[Interpreter] Enable tracing of bytecode handler dispatches.

src/interpreter/interpreter.cc

Index: src/interpreter/interpreter.cc
diff --git a/src/interpreter/interpreter.cc b/src/interpreter/interpreter.cc
index 5084300dfee60294b3af19832d026410b5834c6f..327b4b5caa44bc5c58ea8ee3fd54be9932ddb29a 100644
--- a/src/interpreter/interpreter.cc
+++ b/src/interpreter/interpreter.cc
@@ -33,6 +33,15 @@ void Interpreter::Initialize() {
   Zone zone(isolate_->allocator());
   HandleScope scope(isolate_);
 
+  if (FLAG_trace_ignition_dispatches) {
+    static const int kCountersTableRowSize =

[rmcilroy, 2016/04/08 16:40:31]

kBytecodeCount would be a more appropriate name (given it is both the row and
column count). You could add this as a constant in Bytecodes.h if you like and
reuse it everywhere we currently use static_cast<int>(Bytecode::kLast) + 1.

[Stefano Sanfilippo, 2016/04/08 17:01:05]

I second this proposal, however I fill it qualifies for a separate CL. For the
moment I am renaming the local variable, though.

[rmcilroy, 2016/04/08 17:15:47]

Sure.

+        static_cast<int>(Bytecode::kLast) + 1;
+    bytecode_dispatch_count_table_.Reset(
+        new uintptr_t[kCountersTableRowSize * kCountersTableRowSize]);
+    memset(bytecode_dispatch_count_table_.get(), 0,
+           sizeof(uintptr_t) * kCountersTableRowSize * kCountersTableRowSize);
+  }
+
   // Generate bytecode handlers for all bytecodes and scales.
   for (OperandScale operand_scale = OperandScale::kSingle;
        operand_scale <= OperandScale::kMaxValid;
@@ -148,9 +157,11 @@ bool Interpreter::MakeBytecode(CompilationInfo* info) {
 }
 
 bool Interpreter::IsDispatchTableInitialized() {
-  if (FLAG_trace_ignition || FLAG_trace_ignition_codegen) {
-    // Regenerate table to add bytecode tracing operations
-    // or to print the assembly code generated by TurboFan.
+  if (FLAG_trace_ignition || FLAG_trace_ignition_codegen ||
+      FLAG_trace_ignition_dispatches) {
+    // Regenerate table to add bytecode tracing operations,
+    // print the assembly code generated by TurboFan,
+    // or instrument handlers with dispatch counters.
     return false;
   }
   return dispatch_table_[0] != nullptr;