refactor: swap core::hint::cold_path for a stable #[cold] shim - #102
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`core::hint::cold_path()` is stable only since Rust 1.95, which made it the single reason the library could not build on any earlier toolchain. It is replaced by a private empty `#[cold] #[inline(never)]` function: LLVM proves the empty body side-effect free and deletes the call, so all that survives is the block-placement hint the attribute carries — exactly what the intrinsic provides. The three call sites sit in the hot loops of the difference iterators, where the hint keeps the rare rescue scan off the loop-carried dependency chain, so the swap was verified by disassembly rather than by inspection: the emitted code for `Ipv4NetworkDiff::next`/`next_back` and `Ipv6NetworkDiff::next`/ `next_back` is byte-identical before and after, under both baseline x86-64 and `-C target-cpu=native`. The only change to the object file is the (never called) stub itself. With this the library compiles on Rust 1.88.
This was referenced Jul 13, 2026
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core::hint::cold_path()is stable only since Rust 1.95, which made it the single reason the library could not build on any earlier toolchain. It is replaced by a private empty#[cold] #[inline(never)]function: LLVM proves the empty body side-effect free and deletes the call, so all that survives is the block-placement hint the attribute carries — exactly what the intrinsic provides.The three call sites sit in the hot loops of the difference iterators, where the hint keeps the rare rescue scan off the loop-carried dependency chain, so the swap was verified by disassembly rather than by inspection.
Verification
Emitted code for the four affected functions, before vs after:
-C target-cpu=nativeIpv4NetworkDiff::nextIpv4NetworkDiff::next_backIpv6NetworkDiff::nextIpv6NetworkDiff::next_backNo
callis emitted at any of the three sites, no register spills appear in the hot loops, and the rescue branch keeps its.text.unlikelyplacement. The only change to the object file is the never-called stub itself — byte-identical machine code makes benchmarking moot.With this the library compiles on Rust 1.88 (
cargo +1.88.0 check --lib); declaring the MSRV follows in a separate PR.