src/v8/src/builtins/builtins-iterator-gen.cc

// Copyright 2017 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-iterator-gen.h"
#include "src/builtins/growable-fixed-array-gen.h"

#include "src/builtins/builtins-collections-gen.h"
#include "src/builtins/builtins-string-gen.h"
#include "src/builtins/builtins-utils-gen.h"
#include "src/builtins/builtins.h"
#include "src/codegen/code-stub-assembler.h"
#include "src/heap/factory-inl.h"

namespace v8 {
namespace internal {

using IteratorRecord = TorqueStructIteratorRecord;
using compiler::Node;

TNode<Object> IteratorBuiltinsAssembler::GetIteratorMethod(Node* context,
                                                           Node* object) {
  return GetProperty(context, object, factory()->iterator_symbol());
}

IteratorRecord IteratorBuiltinsAssembler::GetIterator(Node* context,
                                                      Node* object,
                                                      Label* if_exception,
                                                      Variable* exception) {
  Node* method = GetIteratorMethod(context, object);
  return GetIterator(context, object, method, if_exception, exception);
}

IteratorRecord IteratorBuiltinsAssembler::GetIterator(Node* context,
                                                      Node* object,
                                                      Node* method,
                                                      Label* if_exception,
                                                      Variable* exception) {
  GotoIfException(method, if_exception, exception);

  Label if_not_callable(this, Label::kDeferred), if_callable(this);
  GotoIf(TaggedIsSmi(method), &if_not_callable);
  Branch(IsCallable(method), &if_callable, &if_not_callable);

  BIND(&if_not_callable);
  {
    Node* ret = CallRuntime(Runtime::kThrowIteratorError, context, object);
    GotoIfException(ret, if_exception, exception);
    Unreachable();
  }

  BIND(&if_callable);
  {
    Callable callable = CodeFactory::Call(isolate());
    Node* iterator = CallJS(callable, context, method, object);
    GotoIfException(iterator, if_exception, exception);

    Label get_next(this), if_notobject(this, Label::kDeferred);
    GotoIf(TaggedIsSmi(iterator), &if_notobject);
    Branch(IsJSReceiver(iterator), &get_next, &if_notobject);

    BIND(&if_notobject);
    {
      Node* ret = CallRuntime(Runtime::kThrowSymbolIteratorInvalid, context);
      GotoIfException(ret, if_exception, exception);
      Unreachable();
    }

    BIND(&get_next);
    Node* const next = GetProperty(context, iterator, factory()->next_string());
    GotoIfException(next, if_exception, exception);

    return IteratorRecord{TNode<JSReceiver>::UncheckedCast(iterator),
                          TNode<Object>::UncheckedCast(next)};
  }
}

TNode<JSReceiver> IteratorBuiltinsAssembler::IteratorStep(
    Node* context, const IteratorRecord& iterator, Label* if_done,
    Node* fast_iterator_result_map, Label* if_exception, Variable* exception) {
  DCHECK_NOT_NULL(if_done);
  // 1. a. Let result be ? Invoke(iterator, "next", « »).
  Callable callable = CodeFactory::Call(isolate());
  Node* result = CallJS(callable, context, iterator.next, iterator.object);
  GotoIfException(result, if_exception, exception);

  // 3. If Type(result) is not Object, throw a TypeError exception.
  Label if_notobject(this, Label::kDeferred), return_result(this);
  GotoIf(TaggedIsSmi(result), &if_notobject);
  Node* result_map = LoadMap(result);

  if (fast_iterator_result_map != nullptr) {
    // Fast iterator result case:
    Label if_generic(this);

    // 4. Return result.
    GotoIfNot(WordEqual(result_map, fast_iterator_result_map), &if_generic);

    // IteratorComplete
    // 2. Return ToBoolean(? Get(iterResult, "done")).
    Node* done = LoadObjectField(result, JSIteratorResult::kDoneOffset);
    BranchIfToBooleanIsTrue(done, if_done, &return_result);

    BIND(&if_generic);
  }

  // Generic iterator result case:
  {
    // 3. If Type(result) is not Object, throw a TypeError exception.
    GotoIfNot(IsJSReceiverMap(result_map), &if_notobject);

    // IteratorComplete
    // 2. Return ToBoolean(? Get(iterResult, "done")).
    Node* done = GetProperty(context, result, factory()->done_string());
    GotoIfException(done, if_exception, exception);
    BranchIfToBooleanIsTrue(done, if_done, &return_result);
  }

  BIND(&if_notobject);
  {
    Node* ret =
        CallRuntime(Runtime::kThrowIteratorResultNotAnObject, context, result);
    GotoIfException(ret, if_exception, exception);
    Unreachable();
  }

