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LibJS: Add the "fast non-local access" optimization to the bytecode VM

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The GetVariable bytecode op now caches environment coordinates for fast
cross-scope variable lookup.
This commit is contained in:
Andreas Kling 2021-10-24 15:36:24 +02:00
parent da98212001
commit 715e7fada8
2 changed files with 24 additions and 3 deletions
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24
Userland/Libraries/LibJS/Bytecode/Op.cpp
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@ -238,9 +238,27 @@ void ConcatString::execute_impl(Bytecode::Interpreter& interpreter) const
void GetVariable::execute_impl(Bytecode::Interpreter& interpreter) const void GetVariable::execute_impl(Bytecode::Interpreter& interpreter) const
{ {
auto& vm = interpreter.vm(); auto reference = [&] {
auto reference = vm.resolve_binding(interpreter.current_executable().get_identifier(m_identifier)); auto const& string = interpreter.current_executable().get_identifier(m_identifier);
if (vm.exception()) if (m_cached_environment_coordinate.has_value()) {
auto* environment = interpreter.vm().running_execution_context().lexical_environment;
for (size_t i = 0; i < m_cached_environment_coordinate->hops; ++i)
environment = environment->outer_environment();
VERIFY(environment);
VERIFY(environment->is_declarative_environment());
if (!environment->is_permanently_screwed_by_eval()) {
return Reference { *environment, string, interpreter.vm().in_strict_mode(), m_cached_environment_coordinate };
}
m_cached_environment_coordinate = {};
}
auto reference = interpreter.vm().resolve_binding(string);
if (reference.environment_coordinate().has_value())
m_cached_environment_coordinate = reference.environment_coordinate();
return reference;
}();
if (interpreter.vm().exception())
return; return;
interpreter.accumulator() = reference.get_value(interpreter.global_object()); interpreter.accumulator() = reference.get_value(interpreter.global_object());

3
Userland/Libraries/LibJS/Bytecode/Op.h
View file

@ -16,6 +16,7 @@
#include <LibJS/Bytecode/StringTable.h> #include <LibJS/Bytecode/StringTable.h>
#include <LibJS/Heap/Cell.h> #include <LibJS/Heap/Cell.h>
#include <LibJS/Runtime/Environment.h> #include <LibJS/Runtime/Environment.h>
#include <LibJS/Runtime/EnvironmentCoordinate.h>
#include <LibJS/Runtime/Value.h> #include <LibJS/Runtime/Value.h>
namespace JS::Bytecode::Op { namespace JS::Bytecode::Op {
@ -310,6 +311,8 @@ public:
private: private:
IdentifierTableIndex m_identifier; IdentifierTableIndex m_identifier;
Optional<EnvironmentCoordinate> mutable m_cached_environment_coordinate;
}; };
class GetById final : public Instruction { class GetById final : public Instruction {