[Interpreter] Internalize AST before print-ast is triggered

Print AST needs access to the internalized strings, so make sure AST
is internalized before we print it.

BUG=v8:5203

Change-Id: Ia4995147feb7ec466523a0c4a89620749b23dcab
Reviewed-on: https://chromium-review.googlesource.com/593648Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47006}

src/codegen.cc

@@ -17,6 +17,7 @@
 #include "src/debug/debug.h"
 #include "src/eh-frame.h"
 #include "src/objects-inl.h"
+#include "src/parsing/parse-info.h"
 #include "src/runtime/runtime.h"
 
 namespace v8 {
@@ -96,6 +97,14 @@ void CodeGenerator::MakeCodePrologue(CompilationInfo* info, const char* kind) {
     ftype = "user-defined";
   }
 
+  if (!FLAG_trace_codegen && !print_ast) return;
+
+  // Requires internalizing the AST, so make sure we are on the main thread.
+  DCHECK(ThreadId::Current().Equals(info->isolate()->thread_id()));
+  AllowDeferredHandleDereference allow_deref;
+  AllowHeapAllocation allow_gc;
+  info->parse_info()->ast_value_factory()->Internalize(info->isolate());
+
   if (FLAG_trace_codegen || print_ast) {
     std::unique_ptr<char[]> name = info->GetDebugName();
     PrintF("[generating %s code for %s function: %s]\n", kind, ftype,

src/interpreter/interpreter.cc

@@ -150,6 +150,7 @@ InterpreterCompilationJob::InterpreterCompilationJob(CompilationInfo* info)
       background_execute_counter_("CompileBackgroundIgnition") {}
 
 InterpreterCompilationJob::Status InterpreterCompilationJob::PrepareJobImpl() {
+  // TODO(5203): Move code out of codegen.cc once FCG goes away.
   CodeGenerator::MakeCodePrologue(info(), "interpreter");
   return SUCCEEDED;
 }

test/mjsunit/ignition/print-ast.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --print-ast
+
+// Ensures that the --print-ast flag doesn't crash.
+function foo(a) {
+  var b = 2;
+  return function bar() { return a + b; };
+}
+
+foo()();