Deoptimization is easier to diagnose when there is a text reason.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1230 matching lines @@
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
   DECLARE_CONCRETE_INSTRUCTION(DummyUse);
 };
 
 
 class HDeoptimize: public HTemplateInstruction<0> {
  public:
-  DECLARE_INSTRUCTION_FACTORY_P1(HDeoptimize, Deoptimizer::BailoutType);
+  DECLARE_INSTRUCTION_FACTORY_P2(HDeoptimize, const char*,
+                                 Deoptimizer::BailoutType);
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::None();
   }
 
+  const char* reason() const { return reason_; }
   Deoptimizer::BailoutType type() { return type_; }
 
   DECLARE_CONCRETE_INSTRUCTION(Deoptimize)
 
  private:
-  explicit HDeoptimize(Deoptimizer::BailoutType type) : type_(type) {}
+  explicit HDeoptimize(const char* reason, Deoptimizer::BailoutType type)
+      : reason_(reason), type_(type) {}
 
+  const char* reason_;
   Deoptimizer::BailoutType type_;
 };
 
 
 // Inserts an int3/stop break instruction for debugging purposes.
 class HDebugBreak: public HTemplateInstruction<0> {
  public:
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::None();
   }
@@ skipping 5504 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_