LLVM ist a mess

Posted Mar 18, 2024 15:18 UTC (Mon) by paulj (subscriber, #341)
In reply to: LLVM ist a mess by willy
Parent article: Cranelift code generation comes to Rust

"writing a [blah] is not a hard problem" -> links to something written by one of the most prodigious, genius authors of Free Software. Hmm... ;)

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LLVM ist a mess

Posted Mar 18, 2024 16:28 UTC (Mon) by willy (subscriber, #9762) [Link] (5 responses)

You've completely missed the point of that comment, but to refute the uninteresting part you're quibbling with:

https://student.cs.uwaterloo.ca/~cs444/

Team of four students builds a compiler in three months.

LLVM ist a mess

Posted Mar 18, 2024 18:15 UTC (Mon) by paulj (subscriber, #341) [Link] (4 responses)

It was mostly humour. I too, like most students who've done a CS degree, have had to write some kind compiler for a class assignment (a toy front-end with type-checker for a subset of a typed JS-ish language). I've written compilers for simple DSLs - in AWK even ;). A compiler itself is not /that/ hard - completely agreed.

I was just pointing out the humour in the irony of making that point via an example written by an author who has a (prodigious) habit of solving difficult problems. ;)

I agree though that, even if a basic compiler is simple, there is a /lot/ more to making a _good_ C/C++ compiler.

LLVM ist a mess

Posted Mar 18, 2024 23:48 UTC (Mon) by NYKevin (subscriber, #129325) [Link] (1 responses)

> I too, like most students who've done a CS degree, have had to write some kind compiler for a class assignment (a toy front-end with type-checker for a subset of a typed JS-ish language).

Fun fact: If your professor is sufficiently insane, it is possible that you will end up having to write an interpreter for the (untyped) lambda calculus. So count yourself lucky that you got a language that actually looked vaguely modern.

OTOH, I must admit that the lambda calculus is much, *much* easier to implement than most real languages. It only has 2½ rules, or 1½ if you use De Bruijn indexing. But I would've liked to do a real language, or at least something resembling a real language. I often feel that the most difficult courses were the only ones that actually taught me anything useful.

LLVM ist a mess

Posted Mar 20, 2024 20:14 UTC (Wed) by ringerc (subscriber, #3071) [Link]

You can always make the course more interesting.

I had a comp sci course on concurrency proofs and theory. The tool they used for it sucked so I updated it from the ancient RH4 target it required and replaced the build system. Then fixed some bugs and memory issues. Improved the error messages and generally made the tool nicer to use.

LLVM ist a mess

Posted Mar 19, 2024 4:42 UTC (Tue) by buck (subscriber, #55985) [Link] (1 responses)

> I was just pointing out the humour in the irony of making that point via an example written by an author who has a (prodigious) habit of solving difficult problems. ;)

Well, I'm with you: a compiler written by Fabrice Bellard is not your run-of-the-mill hobby project.

But, I'm really more just pointing out that this still blows me away:

https://bellard.org/jslinux/index.html

which i think saves this comment from being (rightly) criticized for being OT, since it's more Linux-y than the article, and this is LWN after all, dang it.

Well, to get this right back on topic, i can actually just point out that JSLinux features tcc and gcc but not clang:

localhost:~# cat readme.txt
Some tests:

- Compile hello.c with gcc (or tcc):

gcc hello.c -o hello
./hello

- Run QuickJS:

qjs hello.js

- Run python:

python3 bench.py
localhost:~#

b/c the performance win:

[`time gcc -o hello -c hello.c -O0` output elided to spare my old laptop's feelings]

LLVM ist a mess

Posted Mar 19, 2024 4:47 UTC (Tue) by buck (subscriber, #55985) [Link]

Sorry. Let me stand corrected by myself:

Quoth https://bellard.org/jslinux/news.html:

2020-07-05:

Added the Alpine Linux distribution. Many packages are included such as gcc, Clang, Python 2.7 and 3.8, Node.js, Ruby, PHP, ... The more adventurous (and patient) people can also try to run Wine or Firefox.
Added SSE2 support to the x86 emulator
Added dynamic resizing of the terminal

LLVM ist a mess

Posted Mar 18, 2024 18:02 UTC (Mon) by farnz (subscriber, #17727) [Link]

I've written more than one compiler, and I would not count myself as a Fabrice Bellard level developer. You should be able to write a simple optimizing C compiler following a book like this in about 3 months full-time effort if you're a competent developer (less if you're willing to reuse tools like gas and ld rather than doing everything yourself).

LLVM ist a mess

Posted Mar 18, 2024 19:57 UTC (Mon) by Cyberax (✭ supporter ✭, #52523) [Link] (2 responses)

Writing a "toy C" compiler had been a course project in my university. It was C with most of its functionality, except things that are baffling, like syntactic ambiguity between function pointers and definitions, dangling else, etc.

It really is not a hard problem. Annoying and somewhat long, but not hard.

LLVM ist a mess

Posted Mar 19, 2024 5:40 UTC (Tue) by adobriyan (subscriber, #30858) [Link] (1 responses)

And you'll learn operator precedence table for FREE!

LLVM ist a mess

Posted Mar 19, 2024 5:56 UTC (Tue) by Cyberax (✭ supporter ✭, #52523) [Link]

I actually promptly forgot it. I always just spam the code with braces to disambiguate anything that is more complex than 2*2+1.