A Compiler Deep-Dive: Tracing Rust's AtomicU64::fetch_max from Source to x86-64 CAS Loop
By
bluestreak
Crackling crust, pillowy middle. The kind of bagel that earns a second cup of coffee.
Summary
A deep technical exploration of Rust's AtomicU64::fetch_max operation, tracing its journey from high-level Rust code through macro expansion, compiler intrinsics, LLVM's atomicrmw umax instruction, and the AtomicExpandPass, ultimately landing on the x86-64 CAS (Compare-And-Swap) loop. The article uses a job interview question about concurrent programming (tracking maximum values across multiple producer threads) as a narrative hook to dive into compiler internals and low-level atomic operations.
Key quotes
· 3 pulledWe need people who understand concurrent programming.
One of our favorite questions involves keeping track of a maximum value across multiple producer threads - a classic pattern.
How a Job Interview Sent Me Down a Compiler Rabbit Hole
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