);
        GotoUnless(SmiEqual(match_length, smi_zero), &loop);

        Node* last_index = LoadLastIndex(context, regexp, is_fastpath);

        Callable tolength_callable = CodeFactory::ToLength(isolate);
        last_index = CallStub(tolength_callable, context, last_index);

        Node* const new_last_index =
            AdvanceStringIndex(string, last_index, is_unicode);

        StoreLastIndex(context, regexp, new_last_index, is_fastpath);

        Goto(&loop);
      }
    }

    Bind(&out);
    {
      // Wrap the match in a JSArray.

      Node* const result = array.ToJSArray(context);
      Return(result);
    }
  }
}

// ES#sec-regexp.prototype-@@match
// RegExp.prototype [ @@match ] ( string )
TF_BUILTIN(RegExpPrototypeMatch, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const maybe_string = Parameter(1);
  Node* const context = Parameter(4);

  // Ensure {maybe_receiver} is a JSReceiver.
  Node* const map = ThrowIfNotJSReceiver(
      context, maybe_receiver, MessageTemplate::kIncompatibleMethodReceiver,
      "RegExp.prototype.@@match");
  Node* const receiver = maybe_receiver;

  // Convert {maybe_string} to a String.
  Node* const string = ToString(context, maybe_string);

  Label fast_path(this), slow_path(this);
  BranchIfFastRegExp(context, map, &fast_path, &slow_path);

  Bind(&fast_path);
  RegExpPrototypeMatchBody(context, receiver, string, true);

  Bind(&slow_path);
  RegExpPrototypeMatchBody(context, receiver, string, false);
}

void RegExpBuiltinsAssembler::RegExpPrototypeSearchBodyFast(
    Node* const context, Node* const regexp, Node* const string) {
  // Grab the initial value of last index.
  Node* const previous_last_index = FastLoadLastIndex(regexp);

  // Ensure last index is 0.
  FastStoreLastIndex(regexp, SmiConstant(Smi::kZero));

  // Call exec.
  Label if_didnotmatch(this);
  Node* const match_indices = RegExpPrototypeExecBodyWithoutResult(
      context, regexp, string, &if_didnotmatch, true);

  // Successful match.
  {
    // Reset last index.
    FastStoreLastIndex(regexp, previous_last_index);

    // Return the index of the match.
    Node* const index = LoadFixedArrayElement(
        match_indices, RegExpMatchInfo::kFirstCaptureIndex);
    Return(index);
  }

  Bind(&if_didnotmatch);
  {
    // Reset last index and return -1.
    FastStoreLastIndex(regexp, previous_last_index);
    Return(SmiConstant(-1));
  }
}

void RegExpBuiltinsAssembler::RegExpPrototypeSearchBodySlow(
    Node* const context, Node* const regexp, Node* const string) {
  Isolate* const isolate = this->isolate();

  Node* const smi_zero = SmiConstant(Smi::kZero);

  // Grab the initial value of last index.
  Node* const previous_last_index = SlowLoadLastIndex(context, regexp);

  // Ensure last index is 0.
  {
    Label next(this);
    GotoIf(SameValue(previous_last_index, smi_zero, context), &next);

    SlowStoreLastIndex(context, regexp, smi_zero);
    Goto(&next);
    Bind(&next);
  }

  // Call exec.
  Node* const exec_result = RegExpExec(context, regexp, string);

  // Reset last index if necessary.
  {
    Label next(this);
    Node* const current_last_index = SlowLoadLastIndex(context, regexp);

    GotoIf(SameValue(current_last_index, previous_last_index, context), &next);

    SlowStoreLastIndex(context, regexp, previous_last_index);
    Goto(&next);

    Bind(&next);
  }

  // Return -1 if no match was found.
  {
    Label next(this);
    GotoUnless(WordEqual(exec_result, NullConstant()), &next);
    Return(SmiConstant(-1));
    Bind(&next);
  }

