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

runtime/vm/intermediate_language_x64.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/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 2588 matching lines @@
           break;
         } else if (value == -1) {
           // Check the corner case of dividing the 'MIN_SMI' with -1, in which
           // case we cannot negate the result.
           __ cmpq(left, Immediate(0x8000000000000000));
           __ j(EQUAL, deopt);
           __ negq(left);
           break;
         }
 
-        ASSERT((value != 0) && Utils::IsPowerOfTwo(Utils::Abs(value)));
+        ASSERT(Utils::IsPowerOfTwo(Utils::Abs(value)));
         const intptr_t shift_count =
             Utils::ShiftForPowerOfTwo(Utils::Abs(value)) + kSmiTagSize;
         ASSERT(kSmiTagSize == 1);
         Register temp = locs()->temp(0).reg();
         __ movq(temp, left);
         __ sarq(temp, Immediate(63));
         ASSERT(shift_count > 1);  // 1, -1 case handled above.
         __ shrq(temp, Immediate(64 - shift_count));
         __ addq(left, temp);
         ASSERT(shift_count > 0);
@@ skipping 2261 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64