Split arguments[] values on delete.

js2/src/js2eval.cpp

@@ -855,7 +855,10 @@ namespace MetaData {
                 && (multiname->nsList->back() == meta->publicNamespace) 
                 && isValidIndex(multiname->name, index)
                 && (index < args->mSlots->size())) {
-            *rval = (*args->mSlots)[index];
+            if (args->mSplit[index])
+                *rval = (*args->mSplitValue)[index];
+            else
+                *rval = (*args->mSlots)[index];
             return true;
         }
         else
@@ -873,7 +876,10 @@ namespace MetaData {
                 && (multiname->nsList->back() == meta->publicNamespace) 
                 && isValidIndex(multiname->name, index)
                 && (index < args->mSlots->size())) {
-            (*args->mSlots)[index] = newValue;
+            if (args->mSplit[index])
+                (*args->mSplitValue)[index] = newValue;
+            else
+                (*args->mSlots)[index] = newValue;
             return true;
         }
         else
@@ -882,7 +888,23 @@ namespace MetaData {
 
     bool JS2ArgumentsClass::Delete(JS2Metadata *meta, js2val base, Multiname *multiname, Environment *env, bool *result)
     {
-        return JS2Class::Delete(meta, base, multiname, env, result);
+        ASSERT(JS2VAL_IS_OBJECT(base));
+        JS2Object *obj = JS2VAL_TO_OBJECT(base);
+        ArgumentsInstance *args = checked_cast<ArgumentsInstance *>(obj);
+
+        uint32 index;
+        if ((multiname->nsList->size() == 1) 
+                && (multiname->nsList->back() == meta->publicNamespace) 
+                && isValidIndex(multiname->name, index)
+                && (index < args->mSlots->size())) {
+            if (!args->mSplitValue)
+                args->mSplitValue = new std::vector<js2val>(slotCount);
+            args->mSplit[index] = true;
+            (*args->mSplitValue)[index] = JS2VAL_VOID;
+            return true;
+        }
+        else
+            return JS2Class::Delete(meta, base, multiname, env, result);
     }
 
     bool JS2ArrayClass::BracketRead(JS2Metadata *meta, js2val *base, js2val indexVal, Phase phase, js2val *rval)

js2/src/js2metadata.cpp

@@ -5066,12 +5066,20 @@ XXX see EvalAttributeExpression, where identifiers are being handled for now...
             for (uint32 i = 0; i < mSlots->size(); i++)
                 GCMARKVALUE((*mSlots)[i]);
         }
+        if (mSplitValue) {
+            for (uint32 i = 0; i < mSlots->size(); i++)
+                GCMARKVALUE((*mSplitValue)[i]);
+        }
     }
 
     ArgumentsInstance::~ArgumentsInstance()
     {
         if (mSlots)
             delete mSlots;
+        if (mSplit)
+            delete mSplit;
+        if (mSplitValue)
+            delete mSplitValue;
     }
 
 /************************************************************************************
@@ -5175,6 +5183,7 @@ XXX see EvalAttributeExpression, where identifiers are being handled for now...
     // Pad out to 'length' args with undefined values if argCount is insufficient
     void ParameterFrame::assignArguments(JS2Metadata *meta, JS2Object *fnObj, js2val *argBase, uint32 argCount, uint32 length)
     {
+        uint32 i;
         ASSERT(pluralFrame->kind == ParameterFrameKind);
         ParameterFrame *plural = checked_cast<ParameterFrame *>(pluralFrame);
         
@@ -5191,8 +5200,12 @@ XXX see EvalAttributeExpression, where identifiers are being handled for now...
             argsObj = new ArgumentsInstance(meta, meta->objectClass->prototype, meta->argumentsClass);
 			if (argCount > slotCount)
 				slotCount = argCount;
-			if (slotCount)
+            if (slotCount) {
                 argsObj->mSlots = new std::vector<js2val>(slotCount);
+                argsObj->mSplit = new bool[slotCount];
+                for (i = 0; (i < slotCount); i++)
+                    argsObj->mSplit[i] = false;
+            }
             frameSlots = argsObj->mSlots;
             // Add the 'arguments' property
             String name(widenCString("arguments"));
@@ -5203,7 +5216,6 @@ XXX see EvalAttributeExpression, where identifiers are being handled for now...
             localBindings.insert(name, lbe);
         }
 
-        uint32 i;
         for (i = 0; (i < argCount); i++) {
             if (i < slotCount) {
                 (*frameSlots)[i] = argBase[i];

js2/src/js2metadata.h

@@ -1059,11 +1059,21 @@ public:
     virtual ~RegExpInstance()             { }
 };
 
+
+// Instances of Arguments class:
+// The n arguments supplied to a function are also stored in a variable 'arguments' with properties [0] ..[n]
+// FrameVariable references from the ParameterFrame are directed to this array because the FrameParameter's
+// slot list points here instead.
+// When an element in arguments[] is deleted, that splits the alias. New values added afterwards are kept in a 
+// separate value list instead.
 class ArgumentsInstance : public SimpleInstance {
 public:
-    ArgumentsInstance(JS2Metadata *meta, js2val parent, JS2Class *type) : SimpleInstance(meta, parent, type), mSlots(NULL) { }
+    ArgumentsInstance(JS2Metadata *meta, js2val parent, JS2Class *type) 
+                        : SimpleInstance(meta, parent, type), mSlots(NULL), mSplit(NULL), mSplitValue(NULL) { }
 
     ValueList *mSlots;
+    bool *mSplit;
+    ValueList *mSplitValue;
 
     virtual void markChildren();
     virtual ~ArgumentsInstance();