[Interpreter] Collect type feedback for calls in the bytecode handler

src/interpreter/bytecode-generator.cc

 // Copyright 2015 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.
 
 #include "src/interpreter/bytecode-generator.h"
 
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-register-allocator.h"
@@ skipping 2504 matching lines @@
         .LoadLiteral(Smi::FromInt(expr->position()))
         .StoreAccumulatorInRegister(eval_position);
 
     // Call ResolvePossiblyDirectEval and modify the callee.
     builder()
         ->CallRuntime(Runtime::kResolvePossiblyDirectEval, callee_for_eval, 6)
         .StoreAccumulatorInRegister(callee);
   }
 
   builder()->SetExpressionPosition(expr);
-  builder()->Call(callee, receiver, 1 + args->length(),
-                  feedback_index(expr->CallFeedbackICSlot()),
+  int feedback_slot_index = feedback_index(expr->CallFeedbackICSlot());
+  if (expr->CallFeedbackICSlot().IsInvalid()) {
+    DCHECK(call_type == Call::POSSIBLY_EVAL_CALL);
+    // Valid type feedback slots can only be greater than kReservedIndexCount.
+    // We use 0 to indicate an invalid slot it. Statically assert that 0 cannot
+    // be a valid slot id.
+    STATIC_ASSERT(TypeFeedbackVector::kReservedIndexCount > 0);
+    feedback_slot_index = 0;

[mythria, 2016/07/12 09:01:34]

@mvstanton, this is where we pass 0 for invalid slot id. As discussed offline I
added a static assert. PTAL.

[rmcilroy, 2016/07/12 09:36:20]

I think feedback_slot_index will already be zero for an invalid slot. Could we
just do:

int feedback_slot_index = feedback_index(expr->CallFeedbackICSlot());

// Comment...
STATIC_ASSERT(TypeFeedbackVector::kReservedIndexCount > 0);
DCHECK(expr->CallFeedbackICSlot().Valid() || (
       (feedback_slot_index == 0 && call_type == Call::POSSIBLY_EVAL_CALL));

?

[mvstanton, 2016/07/12 13:25:22]

Sounds good.

[mythria, 2016/07/12 15:20:35]

As discussed offline, it will be 0 but it is dependent on kReservedIndexCount
being 1. Updated the code to if else to make it more readable. Done.

+  }
+  builder()->Call(callee, receiver, 1 + args->length(), feedback_slot_index,
                   expr->tail_call_mode());
   execution_result()->SetResultInAccumulator();
 }
 
 void BytecodeGenerator::VisitCallSuper(Call* expr) {
   RegisterAllocationScope register_scope(this);
   SuperCallReference* super = expr->expression()->AsSuperCallReference();
 
   // Prepare the constructor to the super call.
   Register this_function = register_allocator()->NewRegister();
@@ skipping 630 matching lines @@
   return execution_context()->scope()->language_mode();
 }
 
 int BytecodeGenerator::feedback_index(FeedbackVectorSlot slot) const {
   return TypeFeedbackVector::GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8