Don't use string slices when processing RexExp replace

src/runtime.cc

Index: src/runtime.cc
===================================================================
--- src/runtime.cc	(revision 3152)
+++ src/runtime.cc	(working copy)
@@ -1357,8 +1357,9 @@
           StringBuilderSubstringPosition::encode(from);
       AddElement(Smi::FromInt(encoded_slice));
     } else {
-      Handle<String> slice = Factory::NewStringSlice(subject_, from, to);
-      AddElement(*slice);
+      // Otherwise encode as two smis.
+      AddElement(Smi::FromInt(-length));
+      AddElement(Smi::FromInt(from));
     }
     IncrementCharacterCount(length);
   }
@@ -3766,9 +3767,21 @@
   for (int i = 0; i < array_length; i++) {
     Object* element = fixed_array->get(i);
     if (element->IsSmi()) {
+      // Smi encoding of position and length.
       int encoded_slice = Smi::cast(element)->value();
-      int pos = StringBuilderSubstringPosition::decode(encoded_slice);
-      int len = StringBuilderSubstringLength::decode(encoded_slice);
+      int pos;
+      int len;
+      if (encoded_slice > 0) {
+        // Position and length encoded in one smi.
+        pos = StringBuilderSubstringPosition::decode(encoded_slice);
+        len = StringBuilderSubstringLength::decode(encoded_slice);
+      } else {
+        // Position and length encoded in two smis.
+        Object* obj = fixed_array->get(++i);
+        ASSERT(obj->IsSmi());
+        pos = Smi::cast(obj)->value();
+        len = -encoded_slice;
+      }
       String::WriteToFlat(special,
                           sink + position,
                           pos,
@@ -3789,6 +3802,10 @@
   ASSERT(args.length() == 2);
   CONVERT_CHECKED(JSArray, array, args[0]);
   CONVERT_CHECKED(String, special, args[1]);
+
+  // This assumption is used by the slice encoding in one or two smis.
+  ASSERT(Smi::kMaxValue >= String::kMaxLength);
+
   int special_length = special->length();
   Object* smi_array_length = array->length();
   if (!smi_array_length->IsSmi()) {
@@ -3816,13 +3833,29 @@
   for (int i = 0; i < array_length; i++) {
     Object* elt = fixed_array->get(i);
     if (elt->IsSmi()) {
+      // Smi encoding of position and length.
       int len = Smi::cast(elt)->value();
-      int pos = len >> 11;
-      len &= 0x7ff;
-      if (pos + len > special_length) {
-        return Top::Throw(Heap::illegal_argument_symbol());
+      if (len > 0) {
+        // Position and length encoded in one smi.
+        int pos = len >> 11;
+        len &= 0x7ff;
+        if (pos + len > special_length) {
+          return Top::Throw(Heap::illegal_argument_symbol());
+        }
+        position += len;
+      } else {
+        // Position and length encoded in two smis.
+        position += (-len);
+        // Get the position and check that it is also a smi.
+        i++;
+        if (i >= array_length) {
+          return Top::Throw(Heap::illegal_argument_symbol());
+        }
+        Object* pos = fixed_array->get(i);
+        if (!pos->IsSmi()) {
+          return Top::Throw(Heap::illegal_argument_symbol());
+        }
       }
-      position += len;
     } else if (elt->IsString()) {
       String* element = String::cast(elt);
       int element_length = element->length();