It depends on the likelihood of shortage. Some industries are better at this than others: automotive do multiple vendors for everything (most easily evident are tires: the same model could be supplied with tires from two or three different vendors).
About a decade ago I visited a European fab of one of the European semiconductor manufacturers, where they told me they are also manufacturing for an American semiconductor firm (which had its own network of fabs). The reason was insistence from auto companies to diversify the supply chain, getting the same processor from multiple fabs in different continents.
About a decade ago I visited a European fab of one of the European semiconductor manufacturers, where they told me they are also manufacturing for an American semiconductor firm (which had its own network of fabs). The reason was insistence from auto companies to diversify the supply chain, getting the same processor from multiple fabs in different continents.