Rust's `fetch_max`: A Deep Dive into Compiler Optimization
During a recent engineering interview, a candidate used a single line of Rust code to solve a classic concurrency problem—tracking the maximum value across multiple producer threads. This sparked the author's curiosity: how does Rust's `fetch_max` actually work? The article delves into the compilation process from Rust code to assembly, revealing the layers of optimization involving macros, LLVM intermediate representation, compiler intrinsics, and target architecture specifics. On x86-64, `fetch_max` compiles down to a compare-and-swap (CAS) loop; on ARM, it directly utilizes the hardware's atomic max instruction. This article demonstrates the power of modern compilers and the low-level details behind high-level abstractions.
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