Turn AllowsLazyParsingWithoutUnresolvedVariables into a whitelist stopping at...

Turn AllowsLazyParsingWithoutUnresolvedVariables into a whitelist stopping at the outer parsed context.

Any context outer to what we're parsing already has proper context allocation, so we don't need to check those scopes.

BUG=v8:5501

Review-Url: https://codereview.chromium.org/2417643003
Cr-Commit-Position: refs/heads/master@{#40256}

src/ast/scopes.cc

@@ -1114,14 +1114,29 @@ void DeclarationScope::AllocateVariables(ParseInfo* info, AnalyzeMode mode) {
   }
 }
 
-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;
-    if (s->is_function_scope()) return false;
-    if (s->is_eval_scope() && is_strict(s->language_mode())) return false;
+bool Scope::AllowsLazyParsingWithoutUnresolvedVariables(
+    const Scope* outer) const {
+  // If none of the outer scopes need to decide whether to context allocate
+  // specific variables, we can preparse inner functions without unresolved
+  // variables. Otherwise we need to find unresolved variables to force context
+  // allocation of the matching declarations. We can stop at the outer scope for
+  // the parse, since context allocation of those variables is already
+  // guaranteed to be correct.
+  for (const Scope* s = this; s != outer; s = s->outer_scope_) {
+    // Eval forces context allocation on all outer scopes, so we don't need to
+    // look at those scopes. Sloppy eval makes all top-level variables dynamic,
+    // whereas strict-mode requires context allocation.
+    if (s->is_eval_scope()) return !is_strict(s->language_mode());
+    // Catch scopes force context allocation of all variables.
+    if (s->is_catch_scope()) continue;
+    // With scopes do not introduce variables that need allocation.
+    if (s->is_with_scope()) continue;
+    // If everything is guaranteed to be context allocated we can ignore the
+    // scope.
+    if (s->has_forced_context_allocation()) continue;
+    // Only block scopes and function scopes should disallow preparsing.
+    DCHECK(s->is_block_scope() || s->is_function_scope());
+    return false;
   }
   return true;
 }

src/ast/scopes.h

@@ -346,7 +346,7 @@ class Scope: public ZoneObject {
 
   // Determine if we can parse a function literal in this scope lazily without
   // caring about the unresolved variables within.
-  bool AllowsLazyParsingWithoutUnresolvedVariables() const;
+  bool AllowsLazyParsingWithoutUnresolvedVariables(const Scope* outer) const;
 
   // The number of contexts between this and scope; zero if this == scope.
   int ContextChainLength(Scope* scope) const;

src/parsing/parser-base.h

@@ -3924,7 +3924,7 @@ ParserBase<Impl>::ParseArrowFunctionLiteral(
   // TODO(marja): consider lazy-parsing inner arrow functions too. is_this
   // handling in Scope::ResolveVariable needs to change.
   bool is_lazy_top_level_function =
-      can_preparse && scope()->AllowsLazyParsingWithoutUnresolvedVariables();
+      can_preparse && impl()->AllowsLazyParsingWithoutUnresolvedVariables();
   bool should_be_used_once_hint = false;
   {
     FunctionState function_state(&function_state_, &scope_state_,

src/parsing/parser.cc

@@ -795,10 +795,6 @@ FunctionLiteral* Parser::DoParseProgram(ParseInfo* info) {
     } else if (parsing_module_) {
       DCHECK_EQ(outer, info->script_scope());
       outer = NewModuleScope(info->script_scope());
-      // Never do lazy parsing in modules.  If we want to support this in the
-      // future, we must force context-allocation for all variables that are
-      // declared at the module level but not MODULE-allocated.
-      parsing_mode = PARSE_EAGERLY;
     }
 
     DeclarationScope* scope = outer->AsDeclarationScope();
@@ -2625,7 +2621,7 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
                       eager_compile_hint == FunctionLiteral::kShouldLazyCompile;
 
   bool is_lazy_top_level_function =
-      can_preparse && scope()->AllowsLazyParsingWithoutUnresolvedVariables();
+      can_preparse && impl()->AllowsLazyParsingWithoutUnresolvedVariables();
 
   // Determine whether we can still lazy parse the inner function.
   // The preconditions are:

src/parsing/parser.h

@@ -205,6 +205,11 @@ class Parser : public ParserBase<Parser> {
   friend class ParserBase<Parser>;
   friend class v8::internal::ExpressionClassifier<ParserTypes<Parser>>;
 
+  bool AllowsLazyParsingWithoutUnresolvedVariables() const {
+    return scope()->AllowsLazyParsingWithoutUnresolvedVariables(
+        original_scope_);
+  }
+
   // Runtime encoding of different completion modes.
   enum CompletionKind {
     kNormalCompletion,

src/parsing/preparser.h

@@ -911,6 +911,8 @@ class PreParser : public ParserBase<PreParser> {
       const PreParserFormalParameters& parameters, FunctionKind kind,
       FunctionLiteral::FunctionType function_type, bool* ok);
 
+  bool AllowsLazyParsingWithoutUnresolvedVariables() const { return false; }
+
   V8_INLINE LazyParsingResult SkipLazyFunctionBody(
       int* materialized_literal_count, int* expected_property_count,
       bool track_unresolved_variables, bool may_abort, bool* ok) {