Implement Dart VM option '--trace_sim_after' in DBC simulator

runtime/vm/simulator_dbc.cc

Index: runtime/vm/simulator_dbc.cc
diff --git a/runtime/vm/simulator_dbc.cc b/runtime/vm/simulator_dbc.cc
index afb5487f7b648781c6d84937682f9aff3616295b..12423cac0a067e4c8b7dc35f2fc2728b161d80f9 100644
--- a/runtime/vm/simulator_dbc.cc
+++ b/runtime/vm/simulator_dbc.cc
@@ -529,7 +529,7 @@ void Simulator::InitOnce() {
 }
 
 
-Simulator::Simulator() : stack_(NULL), fp_(NULL) {
+Simulator::Simulator() : stack_(NULL), fp_(NULL), icount_(0) {
   // Setup simulator support first. Some of this information is needed to
   // setup the architecture state.
   // We allocate the stack here, the size is computed as the sum of
@@ -575,6 +575,24 @@ uword Simulator::StackTop() const {
 }
 
 
+// Returns true if tracing of executed instructions is enabled.
+DART_FORCE_INLINE bool Simulator::IsTracingExecution() const {
+  return icount_ > FLAG_trace_sim_after;
+}
+
+
+// Prints bytecode instruction at given pc for instruction tracing.
+DART_NOINLINE void Simulator::TraceInstruction(uint32_t* pc) const {
+  THR_Print("%" Pu64 " ", icount_);
+  if (FLAG_support_disassembler) {
+    Disassembler::Disassemble(reinterpret_cast<uword>(pc),
+                              reinterpret_cast<uword>(pc + 1));
+  } else {
+    THR_Print("Disassembler not supported in this mode.\n");
+  }
+}
+
+
 // Calls into the Dart runtime are based on this interface.
 typedef void (*SimulatorRuntimeCall)(NativeArguments arguments);
 
@@ -984,12 +1002,24 @@ static DART_NOINLINE bool InvokeNativeAutoScopeWrapper(Thread* thread,
 
 // Note: all macro helpers are intended to be used only inside Simulator::Call.
 
+// Counts and prints executed bytecode instructions (in a non-PRODUCT mode).
+#if !defined(PRODUCT)
+#define TRACE_INSTRUCTION                                                      \
+  icount_++;                                                                   \
+  if (IsTracingExecution()) {                                                  \
+    TraceInstruction(pc - 1);                                                  \
+  }
+#else
+#define TRACE_INSTRUCTION
+#endif
+
 // Decode opcode and A part of the given value and dispatch to the
 // corresponding bytecode handler.
 #define DISPATCH_OP(val)                                                       \
   do {                                                                         \
     op = (val);                                                                \
     rA = ((op >> 8) & 0xFF);                                                   \
+    TRACE_INSTRUCTION                                                          \
     goto* dispatch[op & 0xFF];                                                 \
   } while (0)