[Interpreter] Enable tracing of bytecode handler dispatches.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index c23c1a4a9c722f0839fd4ca4976c41e90b10cda0..e12a2451e1856e7a776432f033bd60e753aceb12 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -12,6 +12,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <fstream>
 
 #ifdef V8_SHARED
 #include <assert.h>
@@ -41,6 +42,7 @@
 #include "src/base/platform/platform.h"
 #include "src/base/sys-info.h"
 #include "src/basic-block-profiler.h"
+#include "src/interpreter/interpreter.h"
 #include "src/snapshot/natives.h"
 #include "src/utils.h"
 #include "src/v8.h"
@@ -1275,6 +1277,63 @@ struct CounterAndKey {
 inline bool operator<(const CounterAndKey& lhs, const CounterAndKey& rhs) {
   return strcmp(lhs.key, rhs.key) < 0;
 }
+
+void Shell::WriteInterpreterDispatchCounters(Isolate* isolate) {

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

Actually thinking about it, let's move this function to the interpreter class so
we can call it in Chrome in the future.

[Stefano Sanfilippo, 2016/04/08 18:10:02]

Done.

+  std::ofstream stream(i::FLAG_trace_ignition_dispatches_output_file);
+
+  uintptr_t* bytecode_dispatch_count_table =
+      reinterpret_cast<i::Isolate*>(isolate)
+          ->interpreter()
+          ->bytecode_dispatch_count_table();
+
+  static const int kCountersTableRowSize =
+      static_cast<int>(i::interpreter::Bytecode::kLast) + 1;

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

Update this constant name too.

[Stefano Sanfilippo, 2016/04/08 18:10:02]

Done.

+
+  // Output is a JSON-encoded object of objects.
+  //
+  // Keys on the top level object are the source bytecodes,
+  // and corresponding value are objects. Keys on these last are the
+  // destinations of the dispatch and the value associated is a counter for
+  // the correspondent source-destination dispatch chain.
+  //
+  // Only non-zero counters are written to file, but an entry in the top-level
+  // object is always present, even if the value is empty because all counters
+  // for that source are zero.
+
+  stream << '{';
+
+  for (int from_index = 0; from_index < kCountersTableRowSize; ++from_index) {
+    if (from_index > 0) stream << ",\n ";
+
+    i::interpreter::Bytecode from_bytecode =
+        i::interpreter::Bytecodes::FromByte(from_index);
+    stream << "\"" << i::interpreter::Bytecodes::ToString(from_bytecode)
+           << "\": {";
+
+    bool emitted_first = false;
+    for (int to_index = 0; to_index < kCountersTableRowSize; ++to_index) {
+      uintptr_t counter =
+          bytecode_dispatch_count_table[from_index * kCountersTableRowSize +
+                                        to_index];
+      if (counter > 0) {
+        if (emitted_first) {
+          stream << ", ";
+        } else {
+          emitted_first = true;
+        }
+
+        i::interpreter::Bytecode to_bytecode =
+            i::interpreter::Bytecodes::FromByte(to_index);
+        stream << '"' << i::interpreter::Bytecodes::ToString(to_bytecode)
+               << "\": " << counter;
+      }
+    }
+
+    stream << "}";
+  }
+  stream << '}';
+}
+
 #endif  // !V8_SHARED
 
 
@@ -1312,6 +1371,11 @@ void Shell::OnExit(v8::Isolate* isolate) {
            "-------------+\n");
     delete [] counters;
   }
+
+  if (i::FLAG_trace_ignition_dispatches) {
+    WriteInterpreterDispatchCounters(isolate);
+  }
+
   delete counters_file_;
   delete counter_map_;
 #endif  // !V8_SHARED