Fixing dead code in empty array init.

src/ia32/builtins-ia32.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 978 matching lines @@
     // Use a scratch register here to have only one reloc info when unfolding
     // the loop.
     __ mov(scratch3, factory->the_hole_value());
     for (int i = 0; i < initial_capacity; i++) {
       __ mov(FieldOperand(scratch1,
                           FixedArray::kHeaderSize + i * kPointerSize),
              scratch3);
     }
   } else {
     Label loop, entry;
+    __ add(scratch1, Immediate(FixedArray::kHeaderSize - kHeapObjectTag));

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

On ia32, there's usually no need to untag like this because we can build
untagging into the operand's offset.  (See FieldOperand.)

In this case, we can get slightly tighter loop by using a counted loop,
something like:

    mov scratch2, initial_capacity
    jmp entry
loop:
    mov FieldOperand(scratch1, scratch2, kPointerSize, 0), the_hole_value
entry:
    dec scratch2
    j not_sign, loop

     __ jmp(&entry);
     __ bind(&loop);
     __ mov(Operand(scratch1, 0), factory->the_hole_value());
     __ add(scratch1, Immediate(kPointerSize));
     __ bind(&entry);
     __ cmp(scratch1, scratch2);
     __ j(below, &loop);
   }
 }
 
@@ skipping 663 matching lines @@
   Deoptimizer::EntryGenerator generator(masm, Deoptimizer::OSR);
   generator.Generate();
 }
 
 
 #undef __
 }
 }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32