Date: Fri, 9 Jan 2009 12:05:08 +0100 From: Roman Divacky <rdivacky@freebsd.org> To: Christoph Mallon <christoph.mallon@gmx.de> Cc: Andrew Reilly <andrew-freebsd@areilly.bpc-users.org>, freebsd-current@freebsd.org, Ollivier Robert <roberto@keltia.freenix.fr> Subject: Re: gcc 4.3: when will it become standard compiler? Message-ID: <20090109110508.GA12123@freebsd.org> In-Reply-To: <49672189.5060109@gmx.de> References: <49668763.8020705@mail.zedat.fu-berlin.de> <20090108233311.GA69883@keltia.freenix.fr> <20090109031147.GB44317@duncan.reilly.home> <49672189.5060109@gmx.de>
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On Fri, Jan 09, 2009 at 11:06:01AM +0100, Christoph Mallon wrote: > Andrew Reilly schrieb: > >On Fri, Jan 09, 2009 at 12:33:11AM +0100, Ollivier Robert wrote: > >>According to O. Hartmann: > >>>When will gcc 4.3 incorporated in FreeBSD 8 and become the standard > >>>compiler suite? We figured out that gcc 4.3 does have a speed gain in > >>>some numerical code of 3 - 8 % and I guess we can use this in the basic > >>>OS as well ... > >>I'd rather have llvm instead... > > > >I wouldn't mind that, either. I've got the llvm port installed myself, in > >preparation for doing some experiments of my own, but haven't tried using > >it to > >build the kernel or user-land (or even any of the ports). Has anyone > >given it a > >go? Is it missing any crucial features? I believe that it had different > >(or > >no?) support for PIC code generation, which could affect the ability to do > >shared libraries, but recent release notes seem to indicate that that's > >been > >addressed. > > One quite important difference between GCC and LLVM is that GCC has been > used to compile literally billions and billions of lines of code. Sure, > LLVM has compiled many lines, too, but it's hard to beat GCC in terms of > stability in this respect (yes, I am well aware that GCC had and has its > share of bugs). You have to do *lots* of testing before you can honestly > say that a compiler can really be used to compile a whole operating system. > Another aspect is that LLVM is in some parts more aggressive at > optimisation than GCC. So sloppy code, which GCC let you get away with, > may suddenly break - though it was wrong all along, but you just never > noticed. Of course the code has to be fixed, but this takes time. > I'm not saying it's wrong to look for alternatives, but you cannot just > change your system compiler like you change underwear. well... the first step is imho starting to compile world with C99... that might reveal some bugs, note that as of a few months ago 8-current compiles cleanly with C99, that does not mean that it's working when you run those programs correctly :) > >There's also someone working on a BSD-licenced retooling > >(ANSI/ISO-ification) of > >the PCC compiler, which is getting close to being useful as a system > >compiler, I > >believe. (http://www.ludd.ltu.se/~ragge/pcc/ in ports/lang/pcc) > > PCC cannot seriously be considered. Its design is stuck in the > seventies. From the point of view of compiler construction it is plain > plain out of question. I especially was amused by the statement of the > author who claimed PCC supports SSA - except for phi-functions. what's wrong with design stuck in 70's when it compiles the whole world/kernel? I would not use it for default compilation of releases but it might be useful when you are developing - because of its fast compilation times btw.. are you sure the design is stuck in the 70's? the author claims to have rewritten almost the whole thing. have you looked at the recent code? another question - how is libfirm/cparser? last time I tried it didnt support much of the gcc options (-Wsomething -f-something etc.) so it could not be used as a direct drop-in
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