  // Return the index of the match.
  {
    Label fast_result(this), slow_result(this, Label::kDeferred);
    BranchIfFastRegExpResult(context, LoadMap(exec_result), &fast_result,
                             &slow_result);

    Bind(&fast_result);
    {
      Node* const index =
          LoadObjectField(exec_result, JSRegExpResult::kIndexOffset);
      Return(index);
    }

    Bind(&slow_result);
    {
      Node* const name = HeapConstant(isolate->factory()->index_string());
      Callable getproperty_callable = CodeFactory::GetProperty(isolate);
      Node* const index =
          CallStub(getproperty_callable, context, exec_result, name);
      Return(index);
    }
  }
}

// ES#sec-regexp.prototype-@@search
// RegExp.prototype [ @@search ] ( string )
TF_BUILTIN(RegExpPrototypeSearch, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const maybe_string = Parameter(1);
  Node* const context = Parameter(4);

  // Ensure {maybe_receiver} is a JSReceiver.
  Node* const map = ThrowIfNotJSReceiver(
      context, maybe_receiver, MessageTemplate::kIncompatibleMethodReceiver,
      "RegExp.prototype.@@search");
  Node* const receiver = maybe_receiver;

  // Convert {maybe_string} to a String.
  Node* const string = ToString(context, maybe_string);

  Label fast_path(this), slow_path(this);
  BranchIfFastRegExp(context, map, &fast_path, &slow_path);

  Bind(&fast_path);
  RegExpPrototypeSearchBodyFast(context, receiver, string);

  Bind(&slow_path);
  RegExpPrototypeSearchBodySlow(context, receiver, string);
}

// Generates the fast path for @@split. {regexp} is an unmodified JSRegExp,
// {string} is a String, and {limit} is a Smi.
void RegExpBuiltinsAssembler::RegExpPrototypeSplitBody(Node* const context,
                                                       Node* const regexp,
                                                       Node* const string,
                                                       Node* const limit) {
  Isolate* isolate = this->isolate();

  Node* const null = NullConstant();
  Node* const smi_zero = SmiConstant(0);
  Node* const int_zero = IntPtrConstant(0);
  Node* const int_limit = SmiUntag(limit);

  const ElementsKind kind = FAST_ELEMENTS;
  const ParameterMode mode = CodeStubAssembler::INTPTR_PARAMETERS;

  Node* const allocation_site = nullptr;
  Node* const native_context = LoadNativeContext(context);
  Node* const array_map = LoadJSArrayElementsMap(kind, native_context);

  Label return_empty_array(this, Label::kDeferred);

  // If limit is zero, return an empty array.
  {
    Label next(this), if_limitiszero(this, Label::kDeferred);
    Branch(SmiEqual(limit, smi_zero), &return_empty_array, &next);
    Bind(&next);
  }

  Node* const string_length = LoadStringLength(string);

  // If passed the empty {string}, return either an empty array or a singleton
  // array depending on whether the {regexp} matches.
  {
    Label next(this), if_stringisempty(this, Label::kDeferred);
    Branch(SmiEqual(string_length, smi_zero), &if_stringisempty, &next);

    Bind(&if_stringisempty);
    {
      Node* const last_match_info = LoadContextElement(
          native_context, Context::REGEXP_LAST_MATCH_INFO_INDEX);

      Callable exec_callable = CodeFactory::RegExpExec(isolate);
      Node* const match_indices = CallStub(exec_callable, context, regexp,
                                           string, smi_zero, last_match_info);

      Label return_singleton_array(this);
      Branch(WordEqual(match_indices, null), &return_singleton_array,
             &return_empty_array);

      Bind(&return_singleton_array);
      {
        Node* const length = SmiConstant(1);
        Node* const capacity = IntPtrConstant(1);
        Node* const result = AllocateJSArray(kind, array_map, capacity, length,
                                             allocation_site, mode);

        Node* const fixed_array = LoadElements(result);
        StoreFixedArrayElement(fixed_array, 0, string);

        Return(result);
      }
    }

    Bind(&next);
  }

  // Loop preparations.

