4fa5748093
This gives FunctionNode a "might need arguments object" boolean flag and
sets it based on the simplest possible heuristic for this: if we
encounter an identifier called "arguments" or "eval" up to the next
(nested) function declaration or expression, we won't need an arguments
object. Otherwise, we *might* need one - the final decision is made in
the FunctionDeclarationInstantiation AO.
Now, this is obviously not perfect. Even if you avoid eval, something
like `foo.arguments` will still trigger a false positive - but it's a
start and already massively cuts down on needlessly allocated objects,
especially in real-world code that is often minified, and so a full
"arguments" identifier will be an actual arguments object more often
than not.
To illustrate the actual impact of this change, here's the number of
allocated arguments objects during a full test-js run:
Before:
- Unmapped arguments objects: 78765
- Mapped arguments objects: 2455
After:
- Unmapped arguments objects: 18
- Mapped arguments objects: 37
This results in a ~5% speedup of test-js on my Linux host machine, and
about 3.5% on i686 Serenity in QEMU (warm runs, average of 5).
The following microbenchmark (calling an empty function 1M times) runs
25% faster on Linux and 45% on Serenity:
function foo() {}
for (var i = 0; i < 1_000_000; ++i)
foo();
test262 reports no changes in either direction, apart from a speedup :^)
68 lines
2.5 KiB
C++
68 lines
2.5 KiB
C++
/*
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* Copyright (c) 2021, Matthew Olsson <mattco@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Debug.h>
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#include <AK/Optional.h>
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#include <LibJS/Bytecode/Interpreter.h>
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#include <LibJS/Lexer.h>
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#include <LibJS/Parser.h>
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#include <LibJS/Runtime/ECMAScriptFunctionObject.h>
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#include <LibJS/Runtime/FunctionConstructor.h>
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#include <LibJS/Runtime/GeneratorFunctionConstructor.h>
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#include <LibJS/Runtime/GlobalObject.h>
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namespace JS {
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GeneratorFunctionConstructor::GeneratorFunctionConstructor(GlobalObject& global_object)
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: NativeFunction(*static_cast<Object*>(global_object.function_constructor()))
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{
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}
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void GeneratorFunctionConstructor::initialize(GlobalObject& global_object)
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{
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auto& vm = this->vm();
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NativeFunction::initialize(global_object);
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// 27.3.2.1 GeneratorFunction.length, https://tc39.es/ecma262/#sec-generatorfunction.length
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define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
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// 27.3.2.2 GeneratorFunction.prototype, https://tc39.es/ecma262/#sec-generatorfunction.length
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define_direct_property(vm.names.prototype, global_object.generator_function_prototype(), 0);
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}
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GeneratorFunctionConstructor::~GeneratorFunctionConstructor()
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{
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}
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// 27.3.1.1 GeneratorFunction ( p1, p2, … , pn, body ), https://tc39.es/ecma262/#sec-generatorfunction
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Value GeneratorFunctionConstructor::call()
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{
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return construct(*this);
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}
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// 27.3.1.1 GeneratorFunction ( p1, p2, … , pn, body ), https://tc39.es/ecma262/#sec-generatorfunction
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Value GeneratorFunctionConstructor::construct(FunctionObject& new_target)
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{
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auto function = FunctionConstructor::create_dynamic_function_node(global_object(), new_target, FunctionKind::Generator);
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if (!function)
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return {};
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auto* bytecode_interpreter = Bytecode::Interpreter::current();
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VERIFY(bytecode_interpreter);
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auto executable = Bytecode::Generator::generate(function->body(), true);
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auto& passes = JS::Bytecode::Interpreter::optimization_pipeline();
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passes.perform(executable);
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if constexpr (JS_BYTECODE_DEBUG) {
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dbgln("Optimisation passes took {}us", passes.elapsed());
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dbgln("Compiled Bytecode::Block for function '{}':", function->name());
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for (auto& block : executable.basic_blocks)
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block.dump(executable);
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}
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return ECMAScriptFunctionObject::create(global_object(), function->name(), function->body(), function->parameters(), function->function_length(), vm().lexical_environment(), FunctionKind::Generator, function->is_strict_mode(), function->might_need_arguments_object());
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}
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}
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