Back when I was in college I took a computer engineering class around 2010 I think with a professor who had done CPU design at one of the big chip manufacturers. He had a story about how no human knows how they work anymore because they'll do the designs, then feed them through some optimization algorithm thing before the fabrication. Then when they would evaluate the chip they'd find that it was behaving in completely unexpected ways due to the optimization finding crazy efficient but unintuitive (to a human) ways of performing different operations.

I wish I could remember the details of what he talked about better, but that was a long time ago.