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[JSC] Add Array.from(Array) fast path
https://bugs.webkit.org/show_bug.cgi?id=263490 rdar://117290480 Reviewed by Michael Saboff. This patch adds Array.from fast path for simple arrays without callbacks, like, `Array.from(array)`. This is because this pattern can be used for fast array cloning. The fast path is 8.14x faster than the Array.from generic path. We should take Array.from fast path when array iterator protocol allows. This ensures that we can iterate an array without creating an iterator. And it also ensures that our Array prototype chain is sane. So, we can skip many costly operations and directly copy data. array-from-array 2.6646+-0.0174 ^ 0.3271+-0.0155 ^ definitely 8.1469x faster * JSTests/microbenchmarks/array-from-array.js: Added. * Source/JavaScriptCore/builtins/ArrayConstructor.js: * Source/JavaScriptCore/builtins/BuiltinNames.h: * Source/JavaScriptCore/bytecode/LinkTimeConstant.h: * Source/JavaScriptCore/runtime/ArrayPrototype.cpp: (JSC::JSC_DEFINE_HOST_FUNCTION): * Source/JavaScriptCore/runtime/ArrayPrototype.h: * Source/JavaScriptCore/runtime/JSGlobalObject.cpp: (JSC::JSGlobalObject::init): Canonical link: https://commits.webkit.org/269690@main
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‎JSTests/microbenchmarks/array-from-array.js‎

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@@ -0,0 +1,4 @@
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var a1 = new Array(1024);
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a1.fill(99);
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for (var i = 0; i < 1e2; ++i)
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var a2 = Array.from(a1);

‎Source/JavaScriptCore/builtins/ArrayConstructor.js‎

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@@ -52,6 +52,12 @@ function from(items /*, mapFn, thisArg */)
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var arrayLike = @toObject(items, "Array.from requires an array-like object - not null or undefined");
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if (!mapFn) {
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var fastResult = @arrayFromFast(this, arrayLike);
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if (fastResult)
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return fastResult;
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}
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var iteratorMethod = items.@@iterator;
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if (!@isUndefinedOrNull(iteratorMethod)) {
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if (!@isCallable(iteratorMethod))

‎Source/JavaScriptCore/builtins/BuiltinNames.h‎

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@@ -198,6 +198,7 @@ namespace JSC {
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macro(sentinelString) \
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macro(createRemoteFunction) \
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macro(isRemoteFunction) \
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macro(arrayFromFast) \
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macro(arraySort) \
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macro(jsonParse) \
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macro(jsonStringify) \

‎Source/JavaScriptCore/bytecode/LinkTimeConstant.h‎

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@@ -122,6 +122,7 @@ class JSGlobalObject;
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v(sentinelString, nullptr) \
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v(createRemoteFunction, nullptr) \
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v(isRemoteFunction, nullptr) \
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v(arrayFromFast, nullptr) \
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v(arraySort, nullptr) \
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v(jsonParse, nullptr) \
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v(jsonStringify, nullptr) \

