问题
How to write a conditional statement in Z3.
eg:
if (a%2==0){
value=1
}
I am trying to achieve this in Z3 Solver by Microsoft Research but so far no luck
回答1:
Look up SSA form: https://en.wikipedia.org/wiki/Static_single_assignment_form
Essentially, you'll have to change your program to look something like:
value_0 = 0
value_1 = (a%2 == 0) ? 1 : value_0
Once it is in this so called static single assignment form, you can now translate each line more or less directly; with the latest assignment to value_N being the final value of value.
Loops will be problematic: The usual strategy is to unroll them up to a certain count (bounded model checking), and hope that this suffices. If you detect that the last unrolling isn't sufficient, then you can generate an uninterpreted value at that point; which might cause your proofs to fail with spurious counter-examples; but that's the best you can do without a scheme that involves proper handling of induction and loop-invariants.
Note that this field of study is called "symbolic execution" and has a long history, with active research still being conducted. You might want to read through this: https://en.wikipedia.org/wiki/Symbolic_execution
来源：https://stackoverflow.com/questions/44314486/z3-conditional-statement