Fix a compiler bug caused by Utils::IsPowerOfTwo treating zero as a power of two.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 1212 matching lines @@
     return InlineFloat32x4BinaryOp(call, op_kind);
   } else if (operands_type == kUint32x4Cid) {
     return InlineUint32x4BinaryOp(call, op_kind);
   } else if (op_kind == Token::kMOD) {
     // TODO(vegorov): implement fast path code for modulo.
     ASSERT(operands_type == kSmiCid);
     if (!right->IsConstant()) return false;
     const Object& obj = right->AsConstant()->value();
     if (!obj.IsSmi()) return false;
     const intptr_t value = Smi::Cast(obj).Value();
-    if ((value <= 0) || !Utils::IsPowerOfTwo(value)) return false;
+    if (!Utils::IsPowerOfTwo(value)) return false;
 
     // Insert smi check and attach a copy of the original environment
     // because the smi operation can still deoptimize.
     InsertBefore(call,
                  new CheckSmiInstr(new Value(left), call->deopt_id()),
                  call->env(),
                  Definition::kEffect);
     ConstantInstr* constant =
         flow_graph()->GetConstant(Smi::Handle(Smi::New(value - 1)));
     BinarySmiOpInstr* bin_op =
@@ skipping 6231 matching lines @@
   }
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits.length(); i++) {
     CreateMaterializationAt(exits[i], alloc, alloc->cls(), *fields);
   }
 }
 
 
 }  // namespace dart