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LibJS: Skip allocating locals for arguments that allowed to be local

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This allows us to get rid of instructions that move arguments to locals
and allocate smaller JS::Value vector in ExecutionContext by reusing
slots that were already allocated for arguments.

With this change for following function:
```js
function f(x, y) {
    return x + y;
}
```

we now produce following bytecode:
```
[   0]    0: Add dst:reg6, lhs:arg0, rhs:arg1
[  10]       Return value:reg6
```

instead of:
```
[   0]    0: GetArgument 0, dst:x~1
[  10]       GetArgument 1, dst:y~0
[  20]       Add dst:reg6, lhs:x~1, rhs:y~0
[  30]       Return value:reg6
```
This commit is contained in:
Aliaksandr Kalenik 2025-04-25 17:10:47 +02:00 • committed by Andreas Kling
parent 3f04d18ef7
commit 2d732b2251
Notes: github-actions[bot] 2025-04-26 09:03:23 +00:00
6 changed files with 102 additions and 39 deletions
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17
Libraries/LibJS/Parser.cpp
View file

@ -326,9 +326,10 @@ public:
scope_has_declaration = false;
}
bool is_function_parameter = false;
if (m_type == ScopeType::Function) {
if (!m_contains_access_to_arguments_object_in_non_strict_mode && m_function_parameters_candidates_for_local_variables.contains(identifier_group_name)) {
scope_has_declaration = true;
is_function_parameter = true;
} else if (m_forbidden_lexical_names.contains(identifier_group_name)) {
// NOTE: If an identifier is used as a function parameter that cannot be optimized locally or globally, it is simply ignored.
continue;
@ -346,7 +347,7 @@ public:
for (auto& identifier : identifier_group.identifiers)
identifier->set_is_global();
}
} else if (scope_has_declaration) {
} else if (scope_has_declaration || is_function_parameter) {
if (hoistable_function_declaration)
continue;
@ -368,9 +369,15 @@ public:
local_scope = m_top_level_scope;
}
auto local_variable_index = local_scope->m_node->add_local_variable(identifier_group_name);
for (auto& identifier : identifier_group.identifiers)
identifier->set_local_variable_index(local_variable_index);
if (is_function_parameter) {
auto argument_index = local_scope->m_function_parameters->get_index_of_parameter_name(identifier_group_name);
for (auto& identifier : identifier_group.identifiers)
identifier->set_argument_index(argument_index.value());
} else {
auto local_variable_index = local_scope->m_node->add_local_variable(identifier_group_name);
for (auto& identifier : identifier_group.identifiers)
identifier->set_local_variable_index(local_variable_index);
}
}
} else {
if (m_function_parameters || m_type == ScopeType::ClassField || m_type == ScopeType::ClassStaticInit) {