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LibJS: Remove derivable fields from ExecutionContext

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Remove four fields that are trivially derivable from other fields
already present in the ExecutionContext:

- global_object (from realm)
- global_declarative_environment (from realm)
- identifier_table (from executable)
- property_key_table (from executable)

This shrinks ExecutionContext from 192 to 160 bytes (-17%).

The asmint's GetGlobal/SetGlobal handlers now load through the realm
pointer, taking advantage of the cached declarative environment
pointer added in the previous commit.
This commit is contained in:
Andreas Kling
2026-03-08 11:34:32 +01:00
committed by Andreas Kling
parent e70f580e5c
commit 96d02d5249
Notes: github-actions[bot] 2026-03-11 12:35:42 +00:00 
Author: https://github.com/awesomekling
Commit: https://github.com/LadybirdBrowser/ladybird/commit/96d02d5249d
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/8360
Reviewed-by: https://github.com/shannonbooth
6 changed files with 24 additions and 28 deletions
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14
Libraries/LibJS/Bytecode/AsmInterpreter/asmint.asm
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@@ -1717,9 +1717,10 @@ end
# Inline cache fast path for global variable access via the global object.
handler GetGlobal
# Load global_declarative_environment and global_object
load64 t1, [exec_ctx, EXECUTION_CONTEXT_GLOBAL_DECLARATIVE_ENVIRONMENT]
load64 t2, [exec_ctx, EXECUTION_CONTEXT_GLOBAL_OBJECT]
# Load global_declarative_environment and global_object via realm
load64 t0, [exec_ctx, EXECUTION_CONTEXT_REALM]
load64 t2, [t0, REALM_GLOBAL_OBJECT]
load64 t1, [t0, REALM_GLOBAL_DECLARATIVE_ENVIRONMENT]
# Get GlobalVariableCache* (direct pointer from instruction stream)
load64 t3, [pb, pc, m_cache]
# Check environment_serial_number matches
@@ -1774,9 +1775,10 @@ end
# Inline cache fast path for global variable store via the global object.
handler SetGlobal
# Load global_declarative_environment and global_object
load64 t1, [exec_ctx, EXECUTION_CONTEXT_GLOBAL_DECLARATIVE_ENVIRONMENT]
load64 t2, [exec_ctx, EXECUTION_CONTEXT_GLOBAL_OBJECT]
# Load global_declarative_environment and global_object via realm
load64 t0, [exec_ctx, EXECUTION_CONTEXT_REALM]
load64 t2, [t0, REALM_GLOBAL_OBJECT]
load64 t1, [t0, REALM_GLOBAL_DECLARATIVE_ENVIRONMENT]
# Get GlobalVariableCache* (direct pointer from instruction stream)
load64 t3, [pb, pc, m_cache]
# Check environment_serial_number matches

9
Libraries/LibJS/Bytecode/AsmInterpreter/gen_asm_offsets.cpp
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@@ -17,6 +17,7 @@
#include <LibJS/Runtime/FunctionObject.h>
#include <LibJS/Runtime/IndexedProperties.h>
#include <LibJS/Runtime/Object.h>
#include <LibJS/Runtime/Realm.h>
#include <LibJS/Runtime/Shape.h>
#include <LibJS/Runtime/TypedArray.h>
@@ -85,13 +86,17 @@ int main()
// ExecutionContext layout
outln("\n# ExecutionContext layout");
EMIT_OFFSET(EXECUTION_CONTEXT_EXECUTABLE, ExecutionContext, executable);
EMIT_OFFSET(EXECUTION_CONTEXT_GLOBAL_OBJECT, ExecutionContext, global_object);
EMIT_OFFSET(EXECUTION_CONTEXT_GLOBAL_DECLARATIVE_ENVIRONMENT, ExecutionContext, global_declarative_environment);
EMIT_OFFSET(EXECUTION_CONTEXT_REALM, ExecutionContext, realm);
EMIT_OFFSET(EXECUTION_CONTEXT_LEXICAL_ENVIRONMENT, ExecutionContext, lexical_environment);
EMIT_OFFSET(EXECUTION_CONTEXT_CALLER_FRAME, ExecutionContext, caller_frame);
EMIT_OFFSET(EXECUTION_CONTEXT_PROGRAM_COUNTER, ExecutionContext, program_counter);
EMIT_SIZEOF(SIZEOF_EXECUTION_CONTEXT, ExecutionContext);
// Realm layout
outln("\n# Realm layout");
EMIT_OFFSET(REALM_GLOBAL_OBJECT, Realm, m_global_object);
EMIT_OFFSET(REALM_GLOBAL_DECLARATIVE_ENVIRONMENT, Realm, m_global_declarative_environment);
// Interpreter layout
outln("\n# Interpreter layout");
EMIT_OFFSET(INTERPRETER_RUNNING_EXECUTION_CONTEXT, Interpreter, m_running_execution_context);

