Since non-strict direct eval() can insert new bindings into a
surrounding var scope, we cannot safely cache some assumptions about
environment chain layout after eval() has taken place.
Since eval() is rare, let's do what other engines do and simply
deoptimize in its presence. This patch adds a new "permanently screwed"
flag to JS::Environment that will be set on the entire variable
environment chain upon non-strict direct eval().
This patch adds two DeclarativeEnvironment APIs:
- get_binding_value_direct()
- set_mutable_binding_direct()
These work identically to their non-direct-suffixed counterparts, but
take an index instead of a bound name. This will allow someone who has
a binding index to get/set that binding directly without any additional
hash lookups.
The previous storage for DeclarativeEnvironment looked like this:
HashMap<FlyString, Binding> m_bindings;
This patch changes that to:
HashMap<FlyString, size_t> m_names;
Vector<Binding> m_bindings;
The main goal here is to give each binding an index that can ultimately
be cached and used for optimized environment accesses.
Before this we used an ad-hoc combination of references and 'variables'
stored in a hashmap. This worked in most cases but is not spec like.
Additionally hoisting, dynamically naming functions and scope analysis
was not done properly.
This patch fixes all of that by:
- Implement BindingInitialization for destructuring assignment.
- Implementing a new ScopePusher which tracks the lexical and var
scoped declarations. This hoists functions to the top level if no
lexical declaration name overlaps. Furthermore we do checking of
redeclarations in the ScopePusher now requiring less checks all over
the place.
- Add methods for parsing the directives and statement lists instead
of having that code duplicated in multiple places. This allows
declarations to pushed to the appropriate scope more easily.
- Remove the non spec way of storing 'variables' in
DeclarativeEnvironment and make Reference follow the spec instead of
checking both the bindings and 'variables'.
- Remove all scoping related things from the Interpreter. And instead
use environments as specified by the spec. This also includes fixing
that NativeFunctions did not produce a valid FunctionEnvironment
which could cause issues with callbacks and eval. All
FunctionObjects now have a valid NewFunctionEnvironment
implementation.
- Remove execute_statements from Interpreter and instead use
ASTNode::execute everywhere this simplifies AST.cpp as you no longer
need to worry about which method to call.
- Make ScopeNodes setup their own environment. This uses four
different methods specified by the spec
{Block, Function, Eval, Global}DeclarationInstantiation with the
annexB extensions.
- Implement and use NamedEvaluation where specified.
Additionally there are fixes to things exposed by these changes to eval,
{for, for-in, for-of} loops and assignment.
Finally it also fixes some tests in test-js which where passing before
but not now that we have correct behavior :^).
This code is non-conforming and will eventually get cleaned out once
we implement proper variable bindings. However, this will aid us in
improving other parts of the code right now.
