Clang/LLVM using the built in assembler builds all of FreeBSD

http://lists.cs.uiuc.edu/pipermail/cfe-dev/2010-October/011813.html

by X-Istence • 16 years ago

72 37 16 years ago

lists.cs.uiuc.edu

avar3• 16 years ago

Great news, with this and clang compiling Linux we might see it replace GCC on most/all free operating systems within a few years.

apl2• 16 years ago

No, we won't. The respective communities have been developing with GCC in mind for years. While clang is fantastic, I doubt that an outright replacement will take place.

But emancipated co-existence would be neat.

JoachimSchipper2• 16 years ago

Actually, quite a few BSD people will be happy to have a non-GPL compiler.

AFAIK, your comment is spot on for Linux, though.

dazzawazza• 16 years ago

The main reason for moving to clang is to remove as much GPL code from *BSD as possible (kernel and system libs).

You are correct regarding many of the 'ports' (packaging system) though as there will no doubt be some GCC idiosyncratic code in many of them.

avar3• 16 years ago

Ubuntu is already considering switching. Most people don't develop with "GCC in mind". They just target it, but now that there's another compiler that compiles almost all GCC C out there the cost of switching is very low.

X-Istence3• 16 years ago

From what I have gathered in the past, and what has been said here on Hacker News as well, FreeBSD is looking to replace GCC in the base with clang/LLVM, and that is exactly where this move is going.

As the mailing list message specified clang is going to be the default on i386 and x86_64. GCCisms will eventually go away and the code base will be cleaner and more manageable based upon it.

As states in the FreeBSD status report for this last quarter there are already experimental tests being run on the FreeBSD ports build system whereby clang/LLVM are used to compile all of the ports in an attempt to see how far clang/LLVM can get.

StavrosK5• 16 years ago

Can someone explain why LLVM is better than native code (if it is)? If it's not, what's the use for this?

yan• 16 years ago

That's really comparing apples to oranges.

LLVM can compile to intermediate code in order to make code optimizing passes more generic and better-defined, to cleaner separate compiler components and phases, to better abstract multiple architectures and to impose restrictions that make some analysis and optimization easier (like enforcing Static Single Assignment for forms), you can create a VM that runs IR directly and distribute that, among many other reasons. So IR does eventually make it to machine code, otherwise it won't be able to do anything.

Why LLVM is better than GCC is a different question. It's better, in my opinion, for being a much cleaner, more well-architected, modern, and much much better modularized code base. Also, I am a happy person when I read Clang docs on parsing vs when I read GCC docs on how to manipulate GIMPLE trees. There are also more objective metrics, like the front end being a very nice, portable library for parsing C-derived languages and exposing more functionality via libclang. (This makes very code-aware IDEs more possible and much easier to write, the use of C syntax for custom work, making custom code scanners and analyzers far easier, etc, etc)

Find more out at http://www.llvm.org

StavrosK5• 16 years ago

Thank you, I thought it was just the vm, but apparently it's a whole suite of compiler tools.

eliben• 16 years ago

You can't compare LLVM to native code, since these are different things. LLVM IR can be compiled to efficient native code if that's what you want. In fact, this is what happens when you use clang+llvm to compile code into native executables.

LLVM is much more than that, however. You might want to use it as a JITting interpreter of the IR instead of as a native compiler with all the benefits that may result from this. You may also use it as a sophisticated optimization framework (including cross-object, link-time optimization) taking IR and giving (optimized) IR back.

rbanffy5• 16 years ago

Just playing devil's advocate here: how much Clang/LLVM users are protected against patent lawsuits from companies (or individuals) who contributed patented technology to it?

I understand it never happened, but I am afraid someone somewhere may contribute something relevant and then have the patents bought by a troll.

pohl5• 16 years ago

I had to go back and check, but it appears I've had this conversation with you before:

http://news.ycombinator.com/item?id=1833560

Why don't we pick up where you left off: you can tell us what compilers you use yourself, and tell us how you are protected from the same.

rbanffy5• 16 years ago

At that time the only argument you were able to produce was that, if Apple decided to go belligerent on whatever patented tech they collaborated to Clang/LLVM, we would have to go to a previous, pre-Apple, version and fork it from that. That would be a version from a good couple years back.

Being able to fork is the ultimate defense to certain corporate evils, but a license that doesn't provide some protection against patents, obviously, won't protect you against that specific evil.

BTW, I use GCC most of the time. And I am shielded from any patented technology Apple may have contributed to it since the NeXT days by the redistribution clause of the GPL.

X-Istence3• 16 years ago

Apple has also contributed to GCC in various ways, what is to say that they didn't contribute some piece of code that they hold a patent on and thus could sue anyone that uses GCC?

rbanffy5• 16 years ago

They can't sue anyone that uses GCC because GCC is GPL-licensed and, by requiring Apple to give unrestricted redistribution rights, the GPL effectively shield downstream users.

SageRaven• 16 years ago

As a big fan of FreeBSD, I've been following this development with great interest. I just compiled a few select ports with clang, and I look forward to rebuilding all my ports to see what compiles and see how the system feels speed-wise.

However, as a server admin, I've become fond of the extra layer of protection ProPolice (gcc's "-fstack-protector" option) provides. I know it's a small thing, but does anyone know if clang has a similar feature?

Also, are there any non-default optizations I can try out? With the stock gcc in FreeBSD, I've been able to get away with using "-O3" on everything with no build failures or instability.

pohl5• 16 years ago

It looks like LLVM does have a stack protector pass:

https://llvm.org/svn/llvm-project/cfe/tags/Apple/clang-54.1/...

As for non-default optimizations, this passage from the following article best explains how much there is for you to explore:

Which LLVM passes to use, and which order to run them, with what analysis in between, is a huge search problem, though. There are roughly 200 optimization and analysis flags, and these, mostly, can be run in any order, any number of times. If we want to run say, twenty of the passes (about what -O3 does), that’s what, about 10^46 arrangements!

http://donsbot.wordpress.com/2010/03/01/evolving-faster-hask...

Clang/LLVM using the built in assembler builds all of FreeBSD

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