Incremental mode now works for x64. The only difference

src/arm/full-codegen-arm.cc

 // 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 3257 matching lines @@
 
   Label no_remembered_set;
   __ CheckPageFlag(elements,
                    scratch1,
                    MemoryChunk::SCAN_ON_SCAVENGE,
                    ne,
                    &no_remembered_set);
   // Possible optimization: do a check that both values are Smis
   // (or them and test against Smi mask.)
 
+  // Since we are swapping two objects, the incremental marker is not disturbed,
+  // so we don't call the stub that handles this.

[Lasse Reichstein, 2011/06/10 13:55:44]

More explanation (e.g. that the incremental marker is never in the middle of a
FixedArray).

[Erik Corry, 2011/06/10 21:57:29]

Done.

   __ RememberedSetHelper(
       index1, scratch2, kDontSaveFPRegs, MacroAssembler::kFallThroughAtEnd);
   __ RememberedSetHelper(
       index2, scratch2, kDontSaveFPRegs, MacroAssembler::kFallThroughAtEnd);
 
   __ bind(&no_remembered_set);
   // We are done. Drop elements from the stack, and return undefined.
   __ Drop(3);
   __ LoadRoot(r0, Heap::kUndefinedValueRootIndex);
   __ jmp(&done);
@@ skipping 1098 matching lines @@
   __ mov(r1, Operand(r1, ASR, 1));  // Un-smi-tag value.
   __ add(pc, r1, Operand(masm_->CodeObject()));
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM