Fixing dead code in empty array init.

src/x64/builtins-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 1057 matching lines @@
   if (initial_capacity <= kLoopUnfoldLimit) {
     // Use a scratch register here to have only one reloc info when unfolding
     // the loop.
     for (int i = 0; i < initial_capacity; i++) {
       __ movq(FieldOperand(scratch1,
                            FixedArray::kHeaderSize + i * kPointerSize),
               scratch3);
     }
   } else {
     Label loop, entry;
+    __ addq(scratch1, Immediate(FixedArray::kHeaderSize - kHeapObjectTag));

[Kevin Millikin (Chromium), 2011/10/27 10:35:54]

No need to untag here.  Could use a counted loop so that the update sets the
flags (no need for explicit cmp), see my comment on ia32.

     __ jmp(&entry);
     __ bind(&loop);
     __ movq(Operand(scratch1, 0), scratch3);
     __ addq(scratch1, Immediate(kPointerSize));
     __ bind(&entry);
     __ cmpq(scratch1, scratch2);
     __ j(below, &loop);
   }
 }
 
@@ skipping 481 matching lines @@
   Deoptimizer::EntryGenerator generator(masm, Deoptimizer::OSR);
   generator.Generate();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64