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Note that "feedback optimization" using data from actual real-world perf data has been a standard part of compilers for decades. SPECcpu limits what you're allowed to do with it to avoid over-fitting.

This sounds a lot like JIT compilation techniques, but applied to an already-compiled binary.

I would think it's closer to branch prediction but on a larger scale than just instruction pipelines.

I'm curious if it modifies the original binary.

GCC supports the hot and cold attributes so you can manually instruct the compiler how to arrange compilation sections. They basically set the PGO counts to +/- infinity for those functions.

While nowhere near as nice as real profile guided optimization (and likely to grow stale over time), these attributes are much easier to insert compared to fighting with whatever build toolchain you’re using.

cold functions are also optimised at -Os.