From d7e5a2058d6ad0412aa4d018f1d7084ff1ce279e Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Thu, 10 Nov 2022 20:55:03 +0100
Subject: [PATCH] LibJS: Cache access to bindings in the global environment

This patch adds a special EnvironmentCoordinate::global_marker value
that signifies that a binding lookup ended up searching the global
environment. It doesn't matter if we find it there or not, the global
marker is always returned. This allows us to bypass other environments
on subsequent access, going directly to the global environment.
---
 Userland/Libraries/LibJS/AST.cpp                  | 15 ++++++++++-----
 .../LibJS/Runtime/EnvironmentCoordinate.h         |  2 ++
 .../Libraries/LibJS/Runtime/GlobalEnvironment.cpp |  5 ++++-
 Userland/Libraries/LibJS/Runtime/Reference.cpp    |  4 ++--
 4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/Userland/Libraries/LibJS/AST.cpp b/Userland/Libraries/LibJS/AST.cpp
index cfdfec846c4..012d3690539 100644
--- a/Userland/Libraries/LibJS/AST.cpp
+++ b/Userland/Libraries/LibJS/AST.cpp
@@ -1376,11 +1376,16 @@ ThrowCompletionOr<Reference> Expression::to_reference(Interpreter&) const
 ThrowCompletionOr<Reference> Identifier::to_reference(Interpreter& interpreter) const
 {
     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());
+        Environment* environment = nullptr;
+        if (m_cached_environment_coordinate->index == EnvironmentCoordinate::global_marker) {
+            environment = &interpreter.vm().current_realm()->global_environment();
+        } else {
+            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 };
         }
diff --git a/Userland/Libraries/LibJS/Runtime/EnvironmentCoordinate.h b/Userland/Libraries/LibJS/Runtime/EnvironmentCoordinate.h
index f2ca2b00505..54eb605215e 100644
--- a/Userland/Libraries/LibJS/Runtime/EnvironmentCoordinate.h
+++ b/Userland/Libraries/LibJS/Runtime/EnvironmentCoordinate.h
@@ -14,6 +14,8 @@ namespace JS {
 struct EnvironmentCoordinate {
     size_t hops { 0 };
     size_t index { 0 };
+
+    static constexpr size_t global_marker = 0xffffffff;
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
index ec1dbc729e4..5d00a5fdf93 100644
--- a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
@@ -39,8 +39,11 @@ ThrowCompletionOr<Value> GlobalEnvironment::get_this_binding(VM&) const
 }
 
 // 9.1.1.4.1 HasBinding ( N ), https://tc39.es/ecma262/#sec-global-environment-records-hasbinding-n
-ThrowCompletionOr<bool> GlobalEnvironment::has_binding(FlyString const& name, Optional<size_t>*) const
+ThrowCompletionOr<bool> GlobalEnvironment::has_binding(FlyString const& name, Optional<size_t>* out_index) const
 {
+    if (out_index)
+        *out_index = EnvironmentCoordinate::global_marker;
+
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If ! DclRec.HasBinding(N) is true, return true.
     if (MUST(m_declarative_record->has_binding(name)))
diff --git a/Userland/Libraries/LibJS/Runtime/Reference.cpp b/Userland/Libraries/LibJS/Runtime/Reference.cpp
index c6bff072eca..9cf9e47af12 100644
--- a/Userland/Libraries/LibJS/Runtime/Reference.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Reference.cpp
@@ -68,7 +68,7 @@ ThrowCompletionOr<void> Reference::put_value(VM& vm, Value value)
     VERIFY(m_base_environment);
 
     // c. Return ? base.SetMutableBinding(V.[[ReferencedName]], W, V.[[Strict]]) (see 9.1).
-    if (m_environment_coordinate.has_value())
+    if (m_environment_coordinate.has_value() && m_environment_coordinate->index != EnvironmentCoordinate::global_marker)
         return static_cast<DeclarativeEnvironment*>(m_base_environment)->set_mutable_binding_direct(vm, m_environment_coordinate->index, value, m_strict);
     else
         return m_base_environment->set_mutable_binding(vm, m_name.as_string(), value, m_strict);
@@ -138,7 +138,7 @@ ThrowCompletionOr<Value> Reference::get_value(VM& vm) const
     VERIFY(m_base_environment);
 
     // c. Return ? base.GetBindingValue(V.[[ReferencedName]], V.[[Strict]]) (see 9.1).
-    if (m_environment_coordinate.has_value())
+    if (m_environment_coordinate.has_value() && m_environment_coordinate->index != EnvironmentCoordinate::global_marker)
         return static_cast<DeclarativeEnvironment*>(m_base_environment)->get_binding_value_direct(vm, m_environment_coordinate->index, m_strict);
     return m_base_environment->get_binding_value(vm, m_name.as_string(), m_strict);
 }