Introduce builtin for Array.unshift function.

Review URL: http://codereview.chromium.org/600124

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3859 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/bootstrapper.cc

@@ -1494,6 +1494,8 @@ void Genesis::BuildSpecialFunctionTable() {
                      Handle<Code>(Builtins::builtin(Builtins::ArrayPush)));
   AddSpecialFunction(special_prototype, "shift",
                      Handle<Code>(Builtins::builtin(Builtins::ArrayShift)));
+  AddSpecialFunction(special_prototype, "unshift",
+                     Handle<Code>(Builtins::builtin(Builtins::ArrayUnshift)));
 }
 
 

src/builtins.cc

@@ -246,19 +246,16 @@ BUILTIN(ArrayPush) {
   JSArray* array = JSArray::cast(*args.receiver());
   ASSERT(array->HasFastElements());
 
-  // Make sure we have space for the elements.
   int len = Smi::cast(array->length())->value();
+  int to_add = args.length() - 1;
+  if (to_add == 0) {
+    return Smi::FromInt(len);
+  }
 
-  // Set new length.
-  int new_length = len + args.length() - 1;
+  int new_length = len + to_add;
   FixedArray* elms = FixedArray::cast(array->elements());
 
-  if (new_length <= elms->length()) {
-    // Backing storage has extra space for the provided values.
-    for (int index = 0; index < args.length() - 1; index++) {
-      elms->set(index + len, args[index+1]);
-    }
-  } else {
+  if (new_length > elms->length()) {
     // New backing storage is needed.
     int capacity = new_length + (new_length >> 1) + 16;
     Object* obj = Heap::AllocateFixedArrayWithHoles(capacity);
@@ -269,16 +266,21 @@ BUILTIN(ArrayPush) {
     WriteBarrierMode mode = new_elms->GetWriteBarrierMode(no_gc);
     // Fill out the new array with old elements.
     for (int i = 0; i < len; i++) new_elms->set(i, elms->get(i), mode);
-    // Add the provided values.
-    for (int index = 0; index < args.length() - 1; index++) {
-      new_elms->set(index + len, args[index+1], mode);
-    }
-    // Set the new backing storage.
-    array->set_elements(new_elms);
+    elms = new_elms;
+    array->set_elements(elms);
+  }
+
+  AssertNoAllocation no_gc;
+  WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
+
+  // Add the provided values.
+  for (int index = 0; index < to_add; index++) {
+    elms->set(index + len, args[index + 1], mode);
   }
+
   // Set the length.
   array->set_length(Smi::FromInt(new_length));
-  return array->length();
+  return Smi::FromInt(new_length);
 }
 
 
@@ -313,6 +315,17 @@ BUILTIN(ArrayPop) {
 }
 
 
+static Object* GetElementToMove(uint32_t index,
+                                FixedArray* elms,
+                                JSObject* prototype) {
+  Object* e = elms->get(index);
+  if (e->IsTheHole() && prototype->HasElement(index)) {
+    e = prototype->GetElement(index);
+  }
+  return e;
+}
+
+
 BUILTIN(ArrayShift) {
   JSArray* array = JSArray::cast(*args.receiver());
   ASSERT(array->HasFastElements());
@@ -325,21 +338,17 @@ BUILTIN(ArrayShift) {
       Top::context()->global_context()->array_function();
   JSObject* prototype = JSObject::cast(array_function->prototype());
 
-  // Get first element
   FixedArray* elms = FixedArray::cast(array->elements());
-  Object* first = elms->get(0);
 
+  // Get first element
+  Object* first = elms->get(0);
   if (first->IsTheHole()) {
     first = prototype->GetElement(0);
   }
 
   // Shift the elements.
   for (int i = 0; i < len - 1; i++) {
-    Object* e = elms->get(i + 1);
-    if (e->IsTheHole() && prototype->HasElement(i + 1)) {
-      e = prototype->GetElement(i + 1);
-    }
-    elms->set(i, e);
+    elms->set(i, GetElementToMove(i + 1, elms, prototype));
   }
   elms->set(len - 1, Heap::the_hole_value());
 