‎Source/JavaScriptCore/runtime/ArrayPrototype.cpp‎

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@@ -1523,4 +1523,59 @@ JSC_DEFINE_HOST_FUNCTION(arrayProtoPrivateFuncAppendMemcpy, (JSGlobalObject* glo
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return JSValue::encode(jsUndefined());
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}
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JSC_DEFINE_HOST_FUNCTION(arrayProtoPrivateFuncFromFast, (JSGlobalObject* globalObject, CallFrame* callFrame))
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{
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VM& vm = globalObject->vm();
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auto scope = DECLARE_THROW_SCOPE(vm);
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JSValue constructor = callFrame->uncheckedArgument(0);
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if (UNLIKELY(constructor != globalObject->arrayConstructor() && constructor.isObject()))
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return JSValue::encode(jsUndefined());
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auto* array = jsDynamicCast<JSArray*>(callFrame->uncheckedArgument(1));
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if (!array)
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return JSValue::encode(jsUndefined());
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if (UNLIKELY(!array->isIteratorProtocolFastAndNonObservable()))
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return JSValue::encode(jsUndefined());
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IndexingType type = array->indexingType();
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if (UNLIKELY(shouldUseSlowPut(type)))
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return JSValue::encode(jsUndefined());
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Butterfly* butterfly= array->butterfly();
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unsigned resultSize = butterfly->publicLength();
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if (hasAnyArrayStorage(type) || resultSize >= MIN_SPARSE_ARRAY_INDEX) {
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JSArray* result = constructEmptyArray(globalObject, nullptr, resultSize);
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RETURN_IF_EXCEPTION(scope, { });
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scope.release();
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moveElements(globalObject, vm, result, 0, array, resultSize);
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return JSValue::encode(result);
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}
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Structure* resultStructure = globalObject->arrayStructureForIndexingTypeDuringAllocation(type);
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if (UNLIKELY(hasAnyArrayStorage(resultStructure->indexingType())))
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return JSValue::encode(jsUndefined());
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ASSERT(!globalObject->isHavingABadTime());
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ObjectInitializationScope initializationScope(vm);
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JSArray* result = JSArray::tryCreateUninitializedRestricted(initializationScope, resultStructure, resultSize);
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if (UNLIKELY(!result)) {
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throwOutOfMemoryError(globalObject, scope);
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return { };
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}
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if (type == ArrayWithDouble) {
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double* buffer = result->butterfly()->contiguousDouble().data();
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copyElements(buffer, 0, butterfly->contiguousDouble().data(), resultSize, ArrayWithDouble);
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} else if (type != ArrayWithUndecided) {
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WriteBarrier<Unknown>* buffer = result->butterfly()->contiguous().data();
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copyElements(buffer, 0, butterfly->contiguous().data(), resultSize, type);
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}
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ASSERT(result->butterfly()->publicLength() == resultSize);
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return JSValue::encode(result);
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}
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} // namespace JSC

‎Source/JavaScriptCore/runtime/ArrayPrototype.h‎

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@@ -50,5 +50,6 @@ JSC_DECLARE_HOST_FUNCTION(arrayProtoFuncToString);
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JSC_DECLARE_HOST_FUNCTION(arrayProtoFuncValues);
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JSC_DECLARE_HOST_FUNCTION(arrayProtoPrivateFuncConcatMemcpy);
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JSC_DECLARE_HOST_FUNCTION(arrayProtoPrivateFuncAppendMemcpy);
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JSC_DECLARE_HOST_FUNCTION(arrayProtoPrivateFuncFromFast);
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} // namespace JSC

‎Source/JavaScriptCore/runtime/JSGlobalObject.cpp‎

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@@ -1537,6 +1537,9 @@ capitalName ## Constructor* lowerName ## Constructor = featureFlag ? capitalName
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m_linkTimeConstants[static_cast<unsigned>(LinkTimeConstant::typedArrayFromFast)].initLater([] (const Initializer<JSCell>& init) {
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init.set(JSFunction::create(init.vm, jsCast<JSGlobalObject*>(init.owner), 2, "typedArrayViewTypedArrayFromFast"_s, typedArrayViewPrivateFuncTypedArrayFromFast, ImplementationVisibility::Private));
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});
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m_linkTimeConstants[static_cast<unsigned>(LinkTimeConstant::arrayFromFast)].initLater([] (const Initializer<JSCell>& init) {
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init.set(JSFunction::create(init.vm, jsCast<JSGlobalObject*>(init.owner), 2, "arrayFromFast"_s, arrayProtoPrivateFuncFromFast, ImplementationVisibility::Private));
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});
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m_linkTimeConstants[static_cast<unsigned>(LinkTimeConstant::isDetached)].initLater([] (const Initializer<JSCell>& init) {
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init.set(JSFunction::create(init.vm, jsCast<JSGlobalObject*>(init.owner), 1, "typedArrayViewIsDetached"_s, typedArrayViewPrivateFuncIsDetached, ImplementationVisibility::Private));
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});

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