Don't store last use

[gjh33]

In the last use of something on the stack, instead of storing and loading we can just let it be removed from the stack for good. It is no longer needed.

EXAMPLE from bench01/backtracksolver.j

.method public getVal(II)I
  .limit locals 8
  .limit stack 2
  aload_0
  getfield SudokuSolver/grid Ljava/util/Vector;
  iload_1
  invokevirtual java/util/Vector/elementAt(I)Ljava/lang/Object;
  astore_3
  aload_3
  checkcast java/util/Vector
  astore 5
  aload 5
  iload_2
  invokevirtual java/util/Vector/elementAt(I)Ljava/lang/Object;
  astore 4
  aload 4
  checkcast java/lang/Integer
  astore 6
  aload 6
  invokevirtual java/lang/Integer/intValue()I
  ireturn
  nop
.end method

We can remove all of these astore/aload combos eliminating 8 lines!!!

Optimized:

.method public getVal(II)I
  .limit locals 8
  .limit stack 2
  aload_0
  getfield SudokuSolver/grid Ljava/util/Vector;
  iload_1
  invokevirtual java/util/Vector/elementAt(I)Ljava/lang/Object;
  checkcast java/util/Vector
  iload_2
  invokevirtual java/util/Vector/elementAt(I)Ljava/lang/Object;
  checkcast java/lang/Integer
  invokevirtual java/lang/Integer/intValue()I
  ireturn
  nop
.end method

[gjh33]

Conditions

• store followed by a load
• that load is the last load of that local before the next store of that local

[gjh33]

New condition:

• No jump operations before the next store (there could be a jump to a label above that relies on the local variable). Checking recursively for jump is very difficult and requires a stack, so this rule is simplified to NO jump operations