@@ -350,6 +359,66 @@ BUILTIN(ArrayShift) {
 }
 
 
+BUILTIN(ArrayUnshift) {
+  JSArray* array = JSArray::cast(*args.receiver());
+  ASSERT(array->HasFastElements());
+
+  int len = Smi::cast(array->length())->value();
+  int to_add = args.length() - 1;
+  // Note that we cannot quit early if to_add == 0 as
+  // values should be lifted from prototype into
+  // the array.
+
+  int new_length = len + to_add;
+  FixedArray* elms = FixedArray::cast(array->elements());
+
+  // Fetch the prototype.
+  JSFunction* array_function =
+      Top::context()->global_context()->array_function();
+  JSObject* prototype = JSObject::cast(array_function->prototype());
+
+  if (new_length > elms->length()) {
+    // New backing storage is needed.
+    int capacity = new_length + (new_length >> 1) + 16;
+    Object* obj = Heap::AllocateFixedArrayWithHoles(capacity);
+    if (obj->IsFailure()) return obj;
+
+    AssertNoAllocation no_gc;
+    FixedArray* new_elms = FixedArray::cast(obj);
+    WriteBarrierMode mode = new_elms->GetWriteBarrierMode(no_gc);
+    // Fill out the new array with old elements.
+    for (int i = 0; i < len; i++)
+      new_elms->set(to_add + i,
+                    GetElementToMove(i, elms, prototype),
+                    mode);
+
+    elms = new_elms;
+    array->set_elements(elms);
+  } else {
+    AssertNoAllocation no_gc;
+    WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
+
+    // Move elements to the right
+    for (int i = 0; i < len; i++) {
+      elms->set(new_length - i - 1,
+                GetElementToMove(len - i - 1, elms, prototype),
+                mode);
+    }
+  }
+
+  // Add the provided values.
+  AssertNoAllocation no_gc;
+  WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
+  for (int i = 0; i < to_add; i++) {
+    elms->set(i, args[i + 1], mode);
+  }
+
+  // Set the length.
+  array->set_length(Smi::FromInt(new_length));
+  return Smi::FromInt(new_length);
+}
+
+
 // -----------------------------------------------------------------------------
 //
 

src/builtins.h

@@ -49,6 +49,7 @@ enum BuiltinExtraArguments {
   V(ArrayPush, NO_EXTRA_ARGUMENTS)                                  \
   V(ArrayPop, NO_EXTRA_ARGUMENTS)                                   \
   V(ArrayShift, NO_EXTRA_ARGUMENTS)                                 \
+  V(ArrayUnshift, NO_EXTRA_ARGUMENTS)                               \
                                                                     \
   V(HandleApiCall, NEEDS_CALLED_FUNCTION)                           \
   V(FastHandleApiCall, NO_EXTRA_ARGUMENTS)                          \

test/mjsunit/array-unshift.js

+// Copyright 2010 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Check that unshifting array of holes keeps the original array
+// as array of holes
+(function() {
+  var array = new Array(10);
+  assertEquals(13, array.unshift('1st', '2ns', '3rd'));
+  assertTrue(0 in array);
+  assertTrue(1 in array);
+  assertTrue(2 in array);
+  assertFalse(3 in array);
+})();
+
+
+// Check that unshif with no args has a side-effect of
+// feeling the holes with elements from the prototype
+// (if present, of course)
+(function() {
+  var len = 3;
+  var array = new Array(len);
+
+  var at0 = '@0';
+  var at2 = '@2';
+
+  Array.prototype[0] = at0;
+  Array.prototype[2] = at2;
+
+  // array owns nothing...
+  assertFalse(array.hasOwnProperty(0));
+  assertFalse(array.hasOwnProperty(1));
+  assertFalse(array.hasOwnProperty(2));
+
+  // ... but sees values from Array.prototype
+  assertEquals(array[0], at0);
+  assertEquals(array[1], undefined);
+  assertEquals(array[2], at2);
+
+  assertEquals(len, array.unshift());
+
+  assertTrue(delete Array.prototype[0]);
+  assertTrue(delete Array.prototype[2]);
+
+  // unshift makes array own 0 and 2...
+  assertTrue(array.hasOwnProperty(0));
+  assertFalse(array.hasOwnProperty(1));
+  assertTrue(array.hasOwnProperty(2));
+
+  // ... so they are not affected be delete.
+  assertEquals(array[0], at0);
+  assertEquals(array[1], undefined);
+  assertEquals(array[2], at2);
+})();
+
+
+// Now check the case with array of holes and some elements on prototype.
+(function() {
+  var len = 9;
+  var array = new Array(len);
+  Array.prototype[3] = "@3";
+  Array.prototype[7] = "@7";
+
+  assertEquals(len, array.length);
+  for (var i = 0; i < array.length; i++) {
+    assertEquals(array[i], Array.prototype[i]);
+  }
+
+  assertEquals(len + 1, array.unshift('head'));
+
+  assertEquals(len + 1, array.length);
+  // Note that unshift copies values from prototype into the array.
+  assertEquals(array[4], Array.prototype[3]);
+  assertTrue(array.hasOwnProperty(4));
+
+  assertEquals(array[8], Array.prototype[7]);
+  assertTrue(array.hasOwnProperty(8));
+
+  // ... but keeps the rest as holes:
+  Array.prototype[5] = "@5";
+  assertEquals(array[5], Array.prototype[5]);
+  assertFalse(array.hasOwnProperty(5));
+
+  assertEquals(array[3], Array.prototype[3]);
+  assertFalse(array.hasOwnProperty(3));
+
+  assertEquals(array[7], Array.prototype[7]);
+  assertFalse(array.hasOwnProperty(7));
+
+  assertTrue(delete Array.prototype[3]);
+  assertTrue(delete Array.prototype[5]);
+  assertTrue(delete Array.prototype[7]);
+})();