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

test/cctest/test-strings.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 
 // Check that we can traverse very deep stacks of ConsStrings using
 // StringInputBuffer.  Check that Get(int) works on very deep stacks
 // of ConsStrings.  These operations may not be very fast, but they
 // should be possible without getting errors due to too deep recursion.
 
 #include <stdlib.h>
 
 #include "v8.h"
@@ skipping 463 matching lines @@
     v8::Local<v8::Value> result =
         v8::Script::Compile(v8::String::New(line))->Run();
     CHECK_EQ(results[i]->IsUndefined(), result->IsUndefined());
     CHECK_EQ(results[i]->IsNumber(), result->IsNumber());
     if (result->IsNumber()) {
       CHECK_EQ(Smi::cast(results[i]->ToSmi()->ToObjectChecked())->value(),
                result->ToInt32()->Value());
     }
   }
 }
+
+
+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()));
+}