  BIND(&return_result);
  return CAST(result);
}

TNode<Object> IteratorBuiltinsAssembler::IteratorValue(
    TNode<Context> context, TNode<JSReceiver> result,
    base::Optional<TNode<Map>> fast_iterator_result_map, Label* if_exception,
    Variable* exception) {
  Label exit(this);
  TVARIABLE(Object, var_value);
  if (fast_iterator_result_map) {
    // Fast iterator result case:
    Label if_generic(this);
    Node* map = LoadMap(result);
    GotoIfNot(WordEqual(map, *fast_iterator_result_map), &if_generic);
    var_value = LoadObjectField(result, JSIteratorResult::kValueOffset);
    Goto(&exit);

    BIND(&if_generic);
  }

  // Generic iterator result case:
  {
    TNode<Object> value =
        GetProperty(context, result, factory()->value_string());
    GotoIfException(value, if_exception, exception);
    var_value = value;
    Goto(&exit);
  }

  BIND(&exit);
  return var_value.value();
}

void IteratorBuiltinsAssembler::IteratorCloseOnException(
    Node* context, const IteratorRecord& iterator, Label* if_exception,
    Variable* exception) {
  // Perform ES #sec-iteratorclose when an exception occurs. This simpler
  // algorithm does not include redundant steps which are never reachable from
  // the spec IteratorClose algorithm.
  DCHECK((if_exception != nullptr && exception != nullptr));
  CSA_ASSERT(this, IsNotTheHole(exception->value()));
  CSA_ASSERT(this, IsJSReceiver(iterator.object));

  // Let return be ? GetMethod(iterator, "return").
  Node* method =
      GetProperty(context, iterator.object, factory()->return_string());
  GotoIfException(method, if_exception, exception);

  // If return is undefined, return Completion(completion).
  GotoIf(Word32Or(IsUndefined(method), IsNull(method)), if_exception);

  {
    // Let innerResult be Call(return, iterator, « »).
    // If an exception occurs, the original exception remains bound
    Node* inner_result =
        CallJS(CodeFactory::Call(isolate()), context, method, iterator.object);
    GotoIfException(inner_result, if_exception, nullptr);

    // (If completion.[[Type]] is throw) return Completion(completion).
    Goto(if_exception);
  }
}

void IteratorBuiltinsAssembler::IteratorCloseOnException(
    Node* context, const IteratorRecord& iterator, TNode<Object> exception) {
  Label rethrow(this, Label::kDeferred);
  TVARIABLE(Object, exception_variable, exception);
  IteratorCloseOnException(context, iterator, &rethrow, &exception_variable);

  BIND(&rethrow);
  CallRuntime(Runtime::kReThrow, context, exception_variable.value());
  Unreachable();
}

TNode<JSArray> IteratorBuiltinsAssembler::IterableToList(
    TNode<Context> context, TNode<Object> iterable, TNode<Object> iterator_fn) {
  // 1. Let iteratorRecord be ? GetIterator(items, method).
  IteratorRecord iterator_record = GetIterator(context, iterable, iterator_fn);

  // 2. Let values be a new empty List.
  GrowableFixedArray values(state());

  Variable* vars[] = {values.var_array(), values.var_length(),
                      values.var_capacity()};
  Label loop_start(this, 3, vars), done(this);
  Goto(&loop_start);
  // 3. Let next be true.
  // 4. Repeat, while next is not false
  BIND(&loop_start);
  {
    //  a. Set next to ? IteratorStep(iteratorRecord).
    TNode<JSReceiver> next = IteratorStep(context, iterator_record, &done);
    //  b. If next is not false, then
    //   i. Let nextValue be ? IteratorValue(next).
    TNode<Object> next_value = IteratorValue(context, next);
    //   ii. Append nextValue to the end of the List values.
    values.Push(next_value);
    Goto(&loop_start);
  }

  BIND(&done);
  return values.ToJSArray(context);
}

TF_BUILTIN(IterableToList, IteratorBuiltinsAssembler) {
  TNode<Context> context = CAST(Parameter(Descriptor::kContext));
  TNode<Object> iterable = CAST(Parameter(Descriptor::kIterable));
  TNode<Object> iterator_fn = CAST(Parameter(Descriptor::kIteratorFn));

