Simplify feedback vector creation and store in SharedFunctionInfo.

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index 6fa60a3dea6efe24cbcf5e7b064bf4e2a296544e..8e2f890fbb4ee90fda7e500e80ea1771fa1ea78d 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -141,6 +141,13 @@ void CompilationInfo::Initialize(Isolate* isolate,
     SetStrictMode(shared_info_->strict_mode());
   }
   set_bailout_reason(kUnknown);
+
+  if (!shared_info().is_null() && shared_info()->is_compiled()) {
+    // We should initialize the CompilationInfo feedback vector from the
+    // passed in shared info, rather than creating a new one.
+    feedback_vector_ = Handle<FixedArray>(shared_info()->feedback_vector(),
+                                          isolate);
+  }
 }
 
 
@@ -249,7 +256,22 @@ bool CompilationInfo::ShouldSelfOptimize() {
 void CompilationInfo::PrepareForCompilation(Scope* scope) {
   ASSERT(scope_ == NULL);
   scope_ = scope;
-  function()->ProcessFeedbackSlots(isolate_);
+
+  int length = function()->slot_count();
+  if (feedback_vector_.is_null()) {
+    // Allocate the feedback vector too.
+    feedback_vector_ = isolate()->factory()->NewFixedArray(length, TENURED);

[Benedikt Meurer, 2014/04/28 19:17:00]

How about adding a factory wrapper for Heap::AllocateFixedArrayWithFiller() and
call that wrapper, i.e. NewFixedArrayWithFiller(length, TENURED, sentinel)
instead of allocating a FixedArray filled with undefined and then overwriting
undefined with sentinel?

[mvstanton, 2014/04/30 08:31:18]

Great idea, done, but I went ahead and made the factory method called
NewTypeFeedbackVector(count), which hides the TENURED information as well as the
sentinel used. A future CL already needs that because the feedback vector will
be allocatable in one other place.

+    // Ensure we can skip the write barrier
+    ASSERT_EQ(isolate()->heap()->uninitialized_symbol(),
+              *TypeFeedbackInfo::UninitializedSentinel(isolate()));
+    for (int i = 0; i < length; i++) {
+      feedback_vector_->set(
+          i,
+          *TypeFeedbackInfo::UninitializedSentinel(isolate()),
+          SKIP_WRITE_BARRIER);
+    }
+  }
+  ASSERT(feedback_vector_->length() == length);
 }
 
 
@@ -571,6 +593,8 @@ static void UpdateSharedFunctionInfo(CompilationInfo* info) {
   shared->ReplaceCode(*code);
   if (shared->optimization_disabled()) code->set_optimizable(false);
 
+  shared->set_feedback_vector(*info->feedback_vector());
+
   // Set the expected number of properties for instances.
   FunctionLiteral* lit = info->function();
   int expected = lit->expected_property_count();
@@ -829,7 +853,8 @@ static Handle<SharedFunctionInfo> CompileToplevel(CompilationInfo* info) {
         lit->materialized_literal_count(),
         lit->is_generator(),
         info->code(),
-        ScopeInfo::Create(info->scope(), info->zone()));
+        ScopeInfo::Create(info->scope(), info->zone()),
+        info->feedback_vector());
 
     ASSERT_EQ(RelocInfo::kNoPosition, lit->function_token_position());
     SetFunctionInfo(result, lit, true, script);
@@ -1027,7 +1052,8 @@ Handle<SharedFunctionInfo> Compiler::BuildFunctionInfo(FunctionLiteral* literal,
                                      literal->materialized_literal_count(),
                                      literal->is_generator(),
                                      info.code(),
-                                     scope_info);
+                                     scope_info,
+                                     info.feedback_vector());
   SetFunctionInfo(result, literal, false, script);
   RecordFunctionCompilation(Logger::FUNCTION_TAG, &info, result);
   result->set_allows_lazy_compilation(allow_lazy);