this is exactly what I was thinking regarding the $$$ thing. If you get a PhD in compiler design then end up working as a regular software engineer then sure your PhD was a "waste". But if you get a PhD in ML then find a ML related job at Google/FB, you're going to get paid so much more, even including the years of salary you lost doing the phd. There are so many job postings out there from big companies which require a phd and you will have so much less competition. I mean there are people who don't even have a CS degree who end up working as SDEs (eg SYDE, Man Eng at this school). It makes me uncomfortable how little job security software developers have in general, especially with how common it is to start coding as a kid now.