1. A non-transitory computer readable storage media having instructions stored thereon that, when executed by a computer, implement a method for optimizing if statements in a program, the method comprising: obtaining, for a conditional expression used in a conditional statement in the program, a set of conditional expressions having an inclusion relation; computing a first provisional cost corresponding to the conditional expression being positive, and a second provisional cost corresponding to the conditional expression being negative; and moving the conditional expression to a move destination, wherein moving the conditional expression comprises: in response to a result of the conditional expression not being cached in a variable, generating an if statement for the conditional expression and caching the result of the conditional expression in a new variable, wherein the if statement is generated in increasing order of the first provisional cost and the second provisional cost; and in response to the result of the conditional expression being cached in a variable, replacing a conditional operator of the conditional expression with a logical operator, prior to caching the result in the new variable.