I think Merida (a big Taiwanese bike company, similar to Giant) actually owns a big chunk of Specialized. All Specialized bikes are made at the Merida factories in Taiwan, except the cheapest ones may be outsourced to mainland China.
Last time I checked, Giant did make most (maybe all) aluminum bikes for Trek. Giant has factories in both Taiwan and mainland China. I think some of the cheapest Treks are made in mainland China. My Trek dealer claimed that Trek bike quality is higher than Giant, because Trek has their own quality control people on-site at the Giant factory. Who knows?