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LibJS/JIT: Add fast path for GetById of Array.length

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Array.length is magical (since it has to reflect the number of elements
in the object's property storage).

We now handle it specially in jitted code, giving us a massive speed-up
on Kraken/ai-astar.js (and probably many other things as well) :^)
This commit is contained in:
Andreas Kling 2023-11-12 15:04:23 +01:00
parent e41f0d9dec
commit b532dedc91
Notes: sideshowbarker 2024-07-17 06:39:26 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/b532dedc91
Pull-request: https://github.com/SerenityOS/serenity/pull/21910
Reviewed-by: https://github.com/Hendiadyoin1
3 changed files with 65 additions and 0 deletions
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60
Userland/Libraries/LibJS/JIT/Compiler.cpp
View File

@ -1239,6 +1239,66 @@ void Compiler::compile_get_by_id(Bytecode::Op::GetById const& op)
branch_if_object(ARG1, [&] {
extract_object_pointer(GPR0, ARG1);
// NOTE: Fast path for Array.length which magically reflects
// the "array-like size" of the array object's property storage.
if (m_bytecode_executable.get_identifier(op.property()) == "length"sv) {
Assembler::Label no_magical_length_property_case;
// if (!object.has_magical_length_property) goto no_magical_length_property_case;
m_assembler.mov8(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Mem64BaseAndOffset(GPR0, Object::has_magical_length_property_offset()));
m_assembler.jump_if(
Assembler::Operand::Register(GPR1),
Assembler::Condition::EqualTo,
Assembler::Operand::Imm(0),
no_magical_length_property_case);
// NOTE: The base object has a magical "length" property, so now we just need
// to extract the "array-like size" from the object property storage.
// If we run into any issues, we'll jump to the slow case and figure things out in C++.
// GPR0 = object->indexed_properties().storage()
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Mem64BaseAndOffset(GPR0, Object::indexed_properties_offset() + IndexedProperties::storage_offset()));
// if (GPR0 == nullptr) goto slow_case;
m_assembler.jump_if(
Assembler::Operand::Register(GPR0),
Assembler::Condition::EqualTo,
Assembler::Operand::Imm(0),
slow_case);
// if (!GPR0->is_simple_storage()) goto slow_case;
m_assembler.mov8(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Mem64BaseAndOffset(GPR0, IndexedPropertyStorage::is_simple_storage_offset()));
m_assembler.jump_if(
Assembler::Operand::Register(GPR1),
Assembler::Condition::EqualTo,
Assembler::Operand::Imm(0),
slow_case);
// accumulator = GPR0->array_like_size() | SHIFT_INT32_TAG
// return
m_assembler.mov(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Mem64BaseAndOffset(GPR0, SimpleIndexedPropertyStorage::array_size_offset()));
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm(SHIFTED_INT32_TAG));
m_assembler.bitwise_or(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Register(GPR0));
store_accumulator(GPR1);
m_assembler.jump(end);
no_magical_length_property_case.link(m_assembler);
}
// if (cache.shape != &object->shape()) goto slow_case;
m_assembler.mov(
Assembler::Operand::Register(GPR2),

1
Userland/Libraries/LibJS/Runtime/Array.cpp
View File

@ -64,6 +64,7 @@ NonnullGCPtr<Array> Array::create_from(Realm& realm, Vector<Value> const& elemen
Array::Array(Object& prototype)
: Object(ConstructWithPrototypeTag::Tag, prototype)
{
m_has_magical_length_property = true;
}
// 10.4.2.4 ArraySetLength ( A, Desc ), https://tc39.es/ecma262/#sec-arraysetlength

4
Userland/Libraries/LibJS/Runtime/Object.h
View File

@ -221,6 +221,8 @@ public:
static FlatPtr may_interfere_with_indexed_property_access_offset() { return OFFSET_OF(Object, m_may_interfere_with_indexed_property_access); }
static FlatPtr indexed_properties_offset() { return OFFSET_OF(Object, m_indexed_properties); }
static FlatPtr has_magical_length_property_offset() { return OFFSET_OF(Object, m_has_magical_length_property); }
protected:
enum class GlobalObjectTag { Tag };
enum class ConstructWithoutPrototypeTag { Tag };
@ -238,6 +240,8 @@ protected:
// [[ParameterMap]]
bool m_has_parameter_map { false };
bool m_has_magical_length_property { false };
private:
void set_shape(Shape& shape) { m_shape = &shape; }