Introduce LexicalScopeFeatures to enable future bytecode optimizations
https://bugs.webkit.org/show_bug.cgi?id=224072
Reviewed by Keith Miller.
Before this , BytecodeGenerator was capable of reasoning about the presence of with
statements, direct eval, or any other code features only within the current executable:
with (foo) {
(function() {
There was no way to detect WithScope during generation of this function.
})();
}
This change is required for op_to_this rewrite (#225397): if FunctionCallResolveNode and
friends knew there is no WithScope, op_call could be emitted with |this| value of
undefined as per spec [1], instead of resolved scope. This would:
- simplify op_to_this on all tiers, likely resulting in minor perf boost;
- save 1 instruction per strict function by removing op_to_this;
- remove toThis() from the method table and ~30 its call sites from built-ins;
- fix built-in methods that were observably lacking toThis();
- fix proto getter / setter called on global scope;
- fix WebIDL accessors called with |this| value of
undefined and null.
Also, if ResolveNode knew that unforgeable global properties are not shadowed and there
is no with statement or sloppy mode direct eval, then undefined / Infinity / NaN
lookups could be constant-folded. This would save up to 3 bytecode ops per each usage
and allow emitting op_is_undefined_or_null for x === undefined || x === null.
V8 performs this optimization [2].
This introduces LexicalScopeFeatures to allow passing such information from Parser
to BytecodeGenerator with a minimal code diff. These features are kept separate from
CodeFeature to simplify reasoning about feature's scope and because we need to propagate
lexical features from parent to child scope.
Strict mode is the first use case of LexicalScopeFeatures, which this change carefully
fits into existing abstractions without increasing their memory usage even by 1 byte.
[1]: https://tc39.es/ecma262/#sec-evaluatecall (step 2)
[2]: https://medium.com/@bmeurer/sometimes-undefined-is-defined-7701e1c9eff8
- builtins/BuiltinExecutables.cpp:
(JSC::BuiltinExecutables::createExecutable):
- bytecode/UnlinkedCodeBlock.cpp:
(JSC::UnlinkedCodeBlock::UnlinkedCodeBlock):
- bytecode/UnlinkedCodeBlock.h:
(JSC::UnlinkedCodeBlock::recordParse):
(JSC::UnlinkedCodeBlock::lexicalScopeFeatures const):
- bytecode/UnlinkedFunctionExecutable.cpp:
(JSC::generateUnlinkedFunctionCodeBlock):
(JSC::UnlinkedFunctionExecutable::UnlinkedFunctionExecutable):
(JSC::UnlinkedFunctionExecutable::setInvalidTypeProfilingOffsets):
- bytecode/UnlinkedFunctionExecutable.h:
- bytecompiler/BytecodeGenerator.cpp:
(JSC::BytecodeGenerator::BytecodeGenerator):
(JSC::BytecodeGenerator::emitNewClassFieldInitializerFunction):
- bytecompiler/BytecodeGenerator.h:
(JSC::BytecodeGenerator::lexicalScopeFeatures const):
(JSC::BytecodeGenerator::generate):
(JSC::ASTBuilder::createFunctionMetadata):
(JSC::ScopeNode::ScopeNode):
(JSC::ProgramNode::ProgramNode):
(JSC::ModuleProgramNode::ModuleProgramNode):
(JSC::EvalNode::EvalNode):
(JSC::FunctionMetadataNode::FunctionMetadataNode):
(JSC::FunctionMetadataNode::operator== const):
(JSC::FunctionMetadataNode::dump const):
(JSC::FunctionNode::FunctionNode):
(JSC::ScopeNode::lexicalScopeFeatures):
(JSC::ScopeNode::isStrictMode const):
(JSC::Parser<LexerType>::parseInner):
(JSC::Parser<LexerType>::parseGeneratorFunctionSourceElements):
(JSC::Parser<LexerType>::parseAsyncFunctionSourceElements):
(JSC::Parser<LexerType>::parseAsyncGeneratorFunctionSourceElements):
(JSC::Parser<LexerType>::parseFunctionBody):
(JSC::Parser<LexerType>::parseFunctionInfo):
(JSC::Scope::Scope):
(JSC::Scope::lexicalScopeFeatures const):
(JSC::Scope::setStrictMode):
(JSC::Scope::strictMode const):
(JSC::Scope::fillParametersForSourceProviderCache):
(JSC::Scope::restoreFromSourceProviderCache):
(JSC::Parser::pushScope):
(JSC::Parser::lexicalScopeFeatures):
(JSC::Parser<LexerType>::parse):
- parser/ParserModes.h:
- parser/SourceProviderCacheItem.h:
(JSC::SourceProviderCacheItem::lexicalScopeFeatures const):
(JSC::SourceProviderCacheItem::SourceProviderCacheItem):
(JSC::SyntaxChecker::createFunctionMetadata):
- runtime/CachedBytecode.cpp:
(JSC::CachedBytecode::addFunctionUpdate):
(JSC::CachedFunctionExecutable::lexicalScopeFeatures const):
(JSC::CachedCodeBlock::lexicalScopeFeatures const):
(JSC::UnlinkedCodeBlock::UnlinkedCodeBlock):
(JSC::CachedFunctionExecutable::encode):
(JSC::UnlinkedFunctionExecutable::UnlinkedFunctionExecutable):
(JSC::CachedCodeBlock<CodeBlockType>::encode):
(JSC::CachedFunctionExecutable::isInStrictContext const): Deleted.
- runtime/CachedTypes.h:
- runtime/CodeCache.cpp:
(JSC::generateUnlinkedCodeBlockImpl):
(JSC::CodeCache::getUnlinkedGlobalCodeBlock):
(JSC::ECMAMode::fromBool):
- runtime/FunctionExecutable.cpp:
(JSC::FunctionExecutable::FunctionExecutable):
- runtime/GlobalExecutable.h:
(JSC::GlobalExecutable::recordParse):
(JSC::GlobalExecutable::GlobalExecutable):
- runtime/ScriptExecutable.cpp:
(JSC::ScriptExecutable::ScriptExecutable):
(JSC::ScriptExecutable::newCodeBlockFor):
(JSC::ScriptExecutable::recordParse):
- runtime/ScriptExecutable.h:
(JSC::ScriptExecutable::isInStrictContext const):
(JSC::ScriptExecutable::recordParse):
