Reland of Preparse inner functions (new try)

src/ast/scopes.cc

Index: src/ast/scopes.cc
diff --git a/src/ast/scopes.cc b/src/ast/scopes.cc
index b6ae337877ca8368a03a90364f6b205d0775b771..8d23875ab6bca368251b9dd13d2172e8291a571d 100644
--- a/src/ast/scopes.cc
+++ b/src/ast/scopes.cc
@@ -1073,12 +1073,14 @@
   }
 }
 
-bool Scope::AllowsLazyParsing() const {
-  // If we are inside a block scope, we must parse eagerly to find out how
-  // to allocate variables on the block scope. At this point, declarations may
-  // not have yet been parsed.
+bool Scope::AllowsLazyParsingWithoutUnresolvedVariables() const {
+  // If we are inside a block scope, we must find unresolved variables in the
+  // inner scopes to find out how to allocate variables on the block scope. At
+  // this point, declarations may not have yet been parsed.
   for (const Scope* s = this; s != nullptr; s = s->outer_scope_) {
     if (s->is_block_scope()) return false;
+    // TODO(marja): Refactor parsing modes: also add s->is_function_scope()
+    // here.
   }
   return true;
 }
@@ -1178,7 +1180,7 @@
 
 Handle<StringSet> DeclarationScope::CollectNonLocals(
     ParseInfo* info, Handle<StringSet> non_locals) {
-  VariableProxy* free_variables = FetchFreeVariables(this, info);
+  VariableProxy* free_variables = FetchFreeVariables(this, true, info);
   for (VariableProxy* proxy = free_variables; proxy != nullptr;
        proxy = proxy->next_unresolved()) {
     non_locals = StringSet::Add(non_locals, proxy->name());
@@ -1191,8 +1193,9 @@
   // Try to resolve unresolved variables for this Scope and migrate those which
   // cannot be resolved inside. It doesn't make sense to try to resolve them in
   // the outer Scopes here, because they are incomplete.
-  for (VariableProxy* proxy = FetchFreeVariables(this); proxy != nullptr;
-       proxy = proxy->next_unresolved()) {
+  for (VariableProxy* proxy =
+           FetchFreeVariables(this, !FLAG_lazy_inner_functions);
+       proxy != nullptr; proxy = proxy->next_unresolved()) {
     DCHECK(!proxy->is_resolved());
     VariableProxy* copy = ast_node_factory->CopyVariableProxy(proxy);
     migrate_to->AddUnresolved(copy);
@@ -1515,6 +1518,29 @@
   DCHECK(!proxy->is_resolved());
   Variable* var = LookupRecursive(proxy, nullptr);
   ResolveTo(info, proxy, var);
+
+  if (FLAG_lazy_inner_functions) {
+    if (info != nullptr && info->is_native()) return;
+    // Pessimistically force context allocation for all variables to which inner
+    // scope variables could potentially resolve to.
+    Scope* scope = GetClosureScope()->outer_scope_;
+    while (scope != nullptr && scope->scope_info_.is_null()) {
+      var = scope->LookupLocal(proxy->raw_name());
+      if (var != nullptr) {
+        // Since we don't lazy parse inner arrow functions, inner functions
+        // cannot refer to the outer "this".
+        if (!var->is_dynamic() && !var->is_this() &&
+            !var->has_forced_context_allocation()) {
+          var->ForceContextAllocation();
+          var->set_is_used();
+          // We don't know what the (potentially lazy parsed) inner function
+          // does with the variable; pessimistically assume that it's assigned.
+          var->set_maybe_assigned();
+        }
+      }
+      scope = scope->outer_scope_;
+    }
+  }
 }
 
 void Scope::ResolveTo(ParseInfo* info, VariableProxy* proxy, Variable* var) {
@@ -1560,13 +1586,16 @@
 }
 
 VariableProxy* Scope::FetchFreeVariables(DeclarationScope* max_outer_scope,
-                                         ParseInfo* info,
+                                         bool try_to_resolve, ParseInfo* info,
                                          VariableProxy* stack) {
   for (VariableProxy *proxy = unresolved_, *next = nullptr; proxy != nullptr;
        proxy = next) {
     next = proxy->next_unresolved();
     DCHECK(!proxy->is_resolved());
-    Variable* var = LookupRecursive(proxy, max_outer_scope->outer_scope());
+    Variable* var = nullptr;
+    if (try_to_resolve) {
+      var = LookupRecursive(proxy, max_outer_scope->outer_scope());
+    }
     if (var == nullptr) {
       proxy->set_next_unresolved(stack);
       stack = proxy;
@@ -1579,7 +1608,8 @@
   unresolved_ = nullptr;
 
   for (Scope* scope = inner_scope_; scope != nullptr; scope = scope->sibling_) {
-    stack = scope->FetchFreeVariables(max_outer_scope, info, stack);
+    stack =
+        scope->FetchFreeVariables(max_outer_scope, try_to_resolve, info, stack);
   }
 
   return stack;