/devirt-dyn-write-test

Primary LanguageRust

rust-devirt-bufio-repro

Minimal workspace to reproduce intra-crate vs cross-crate optimization differences for buffered I/O style loops with dyn Write vs generic Write.

It contains:

  • crates/intra_single_crate: single binary crate with two functions:
    • write_bytes_dyn(&mut dyn Write, &[u8]) (trait object, same crate)
    • write_bytes_generic<W: Write>(W, &[u8]) (monomorphized generic)
  • crates/inter_two_crates/writerlib: library crate exporting write_bytes_dyn_lib that takes &mut dyn Write.
  • crates/inter_two_crates/app: binary crate that calls into the library.

The goal: compare code generation and runtime between:

  1. Intra‑crate dyn vs generic in one crate.
  2. Cross‑crate dyn (lib + app) with LTO off vs ThinLTO vs codegen‑units=1.

Build and run

Use cargo-show-asm invoked as cargo asm to get the assembly readouts. Try toggling LTO=off, ThinLTO, codegen-units=1, etc.