[Interpreter] Add dispatch counters for each bytecode.

src/interpreter/interpreter.h

Index: src/interpreter/interpreter.h
diff --git a/src/interpreter/interpreter.h b/src/interpreter/interpreter.h
index 075fe741e943f064f22184c727cc04c823ea3fb3..4f1edfa1f385183c3e584b35615021d257852afe 100644
--- a/src/interpreter/interpreter.h
+++ b/src/interpreter/interpreter.h
@@ -53,10 +53,19 @@ class Interpreter {
     return reinterpret_cast<Address>(&dispatch_table_[0]);
   }
 
+  uint32_t* handlers_dispatch_counters() {
+    return &handlers_dispatch_counters_[0];
+  }
+
   // Returns true if a handler is generated for a bytecode at a given
   // operand scale.
   static bool BytecodeHasHandler(Bytecode bytecode, OperandScale operand_scale);
 
+  static const int kNumberOfWideVariants = 3;
+  static const int kDispatchTableSize = kNumberOfWideVariants * (kMaxUInt8 + 1);
+  static const int kCountersTableRowSize =
+      static_cast<int>(Bytecode::kLast) + 1;

[rmcilroy, 2016/04/05 10:00:46]

Please keep these private. I don't think you need kCountersTableRowSize either
(just use Bytecode::kLast + 1 where needed).

[Stefano Sanfilippo, 2016/04/05 14:01:46]

Moved to private.

I'd be in favour of keeping the kCountersTableRowSize constant, it will be
useful for the follow-up CL (handler to handler counters).

+
  private:
 // Bytecode handler generator functions.
 #define DECLARE_BYTECODE_HANDLER_GENERATOR(Name, ...) \
@@ -140,11 +149,9 @@ class Interpreter {
 
   bool IsDispatchTableInitialized();
 
-  static const int kNumberOfWideVariants = 3;
-  static const int kDispatchTableSize = kNumberOfWideVariants * (kMaxUInt8 + 1);
-
   Isolate* isolate_;
   Code* dispatch_table_[kDispatchTableSize];
+  uint32_t handlers_dispatch_counters_[kCountersTableRowSize];

[rmcilroy, 2016/04/05 10:00:46]

Could we make this a smart pointer which is only allocated if the flag is set
(avoid wasting memory). Also, how about we just make this uintptr_t size, (with
appropriate updates in the interpreter-assembler generated code) that way we get
64bit counters on 64bit platforms.

[Stefano Sanfilippo, 2016/04/05 14:01:46]

I replaced the array with a std::vector which gets resize()'d only if the flag
is enabled. Done.

 
   DISALLOW_COPY_AND_ASSIGN(Interpreter);
 };