Replacing a Rust Enum with a 64-bit Word Made My Interpreter 17% Faster

7 relevance

Deep dive into a specific Rust optimization technique (replacing enum with bit-packed word) that improves interpreter performance, directly relevant to systems programming and performance engineering.

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Why It Matters

For a platform or language runtime engineer, this demonstrates a concrete, measurable performance win from a classic low-level optimization technique that directly impacts interpreter throughput and memory efficiency, relevant to anyone building or maintaining dynamic language VMs.

Key Takeaways

Evaluate replacing wide tagged enums with a 64-bit NaN-boxing or low-bit tagging scheme in your interpreter or runtime to reduce memory bandwidth and improve cache performance.

Replacing a Rust Enum with a 64-bit Word Made My Interpreter 17% Faster

Summary

A Plush language interpreter developer replaced a 16-byte Rust enum with a 64-bit word using low-bit tagging, achieving a 17% speedup. The scheme exploits 8-byte heap alignment to store tag bits in the lowest 3 bits of pointers and integers, reducing memory waste in value arrays. Despite added bitwise operations for type dispatch and float unpacking, the performance gain came from better cache utilization and fewer memory accesses.