[Soot-list] LazyCodeMotion issue

[Arie Zilberstein]

Hi,

I want to utilize the LazyCodeMotion analysis to remove some redundancies
from code.
I crafted an example code which I thought was amenable to optimization:

private static void testPre(int a, int b) {
int sum = 0;
int c = a + b;
int d = a + b;
sum += c;
sum += d;
System.out.println(sum);
}

I expected LazyCodeMotion to assign the redundant computation (a+b) to a
temporary variable, and replace all following computations by this
temporary. However, while a temporary is indeed created, the replacement
does not happen.

Debugging through the code I found the following:
1. The code section titled "insert the computations" does its job correctly:
the expression a+b is indeed assigned to a new temporary $lcm0 variable.
2. The code section titled "replace old computations by the helper-vars"
does not replace c or d with an assignment to $lcm0.
3. The reason for that is the condition "if (!latestSet.contains(rhs) &&
notIsolatedSet.contains(rhs))". The left side is false because, latestSet
contains the a+b expression. Therefore no replacement is done.

My question is -- is there a bug in LazyCodeMotion or is it a
misunderstanding on my part?

Best,
Arie
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