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LibJS/JIT: Add fast path for cached GetVariable accesses

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We can now stay in machine code for environment variable read accesses
as long as they are cached and initialized.

20% speed-up on Octane/zlib.js :^)
This commit is contained in:
Andreas Kling 2023-11-06 15:23:49 +01:00
parent 7826c006c1
commit 1d8ec677a3
6 changed files with 147 additions and 3 deletions
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136
Userland/Libraries/LibJS/JIT/Compiler.cpp
View file

@ -1091,15 +1091,145 @@ static Value cxx_get_variable(VM& vm, DeprecatedFlyString const& name, Bytecode:
void Compiler::compile_get_variable(Bytecode::Op::GetVariable const& op)
{
m_assembler.mov(
Assembler::Operand::Register(ARG1),
Assembler::Operand::Imm(bit_cast<u64>(&m_bytecode_executable.get_identifier(op.identifier()))));
Assembler::Label slow_case;
// if (!cache.has_value()) goto slow_case;
m_assembler.mov(
Assembler::Operand::Register(ARG2),
Assembler::Operand::Imm(bit_cast<u64>(&m_bytecode_executable.environment_variable_caches[op.cache_index()])));
// FIXME: Figure out a nicer way to load a single byte. :^)
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Mem64BaseAndOffset(ARG2, Bytecode::EnvironmentVariableCache::has_value_offset()));
m_assembler.bitwise_and(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm(0xff));
m_assembler.jump_if(
Assembler::Operand::Register(GPR0),
Assembler::Condition::EqualTo,
Assembler::Operand::Imm(0),
slow_case);
// auto environment = vm.running_execution_context().lexical_environment;
// GPR1 = current lexical environment
m_assembler.mov(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Mem64BaseAndOffset(RUNNING_EXECUTION_CONTEXT_BASE, ExecutionContext::lexical_environment_offset()));
// for (size_t i = 0; i < cache->hops; ++i)
// environment = environment->outer_environment();
// GPR0 = hops
// FIXME: Load 32 bits directly instead of 64 and masking.
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Mem64BaseAndOffset(ARG2, Bytecode::EnvironmentVariableCache::value_offset() + EnvironmentCoordinate::hops_offset()));
m_assembler.mov(
Assembler::Operand::Register(GPR2),
Assembler::Operand::Imm(0xffffffff));
m_assembler.bitwise_and(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Register(GPR2));
{
// while (GPR0--)
// GPR1 = GPR1->outer_environment()
Assembler::Label loop_start;
Assembler::Label loop_end;
loop_start.link(m_assembler);
m_assembler.jump_if(
Assembler::Operand::Register(GPR0),
Assembler::Condition::EqualTo,
Assembler::Operand::Imm(0),
loop_end);
m_assembler.sub(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm(1));
m_assembler.mov(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Mem64BaseAndOffset(GPR1, Environment::outer_environment_offset()));
m_assembler.jump(loop_start);
loop_end.link(m_assembler);
}
// GPR1 now points to the environment holding our binding.
// if (environment->is_permanently_screwed_by_eval()) goto slow_case;
// FIXME: Load 8 bits here directly instead of loading 64 and masking.
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Mem64BaseAndOffset(GPR1, Environment::is_permanently_screwed_by_eval_offset()));
m_assembler.bitwise_and(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm(0xff));
m_assembler.jump_if(
Assembler::Operand::Register(GPR0),
Assembler::Condition::NotEqualTo,
Assembler::Operand::Imm(0),
slow_case);
// GPR1 = environment->m_bindings.outline_buffer()
m_assembler.mov(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Mem64BaseAndOffset(GPR1, DeclarativeEnvironment::bindings_offset() + Vector<DeclarativeEnvironment::Binding>::outline_buffer_offset()));
// GPR0 = index
// FIXME: Load 32 bits directly instead of 64 and masking.
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Mem64BaseAndOffset(ARG2, Bytecode::EnvironmentVariableCache::value_offset() + EnvironmentCoordinate::index_offset()));
m_assembler.mov(
Assembler::Operand::Register(GPR2),
Assembler::Operand::Imm(0xffffffff));
m_assembler.bitwise_and(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Register(GPR2));
// GPR0 *= sizeof(DeclarativeEnvironment::Binding)
m_assembler.mul32(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm(sizeof(DeclarativeEnvironment::Binding)),
slow_case);
// GPR1 = &binding
m_assembler.add(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Register(GPR0));
// if (!binding.initialized) goto slow_case;
m_assembler.mov(
Assembler ::Operand::Register(GPR0),
Assembler::Operand::Mem64BaseAndOffset(GPR1, DeclarativeEnvironment::Binding::initialized_offset()));
m_assembler.bitwise_and(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm(0xff));
m_assembler.jump_if(
Assembler::Operand::Register(GPR0),
Assembler::Condition::EqualTo,
Assembler::Operand::Imm(0),
slow_case);
// accumulator = binding.value;
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Mem64BaseAndOffset(GPR1, DeclarativeEnvironment::Binding::value_offset()));
store_accumulator(GPR0);
Assembler::Label end;
m_assembler.jump(end);
// Slow case: Uncached access. Call C++ helper.
slow_case.link(m_assembler);
m_assembler.mov(
Assembler::Operand::Register(ARG1),
Assembler::Operand::Imm(bit_cast<u64>(&m_bytecode_executable.get_identifier(op.identifier()))));
native_call((void*)cxx_get_variable);
store_accumulator(RET);
check_exception();
end.link(m_assembler);
}
static Value cxx_get_callee_and_this_from_environment(VM& vm, DeprecatedFlyString const& name, u32 cache_index, Bytecode::Register callee_reg, Bytecode::Register this_reg)

