I've seen it like 2 years ago and it is well prepared course.
>CS 6120 is a PhD-level Cornell CS course by Adrian Sampson on programming language implementation.
I just dont understand why is this "PhD level"
It's really up to the professor.
It would have been if the papers covered were closer to the state of the art. The most recent one is from 2015.
However, this course would actually give you the background required to read more recent paper and work on compiler research, so calling it PhD level is not a huge stretch.
You are right when it comes to programming language design and somewhat wrong when it comes to compiler design.
If you are doing compiler research/development, you have to be familiar with the latest and greatest research because the margins for improving things are fairly slim. It’s usually fine to be not familiar with how things worked ~30 years ago.
For programming languages, you absolutely have to understand the foundations to do absolutely anything.
Someone doing compiler research this might be a first graduate level course to get them used to the technique and concepts used in more recent research for the might have two or three additional courses getting closer and closer to state of the art.
On the other hand, if the margins for improving compiler quality are slim they can be ignored without great consequences: it makes sense to study state of the art research only in the niches that turn out to be relevant for a specific need of a specific project, not blindly and at the expense of important general principles and techniques (i.e. mostly the problems of 75 years ago and the solutions of 25 years ago).
In that vein, it makes a lot more sense to focus on a solid, foundational paper than whatever incrementalism came out most recently. SLP vectorization is a good example here--yeah, the foundational paper is 20 years old at this point, but you'd rather students read and understand that than whatever the most recent addition to SLP vectorization came out in this (or last) year's PLDI. Even the other papers I think I might add or substitute for others in this course aren't going to be substantially newer than the stuff already here.
For example, they read and discuss papers rather than just working out of a textbook.
As more of a math course than a computer engineering course, 6120 was a first-semester Ph.D. level class, and I certainly wouldn't recommend taking it unless you really wanted to dive deep into the depths of programming language implementation. Incoming students were expected to be fluent in discrete mathematics and formal proofwriting skills. I wasn't, so I found myself falling behind at the start even though I had some familiarity with lambda calculus and algebraic datatypes. You definitely benefit from a strong math background.