Z:gnu-www-ja-stallman-kth--bf2beb-But after checking all those t/en

But after checking all those things, then you take the substituted combined expression and put it through a pattern matcher, which recognizes all the valid instructions of your chosen target machine. And if it's recognized, then you replace those two instructions with the combined one, otherwise you leave them alone. And their technique is to combine two or three instructions related by data flow in this way.