  Return(IterableToList(context, iterable, iterator_fn));
}

// This builtin always returns a new JSArray and is thus safe to use even in the
// presence of code that may call back into user-JS. This builtin will take the
// fast path if the iterable is a fast array and the Array prototype and the
// Symbol.iterator is untouched. The fast path skips the iterator and copies the
// backing store to the new array. Note that if the array has holes, the holes
// will be copied to the new array, which is inconsistent with the behavior of
// an actual iteration, where holes should be replaced with undefined (if the
// prototype has no elements). To maintain the correct behavior for holey
// arrays, use the builtins IterableToList or IterableToListWithSymbolLookup.
TF_BUILTIN(IterableToListMayPreserveHoles, IteratorBuiltinsAssembler) {
  TNode<Context> context = CAST(Parameter(Descriptor::kContext));
  TNode<Object> iterable = CAST(Parameter(Descriptor::kIterable));
  TNode<Object> iterator_fn = CAST(Parameter(Descriptor::kIteratorFn));

  Label slow_path(this);

  GotoIfNot(IsFastJSArrayWithNoCustomIteration(context, iterable), &slow_path);

  // The fast path will copy holes to the new array.
  TailCallBuiltin(Builtins::kCloneFastJSArray, context, iterable);

  BIND(&slow_path);
  TailCallBuiltin(Builtins::kIterableToList, context, iterable, iterator_fn);
}

void IteratorBuiltinsAssembler::FastIterableToList(
    TNode<Context> context, TNode<Object> iterable,
    TVariable<Object>* var_result, Label* slow) {
  Label done(this), check_string(this), check_map(this), check_set(this);

  GotoIfNot(
      Word32Or(IsFastJSArrayWithNoCustomIteration(context, iterable),
               IsFastJSArrayForReadWithNoCustomIteration(context, iterable)),
      &check_string);

  // Fast path for fast JSArray.
  *var_result =
      CallBuiltin(Builtins::kCloneFastJSArrayFillingHoles, context, iterable);
  Goto(&done);

  BIND(&check_string);
  {
    Label string_maybe_fast_call(this);
    StringBuiltinsAssembler string_assembler(state());
    string_assembler.BranchIfStringPrimitiveWithNoCustomIteration(
        iterable, context, &string_maybe_fast_call, &check_map);

    BIND(&string_maybe_fast_call);
    TNode<IntPtrT> const length = LoadStringLengthAsWord(CAST(iterable));
    // Use string length as conservative approximation of number of codepoints.
    GotoIf(
        IntPtrGreaterThan(length, IntPtrConstant(JSArray::kMaxFastArrayLength)),
        slow);
    *var_result = CallBuiltin(Builtins::kStringToList, context, iterable);
    Goto(&done);
  }

  BIND(&check_map);
  {
    Label map_fast_call(this);
    BranchIfIterableWithOriginalKeyOrValueMapIterator(
        state(), iterable, context, &map_fast_call, &check_set);

    BIND(&map_fast_call);
    *var_result = CallBuiltin(Builtins::kMapIteratorToList, context, iterable);
    Goto(&done);
  }

  BIND(&check_set);
  {
    Label set_fast_call(this);
    BranchIfIterableWithOriginalValueSetIterator(state(), iterable, context,
                                                 &set_fast_call, slow);

    BIND(&set_fast_call);
    *var_result =
        CallBuiltin(Builtins::kSetOrSetIteratorToList, context, iterable);
    Goto(&done);
  }

  BIND(&done);
}

// This builtin loads the property Symbol.iterator as the iterator, and has fast
// paths for fast arrays, for primitive strings, for sets and set iterators, and
// for map iterators. These fast paths will only be taken if Symbol.iterator and
// the Iterator prototype are not modified in a way that changes the original
// iteration behavior.
// * In case of fast holey arrays, holes will be converted to undefined to
//   reflect iteration semantics. Note that replacement by undefined is only
//   correct when the NoElements protector is valid.
// * In case of map/set iterators, there is an additional requirement that the
//   iterator is not partially consumed. To be spec-compliant, after spreading
//   the iterator is set to be exhausted.
TF_BUILTIN(IterableToListWithSymbolLookup, IteratorBuiltinsAssembler) {
  TNode<Context> context = CAST(Parameter(Descriptor::kContext));
  TNode<Object> iterable = CAST(Parameter(Descriptor::kIterable));

  Label slow_path(this);

  GotoIfForceSlowPath(&slow_path);

  TVARIABLE(Object, var_result);
  FastIterableToList(context, iterable, &var_result, &slow_path);
  Return(var_result.value());

  BIND(&slow_path);
  {
    TNode<Object> iterator_fn = GetIteratorMethod(context, iterable);
    TailCallBuiltin(Builtins::kIterableToList, context, iterable, iterator_fn);
  }
}

}  // namespace internal
}  // namespace v8