  GrowableFixedArray array(this);

  Variable var_last_matched_until(this, MachineRepresentation::kTagged);
  Variable var_next_search_from(this, MachineRepresentation::kTagged);

  var_last_matched_until.Bind(smi_zero);
  var_next_search_from.Bind(smi_zero);

  Variable* vars[] = {array.var_array(), array.var_length(),
                      array.var_capacity(), &var_last_matched_until,
                      &var_next_search_from};
  const int vars_count = sizeof(vars) / sizeof(vars[0]);
  Label loop(this, vars_count, vars), push_suffix_and_out(this), out(this);
  Goto(&loop);

  Bind(&loop);
  {
    Node* const next_search_from = var_next_search_from.value();
    Node* const last_matched_until = var_last_matched_until.value();

    // We're done if we've reached the end of the string.
    {
      Label next(this);
      Branch(SmiEqual(next_search_from, string_length), &push_suffix_and_out,
             &next);
      Bind(&next);
    }

    // Search for the given {regexp}.

    Node* const last_match_info = LoadContextElement(
        native_context, Context::REGEXP_LAST_MATCH_INFO_INDEX);

    Callable exec_callable = CodeFactory::RegExpExec(isolate);
    Node* const match_indices = CallStub(exec_callable, context, regexp, string,
                                         next_search_from, last_match_info);

    // We're done if no match was found.
    {
      Label next(this);
      Branch(WordEqual(match_indices, null), &push_suffix_and_out, &next);
      Bind(&next);
    }

    Node* const match_from = LoadFixedArrayElement(
        match_indices, RegExpMatchInfo::kFirstCaptureIndex);

    // We're done if the match starts beyond the string.
    {
      Label next(this);
      Branch(WordEqual(match_from, string_length), &push_suffix_and_out, &next);
      Bind(&next);
    }

    Node* const match_to = LoadFixedArrayElement(
        match_indices, RegExpMatchInfo::kFirstCaptureIndex + 1);

    // Advance index and continue if the match is empty.
    {
      Label next(this);

      GotoUnless(SmiEqual(match_to, next_search_from), &next);
      GotoUnless(SmiEqual(match_to, last_matched_until), &next);

      Node* const is_unicode = FastFlagGetter(regexp, JSRegExp::kUnicode);
      Node* const new_next_search_from =
          AdvanceStringIndex(string, next_search_from, is_unicode);
      var_next_search_from.Bind(new_next_search_from);
      Goto(&loop);

      Bind(&next);
    }

    // A valid match was found, add the new substring to the array.
    {
      Node* const from = last_matched_until;
      Node* const to = match_from;

      Node* const substr = SubString(context, string, from, to);
      array.Push(substr);

      GotoIf(WordEqual(array.length(), int_limit), &out);
    }

    // Add all captures to the array.
    {
      Node* const num_registers = LoadFixedArrayElement(
          match_indices, RegExpMatchInfo::kNumberOfCapturesIndex);
      Node* const int_num_registers = SmiUntag(num_registers);

      Variable var_reg(this, MachineType::PointerRepresentation());
      var_reg.Bind(IntPtrConstant(2));

      Variable* vars[] = {array.var_array(), array.var_length(),
                          array.var_capacity(), &var_reg};
      const int vars_count = sizeof(vars) / sizeof(vars[0]);
      Label nested_loop(this, vars_count, vars), nested_loop_out(this);
      Branch(IntPtrLessThan(var_reg.value(), int_num_registers), &nested_loop,
             &nested_loop_out);

      Bind(&nested_loop);
      {
        Node* const reg = var_reg.value();
        Node* const from = LoadFixedArrayElement(
            match_indices, reg,
            RegExpMatchInfo::kFirstCaptureIndex * kPointerSize, mode);
        Node* const to = LoadFixedArrayElement(
            match_indices, reg,
            (RegExpMatchInfo::kFirstCaptureIndex + 1) * kPointerSize, mode);

