Disable hoisting CheckClass due to excessive deoptimization.

runtime/vm/deopt_instructions.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/deopt_instructions.h"
 
 #include "vm/assembler.h"
 #include "vm/code_patcher.h"
 #include "vm/intermediate_language.h"
 #include "vm/locations.h"
@@ skipping 566 matching lines @@
 
     uword pc = code.GetPcForDeoptId(deopt_id_, PcDescriptors::kIcCall);
     if (pc != 0) {
       // If the deoptimization happened at an IC call, update the IC data
       // to avoid repeated deoptimization at the same site next time around.
       ICData& ic_data = ICData::Handle();
       CodePatcher::GetInstanceCallAt(pc, code, &ic_data);
       if (!ic_data.IsNull()) {
         ic_data.set_deopt_reason(deopt_context->deopt_reason());
       }
+    } else if (deopt_context->deopt_reason() == kDeoptHoistedCheckClass) {
+      // Prevent excessive deoptimization.
+      Function::Handle(code.function()).set_allows_hoisting_check_class(false);
     }
   }
 
   intptr_t object_table_index() const { return object_table_index_; }
   intptr_t deopt_id() const { return deopt_id_; }
 
  private:
   static const intptr_t kFieldWidth = kBitsPerWord / 2;
   class ObjectTableIndex : public BitField<intptr_t, 0, kFieldWidth> { };
   class DeoptId : public BitField<intptr_t, kFieldWidth, kFieldWidth> { };
@@ skipping 810 matching lines @@
                           Smi* offset,
                           DeoptInfo* info,
                           Smi* reason) {
   intptr_t i = index * kEntrySize;
   *offset ^= table.At(i);
   *info ^= table.At(i + 1);
   *reason ^= table.At(i + 2);
 }
 
 }  // namespace dart