DBC: When calling DRT_OptimizeInvokedFunction, patch the stack to have a stub instead of the to-be-…

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 c02e1bfcaa5dfe5e11de27f647c661240756c608..748be51b4c14a94b22823118d5cf633f15b2211b 100644
--- a/runtime/vm/simulator_dbc.cc
+++ b/runtime/vm/simulator_dbc.cc
@@ -38,6 +38,7 @@ DEFINE_FLAG(uint64_t, stop_sim_at, ULLONG_MAX,
             "Instruction address or instruction count to stop simulator at.");
 
 #define LIKELY(cond) __builtin_expect((cond), 1)
+#define UNLIKELY(cond) __builtin_expect((cond), 0)
 
 // SimulatorSetjmpBuffer are linked together, and the last created one
 // is referenced by the Simulator. When an exception is thrown, the exception
@@ -1435,9 +1436,17 @@ RawObject* Simulator::Call(const Code& code,
       counter += increment;
       f->ptr()->usage_counter_ = counter;
     }
-    if (counter >= threshold) {
+    if (UNLIKELY(counter >= threshold)) {
       FP[0] = f;
       FP[1] = 0;
+
+      // Make the DRT_OptimizeInvokedFunction see a stub as its caller for
+      // consistency with the other architectures, and to avoid needing to
+      // generate a stackmap for the HotCheck pc.
+      const StubEntry* stub = StubCode::OptimizeFunction_entry();

[zra, 2016/11/04 16:01:05]

Is it okay for this to be *any* stub, or does it have to be this one. If it can
be any stub, we should fill in something here that will die in an obvious way.

[rmacnak, 2016/11/04 16:50:27]

Right, any stub because we'll switch to the new optimized code after returning
from the runtime call.

+      FP[kPcMarkerSlotFromFp] = stub->code();
+      pc = reinterpret_cast<uint32_t*>(stub->EntryPoint());
+
       Exit(thread, FP, FP + 2, pc);
       NativeArguments args(thread, 1, FP, FP + 1);
       INVOKE_RUNTIME(DRT_OptimizeInvokedFunction, args);