Boolean expressions optimizations in Java

Question

Consider the following method in Java:

public static boolean expensiveComputation() {
    for (int i = 0; i < Integer.MAX_VALUE; ++i);
    return false;
}         


        

Answer 1

Actually, some compilers can optimise programs like the one you suggested, it just has to make sure that the function has no side-effects. GCC has a compiler directive you can annotate a function with to show that it has no side-effects, which the compiler may then use when optimizing. Java may have something similar.

A classic example is

for(ii = 0; strlen(s) > ii; ii++) < do something >

which gets optimized to

n = strlen(s); for(ii = 0; n > ii; ii++) < do something >

by GCC with optimization level 2, at least on my machine.