Bob Morgan's book Building an Optimizing Compiler is entirely focused on modern compiler optimizations (and it was published in 1997). It goes over building a control flow graph, various optimizations you can do with that, alias analysis, static single assignment form, CFG dominator-based optimizations, instruction scheduling, register allocation, and emitting object code. It doesn't talk about lexing, parsing, NFAs/DFAs, etc. like most compiler books.

Static Program Analysis[1] also seems helpful to someone trying to write a compiler that does optimizations that require advanced analyses: https://cs.au.dk/~amoeller/spa/

For garbage collection, there's the Garbage Collection handbook[2]. I'm not aware of better additional resources, though.

[1]: https://cs.au.dk/~amoeller/spa/

[2]: https://gchandbook.org/