Incremental mode now works for x64. The only difference

src/flag-definitions.h

 // Copyright 2011 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
@@ skipping 248 matching lines @@
             "print one detailed trace line in name=value format "
             "after each garbage collection")
 DEFINE_bool(print_cumulative_gc_stat, false,
             "print cumulative GC statistics in name=value format on exit")
 DEFINE_bool(trace_gc_verbose, false,
             "print more details following each garbage collection")
 DEFINE_bool(collect_maps, true,
             "garbage collect maps from which no objects can be reached")
 DEFINE_bool(flush_code, false,
             "flush code that we expect not to use again before full gc")
-#ifdef V8_TARGET_ARCH_IA32
+#ifdef V8_TARGET_ARCH_ARM
+DEFINE_bool(incremental_marking, false, "use incremental marking")
+#else
 DEFINE_bool(incremental_marking, true, "use incremental marking")
-#else
-DEFINE_bool(incremental_marking, false, "use incremental marking")
 #endif
 DEFINE_bool(incremental_marking_steps, true, "do incremental marking steps")
 DEFINE_bool(trace_incremental_marking, false,
             "trace progress of the incremental marking")
 
 // v8.cc
 DEFINE_bool(use_idle_notification, true,
             "Use idle notification to reduce memory footprint.")
 // ic.cc
 DEFINE_bool(use_ic, true, "use inline caching")
@@ skipping 285 matching lines @@
 #undef FLAG
 
 #undef DEFINE_bool
 #undef DEFINE_int
 #undef DEFINE_string
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META