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

runtime/vm/simulator_dbc.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <setjmp.h>  // NOLINT
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_DBC)
 
@@ skipping 20 matching lines @@
 #include "vm/symbols.h"
 
 namespace dart {
 
 DEFINE_FLAG(uint64_t, trace_sim_after, ULLONG_MAX,
             "Trace simulator execution after instruction count reached.");
 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
 // runtime looks at where to jump and finds the corresponding
 // SimulatorSetjmpBuffer based on the stack pointer of the exception handler.
 // The runtime then does a Longjmp on that buffer to return to the simulator.
 class SimulatorSetjmpBuffer {
  public:
   void Longjmp() {
     // "This" is now the last setjmp buffer.
@@ skipping 1377 matching lines @@
     const uint8_t increment = rA;
     const uint16_t threshold = rD;
     RawFunction* f =  FrameFunction(FP);
     int32_t counter = f->ptr()->usage_counter_;
     // Note: we don't increment usage counter in the prologue of optimized
     // functions.
     if (increment) {
       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);
       {
         // DRT_OptimizeInvokedFunction returns the code object to execute.
         ASSERT(FP[1]->GetClassId() == kFunctionCid);
         RawFunction* function = static_cast<RawFunction*>(FP[1]);
         RawCode* code = function->ptr()->code_;
         SimulatorHelpers::SetFrameCode(FP, code);
         pp = code->ptr()->object_pool_->ptr();
@@ skipping 2303 matching lines @@
   pc_ = pc;
   special_[kExceptionSpecialIndex] = raw_exception;
   special_[kStacktraceSpecialIndex] = raw_stacktrace;
   buf->Longjmp();
   UNREACHABLE();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_DBC