        Label select_capture(this), select_undefined(this), store_value(this);
        Variable var_value(this, MachineRepresentation::kTagged);
        Branch(SmiEqual(to, SmiConstant(-1)), &select_undefined,
               &select_capture);

        Bind(&select_capture);
        {
          Node* const substr = SubString(context, string, from, to);
          var_value.Bind(substr);
          Goto(&store_value);
        }

        Bind(&select_undefined);
        {
          Node* const undefined = UndefinedConstant();
          var_value.Bind(undefined);
          Goto(&store_value);
        }

        Bind(&store_value);
        {
          array.Push(var_value.value());
          GotoIf(WordEqual(array.length(), int_limit), &out);

          Node* const new_reg = IntPtrAdd(reg, IntPtrConstant(2));
          var_reg.Bind(new_reg);

          Branch(IntPtrLessThan(new_reg, int_num_registers), &nested_loop,
                 &nested_loop_out);
        }
      }

      Bind(&nested_loop_out);
    }

    var_last_matched_until.Bind(match_to);
    var_next_search_from.Bind(match_to);
    Goto(&loop);
  }

  Bind(&push_suffix_and_out);
  {
    Node* const from = var_last_matched_until.value();
    Node* const to = string_length;

    Node* const substr = SubString(context, string, from, to);
    array.Push(substr);

    Goto(&out);
  }

  Bind(&out);
  {
    Node* const result = array.ToJSArray(context);
    Return(result);
  }

  Bind(&return_empty_array);
  {
    Node* const length = smi_zero;
    Node* const capacity = int_zero;
    Node* const result = AllocateJSArray(kind, array_map, capacity, length,
                                         allocation_site, mode);
    Return(result);
  }
}

// ES#sec-regexp.prototype-@@split
// RegExp.prototype [ @@split ] ( string, limit )
TF_BUILTIN(RegExpPrototypeSplit, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const maybe_string = Parameter(1);
  Node* const maybe_limit = Parameter(2);
  Node* const context = Parameter(5);

  // Ensure {maybe_receiver} is a JSReceiver.
  Node* const map = ThrowIfNotJSReceiver(
      context, maybe_receiver, MessageTemplate::kIncompatibleMethodReceiver,
      "RegExp.prototype.@@split");
  Node* const receiver = maybe_receiver;

  // Convert {maybe_string} to a String.
  Node* const string = ToString(context, maybe_string);

  Label fast_path(this), slow_path(this);
  BranchIfFastRegExp(context, map, &fast_path, &slow_path);

  Bind(&fast_path);
  {
    // TODO(jgruber): Even if map checks send us to the fast path, we still need
    // to verify the constructor property and jump to the slow path if it has
    // been changed.

    // Convert {maybe_limit} to a uint32, capping at the maximal smi value.
    Variable var_limit(this, MachineRepresentation::kTagged);
    Label if_limitissmimax(this), limit_done(this);

    GotoIf(IsUndefined(maybe_limit), &if_limitissmimax);

    {
      Node* const limit = ToUint32(context, maybe_limit);
      GotoUnless(TaggedIsSmi(limit), &if_limitissmimax);

      var_limit.Bind(limit);
      Goto(&limit_done);
    }

    Bind(&if_limitissmimax);
    {
      // TODO(jgruber): In this case, we can probably generation of limit checks
      // in Generate_RegExpPrototypeSplitBody.
      Node* const smi_max = SmiConstant(Smi::kMaxValue);
      var_limit.Bind(smi_max);
      Goto(&limit_done);
    }

    Bind(&limit_done);
    {
      Node* const limit = var_limit.value();
      RegExpPrototypeSplitBody(context, receiver, string, limit);
    }
  }

  Bind(&slow_path);
  {
    Node* const result = CallRuntime(Runtime::kRegExpSplit, context, receiver,
                                     string, maybe_limit);
    Return(result);
  }
}

Node* RegExpBuiltinsAssembler::ReplaceGlobalCallableFastPath(
    Node* context, Node* regexp, Node* string, Node* replace_callable) {
  // The fast path is reached only if {receiver} is a global unmodified
  // JSRegExp instance and {replace_callable} is callable.

