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LibJS: Skip some declarative env allocations in function instantiation

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If all lexical declaration use local variables then there is no need
to allocate declarative environment.

With this change we skip ~3x more environment allocations on Github.
This commit is contained in:
Aliaksandr Kalenik 2024-05-04 22:36:56 +02:00 • committed by Andreas Kling
parent 5da9af435e
commit f21c0f9dcd
Notes: sideshowbarker 2024-07-16 19:17:47 +09:00
3 changed files with 13 additions and 2 deletions
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10
Userland/Libraries/LibJS/AST.cpp
View file

@ -1440,6 +1440,16 @@ void SequenceExpression::dump(int indent) const
expression->dump(indent + 1);
}
bool ScopeNode::has_non_local_lexical_declarations() const
{
bool result = false;
MUST(for_each_lexically_declared_identifier([&](Identifier const& identifier) {
if (!identifier.is_local())
result = true;
}));
return result;
}
ThrowCompletionOr<void> ScopeNode::for_each_lexically_scoped_declaration(ThrowCompletionOrVoidCallback<Declaration const&>&& callback) const
{
for (auto& declaration : m_lexical_declarations)

1
Userland/Libraries/LibJS/AST.h
View file

@ -306,6 +306,7 @@ public:
void add_hoisted_function(NonnullRefPtr<FunctionDeclaration const> declaration);
[[nodiscard]] bool has_lexical_declarations() const { return !m_lexical_declarations.is_empty(); }
[[nodiscard]] bool has_non_local_lexical_declarations() const;
[[nodiscard]] bool has_var_declarations() const { return !m_var_declarations.is_empty(); }
[[nodiscard]] size_t var_declaration_count() const { return m_var_declarations.size(); }

4
Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
View file

@ -308,7 +308,7 @@ ECMAScriptFunctionObject::ECMAScriptFunctionObject(DeprecatedFlyString name, Byt
// 30. If strict is false, then
if (!m_strict) {
bool can_elide_declarative_environment = !m_contains_direct_call_to_eval && (!scope_body || !scope_body->has_lexical_declarations());
bool can_elide_declarative_environment = !m_contains_direct_call_to_eval && (!scope_body || !scope_body->has_non_local_lexical_declarations());
if (can_elide_declarative_environment) {
lex_environment_size = var_environment_size;
} else {
@ -870,7 +870,7 @@ ThrowCompletionOr<void> ECMAScriptFunctionObject::function_declaration_instantia
// Optimization: We avoid creating empty top-level declarative environments in non-strict mode, if both of these conditions are true:
// 1. there is no direct call to eval() within this function
// 2. there are no lexical declarations that would go into the environment
bool can_elide_declarative_environment = !m_contains_direct_call_to_eval && (!scope_body || !scope_body->has_lexical_declarations());
bool can_elide_declarative_environment = !m_contains_direct_call_to_eval && (!scope_body || !scope_body->has_non_local_lexical_declarations());
if (can_elide_declarative_environment) {
lex_environment = var_environment;
} else {