Expand description
A fast, non-cryptographic hasher for compiler-internal maps keyed by block/variable indices (the rustc “FxHash” scheme).
The decompiler builds and probes millions of tiny HashSet<usize> /
HashMap<usize, _> universes per run (dominators, RPO, region walks).
SipHash-1-3 (std default) costs ~15-20ns per probe; the rotate-xor-
multiply mix below costs ~1ns and is what rustc itself uses for
exactly this key shape. NOT for adversarial-input-facing tables.