[parser] Parse tasks: skip functions using preparse data.

BUG=v8:6093

Change-Id: Icdc0706a3af23fbf538021a7e80fedaf0b5ae866
Reviewed-on: https://chromium-review.googlesource.com/453699
Commit-Queue: Wiktor Garbacz <wiktorg@google.com>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43784}

src/parsing/parser.cc

@@ -2788,6 +2788,31 @@ Parser::LazyParsingResult Parser::SkipFunction(
     cached_parse_data_->Reject();
   }
 
+  if (FLAG_use_parse_tasks && !is_inner_function &&
+      reusable_preparser()->preparse_data()) {
+    // All top-level functions are already preparsed and parser tasks for eager
+    // functions are already created. Use data gathered during the preparse step
+    // to skip the function.
+    PreParseData::FunctionData data =
+        reusable_preparser()->preparse_data()->GetTopLevelFunctionData(
+            function_scope->start_position());
+    if (data.is_valid()) {
+      if (FLAG_trace_parse_tasks) {
+        PrintF("Skipping top level func @ %d : %d using preparse data\n",
+               data.start, data.end);
+      }
+      function_scope->set_end_position(data.end);
+      scanner()->SeekForward(data.end - 1);
+      Expect(Token::RBRACE, CHECK_OK_VALUE(kLazyParsingComplete));
+      *num_parameters = data.num_parameters;
+      *function_length = data.function_length;
+      *has_duplicate_parameters = data.has_duplicate_parameters;
+      *expected_property_count = data.expected_property_count;
+      SkipFunctionLiterals(data.num_inner_functions);
+      return kLazyParsingComplete;
+    }
+  }
+
   // With no cached data, we partially parse the function, without building an
   // AST. This gathers the data needed to build a lazy function.
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.compile"), "V8.PreParse");