Fix duplication of the megamorphic miss function when running a JIT app snapshot.

runtime/vm/dart.cc

 // Copyright (c) 2013, 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 "vm/dart.h"
 
 #include "vm/become.h"
 #include "vm/clustered_snapshot.h"
 #include "vm/code_observers.h"
 #include "vm/cpu.h"
@@ skipping 564 matching lines @@
   DEBUG_ONLY(I->heap()->Verify(kForbidMarked));
 
   {
     NOT_IN_PRODUCT(TimelineDurationScope tds(T, Timeline::GetIsolateStream(),
                                              "StubCode::Init"));
     StubCode::Init(I);
   }
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
   // When running precompiled, the megamorphic miss function/code comes from the
   // snapshot.

[siva, 2017/01/05 23:10:47]

The comment here also probably needs an update
(precompiled and running from an application snapshot) ?

[rmacnak, 2017/01/05 23:32:44]

Done.

-  if (!Snapshot::IncludesCode(Dart::snapshot_kind())) {
+  if (I->object_store()->megamorphic_miss_function() == Function::null()) {
     MegamorphicCacheTable::InitMissHandler(I);
   }
 #endif

[siva, 2017/01/05 23:10:47]

Should this be set up as

#if defined(DART_PRECOMPILED_RUNTIME)
   // When running precompiled, the megamorphic mi.....
   ASSERT(I->object_store()->megamorphic_miss_function() != Function::null());
#else
   // When running from an application snapshot ....
   if (I->object_store()->megamorphic_miss_function() == Function...) {
      ....
    }
#endif  // defined(DART_PRECOMPILED_RUNTIME)

[rmacnak, 2017/01/05 23:32:44]

Done.

 
   const Code& miss_code =
       Code::Handle(I->object_store()->megamorphic_miss_code());
   I->set_ic_miss_code(miss_code);
 
   if ((snapshot_buffer == NULL) || (kernel_program != NULL)) {
     const Error& error = Error::Handle(I->object_store()->PreallocateObjects());
     if (!error.IsNull()) {
       return error.raw();
     }
@@ skipping 138 matching lines @@
   return predefined_handles_->handles_.IsValidScopedHandle(address);
 }
 
 
 bool Dart::IsReadOnlyApiHandle(Dart_Handle handle) {
   ASSERT(predefined_handles_ != NULL);
   return predefined_handles_->api_handles_.IsValidHandle(handle);
 }
 
 }  // namespace dart