Commit 760eed05 authored by Hai Dang's avatar Hai Dang Committed by Commit Bot

Reland "Add fast path for spreading primitive strings."

This is a reland of ef2a19a2.
Use AllocateJSArray to avoid allocating an empty fixed array.

Original change's description:
> Add fast path for spreading primitive strings.
>
> This improves the performance on primitive strings of
> IterableToListWithSymbolLookup, which implements the
> CreateArrayFromIterable bytecode. The fast path is only
> taken if the string iterator protector is valid (that is,
> String.prototype[Symbol.iterator] and
> String.prototype[Symbol.iterator]().next are untouched).
>
> This brings spreading of primitive strings closer to the
> performance of the string iterator optimizations.
> (see https://docs.google.com/document/d/13z1fvRVpe_oEroplXEEX0a3WK94fhXorHjcOMsDmR-8/).
>
> Bug: chromium:881273, v8:7980
> Change-Id: Ic8d8619da2f2afcc9346203613a844f62653fd7a
> Reviewed-on: https://chromium-review.googlesource.com/1243110
> Commit-Queue: Hai Dang <dhai@google.com>
> Reviewed-by: Georg Neis <neis@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56329}

Bug: chromium:881273, v8:7980
Change-Id: I746c57ddfc300e1032057b5125bc824adf5c2cd3
Reviewed-on: https://chromium-review.googlesource.com/c/1267497
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: 's avatarUlan Degenbaev <ulan@chromium.org>
Reviewed-by: 's avatarGeorg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56438}
parent c74db9f6
......@@ -1123,6 +1123,7 @@ namespace internal {
/* StringIterator */ \
/* ES6 #sec-%stringiteratorprototype%.next */ \
TFJ(StringIteratorPrototypeNext, 0, kReceiver) \
TFS(StringToList, kSource) \
\
/* Symbol */ \
/* ES #sec-symbol-constructor */ \
......
......@@ -5,6 +5,7 @@
#include "src/builtins/builtins-iterator-gen.h"
#include "src/builtins/growable-fixed-array-gen.h"
#include "src/builtins/builtins-string-gen.h"
#include "src/builtins/builtins-utils-gen.h"
#include "src/builtins/builtins.h"
#include "src/code-stub-assembler.h"
......@@ -261,20 +262,37 @@ TF_BUILTIN(IterableToListMayPreserveHoles, IteratorBuiltinsAssembler) {
}
// This builtin loads the property Symbol.iterator as the iterator, and has a
// fast path for fast arrays. 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.
// fast path for fast arrays and another one for strings. 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.
TF_BUILTIN(IterableToListWithSymbolLookup, IteratorBuiltinsAssembler) {
TNode<Context> context = CAST(Parameter(Descriptor::kContext));
TNode<Object> iterable = CAST(Parameter(Descriptor::kIterable));
Label slow_path(this);
Label slow_path(this), check_string(this);
GotoIfNot(IsFastJSArrayWithNoCustomIteration(iterable, context), &slow_path);
// Here we are guaranteed that iterable is a fast JSArray with an original
// iterator.
GotoIfForceSlowPath(&slow_path);
GotoIfNot(IsFastJSArrayWithNoCustomIteration(iterable, context),
&check_string);
// Fast path for fast JSArray.
TailCallBuiltin(Builtins::kCloneFastJSArrayFillingHoles, context, iterable);
BIND(&check_string);
{
StringBuiltinsAssembler string_assembler(state());
GotoIfNot(string_assembler.IsStringPrimitiveWithNoCustomIteration(iterable,
context),
&slow_path);
// Fast path for strings.
TailCallBuiltin(Builtins::kStringToList, context, iterable);
}
BIND(&slow_path);
{
TNode<Object> iterator_fn = GetIteratorMethod(context, iterable);
......
......@@ -2493,6 +2493,85 @@ TF_BUILTIN(StringIteratorPrototypeNext, StringBuiltinsAssembler) {
}
}
TNode<BoolT> StringBuiltinsAssembler::IsStringPrimitiveWithNoCustomIteration(
TNode<Object> object, TNode<Context> context) {
Label if_false(this, Label::kDeferred), exit(this);
TVARIABLE(BoolT, var_result);
GotoIf(TaggedIsSmi(object), &if_false);
GotoIfNot(IsString(CAST(object)), &if_false);
// Check that the String iterator hasn't been modified in a way that would
// affect iteration.
Node* protector_cell = LoadRoot(RootIndex::kStringIteratorProtector);
DCHECK(isolate()->heap()->string_iterator_protector()->IsPropertyCell());
var_result =
WordEqual(LoadObjectField(protector_cell, PropertyCell::kValueOffset),
SmiConstant(Isolate::kProtectorValid));
