Comment by aseipp | Hacker News Reader

Comment by aseipp | Hacker News Reader

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There isn't really any value in doing that kind of stuff honestly unless you just like really boring and annoying work. Like, if you are designing your own ISA, you can punt that down to basically the end of the line, because all the actual important stuff comes first.

There's a kind of great irony to compiler work like this where you need some outside thing to drive the design, but if the design being driven ultimately isn't very bespoke, you eventually realize everyone else has done all the work already so everything you have to do is boring (e.g. wire up a new ABI to some existing codegen... how riveting...) Alternatively you have something unique, and find out the compiler is actually the hard part of the whole problem, because now you're on your own.

If you want a tool for early programming your own ISA I recommend using Lisp or something else as a macro assembler to exercise the system. If you simply insist on arbitrary C code, something like WebAssembly might actually be better than patching some random 3rd party code generator (i.e. just write a simple one-shot one-pass compiler that does no advanced regalloc or optimization and just turns it into a binary. This is relatively easy and does not require advanced algorithms and there are already a bunch of WASM compilers available.)

> If you want a tool for early programming your own ISA I recommend using Lisp or something else as a macro assembler to exercise the system.

That something else should be, and hear me out, Forth.

Yes I'm perfectly serious, if you look around you can find some interactive AVR Forth assemblers which are in the 2-4K installed range.

This is Forth's niche, it's a surprisingly capable language for many things but interactive programming a bespoke ISA, this is where Forth comes from.

Firm recommendation to at least read A Problem Oriented Language if working in this space, a combination of memoir and a distinctive philosophy of software development.

But, this is TCC's strength. It IS a simple one-shot, one-pass compiler that does not advance regalloc or optimization! With a single-file code generator that has already been ported. Goes straight from C source to executable binary in memory.

The main problem is that TCC has been "extended" to take on other roles (like linking ELF).

Sure but if you're working on a custom softcore processor, there's a lot to do, and a lot to learn, and it's very easy to stall out on boring parts, because in a production setting there is a lot of boring stuff. A C compiler is "boring stuff." Unless your ISA design is non-traditional, for sequential scalar machines I feel you're mostly just doing tedium to emit slightly different instructions from an existing codebase. It's not that it isn't valuable to have a C compiler, it's that for the purposes of learning and absorbing information and new things, someone else has done most of the "learning" parts for you. So you could probably just... do something else.

My opinion here is broadly informed by two things, which is that 1) if you want to write a compiler, you should write a compiler, not just tweak an instruction emitter (yes I know that's actually a very common part of the job for working compiler devs, but that's not what you're doing.) And 2) people are far too eager to fall into their old ways even when it isn't productive. A C compiler is comfortable. For someone experienced, it would be easy to port an existing one -- but they probably wouldn't have been asking about it in the first place. For those other people, it's boring and a lot of work when a macro assembler like Forth or Lisp can get you going and writing higher-level code in a few hours. When you're doing things like bringing up silicon you wrote, that's way more important and much more valuable.

You shouldn't eschew things like a C compiler forever if you plan to really get serious. Sometimes you can get one for free (MIPS, RISC-V) and that's super valuable. For a production toolset, it would be absolutely essential. But when you're learning it's easy to sink a lot of time into things like that, when that's not where the real meat and potatoes are.

Yeah I figured it's a long shot. Just wanted to see if I had missed something which would allow me to get going without much effort.

> If you want a tool for early programming your own ISA I recommend using Lisp

Good point, maybe this is the time for me to learn Lisp...

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