Fix another x64 compilation error due to some dead code.

src/x64/codegen-x64.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 8258 matching lines @@
     // Get the value and receiver from the stack.
     Result value = frame()->Pop();
     value.ToRegister();
     Result receiver = frame()->Pop();
     receiver.ToRegister();
 
     // Allocate result register.
     result = allocator()->Allocate();
     ASSERT(result.is_valid() && receiver.is_valid() && value.is_valid());
 
-    // Cannot use r12 for receiver, because that changes
-    // the distance between a call and a fixup location,
-    // due to a special encoding of r12 as r/m in a ModR/M byte.
-    if (receiver.reg().is(r12)) {
-      frame()->Spill(receiver.reg());  // It will be overwritten with result.
-      // Swap receiver and value.
-      __ movq(result.reg(), receiver.reg());
-      Result temp = receiver;
-      receiver = result;
-      result = temp;
-    }
+    // r12 is now a reserved register, so it cannot be the receiver.
+    // If it was, the distance to the fixup location would not be constant.
+    ASSERT(!receiver.reg().is(r12));
 
     // Check that the receiver is a heap object.
     Condition is_smi = masm()->CheckSmi(receiver.reg());
     slow.Branch(is_smi, &value, &receiver);
 
     // This is the map check instruction that will be patched.
     // Initially use an invalid map to force a failure. The exact
     // instruction sequence is important because we use the
     // kOffsetToStoreInstruction constant for patching. We avoid using
     // the __ macro for the following two instructions because it
@@ skipping 537 matching lines @@
 }
 
 #endif
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64