Date: Mon, 07 Jan 2013 08:45:32 -0800 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: David Naylor <naylor.b.david@gmail.com> Cc: freebsd-toolchain@freebsd.org, freebsd-arch@freebsd.org Subject: Re: LLVM Image Activator Message-ID: <50EAFBAC.2020808@freebsd.org> In-Reply-To: <201301071825.06439.naylor.b.david@gmail.com> References: <50E9BC2D.7000302@freebsd.org> <201301071825.06439.naylor.b.david@gmail.com>
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On 01/07/13 08:25, David Naylor wrote: > Hi, > > Just my 2c > > On Sunday, 6 January 2013 20:02:21 Nathan Whitehorn wrote: >> Having LLVM/clang in the base system lets us do some interesting things >> that we couldn't do with GCC. One is that LLVM ships with a JIT for LLVM >> IR as well as components of a toolchain for it (this is what Google's >> pNACL uses) and that you can end up producing binary files that are in >> IR instead of native code. The IR isn't really cross-platform, but does >> let you do CPU-specific optimizations when executed by the JIT, etc. >> >> The attached patch causes the LLVM JIT (lli) to be built by default >> (adding ~20 seconds to buildworld on my five-year-old laptop) and adds a >> kernel image activator that invokes it when passed LLVM bitcode files. >> It's not completely finished (see the XXX comment in the middle), but it >> does work, as follows: >> >> $ clang -emit-llvm -c -o hw.ll hw.c >> $ file hw.ll >> hw.ll: LLVM bitcode >> $ lli hw.ll >> Hello world! >> $ chmod a+x hw.ll >> $ ./hw.ll >> Hello world! >> $ >> >> Is there any interest in having features like this? It seems like this >> could provides some interesting possibilities for us and nice >> integration from having imported clang into base. > > Would it be possible to have this as a module (and thus in ports)? Or, > perhaps, change the sources such these things could be loaded as a module... We do support that, but I'm not really sure what would be gained. We have LLVM in base; it seems a shame not to use it. > Also, with modification to LLVM, wouldn't the existing '#!' mechanism work > (aka '#!/usr/bin/lli') at the beginning of the file? In principle, yes, but we'd have to coordinate that with a lot of players since a number of tools operate on LLVM bitcode. The other obstacle is that LLVM bitcode is a giant binary blob, not text, so the standard #! seems a little out of place. > On an aside. Could you imagine shipping a 'x86' llvm-byte code and get the > jit (with caching), thus your computer will get full support (speed) from the > binaries and the binaries will work on all 'x86' related architectures. (My > thinking is for things like i386 vs pentium4). > Yes, this is exactly the kind of thing I had in mind. -Nathan
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