Collect type profile for DevTools.

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index 4e944f7fcda41fdde7cbd60e7f5931be9dfc69bd..86c1f3c0465848ac17871b5aa429fe4918bea1f4 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -321,6 +321,16 @@ void EnsureFeedbackMetadata(CompilationInfo* info) {
     info->shared_info()->set_feedback_metadata(*feedback_metadata);
   }
 
+  // CollectTypeProfile uses its own feedback slot. The decision
+  // whether we collect type profile or not must match the
+  // feedback metadata.
+  // If we have not decided whether we collect type feedback, we
+  // make a decision based on the FLAG. Otherwise we cannot change it.
+  if (!info->shared_info()->computed_collects_type_profile()) {

[Yang, 2017/03/09 10:28:27]

Michael, here's where I'd like you to take a closer look. What we want to
achieve here is:
- We can freely make the decision whether to collect type profile at the first
compile. This decision is made based on a command line flag.
- After the first compile, we need to persist the decision somehow, so that any
subsequent compiles do not conflict with existing feedback metadata.
- We can run into the situation of compiling with existing feedback metadata if
we compile a function from the snapshot, since snapshotting discards the code.

Currently this decision is persisted on the shared function info. So we are
assuming that this is the correct place to keep this decision in sync with the
feedback metadata.

But I wonder whether we persist this decision even closer to the feedback
metadata. For example, if we could figure out the previous decision from looking
at feedback metadata itself, that would be a lot nicer.

[mvstanton, 2017/03/10 12:12:24]

Yep, it makes sense to avoid these flags and just iterate the feedback metadata
looking for your special slot. If you find one, then the metadata was created at
a moment when you wanted type profiling, so now you know that.

[Franzi, 2017/03/10 14:33:49]

I deleted the constants and instead check the FeedbackMetadata. 

+    info->shared_info()->set_collects_type_profile(FLAG_type_profile);
+    info->shared_info()->set_computed_collects_type_profile(true);
+  }
+
   // It's very important that recompiles do not alter the structure of the type
   // feedback vector. Verify that the structure fits the function literal.
   CHECK(!info->shared_info()->feedback_metadata()->SpecDiffersFrom(
@@ -478,9 +488,25 @@ bool Renumber(ParseInfo* parse_info,
               Compiler::EagerInnerFunctionLiterals* eager_literals) {
   RuntimeCallTimerScope runtimeTimer(parse_info->isolate(),
                                      &RuntimeCallStats::CompileRenumber);
+
+  // CollectTypeProfile uses its own feedback slot. The decision
+  // whether we collect type profile or not must match the
+  // feedback metadata.
+  // If we parse for the first time or if we have not decided whether we collect
+  // type feedback, we make a decision based on the FLAG. Otherwise we stick
+  // with the previous decision.
+  bool collect_type_profile =
+      (FLAG_type_profile &&
+       (parse_info->shared_info().is_null() ||
+        !parse_info->shared_info()->computed_collects_type_profile())) ||
+      (!parse_info->shared_info().is_null() &&
+       parse_info->shared_info()->computed_collects_type_profile() &&
+       parse_info->shared_info()->collects_type_profile());

[Yang, 2017/03/09 10:28:27]

This expression seems correct. But can we make this a bit more readable?
Something like

if (parse_info->shared_info().is_null() ||
!parse_info->shared_info()->computed_collects_type_profile())) {
  collect_type_profile = FLAG_type_profile
} else {
  collect_type_profile = parse_info->shared_info()->collects_type_profile();
}

[Franzi, 2017/03/10 12:14:28]

Thanks for the suggestions. Done. 

+
   if (!AstNumbering::Renumber(
           parse_info->isolate()->stack_guard()->real_climit(),
-          parse_info->zone(), parse_info->literal(), eager_literals)) {
+          parse_info->zone(), parse_info->literal(), eager_literals,
+          collect_type_profile)) {
     return false;
   }
   if (!parse_info->shared_info().is_null()) {