Goto(&exit);
BIND(&if_false);
{
var_result = Int32FalseConstant();
Goto(&exit);
}
BIND(&exit);
return var_result.value();
}
TNode<JSArray> StringBuiltinsAssembler::StringToList(TNode<Context> context,
TNode<String> string) {
CSA_ASSERT(this, IsStringPrimitiveWithNoCustomIteration(string, context));
const ElementsKind kind = PACKED_ELEMENTS;
const TNode<IntPtrT> length = LoadStringLengthAsWord(string);
Node* const array_map =
LoadJSArrayElementsMap(kind, LoadNativeContext(context));
Node* const array = AllocateJSArray(kind, array_map, length, SmiTag(length));
Node* const elements = LoadElements(array);
const int first_element_offset = FixedArray::kHeaderSize - kHeapObjectTag;
TNode<IntPtrT> first_to_element_offset =
ElementOffsetFromIndex(IntPtrConstant(0), kind, INTPTR_PARAMETERS, 0);
VARIABLE(
var_offset, MachineType::PointerRepresentation(),
IntPtrAdd(first_to_element_offset, IntPtrConstant(first_element_offset)));
TVARIABLE(IntPtrT, var_position, IntPtrConstant(0));
Label done(this), next_codepoint(this, {&var_position, &var_offset});
Goto(&next_codepoint);
BIND(&next_codepoint);
{
// Loop condition.
GotoIfNot(IntPtrLessThan(var_position.value(), length), &done);
const UnicodeEncoding encoding = UnicodeEncoding::UTF16;
TNode<Int32T> ch =
LoadSurrogatePairAt(string, length, var_position.value(), encoding);
TNode<String> value = StringFromSingleCodePoint(ch, encoding);
Store(elements, var_offset.value(), value);
// Increment the position.
TNode<IntPtrT> ch_length = LoadStringLengthAsWord(value);
var_position = IntPtrAdd(var_position.value(), ch_length);
// Increment the array offset and continue the loop.
var_offset.Bind(
IntPtrAdd(var_offset.value(), IntPtrConstant(kPointerSize)));
Goto(&next_codepoint);
}
BIND(&done);
return UncheckedCast<JSArray>(array);
}
TF_BUILTIN(StringToList, StringBuiltinsAssembler) {
TNode<Context> context = CAST(Parameter(Descriptor::kContext));
TNode<String> string = CAST(Parameter(Descriptor::kSource));
Return(StringToList(context, string));
}
// -----------------------------------------------------------------------------
// ES6 section B.2.3 Additional Properties of the String.prototype object
......
......@@ -23,8 +23,12 @@ class StringBuiltinsAssembler : public CodeStubAssembler {
Node* rhs, Node* rhs_instance_type,
TNode<IntPtrT> length, Label* if_equal,
Label* if_not_equal, Label* if_indirect);
TNode<BoolT> IsStringPrimitiveWithNoCustomIteration(TNode<Object> object,
TNode<Context> context);
protected:
TNode<JSArray> StringToList(TNode<Context> context, TNode<String> string);
void StringEqual_Loop(Node* lhs, Node* lhs_instance_type,
MachineType lhs_type, Node* rhs,
Node* rhs_instance_type, MachineType rhs_type,
......
......@@ -242,6 +242,7 @@ class ContextRef : public HeapObjectRef {
V(JSFunction, promise_function) \
V(Map, fast_aliased_arguments_map) \
V(Map, initial_array_iterator_map) \
V(Map, initial_string_iterator_map) \
V(Map, iterator_result_map) \
V(Map, js_array_holey_double_elements_map) \
V(Map, js_array_holey_elements_map) \
......@@ -257,7 +258,6 @@ class ContextRef : public HeapObjectRef {
V(Map, sloppy_arguments_map) \
V(Map, slow_object_with_null_prototype_map) \
V(Map, strict_arguments_map) \
V(Map, initial_string_iterator_map) \
V(ScriptContextTable, script_context_table)
class NativeContextRef : public ContextRef {
......
......@@ -150,6 +150,7 @@ using v8::MemoryPressureLevel;
V(TypedArraySpeciesProtector) \
V(PromiseSpeciesProtector) \
V(StaleRegister) \
V(StringIteratorProtector) \
V(StringLengthProtector) \
V(StringTableMap) \
V(SymbolMap) \
......
......@@ -4,7 +4,9 @@
// Flags: --allow-natives-syntax --no-stress-opt
// Tests for primitive strings.
// Tests for spreading primitive strings.
assertEquals([...''], []);
var str = 'ott';
assertEquals(['o', 't', 't'], [...str]);
......
......@@ -378,6 +378,7 @@ KNOWN_OBJECTS = {
("OLD_SPACE", 0x02361): "StringLengthProtector",
("OLD_SPACE", 0x02371): "ArrayIteratorProtector",
("OLD_SPACE", 0x02399): "ArrayBufferNeuteringProtector",
("OLD_SPACE", 0x02421): "StringIteratorProtector",
}
# List of known V8 Frame Markers.
......
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