Statement

Given how much Luca loves IT security, you should not be surprised to know that he wants to understand the recent flaw discovered in CPUs: Spectre!. The full paper describing the vulnerability is quite intricated and so he wants to proceed a step at a time. Every respectable programmer knows that a CPU fundamentally executes instructions, one after another. But that is only one part of the story: modern CPUs aim at maximizing performace by executing multiple instructions at once, whenever possible. You are given a list of N instructions, each in the form target_variable = operand1_variable OP operand2_variable where OP is a mathematical operator among +, -, *, /. An instruction j can be executed immediately if it does not have to "wait" that one of its operand has to be computed (more precisely, a variable needs to be computed when it is the target of another instruction i with i<j)...