  Isolate* const isolate = this->isolate();

  Node* const null = NullConstant();
  Node* const undefined = UndefinedConstant();
  Node* const int_zero = IntPtrConstant(0);
  Node* const int_one = IntPtrConstant(1);
  Node* const smi_zero = SmiConstant(Smi::kZero);

  Node* const native_context = LoadNativeContext(context);

  Label out(this);
  Variable var_result(this, MachineRepresentation::kTagged);

  // Set last index to 0.
  FastStoreLastIndex(regexp, smi_zero);

  // Allocate {result_array}.
  Node* result_array;
  {
    ElementsKind kind = FAST_ELEMENTS;
    Node* const array_map = LoadJSArrayElementsMap(kind, native_context);
    Node* const capacity = IntPtrConstant(16);
    Node* const length = smi_zero;
    Node* const allocation_site = nullptr;
    ParameterMode capacity_mode = CodeStubAssembler::INTPTR_PARAMETERS;

    result_array = AllocateJSArray(kind, array_map, capacity, length,
                                   allocation_site, capacity_mode);
  }

  // Call into runtime for RegExpExecMultiple.
  Node* last_match_info =
      LoadContextElement(native_context, Context::REGEXP_LAST_MATCH_INFO_INDEX);
  Node* const res = CallRuntime(Runtime::kRegExpExecMultiple, context, regexp,
                                string, last_match_info, result_array);

  // Reset last index to 0.
  FastStoreLastIndex(regexp, smi_zero);

  // If no matches, return the subject string.
  var_result.Bind(string);
  GotoIf(WordEqual(res, null), &out);

  // Reload last match info since it might have changed.
  last_match_info =
      LoadContextElement(native_context, Context::REGEXP_LAST_MATCH_INFO_INDEX);

  Node* const res_length = LoadJSArrayLength(res);
  Node* const res_elems = LoadElements(res);
  CSA_ASSERT(this, HasInstanceType(res_elems, FIXED_ARRAY_TYPE));

  Node* const num_capture_registers = LoadFixedArrayElement(
      last_match_info, RegExpMatchInfo::kNumberOfCapturesIndex);

  Label if_hasexplicitcaptures(this), if_noexplicitcaptures(this),
      create_result(this);
  Branch(SmiEqual(num_capture_registers, SmiConstant(Smi::FromInt(2))),
         &if_noexplicitcaptures, &if_hasexplicitcaptures);

  Bind(&if_noexplicitcaptures);
  {
    // If the number of captures is two then there are no explicit captures in
    // the regexp, just the implicit capture that captures the whole match. In
    // this case we can simplify quite a bit and end up with something faster.
    // The builder will consist of some integers that indicate slices of the
    // input string and some replacements that were returned from the replace
    // function.

    Variable var_match_start(this, MachineRepresentation::kTagged);
    var_match_start.Bind(smi_zero);

    Node* const end = SmiUntag(res_length);
    Variable var_i(this, MachineType::PointerRepresentation());
    var_i.Bind(int_zero);

    Variable* vars[] = {&var_i, &var_match_start};
    Label loop(this, 2, vars);
    Goto(&loop);
    Bind(&loop);
    {
      Node* const i = var_i.value();
      GotoUnless(IntPtrLessThan(i, end), &create_result);

      Node* const elem = LoadFixedArrayElement(res_elems, i);

      Label if_issmi(this), if_isstring(this), loop_epilogue(this);
      Branch(TaggedIsSmi(elem), &if_issmi, &if_isstring);

