AtomicInteger implementation and code duplication

Question

Warning: the question is a little long, but the part below the separation line is for curiosity only.

Oracle\'s JDK 7 implementation of AtomicInteger includes t

Answer 1

I'll give new supposition. If we look into byte code of AtomicInteger we will see, that the main difference between them is that addAndGet uses iload_ instruction, and incrementAndGet uses iconst_ instruction:

public final int addAndGet(int);
   ...
   4:   istore_2
   5:   iload_2
   6:   iload_1
   7:   iadd

public final int incrementAndGet();
   ...
   4:   istore_1
   5:   iload_1
   6:   iconst_1
   7:   iadd

It seems, that iconst_+iadd translates as INC instruction, due to iload_...iadd as ADD instruction. This all relates to commonly known question about ADD 1 vs INC and so on:

Relative performance of x86 inc vs. add instruction

Is ADD 1 really faster than INC ? x86

This could be the answer, why addAndGet is slightly faster than incrementAndGet