I search through the bug DB and thing #848331 is the same bug. I have also both libllvm3.8 and libllvm3.9 installed. On my laptop, there is a little older testing installed, but no 3.9 and it runs.
I tried to get more information about this issue. I run kdevelop under gdb and get this stack at the crash hread 1 "kdevelop" received signal SIGSEGV, Segmentation fault. 0x00007fffc5a79e8d in llvm::cl::Option::setArgStr(llvm::StringRef) () from /usr/lib/x86_64-linux-gnu/libLLVM-3.9.so.1 (gdb) bt #0 0x00007fffc5a79e8d in llvm::cl::Option::setArgStr(llvm::StringRef) () from /usr/lib/x86_64-linux-gnu/libLLVM-3.9.so.1 #1 0x00007fff8b6de0eb in ?? () from /usr/lib/llvm-3.8/lib/../lib/libLLVM-3.8.so.1 #2 0x00007fff8b6de328 in ?? () from /usr/lib/llvm-3.8/lib/../lib/libLLVM-3.8.so.1 #3 0x00007ffff7de864a in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0x7fffffffe5f8, env=env@entry=0x7fffffffe608) at dl-init.c:72 #4 0x00007ffff7de875b in call_init (env=0x7fffffffe608, argv=0x7fffffffe5f8, argc=1, l=<optimized out>) at dl-init.c:30 #5 _dl_init (main_map=main_map@entry=0x1f44a10, argc=1, argv=0x7fffffffe5f8, env=0x7fffffffe608) at dl-init.c:120 #6 0x00007ffff7deccd8 in dl_open_worker (a=a@entry=0x7fffffffceb0) at dl-open.c:575 #7 0x00007ffff7de84f4 in _dl_catch_error (objname=objname@entry=0x7fffffffcea0, errstring=errstring@entry=0x7fffffffcea8, mallocedp=mallocedp@entry=0x7fffffffce9f, operate=operate@entry=0x7ffff7dec8f0 <dl_open_worker>, args=args@entry=0x7fffffffceb0) at dl-error.c:187 #8 0x00007ffff7dec489 in _dl_open (file=0x1ae2f28 "/usr/lib/x86_64-linux-gnu/qt5/plugins/kdevplatform/25/kdevclangsupport.so", mode=-2147479551, caller_dlopen=0x7ffff5e4cb0e, nsid=-2, argc=<optimized out>, argv=<optimized out>, env=0x7fffffffe608) at dl-open.c:660 #9 0x00007fffed264ee9 in dlopen_doit (a=a@entry=0x7fffffffd0e0) at dlopen.c:66 #10 0x00007ffff7de84f4 in _dl_catch_error (objname=0x65a1d0, errstring=0x65a1d8, mallocedp=0x65a1c8, operate=0x7fffed264e90 <dlopen_doit>, args=0x7fffffffd0e0) at dl-error.c:187 #11 0x00007fffed265521 in _dlerror_run (operate=operate@entry=0x7fffed264e90 <dlopen_doit>, args=args@entry=0x7fffffffd0e0) at dlerror.c:163 #12 0x00007fffed264f82 in __dlopen (file=<optimized out>, mode=<optimized out>) at dlopen.c:87 #13 0x00007ffff5e4cb0e in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #14 0x00007ffff5e45bb5 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #15 0x00007ffff6c85d9a in KPluginLoader::load() () from /usr/lib/x86_64-linux-gnu/libKF5CoreAddons.so.5 #16 0x00007ffff6c85eca in KPluginLoader::instance() () from /usr/lib/x86_64-linux-gnu/libKF5CoreAddons.so.5 #17 0x00007ffff6c85f1c in KPluginLoader::factory() () from /usr/lib/x86_64-linux-gnu/libKF5CoreAddons.so.5 #18 0x00007ffff7ab5a0d in KDevelop::PluginController::loadPluginInternal(QString const&) () from /usr/lib/x86_64-linux-gnu/libKDevPlatformShell.so.10 #19 0x00007ffff7ab76a6 in KDevelop::PluginController::allPluginsForExtension(QString const&, QMap<QString, QVariant> const&) () from /usr/lib/x86_64-linux-gnu/libKDevPlatformShell.so.10 #20 0x00007ffff7af6db8 in KDevelop::LanguageController::languagesForMimetype(QString const&) () from /usr/lib/x86_64-linux-gnu/libKDevPlatformShell.so.10 #21 0x00007ffff7af7a98 in KDevelop::LanguageController::languagesForUrl(QUrl const&) () from /usr/lib/x86_64-linux-gnu/libKDevPlatformShell.so.10 #22 0x00007ffff366d593 in ?? () from /usr/lib/x86_64-linux-gnu/libKDevPlatformLanguage.so.10 #23 0x00007ffff3670562 in ?? () from /usr/lib/x86_64-linux-gnu/libKDevPlatformLanguage.so.10 #24 0x00007ffff366a024 in KDevelop::BackgroundParser::parseDocuments() () from /usr/lib/x86_64-linux-gnu/libKDevPlatformLanguage.so.10 #25 0x00007ffff37f6d45 in ?? () from /usr/lib/x86_64-linux-gnu/libKDevPlatformLanguage.so.10 #26 0x00007ffff5e7d499 in QObject::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #27 0x00007ffff6733b8c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5 #28 0x00007ffff673b341 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5 #29 0x00007ffff5e509e0 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #30 0x00007ffff5e5316d in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #31 0x00007ffff5ea4c43 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #32 0x00007fffecf9a7f7 in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0 #33 0x00007fffecf9aa60 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0 #34 0x00007fffecf9ab0c in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0 #35 0x00007ffff5ea504f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #36 0x00007ffff5e4e9ca in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #37 0x00007ffff5e5713c in QCoreApplication::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 #38 0x000000000040ba2c in ?? () #39 0x00007ffff54d22b1 in __libc_start_main (main=0x405d20, argc=1, argv=0x7fffffffe5f8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>,