Fix invalid array length check in TransitionElementsKindStub.

The stub used to check the length of the JS array to see if
there's a need to duplicate the elements backing store. This
way it will not duplicate the elements array when going from
double to object even if the elements array is not the empty
fixed array. Later on it will then store pointers into a
FixedDoubleArray.

The native code stub used to check whether elements points to
the empty_fixed_array singleton instead of testing the length.
The Hydrogen stub does that as well now.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/19289009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15701 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/code-stubs-hydrogen.cc

@@ -541,21 +541,23 @@ HValue* CodeStubGraphBuilder<TransitionElementsKindStub>::BuildCodeStub() {
     Add<HTrapAllocationMemento>(js_array);
   }
 
-  HInstruction* array_length =
-      AddLoad(js_array, HObjectAccess::ForArrayLength());
-  array_length->set_type(HType::Smi());
+  HInstruction* elements = AddLoadElements(js_array);
+
+  HInstruction* empty_fixed_array = Add<HConstant>(
+      isolate()->factory()->empty_fixed_array(), Representation::Tagged());
 
   IfBuilder if_builder(this);
 
-  if_builder.IfNot<HCompareNumericAndBranch>(array_length,
-                                             graph()->GetConstant0(),
-                                             Token::EQ);
-  if_builder.Then();
+  if_builder.IfNot<HCompareObjectEqAndBranch>(elements, empty_fixed_array);
 
-  HInstruction* elements = AddLoadElements(js_array);
+  if_builder.Then();
 
   HInstruction* elements_length = AddLoadFixedArrayLength(elements);
 
+  HInstruction* array_length = AddLoad(
+      js_array, HObjectAccess::ForArrayLength(), NULL, Representation::Smi());
+  array_length->set_type(HType::Smi());
+
   BuildGrowElementsCapacity(js_array, elements, from_kind, to_kind,
                             array_length, elements_length);
 

test/mjsunit/transition-elements-kind.js

+// Copyright 2013 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.
+
+// Flags: --allow-natives-syntax --compiled-transitions
+// Flags: --track-allocation-sites
+
+// Allocation site for empty double arrays.
+function foo() {
+  return new Array();
+}
+var a = foo();
+a[0] = 1.1;
+
+// Emit a TransitionElementsKindStub which transitions from double to object.
+function store(a,x) {
+  a[0] = x;
+}
+store([1.1], 'a');
+store([1.1], 1.1);
+%OptimizeFunctionOnNextCall(store);
+
+// Use the TransitionElementsKindStub to transition from double to object.
+var b = foo();
+store(b, 'a');