      Bind(&if_issmi);
      {
        // Integers represent slices of the original string.
        Label if_isnegativeorzero(this), if_ispositive(this);
        BranchIfSmiLessThanOrEqual(elem, smi_zero, &if_isnegativeorzero,
                                   &if_ispositive);

        Bind(&if_ispositive);
        {
          Node* const int_elem = SmiUntag(elem);
          Node* const new_match_start =
              IntPtrAdd(WordShr(int_elem, IntPtrConstant(11)),
                        WordAnd(int_elem, IntPtrConstant(0x7ff)));
          var_match_start.Bind(SmiTag(new_match_start));
          Goto(&loop_epilogue);
        }

        Bind(&if_isnegativeorzero);
        {
          Node* const next_i = IntPtrAdd(i, int_one);
          var_i.Bind(next_i);

          Node* const next_elem = LoadFixedArrayElement(res_elems, next_i);

          Node* const new_match_start = SmiSub(next_elem, elem);
          var_match_start.Bind(new_match_start);
          Goto(&loop_epilogue);
        }
      }

      Bind(&if_isstring);
      {
        CSA_ASSERT(this, IsStringInstanceType(LoadInstanceType(elem)));

        Callable call_callable = CodeFactory::Call(isolate);
        Node* const replacement_obj =
            CallJS(call_callable, context, replace_callable, undefined, elem,
                   var_match_start.value(), string);

        Node* const replacement_str = ToString(context, replacement_obj);
        StoreFixedArrayElement(res_elems, i, replacement_str);

        Node* const elem_length = LoadStringLength(elem);
        Node* const new_match_start =
            SmiAdd(var_match_start.value(), elem_length);
        var_match_start.Bind(new_match_start);

        Goto(&loop_epilogue);
      }

      Bind(&loop_epilogue);
      {
        var_i.Bind(IntPtrAdd(var_i.value(), int_one));
        Goto(&loop);
      }
    }
  }

  Bind(&if_hasexplicitcaptures);
  {
    Node* const from = int_zero;
    Node* const to = SmiUntag(res_length);
    const int increment = 1;

    BuildFastLoop(
        MachineType::PointerRepresentation(), from, to,
        [this, res_elems, isolate, native_context, context, undefined,
         replace_callable](Node* index) {
          Node* const elem = LoadFixedArrayElement(res_elems, index);

          Label do_continue(this);
          GotoIf(TaggedIsSmi(elem), &do_continue);

          // elem must be an Array.
          // Use the apply argument as backing for global RegExp properties.

          CSA_ASSERT(this, HasInstanceType(elem, JS_ARRAY_TYPE));

          // TODO(jgruber): Remove indirection through Call->ReflectApply.
          Callable call_callable = CodeFactory::Call(isolate);
          Node* const reflect_apply =
              LoadContextElement(native_context, Context::REFLECT_APPLY_INDEX);

          Node* const replacement_obj =
              CallJS(call_callable, context, reflect_apply, undefined,
                     replace_callable, undefined, elem);

          // Overwrite the i'th element in the results with the string we got
          // back from the callback function.

          Node* const replacement_str = ToString(context, replacement_obj);
          StoreFixedArrayElement(res_elems, index, replacement_str);

          Goto(&do_continue);
          Bind(&do_continue);
        },
        increment, CodeStubAssembler::IndexAdvanceMode::kPost);

    Goto(&create_result);
  }

  Bind(&create_result);
  {
    Node* const result = CallRuntime(Runtime::kStringBuilderConcat, context,
                                     res, res_length, string);
    var_result.Bind(result);
    Goto(&out);
  }

  Bind(&out);
  return var_result.value();
}

Node* RegExpBuiltinsAssembler::ReplaceSimpleStringFastPath(
    Node* context, Node* regexp, Node* string, Node* replace_string) {
  // The fast path is reached only if {receiver} is an unmodified
  // JSRegExp instance, {replace_value} is non-callable, and
  // ToString({replace_value}) does not contain '$', i.e. we're doing a simple
  // string replacement.

