/**
* For each qualified name N in the global scope, we check if: (a) No ancestor of N is ever
* aliased or assigned an unknown value type. (If N = "a.b.c", "a" and "a.b" are never aliased).
* (b) N has exactly one write, and it lives in the global scope. (c) N is aliased in a local
* scope. (d) N is aliased in global scope
*
* <p>If (a) is true, then GlobalNamespace must know all the writes to N. If (a) and (b) are true,
* then N cannot change during the execution of a local scope. If (a) and (b) and (c) are true,
* then the alias can be inlined if the alias obeys the usual rules for how we decide whether a
* variable is inlineable. If (a) and (b) and (d) are true, then inline the alias if possible (if
* it is assigned exactly once unconditionally).
*
* @see InlineVariables
*/
private void inlineAliases(GlobalNamespace namespace) {
// Invariant: All the names in the worklist meet condition (a).
Deque<Name> workList = new ArrayDeque<>(namespace.getNameForest());
while (!workList.isEmpty()) {
Name name = workList.pop();
// Don't attempt to inline a getter or setter property as a variable.
if (name.type == Name.Type.GET || name.type == Name.Type.SET) {
continue;
}
if (!name.inExterns && name.globalSets == 1 && name.localSets == 0 && name.aliasingGets > 0) {
// {@code name} meets condition (b). Find all of its local aliases
// and try to inline them.
List<Ref> refs = new ArrayList<>(name.getRefs());
for (Ref ref : refs) {
if (ref.type == Type.ALIASING_GET && ref.scope.isLocal()) {
// {@code name} meets condition (c). Try to inline it.
// TODO(johnlenz): consider picking up new aliases at the end
// of the pass instead of immediately like we do for global
// inlines.
if (inlineAliasIfPossible(name, ref, namespace)) {
name.removeRef(ref);
}
} else if (ref.type == Type.ALIASING_GET
&& ref.scope.isGlobal()
&& ref.getTwin() == null) { // ignore aliases in chained assignments
if (inlineGlobalAliasIfPossible(name, ref, namespace)) {
name.removeRef(ref);
}
}
}
}
// Check if {@code name} has any aliases left after the
// local-alias-inlining above.
if ((name.type == Name.Type.OBJECTLIT || name.type == Name.Type.FUNCTION)
&& name.aliasingGets == 0
&& name.props != null) {
// All of {@code name}'s children meet condition (a), so they can be
// added to the worklist.
workList.addAll(name.props);
}
}
}
@Override
public void process(Node externs, Node root) {
GlobalNamespace namespace;
namespace = new GlobalNamespace(compiler, root);
if (inlineAliases) {
inlineAliases(namespace);
}
nameMap = namespace.getNameIndex();
globalNames = namespace.getNameForest();
checkNamespaces();
for (Name name : globalNames) {
flattenReferencesToCollapsibleDescendantNames(name, name.getBaseName());
}
// We collapse property definitions after collapsing property references
// because this step can alter the parse tree above property references,
// invalidating the node ancestry stored with each reference.
for (Name name : globalNames) {
collapseDeclarationOfNameAndDescendants(name, name.getBaseName());
}
}