Fix Array.{splice,slice} to set proper ElementsKind of result

TEST=mjsunit/elements-kind.js

Review URL: http://codereview.chromium.org/8430036

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9882 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/builtins.cc

@@ -772,6 +772,13 @@ BUILTIN(ArraySlice) {
 
   // Set the length.
   result_array->set_length(Smi::FromInt(result_len));
+
+  // Set the ElementsKind.
+  ElementsKind elements_kind = JSObject::cast(receiver)->GetElementsKind();
+  if (result_array->GetElementsKind() != elements_kind) {
+    MaybeObject* maybe = result_array->TransitionElementsKind(elements_kind);
+    if (maybe->IsFailure()) return maybe;
+  }
   return result_array;
 }
 
@@ -865,6 +872,13 @@ BUILTIN(ArraySplice) {
 
     // Set the length.
     result_array->set_length(Smi::FromInt(actual_delete_count));
+
+    // Set the ElementsKind.
+    ElementsKind elements_kind = array->GetElementsKind();
+    if (result_array->GetElementsKind() != elements_kind) {
+      MaybeObject* maybe = result_array->TransitionElementsKind(elements_kind);
+      if (maybe->IsFailure()) return maybe;
+    }
   }
 
   int item_count = (n_arguments > 1) ? (n_arguments - 2) : 0;

test/mjsunit/elements-kind.js

@@ -326,5 +326,15 @@ if (support_smi_only_arrays) {
   assertEquals([1, 2, 3, 4, 5], a);
 }
 
+// Test that Array.splice() and Array.slice() return correct ElementsKinds.
+if (support_smi_only_arrays) {
+  var a = ["foo", "bar"];
+  assertKind(elements_kind.fast, a);
+  var b = a.splice(0, 1);
+  assertKind(elements_kind.fast, b);
+  var c = a.slice(0, 1);
+  assertKind(elements_kind.fast, c);
+}
+
 // Throw away type information in the ICs for next stress run.
 gc();