[Soot-list] question about Soot optimization

[Mu Zhang]

Hi,

I have a question about Soot optimization. I'm writing a program to
instrument Java bytecode and using Soot to remove redundant code. However,
I found Soot was not able to optimize the instrumented code in some cases.
Here is an example and the redundant instructions are in black:

public int cryptWrapper(int, tester.BoolWrapper, tester.BoolWrapper,
tester.BoolWrapper)
    {
        tester.B r0;
        int i0, i1, $i2;
        tester.BoolWrapper r1, r2, r3;
        boolean z0, z1, z3, z4;

        r0 := @this: tester.B;
        i0 := @parameter0: int;
        r1 := @parameter1: tester.BoolWrapper;
        r2 := @parameter2: tester.BoolWrapper;
        r3 := @parameter3: tester.BoolWrapper;
        *z0 = r2.<tester.BoolWrapper: boolean b>;*
        z1 = r1.<tester.BoolWrapper: boolean b>;
        z3 = r3.<tester.BoolWrapper: boolean b>;
        $i2 = r0.<tester.B: int key>;
        i1 = i0 ^ $i2;
        z4 = z1 | 0;
       * r2.<tester.BoolWrapper: boolean b> = z0;*
        r1.<tester.BoolWrapper: boolean b> = z1;
        r3.<tester.BoolWrapper: boolean b> = z4;
        return i1;
    }

Basically, z0 is assigned with r2.b and later is assigned to r2.b without
any modification in between. I was wondering if it is because Soot
considers r2.b to be an object field with side-effects and thus doesn't
optimize it. If that is true, I'm curious to know how Soot determine
whether a local has side-effects or not. Does it simply consider all
objects have side-effects? Also, is there a way to trick Soot and bypass
the check, so that it can optimize some certain instructions that may have
side-effects?

Thanks,

Mu
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