  Isolate* const isolate = this->isolate();

  Node* const null = NullConstant();
  Node* const int_zero = IntPtrConstant(0);
  Node* const smi_zero = SmiConstant(Smi::kZero);

  Label out(this);
  Variable var_result(this, MachineRepresentation::kTagged);

  // Load the last match info.
  Node* const native_context = LoadNativeContext(context);
  Node* const last_match_info =
      LoadContextElement(native_context, Context::REGEXP_LAST_MATCH_INFO_INDEX);

  // Is {regexp} global?
  Label if_isglobal(this), if_isnonglobal(this);
  Node* const flags = LoadObjectField(regexp, JSRegExp::kFlagsOffset);
  Node* const is_global =
      WordAnd(SmiUntag(flags), IntPtrConstant(JSRegExp::kGlobal));
  Branch(WordEqual(is_global, int_zero), &if_isnonglobal, &if_isglobal);

  Bind(&if_isglobal);
  {
    // Hand off global regexps to runtime.
    FastStoreLastIndex(regexp, smi_zero);
    Node* const result =
        CallRuntime(Runtime::kStringReplaceGlobalRegExpWithString, context,
                    string, regexp, replace_string, last_match_info);
    var_result.Bind(result);
    Goto(&out);
  }

  Bind(&if_isnonglobal);
  {
    // Run exec, then manually construct the resulting string.
    Callable exec_callable = CodeFactory::RegExpExec(isolate);
    Node* const match_indices = CallStub(exec_callable, context, regexp, string,
                                         smi_zero, last_match_info);

    Label if_matched(this), if_didnotmatch(this);
    Branch(WordEqual(match_indices, null), &if_didnotmatch, &if_matched);

    Bind(&if_didnotmatch);
    {
      FastStoreLastIndex(regexp, smi_zero);
      var_result.Bind(string);
      Goto(&out);
    }

    Bind(&if_matched);
    {
      Node* const subject_start = smi_zero;
      Node* const match_start = LoadFixedArrayElement(
          match_indices, RegExpMatchInfo::kFirstCaptureIndex);
      Node* const match_end = LoadFixedArrayElement(
          match_indices, RegExpMatchInfo::kFirstCaptureIndex + 1);
      Node* const subject_end = LoadStringLength(string);

      Label if_replaceisempty(this), if_replaceisnotempty(this);
      Node* const replace_length = LoadStringLength(replace_string);
      Branch(SmiEqual(replace_length, smi_zero), &if_replaceisempty,
             &if_replaceisnotempty);

      Bind(&if_replaceisempty);
      {
        // TODO(jgruber): We could skip many of the checks that using SubString
        // here entails.

        Node* const first_part =
            SubString(context, string, subject_start, match_start);
        Node* const second_part =
            SubString(context, string, match_end, subject_end);

        Node* const result = StringAdd(context, first_part, second_part);
        var_result.Bind(result);
        Goto(&out);
      }

      Bind(&if_replaceisnotempty);
      {
        Node* const first_part =
            SubString(context, string, subject_start, match_start);
        Node* const second_part = replace_string;
        Node* const third_part =
            SubString(context, string, match_end, subject_end);

        Node* result = StringAdd(context, first_part, second_part);
        result = StringAdd(context, result, third_part);

        var_result.Bind(result);
        Goto(&out);
      }
    }
  }

  Bind(&out);
  return var_result.value();
}

// ES#sec-regexp.prototype-@@replace
// RegExp.prototype [ @@replace ] ( string, replaceValue )
TF_BUILTIN(RegExpPrototypeReplace, RegExpBuiltinsAssembler) {
  Node* const maybe_receiver = Parameter(0);
  Node* const maybe_string = Parameter(1);
  Node* const replace_value = Parameter(2);
  Node* const context = Parameter(5);

