It's not clear from the article, but PGO isn't a new technique. In 1989, my Decstation 3100 running a Berkley kernel based Unix on a MIPS processor had a compiler option that used a profile to guide its C compiler optimizer. I don't recall how well it worked. At that level of optimization I tended to use it very little since I was spending most of my time trying to architect, develop and debug a new distributed system.