Tentative implementation of string slices (hidden under the flag --string-slices).

test/cctest/test-strings.cc

Index: test/cctest/test-strings.cc
diff --git a/test/cctest/test-strings.cc b/test/cctest/test-strings.cc
index 4d9b264e93f4099f28be3142fcd820fba365a10f..d539a5f241d97400c30583f67ba02bd4bc1d0ce8 100644
--- a/test/cctest/test-strings.cc
+++ b/test/cctest/test-strings.cc
@@ -481,3 +481,59 @@ TEST(CachedHashOverflow) {
     }
   }
 }
+
+
+TEST(TruncateSlice) {
+  FLAG_string_slices = true;
+  InitializeVM();
+  v8::HandleScope scope;
+  Handle<String> string =
+      FACTORY->NewStringFromAscii(CStrVector("parentparentparent"));
+  Handle<String> parent = FACTORY->NewConsString(string, string);
+  CHECK(parent->IsConsString());
+  CHECK(!parent->IsFlat());
+  Handle<String> slice = FACTORY->NewSubString(parent, 1, 25);
+  // After slicing, the original string becomes a flat cons.
+  CHECK(parent->IsFlat());
+  CHECK(slice->IsSlicedString());
+  CHECK_EQ(SlicedString::cast(*slice)->parent(),
+           ConsString::cast(*parent)->first());
+  CHECK(SlicedString::cast(*slice)->parent()->IsSeqString());
+  CHECK(!slice->IsTruncated());
+  CHECK(!slice->IsFlatAndTruncated());
+  CHECK(slice->IsFlat());
+  TruncateString(slice);
+  CHECK(slice->IsTruncated());
+  CHECK(slice->IsFlatAndTruncated());
+  CHECK_NE(slice->GetIndirect(), parent->GetIndirect());
+}
+
+
+TEST(TrivialSlice) {
+  // This tests whether a slice that contains the entire parent string
+  // actually creates a new string (it should not).
+  FLAG_string_slices = true;
+  InitializeVM();
+  HandleScope scope;
+  v8::Local<v8::Value> result;
+  Handle<String> string;
+  const char* init = "var str = 'abcdefghijklmnopqrstuvwxyz';";
+  const char* check = "str.slice(0,26)";
+  const char* crosscheck = "str.slice(1,25)";
+
+  v8::Script::Compile(v8::String::New(init))->Run();
+
+  result = v8::Script::Compile(v8::String::New(check))->Run();
+  CHECK(result->IsString());
+  string = v8::Utils::OpenHandle(v8::String::Cast(*result));
+  CHECK(!string->IsSlicedString());
+
+  string = FACTORY->NewSubString(string, 0, 26);
+  CHECK(!string->IsSlicedString());
+
+  result = v8::Script::Compile(v8::String::New(crosscheck))->Run();
+  CHECK(result->IsString());
+  string = v8::Utils::OpenHandle(v8::String::Cast(*result));
+  CHECK(string->IsSlicedString());
+  CHECK_EQ("bcdefghijklmnopqrstuvwxy", *(string->ToCString()));
+}