I view it as two different things. There are many optimizations which work on a simple machine model that hasn't changed much since the VAX. There's memory wit

I view it as two different things. There are many optimizations which work on a simple machine model that hasn't changed much since the VAX. There's memory with constant time lookup, some registers, and assembly code. Real hardware changed long ago. As a simple example, on traditional hardware it's best to save and re-use intermediate values, but on modern hardware RAM lookup is so slow that it can be faster to recompute rather than doing a random lookup. An optimizing compiler isn't going to do much if the code wasn't designed to match the hardware, or expects a different hardware model. While lowering the impedance mismatch between two systems, whether it be two different languages as in your example, or serialization/deserialization, or call thunking, belongs to an old and well-understood set of optimizations which are nearly insensitive to the machine model. RAM lookup, and cache performance, and cache lines, are important for high performance code. Though as the abstract says, most people only work with "freezingly cold" code, so aren't aware of the limitations in the conceptual machine model vs. the actual machine. Fixing this almost always requires deep changes to the code, which an optimizing compiler can't do.