Thread

C++26: Trivial infinite loops are no longer undefined behaviour

173 points · 290 comments · ibobev

BobbyTables2 · 1789744507 · focus · HN ↗
TLDR: For almost 1/6 of a century, the C++ standards broke the simplest infinite loop and only just recently fixed it.
Idiots!
Don’t they really that people write real programs to solve real problems? This isn’t a theoretical academic exercise!
1. bryanlarsen · 1789744808 · focus · HN ↗
  They also realized that people choose compilers based on performance benchmarks, and that insane optimizations let them win.
  1. vlovich123 · 1789745131 · focus · HN ↗
    Until Rust proved actually you can get really good or better performance if the language itself is better. I really don’t know how C++ digs itself out of the UB hole it has dug.
    bryanlarsen · 1789745708 · focus · HN ↗
    Probably by working together with Rust. Eliminating undefined behavior from unsafe Rust is a big deal for the Rust community at the moment. And given that most unsafe rust code exists to call into C or C++, concepts like pointer provenance need to be extended. And proper pointer provenance guarantees can both decrease UB and increase optimization potential.
    IIUC, my understanding is shallow.
    nicoburns · 1789745848 · focus · HN ↗
    This particular case is likely an example of that. Rust used to have this problem, but it wasn't ever intended to. So IIRC it got fixed in LLVM for Rust, and this is probably now C++ taking advantage of that.

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