There are always the sample chapters, and the code from the book is in the public domain. :)
The book is basically a modern and more complete version of the "Small C Handbook" of the 1980's. I goes through all the stages of compilation, including simple optimizations, but keeps complexity to a minimum. So if you just want to learn about compiler writing and see what a complete C compiler look like under the hood, without investing too much into theory, then this is probably one of very few books that will deliver.
Edit: and then Warren Toomey has written "A Compiler Writing Journey" based on PCC, which may shed a bit more light on the book: https://github.com/DoctorWkt/acwj
The book is basically a modern and more complete version of the "Small C Handbook" of the 1980's. I goes through all the stages of compilation, including simple optimizations, but keeps complexity to a minimum. So if you just want to learn about compiler writing and see what a complete C compiler look like under the hood, without investing too much into theory, then this is probably one of very few books that will deliver.
Edit: and then Warren Toomey has written "A Compiler Writing Journey" based on PCC, which may shed a bit more light on the book: https://github.com/DoctorWkt/acwj