18
Libraries/LibJS/Bytecode/Interpreter.cpp
View File

@@ -316,11 +316,6 @@ ExecutionContext* Interpreter::push_inline_frame(
// and global_declarative_environment, since the caller's realm may differ
// in cross-realm calls (e.g. iframe <-> parent).
callee_context->executable = callee_executable;
auto& callee_realm = *callee_context->realm;
callee_context->global_object = callee_realm.global_object();
callee_context->global_declarative_environment = callee_realm.global_environment().declarative_record();
callee_context->identifier_table = callee_executable.identifier_table->identifiers().data();
callee_context->property_key_table = callee_executable.property_key_table->property_keys().data();
// Copy constants (memcpy avoids aliasing issues with the scalar loop).
auto* values = callee_context->registers_and_constants_and_locals_and_arguments();
@@ -808,12 +803,17 @@ void Interpreter::run_bytecode(size_t entry_point)
Utf16FlyString const& Interpreter::get_identifier(IdentifierTableIndex index) const
{
return m_running_execution_context->identifier_table[index.value];
return m_running_execution_context->executable->get_identifier(index);
}
PropertyKey const& Interpreter::get_property_key(PropertyKeyTableIndex index) const
{
return m_running_execution_context->property_key_table[index.value];
return m_running_execution_context->executable->get_property_key(index);
}
DeclarativeEnvironment& Interpreter::global_declarative_environment()
{
return realm().global_declarative_environment();
}
ThrowCompletionOr<Value> Interpreter::run_executable(ExecutionContext& context, Executable& executable, Optional<size_t> entry_point)
@@ -824,10 +824,6 @@ ThrowCompletionOr<Value> Interpreter::run_executable(ExecutionContext& context,
TemporaryChange restore_running_execution_context { m_running_execution_context, &context };
context.executable = executable;
context.global_object = realm().global_object();
context.global_declarative_environment = realm().global_environment().declarative_record();
context.identifier_table = executable.identifier_table->identifiers().data();
context.property_key_table = executable.property_key_table->property_keys().data();
VERIFY(executable.registers_and_locals_count + executable.constants.size() == executable.registers_and_locals_and_constants_count);
VERIFY(executable.registers_and_locals_and_constants_count <= context.registers_and_constants_and_locals_and_arguments_span().size());

4
Libraries/LibJS/Bytecode/Interpreter.h
View File

@@ -27,8 +27,8 @@ public:
~Interpreter();
[[nodiscard]] Realm& realm() { return *m_running_execution_context->realm; }
[[nodiscard]] Object& global_object() { return *m_running_execution_context->global_object; }
[[nodiscard]] DeclarativeEnvironment& global_declarative_environment() { return *m_running_execution_context->global_declarative_environment; }
[[nodiscard]] Object& global_object() { return realm().global_object(); }
[[nodiscard]] DeclarativeEnvironment& global_declarative_environment();
static VM& vm() { return VM::the(); }
ThrowCompletionOr<Value> run(Script&, GC::Ptr<Environment> lexical_environment_override = nullptr);