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

src/hydrogen.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 1252 matching lines @@
   HStoreNamedField* AddStoreMapConstant(HValue *object, Handle<Map>);
   HLoadNamedField* AddLoadElements(HValue *object, HValue *typecheck = NULL);
   HLoadNamedField* AddLoadFixedArrayLength(HValue *object);
 
   HValue* AddLoadJSBuiltin(Builtins::JavaScript builtin);
 
   HValue* TruncateToNumber(HValue* value, Handle<Type>* expected);
 
   void PushAndAdd(HInstruction* instr);
 
-  void FinishExitWithHardDeoptimization(HBasicBlock* continuation);
+  void FinishExitWithHardDeoptimization(const char* reason,
+                                        HBasicBlock* continuation);
 
   void AddIncrementCounter(StatsCounter* counter,
                            HValue* context);
 
   class IfBuilder {
    public:
     explicit IfBuilder(HGraphBuilder* builder,
                        int position = RelocInfo::kNoPosition);
     IfBuilder(HGraphBuilder* builder,
               HIfContinuation* continuation);
@@ skipping 83 matching lines @@
 
     void Or();
     void And();
 
     void CaptureContinuation(HIfContinuation* continuation);
 
     void Then();
     void Else();
     void End();
 
-    void Deopt();
-    void ElseDeopt() {
+    void Deopt(const char* reason);
+    void ElseDeopt(const char* reason) {
       Else();
-      Deopt();
+      Deopt(reason);
     }
 
     void Return(HValue* value);
 
    private:
     void AddCompare(HControlInstruction* compare);
 
     Zone* zone() { return builder_->zone(); }
 
     HGraphBuilder* builder_;
@@ skipping 184 matching lines @@
 
   CompilationInfo* info_;
   HGraph* graph_;
   HBasicBlock* current_block_;
   int no_side_effects_scope_count_;
 };
 
 
 template<>
 inline HInstruction* HGraphBuilder::AddUncasted<HDeoptimize>(
-    Deoptimizer::BailoutType type) {
+    const char* reason, Deoptimizer::BailoutType type) {
   if (type == Deoptimizer::SOFT) {
     isolate()->counters()->soft_deopts_requested()->Increment();
     if (FLAG_always_opt) return NULL;
   }
   if (current_block()->IsDeoptimizing()) return NULL;
-  HDeoptimize* instr = New<HDeoptimize>(type);
+  HDeoptimize* instr = New<HDeoptimize>(reason, type);
   AddInstruction(instr);
   if (type == Deoptimizer::SOFT) {
     isolate()->counters()->soft_deopts_inserted()->Increment();
     graph()->set_has_soft_deoptimize(true);
   }
   current_block()->MarkAsDeoptimizing();
   return instr;
 }
 
 
 template<>
 inline HDeoptimize* HGraphBuilder::Add<HDeoptimize>(
-    Deoptimizer::BailoutType type) {
-  return static_cast<HDeoptimize*>(AddUncasted<HDeoptimize>(type));
+    const char* reason, Deoptimizer::BailoutType type) {
+  return static_cast<HDeoptimize*>(AddUncasted<HDeoptimize>(reason, type));
 }
 
 
 template<>
 inline HInstruction* HGraphBuilder::AddUncasted<HSimulate>(
     BailoutId id,
     RemovableSimulate removable) {
   HSimulate* instr = current_block()->CreateSimulate(id, removable);
   AddInstruction(instr);
   return instr;
@@ skipping 709 matching lines @@
   EmbeddedVector<char, 64> filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_