[hydrogen] don't bailout assignments to consts

src/hydrogen-instructions.h

 // Copyright 2011 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 3431 matching lines @@
  private:
   Handle<Object> name_;
   StrictModeFlag strict_mode_flag_;
 };
 
 
 class HLoadContextSlot: public HUnaryOperation {
  public:
   enum Mode {
     // Perform a normal load of the context slot without checking its value.
-    kLoad,
+    kNoCheck,
     // Load and check the value of the context slot. Deoptimize if it's the
     // hole value. This is used for checking for loading of uninitialized
     // harmony bindings where we deoptimize into full-codegen generated code
     // which will subsequently throw a reference error.
-    kLoadCheck
+    kCheckDeoptimize,
+    // Load and check the value of the context slot. Return undefined if it's
+    // the hole value. This is used for non-harmony const assignments
+    kCheckReturnUndefined
   };
 
   HLoadContextSlot(HValue* context, Variable* var)
       : HUnaryOperation(context), slot_index_(var->index()) {
     ASSERT(var->IsContextSlot());
-    mode_ = (var->mode() == LET || var->mode() == CONST_HARMONY)
-        ? kLoadCheck : kLoad;
+    switch (var->mode()) {
+      case LET:
+      case CONST_HARMONY:
+        mode_ = kCheckDeoptimize;
+        break;
+      case CONST:
+        mode_ = kCheckReturnUndefined;
+        break;
+      default:
+        mode_ = kNoCheck;
+    }
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetFlag(kDependsOnContextSlots);
   }
 
   int slot_index() const { return slot_index_; }
+  Mode mode() const { return mode_; }
+
+  bool DeoptimizesOnHole() {
+    return mode_ == kCheckDeoptimize;
+  }
 
   bool RequiresHoleCheck() {
-    return mode_ == kLoadCheck;
+    return mode_ != kNoCheck;
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
   DECLARE_CONCRETE_INSTRUCTION(LoadContextSlot)
 
  protected:
   virtual bool DataEquals(HValue* other) {
     HLoadContextSlot* b = HLoadContextSlot::cast(other);
     return (slot_index() == b->slot_index());
   }
 
  private:
   int slot_index_;
   Mode mode_;
 };
 
 
 class HStoreContextSlot: public HTemplateInstruction<2> {
  public:
   enum Mode {
     // Perform a normal store to the context slot without checking its previous
     // value.
-    kAssign,
+    kNoCheck,
     // Check the previous value of the context slot and deoptimize if it's the
     // hole value. This is used for checking for assignments to uninitialized
     // harmony bindings where we deoptimize into full-codegen generated code
     // which will subsequently throw a reference error.
-    kAssignCheck
+    kCheckDeoptimize,
+    // Check the previous value and ignore assignment if it isn't a hole value
+    kCheckIgnoreAssignment
   };
 
   HStoreContextSlot(HValue* context, int slot_index, Mode mode, HValue* value)
       : slot_index_(slot_index), mode_(mode) {
     SetOperandAt(0, context);
     SetOperandAt(1, value);
     SetFlag(kChangesContextSlots);
   }
 
   HValue* context() { return OperandAt(0); }
   HValue* value() { return OperandAt(1); }
   int slot_index() const { return slot_index_; }
   Mode mode() const { return mode_; }
 
   bool NeedsWriteBarrier() {
     return StoringValueNeedsWriteBarrier(value());
   }
 
+  bool DeoptimizesOnHole() {
+    return mode_ == kCheckDeoptimize;
+  }
+
   bool RequiresHoleCheck() {
-    return mode_ == kAssignCheck;
+    return mode_ != kNoCheck;
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
   DECLARE_CONCRETE_INSTRUCTION(StoreContextSlot)
 
@@ skipping 927 matching lines @@
 
   DECLARE_CONCRETE_INSTRUCTION(In)
 };
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_