  // Ensure {maybe_receiver} is a JSReceiver.
  Node* const map = ThrowIfNotJSReceiver(
      context, maybe_receiver, MessageTemplate::kIncompatibleMethodReceiver,
      "RegExp.prototype.@@replace");
  Node* const receiver = maybe_receiver;

  // Convert {maybe_string} to a String.
  Callable tostring_callable = CodeFactory::ToString(isolate());
  Node* const string = CallStub(tostring_callable, context, maybe_string);

  // Fast-path checks: 1. Is the {receiver} an unmodified JSRegExp instance?
  Label checkreplacecallable(this), runtime(this, Label::kDeferred),
      fastpath(this);
  BranchIfFastRegExp(context, map, &checkreplacecallable, &runtime);

  Bind(&checkreplacecallable);
  Node* const regexp = receiver;

  // 2. Is {replace_value} callable?
  Label checkreplacestring(this), if_iscallable(this);
  GotoIf(TaggedIsSmi(replace_value), &checkreplacestring);

  Node* const replace_value_map = LoadMap(replace_value);
  Branch(IsCallableMap(replace_value_map), &if_iscallable, &checkreplacestring);

  // 3. Does ToString({replace_value}) contain '$'?
  Bind(&checkreplacestring);
  {
    Node* const replace_string =
        CallStub(tostring_callable, context, replace_value);

    Node* const dollar_char = Int32Constant('$');
    Node* const smi_minusone = SmiConstant(Smi::FromInt(-1));
    GotoUnless(SmiEqual(StringIndexOfChar(context, replace_string, dollar_char,
                                          SmiConstant(0)),
                        smi_minusone),
               &runtime);

    Return(
        ReplaceSimpleStringFastPath(context, regexp, string, replace_string));
  }

  // {regexp} is unmodified and {replace_value} is callable.
  Bind(&if_iscallable);
  {
    Node* const replace_callable = replace_value;

    // Check if the {regexp} is global.
    Label if_isglobal(this), if_isnotglobal(this);
    Node* const is_global = FastFlagGetter(regexp, JSRegExp::kGlobal);
    Branch(is_global, &if_isglobal, &if_isnotglobal);

    Bind(&if_isglobal);
    {
      Node* const result = ReplaceGlobalCallableFastPath(
          context, regexp, string, replace_callable);
      Return(result);
    }

    Bind(&if_isnotglobal);
    {
      Node* const result =
          CallRuntime(Runtime::kStringReplaceNonGlobalRegExpWithFunction,
                      context, string, regexp, replace_callable);
      Return(result);
    }
  }

  Bind(&runtime);
  {
    Node* const result = CallRuntime(Runtime::kRegExpReplace, context, receiver,
                                     string, replace_value);
    Return(result);
  }
}

// Simple string matching functionality for internal use which does not modify
// the last match info.
TF_BUILTIN(RegExpInternalMatch, RegExpBuiltinsAssembler) {
  Node* const regexp = Parameter(1);
  Node* const string = Parameter(2);
  Node* const context = Parameter(5);

  Node* const null = NullConstant();
  Node* const smi_zero = SmiConstant(Smi::FromInt(0));

  Node* const native_context = LoadNativeContext(context);
  Node* const internal_match_info = LoadContextElement(
      native_context, Context::REGEXP_INTERNAL_MATCH_INFO_INDEX);

  Callable exec_callable = CodeFactory::RegExpExec(isolate());
  Node* const match_indices = CallStub(exec_callable, context, regexp, string,
                                       smi_zero, internal_match_info);

  Label if_matched(this), if_didnotmatch(this);
  Branch(WordEqual(match_indices, null), &if_didnotmatch, &if_matched);

  Bind(&if_didnotmatch);
  Return(null);

  Bind(&if_matched);
  {
    Node* result =
        ConstructNewResultFromMatchInfo(context, regexp, match_indices, string);
    Return(result);
  }
}

}  // namespace internal
}  // namespace v8