Boolean field assignment [on hold]

Given the following case:

state = true;

// ..

We could use an alternative pattern like:

if (!state)
{
    state = true;
}

// ..

In either case, field state must be assigned to true. Is there a proper argument to evaluate a boolean before setting it? It would effectively replace one virtual instruction by two.

Assuming that reading is cheaper than writing, I think the latter example could prove as an optimization.

Note that these code fragments recur (heavily), so the value of state cannot be predetermined as false.