[LLVMdev] Transitioning build to cmake

[Brooks Davis]

On Wed, Jul 24, 2013 at 12:40:59PM -0700, Sean Silva wrote:
> On Wed, Jul 24, 2013 at 10:11 AM, Jeremy Huddleston Sequoia <
> jeremyhu at apple.com> wrote:
> > 4) Building clang using installed llvm
> >
> > It looks like there is some support for building clang against an
> > installed llvm by setting CLANG_PATH_TO_LLVM_BUILD.  This fails miserably
> > in part because the installed llvm cmake files reference build time paths,
> > but even after fixing that, there are tons of build failures.  I'm guessing
> > this is still a work in progress, but if I should file bugs, please let me
> > know.
> 
> This is probably not a very good idea because clang evolves in lock-step
> with LLVM. Unless the installed LLVM is the same revision as the clang you
> are building, things are likely to not work due to internal API changes.
> The option you cite is more likely intended for when you build clang in a
> directory separate from LLVM (rather than when it is in llvm/tools/clang/,
> where things just work) but both are still checked out at the same revision.

We do the same thing in FreeBSD and keeping the ability to build with
the installed llvm is critical given our current ports/package
infrastructure.   The build with configure based builds is a bit of a
hack, but seems to break quite infrequently.

-- Brooks
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