1
Userland/Libraries/LibJS/JIT/Compiler.h
View file

@ -27,6 +27,7 @@ private:
# if ARCH(X86_64)
static constexpr auto GPR0 = Assembler::Reg::RAX;
static constexpr auto GPR1 = Assembler::Reg::RCX;
static constexpr auto GPR2 = Assembler::Reg::R12;
static constexpr auto ARG0 = Assembler::Reg::RDI;
static constexpr auto ARG1 = Assembler::Reg::RSI;
static constexpr auto ARG2 = Assembler::Reg::RDX;

5
Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h
View file

@ -19,6 +19,9 @@ class DeclarativeEnvironment : public Environment {
JS_ENVIRONMENT(DeclarativeEnvironment, Environment);
struct Binding {
static FlatPtr value_offset() { return OFFSET_OF(Binding, value); }
static FlatPtr initialized_offset() { return OFFSET_OF(Binding, initialized); }
DeprecatedFlyString name;
Value value;
bool strict { false };
@ -67,6 +70,8 @@ public:
[[nodiscard]] u64 environment_serial_number() const { return m_environment_serial_number; }
static FlatPtr bindings_offset() { return OFFSET_OF(DeclarativeEnvironment, m_bindings); }
private:
ThrowCompletionOr<Value> get_binding_value_direct(VM&, Binding&, bool strict);
ThrowCompletionOr<void> set_mutable_binding_direct(VM&, Binding&, Value, bool strict);

3
Userland/Libraries/LibJS/Runtime/Environment.h
View file

@ -57,6 +57,9 @@ public:
bool is_permanently_screwed_by_eval() const { return m_permanently_screwed_by_eval; }
void set_permanently_screwed_by_eval();
static FlatPtr is_permanently_screwed_by_eval_offset() { return OFFSET_OF(Environment, m_permanently_screwed_by_eval); }
static FlatPtr outer_environment_offset() { return OFFSET_OF(Environment, m_outer_environment); }
protected:
explicit Environment(Environment* parent);

3
Userland/Libraries/LibJS/Runtime/EnvironmentCoordinate.h
View file

@ -15,6 +15,9 @@ struct EnvironmentCoordinate {
u32 hops { invalid_marker };
u32 index { invalid_marker };
static FlatPtr hops_offset() { return OFFSET_OF(EnvironmentCoordinate, hops); }
static FlatPtr index_offset() { return OFFSET_OF(EnvironmentCoordinate, index); }
bool is_valid() const { return hops != invalid_marker && index != invalid_marker; }
static constexpr u32 invalid_marker = 0xfffffffe;

2
Userland/Libraries/LibJS/Runtime/ExecutionContext.h
View file

@ -30,6 +30,8 @@ struct ExecutionContext {
void visit_edges(Cell::Visitor&);
static FlatPtr lexical_environment_offset() { return OFFSET_OF(ExecutionContext, lexical_environment); }
private:
explicit ExecutionContext(MarkedVector<Value> existing_arguments, MarkedVector<Value> existing_local_variables);