Changeset 271343 in webkit for trunk/Source/JavaScriptCore/bytecompiler

Timestamp:

Jan 8, 2021, 8:31:12 PM (4 years ago)

Author:

Alexey Shvayka

Message:

Implement @copyDataProperties in C++ to optimize object rest / spread
​https://bugs.webkit.org/show_bug.cgi?id=193618

Reviewed by Yusuke Suzuki.

JSTests:

• microbenchmarks/object-rest-destructuring.js: Added.
• microbenchmarks/object-spread.js: Added.
• stress/object-rest-deconstruct.js:
• stress/object-spread.js:

Source/JavaScriptCore:

Since @copyDataProperties is inherently polymorphic, implementing it in JS is not beneficial.
This patch:

1. Merges almost identical @copyDataProperties variants and moves them to C++, avoiding allocations of JSArray instances and Identifier wrappers.
2. Skips non-observable Get calls, leveraging slot.isTaintedByOpaqueObject().
3. Performs DefineOwnProperty via putDirectMayBeIndex(), since the spec guarantees property creation to be successful [1]: target is an newly created object that is not yet accessible to userland code. It's impossible for target to be non-extensible nor have a non-configurable property.
4. Introduces a fast path similar to Object.assign, but: a) with no checks on target, because it's guaranteed to be an extensible JSFinalObject; b) with less checks on source, since we are performing putDirect() and don't care about

read-only properties nor proto.

Altogether, these changes result in 3.1x speed-up for object rest / spread.
Also, this patch removes unnecessary target return and @isObject check.

[1]: ​https://tc39.es/ecma262/#sec-copydataproperties (step 6.c.ii.2, note the "!" prefix)

• builtins/BuiltinNames.h:
• builtins/GlobalOperations.js:

(globalPrivate.speciesConstructor):
(globalPrivate.copyDataProperties): Deleted.
(globalPrivate.copyDataPropertiesNoExclusions): Deleted.

• bytecode/BytecodeIntrinsicRegistry.h:
• bytecode/LinkTimeConstant.h:
• bytecompiler/NodesCodegen.cpp:

(JSC::ObjectPatternNode::bindValue const):
(JSC::ObjectSpreadExpressionNode::emitBytecode):
(JSC::BytecodeIntrinsicNode::emit_intrinsic_defineEnumerableWritableConfigurableDataProperty): Deleted.

• runtime/JSGlobalObject.cpp:

(JSC::JSGlobalObject::init):

• runtime/JSGlobalObjectFunctions.cpp:

(JSC::canPerformFastPropertyEnumerationForCopyDataProperties):
(JSC::JSC_DEFINE_HOST_FUNCTION):

• runtime/JSGlobalObjectFunctions.h:

File:

• trunk/Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp (modified) (3 diffs)

trunk/Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp

@@ -1777 +1777 @@
     ASSERT(!m_args->m_listNode);
     return generator.emitCreateArgumentsButterfly(generator.finalDestination(dst));
-}
-
-RegisterID* BytecodeIntrinsicNode::emit_intrinsic_defineEnumerableWritableConfigurableDataProperty(JSC::BytecodeGenerator& generator, JSC::RegisterID* dst)
-{
-    ArgumentListNode* node = m_args->m_listNode;
-    RefPtr<RegisterID> newObj = generator.emitNode(node);
-    node = node->m_next;
-    RefPtr<RegisterID> propertyNameRegister = generator.emitNode(node);
-    node = node->m_next;
-    RefPtr<RegisterID> value = generator.emitNode(node);
-    ASSERT(!node->m_next);
-
-    generator.emitCallDefineProperty(newObj.get(), propertyNameRegister.get(), value.get(), nullptr, nullptr, BytecodeGenerator::PropertyConfigurable | BytecodeGenerator::PropertyWritable | BytecodeGenerator::PropertyEnumerable, m_position);
-    return dst;
 }
 
@@ -5359 +5345 @@
             }
 
-            RefPtr<RegisterID> result = generator.newTemporary();
-            generator.emitCall(result.get(), copyDataProperties.get(), NoExpectedFunction, args, divot(), divotStart(), divotEnd(), DebuggableCall::No);
-            target.pattern->bindValue(generator, result.get());
+            generator.emitCall(generator.newTemporary(), copyDataProperties.get(), NoExpectedFunction, args, divot(), divotStart(), divotEnd(), DebuggableCall::No);
+            target.pattern->bindValue(generator, newObject.get());
         }
     }
@@ -5570 +5555 @@
     generator.emitNode(src.get(), m_expression);
     
-    // load and call @copyDataPropertiesNoExclusions
-    RefPtr<RegisterID> copyDataProperties = generator.moveLinkTimeConstant(nullptr, LinkTimeConstant::copyDataPropertiesNoExclusions);
+    RefPtr<RegisterID> copyDataProperties = generator.moveLinkTimeConstant(nullptr, LinkTimeConstant::copyDataProperties);
     
     CallArguments args(generator, nullptr, 2);