[LLVMdev] RFC: Timeline for deprecating the autoconf build system?

[Tom Stellard]

On Tue, Nov 04, 2014 at 04:04:45PM -0800, Reid Kleckner wrote:
> On Tue, Nov 4, 2014 at 1:17 PM, Dan Liew <dan at su-root.co.uk> wrote:
> 
> > On 4 November 2014 19:08, Brooks Davis <brooks at freebsd.org> wrote:
> > > On Sun, Nov 02, 2014 at 04:48:58PM +0000, David Chisnall wrote:
> > >> On 2 Nov 2014, at 14:17, Joerg Sonnenberger <joerg at britannica.bec.de>
> > wrote:
> > >>
> > >> > Requiring cmake for NetBSD is not acceptable as it is almost as heavy
> > as
> > >> > a C++ compiler itself. That said, I don't really care about the
> > >> > Makefiles, just about configure and the associated loggic to craete
> > >> > Config.h and friends. I would expect FreeBSD to have similar concerns.
> > >>
> > >> For the FreeBSD base system, we use a bmake-based build system for
> > >> LLVM, but that is based on the Makefiles generated by CMake.  I
> > >> believe that we're now using CMake for the version of LLVM in ports.
> > >
> > > For most versions we're using autoconf because it lets us build clang
> > > against an installed LLVM.  The autoconf build system almost supports
> > this
> > > (you need to symlink a couple installed files into the build tree), but
> > > AFACT the cmake build system doesn't.
> > >
> > > It would be really useful if I could build clang against an installed
> > LLVM
> > > and LLDB against an install clang and LLVM.
> >
> > CMake can support this. We need to make use of the "exporting targets"
> > feature
> > that CMake offers so that clients can build against LLVM libraries.
> > LLVM has actually been exporting this information for a while and it
> > is documented here [1].
> >
> > To further complicate matters the clang CMake build system supports
> > two modes. In tree build (i.e. inside tools/clang) and an out of tree
> > build. The problem IIRC with the out of tree build is that the CMake
> > clang build system does not try to use this information at all and
> > instead tries to get its information from the llvm-config executable
> > which doesn't feel very clean.  I should warn that I've never tried
> > the "out of tree" build of clang so I don't know how well it works.
> 
> 
> I agree, I wanted to spend some time today trying to make this work.
> 

I have filed a bug for this: http://www.llvm.org/bugs/show_bug.cgi?id=21560

If anyone has additional information they would look to add, please do so.

Thanks,
Tom

> I think part of the issue is that the current standalone clang build is
> designed to work when all you have is a build directory, not an install
> directory. This way you can have two XCode IDE instances: one for LLVM and
> once for Clang, and just hit build in LLVM before building Clang. It's one
> level of manual dependency management, but worth it for the increase in
> responsiveness.

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