Interesting talk exploring bottom-up vs greedy inlining in LLVM: http://t.co/KwG0bhkZP5 (GCC uses greedy inlining to great effect)
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Exploring the design space and tradeoffs of programming language syntax, and syntactic sugar vs syntactic salt:
https://cs.lmu.edu/~ray/notes/syntaxdesign/
Some fun examples of things you can do with type inference in Rust, from a GCC-rust contributor.
An excellent review of the V language and the features it promotes: https://mawfig.github.io/2022/06/18/v-lang-in-2022.html
The code samples are a great example of how you do PL work: you learn about the intended semantics and try to write programs that are broken in interesting ways.