Comment by kannanvijayan

I've been hacking on some somewhat systemsy rust code, and I've used LLMs from a while back (early co-pilot about a year ago) on a bunch of C++ systems code.

In both of these cases, I found that just the smart auto-complete is a massive time-saver. In fact, it's more valuable to me than the interactive or agentic features.

Here's a snippet of some code that's in one of my recent buffers:

    // The instruction should be skipped if all of its named
    // outputs have been coalesced away.
    if ! self.should_keep_instr(instr) {
      return;
    }

    // Non-dropped should have a choice.
    let instr_choice =
      choices.maybe_instr_choice(instr_ref)
        .expect("No choice for instruction");
    self.pick_map.set_instr_choice(
      instr_ref,
      instr_choice.clone(),
    );

    // Incref all named def inputs to the PIR choice.
    instr_choice.visit_input_defs(|input_def| {
      self.def_incref(input_def);
    });

    // Decref all named def inputs to the SIR instr.
    instr.visit_inputs(
      |input_def| self.def_decref(input_def, sir_graph)
    );

The actual code _I_ wrote were the comments. The savings in not having to type out the syntax is pretty big. About 80% of the time in manual coding would have been that. Little typos, little adjustments to get the formatting right.

The other nice benefit is that I don't have to trust the LLM. I can evaluate each snippet right there and typically the machine does a good job of picking out syntactic style and semantics from the rest of the codebase and file and applying it to the completion.

The snippet, if it's not obvious, is from a bit of compiler backend code I'm working on. I would never have even _attempted_ to write a compiler backend in my spare time without this assistance.

For experienced devs, autocomplete is good enough for massive efficiency gains in dev speed.

I still haven't warmed to the agentic interfaces because I inherently don't trust the LLMs to produce correct code reliably, so I always end up reviewing it, and reviewing greenfield code is often more work than just writing it (esp now that autocomplete is so much more useful at making that writing faster).