alt Hacker NewsThe article title is misleading. It is not that Rust compiler was not able to optimize some low-level operations. Rather the author came up with encoding schema that fit most things the interpreter dealt with into 64 bit. This replaced the previous schema that used 128 bit for everything but that can be directly mapped into Rust enums. The catch was that it was necessary to allocate some things on the heap and use pointer indirection but that was used for rare values so on average the new schema provided nice win.
One cannot expect a compiler to come up with such encoding.
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win311fwg • today at 9:04 PM
What is misleading about the title? A custom encoding scheme is exactly what it suggests. Maybe it has been edited since your comment was posted?
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When I think of how a "compiler" could make these optimizations, I think the right place is an optimizing LLM (so, just a regular coding agent that you prompted to find optimizations like this one), making the changes in source at the request of the developer. That provides the dev with adequate input on whether they would like to opt-in to an unsafe optimization like this one. The compiler can continue to do deterministically-safe optimizations.