replace store double load with dup

[gjh33]

Consider the following situation

.method public doubleRandom()I
  .limit locals 2
  .limit stack 2
  invokevirtual java/util/Random/randomInt() I;
  astore_1
  aload_1
  aload_1
  iadd
  ireturn
.end method

We can replace the double astore, aload, aload with dup.

.method public doubleRandom()I
  .limit locals 2
  .limit stack 2
  invokevirtual java/util/Random/randomInt() I;
  dup
  iadd
  ireturn
.end method

Conditions:

• astore followed by two a loads
• this is the last access of this value (no more aload_1 without a store_1)

Possible Extension:

• Do the aloads need to be in a row? Can we make a more general rule?
• Do we need to limit it to a single dup? what if it's 3 aloads in a row? We can do 2 dups?