another important part might be that it only  happens when I click play in the blizzard update client. The game crashes but the client keeps running. I was working fine the last time I tried which would be about 1 or 2 months ago

driver bug, suspend compositing before primusrunning (shift+alt+f12)

*** This bug has been marked as a duplicate of bug 299333 ***

PS:
since this is different from the other segfaults in the driver path: do you have "suspend compositing for fullscreen windows" enabled (kcmshell4 kwincompositing, 3rd tab) and is it a fullscreen window and does the crash (backtrace) change when disabling it?

I do not have the option enabled, enabling it still causes the same error message with the following backtrace 
Application: KWin (kwin), signal: Segmentation fault
Using host libthread_db library "/lib64/libthread_db.so.1".
81	T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
[Current thread is 1 (Thread 0x7f9b14013900 (LWP 9459))]

Thread 2 (Thread 0x7f9b06e0a700 (LWP 9481)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x0000003bb698f09b in QTWTF::TCMalloc_PageHeap::scavengerThread (this=0x3bb6c8df00 <QTWTF::pageheap_memory>) at ../3rdparty/javascriptcore/JavaScriptCore/wtf/FastMalloc.cpp:2359
#2  0x0000003bb698f0d9 in QTWTF::TCMalloc_PageHeap::runScavengerThread (context=<optimized out>) at ../3rdparty/javascriptcore/JavaScriptCore/wtf/FastMalloc.cpp:1464
#3  0x0000003b94807f33 in start_thread (arg=0x7f9b06e0a700) at pthread_create.c:309
#4  0x0000003b940f4ded in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

Thread 1 (Thread 0x7f9b14013900 (LWP 9459)):
[KCrash Handler]
#6  gen7_update_renderbuffer_surface (brw=0x2656330, rb=0x2649a60, layered=false, unit=0) at gen7_wm_surface_state.c:509
#7  0x00007f9a797be6cc in brw_update_renderbuffer_surfaces (brw=<optimized out>) at brw_wm_surface_state.c:717
#8  0x00007f9a79793faa in brw_upload_state (brw=brw@entry=0x2656330) at brw_state_upload.c:513
#9  0x00007f9a7974feb6 in brw_try_draw_prims (max_index=<optimized out>, min_index=<optimized out>, ib=<optimized out>, nr_prims=<optimized out>, prim=<optimized out>, arrays=<optimized out>, ctx=0x2656330) at brw_draw.c:445
#10 brw_draw_prims (ctx=0x2656330, prim=<optimized out>, nr_prims=<optimized out>, ib=<optimized out>, index_bounds_valid=<optimized out>, min_index=0, max_index=5, tfb_vertcount=0x0) at brw_draw.c:530
#11 0x00007f9a79273de0 in vbo_draw_arrays (ctx=0x2656330, mode=4, start=0, count=6, numInstances=1, baseInstance=0) at ../../../src/mesa/vbo/vbo_exec_array.c:660
#12 0x00000039fd21239e in KWin::GLVertexBuffer::draw (this=this@entry=0x1bf03d0, region=..., primitiveMode=primitiveMode@entry=4, first=first@entry=0, count=6, hardwareClipping=hardwareClipping@entry=false) at /usr/src/debug/kde-workspace-4.11.7/kwin/libkwineffects/kwinglutils.cpp:1949
#13 0x00000039fd215599 in KWin::GLVertexBuffer::render (this=0x1bf03d0, region=..., primitiveMode=4, hardwareClipping=<optimized out>) at /usr/src/debug/kde-workspace-4.11.7/kwin/libkwineffects/kwinglutils.cpp:1902
#14 0x00000039fd21560d in KWin::GLVertexBuffer::render (this=this@entry=0x1bf03d0, primitiveMode=primitiveMode@entry=4) at /usr/src/debug/kde-workspace-4.11.7/kwin/libkwineffects/kwinglutils.cpp:1896
#15 0x00000039fc8dbb7a in KWin::SceneOpenGL2::doPaintBackground (this=<optimized out>, vertices=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/scene_opengl.cpp:748
#16 0x00000039fc8df475 in KWin::SceneOpenGL::paintBackground (this=this@entry=0x27834a0, region=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/scene_opengl.cpp:460
#17 0x00000039fc8ceed6 in KWin::Scene::paintSimpleScreen (this=this@entry=0x27834a0, orig_mask=orig_mask@entry=8, region=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/scene.cpp:367
#18 0x00000039fc8cca65 in KWin::Scene::finalPaintScreen (this=0x27834a0, mask=mask@entry=8, region=..., data=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/scene.cpp:198
#19 0x00000039fc8f018d in KWin::EffectsHandlerImpl::paintScreen (this=0x2abbff0, mask=mask@entry=8, region=..., data=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/effects.cpp:375
#20 0x00000039fbc11baf in KWin::Effect::paintScreen (this=this@entry=0x30eb2b0, mask=mask@entry=8, region=..., data=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/libkwineffects/kwineffects.cpp:522
#21 0x00000039fc8f013a in KWin::EffectsHandlerImpl::paintScreen (this=0x2abbff0, mask=8, region=..., data=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/effects.cpp:372
#22 0x00000039fc8cf0a6 in KWin::Scene::paintScreen (this=this@entry=0x27834a0, mask=mask@entry=0x7fff54364b0c, damage=..., repaint=..., updateRegion=updateRegion@entry=0x7fff54364b20, validRegion=validRegion@entry=0x7fff54364b30) at /usr/src/debug/kde-workspace-4.11.7/kwin/scene.cpp:148
#23 0x00000039fc8e28fe in KWin::SceneOpenGL::paint (this=0x27834a0, damage=..., toplevels=...) at /usr/src/debug/kde-workspace-4.11.7/kwin/scene_opengl.cpp:389
#24 0x00000039fc8c65db in KWin::Compositor::performCompositing (this=0x19fe6c0) at /usr/src/debug/kde-workspace-4.11.7/kwin/composite.cpp:618
#25 0x0000003b9ed9d0a1 in QObject::event (this=0x19fe6c0, e=<optimized out>) at kernel/qobject.cpp:1156
#26 0x0000003ea51c9d8c in QApplicationPrivate::notify_helper (this=this@entry=0x1a25720, receiver=receiver@entry=0x19fe6c0, e=e@entry=0x7fff54365060) at kernel/qapplication.cpp:4562
#27 0x0000003ea51d0725 in QApplication::notify (this=this@entry=0x7fff54365560, receiver=receiver@entry=0x19fe6c0, e=e@entry=0x7fff54365060) at kernel/qapplication.cpp:4348
#28 0x00000039f7e4aa1a in KApplication::notify (this=0x7fff54365560, receiver=0x19fe6c0, event=0x7fff54365060) at /usr/src/debug/kdelibs-4.12.2/kdeui/kernel/kapplication.cpp:311
#29 0x0000003b9ed8439d in QCoreApplication::notifyInternal (this=0x7fff54365560, receiver=0x19fe6c0, event=event@entry=0x7fff54365060) at kernel/qcoreapplication.cpp:949
#30 0x0000003b9edb5ae3 in sendEvent (event=0x7fff54365060, receiver=<optimized out>) at kernel/qcoreapplication.h:231
#31 QTimerInfoList::activateTimers (this=0x1a26118) at kernel/qeventdispatcher_unix.cpp:621
#32 0x0000003b9edb5b60 in QEventDispatcherUNIX::activateTimers (this=this@entry=0x19d0c80) at kernel/qeventdispatcher_unix.cpp:878
#33 0x0000003b9edb6548 in QEventDispatcherUNIX::processEvents (this=this@entry=0x19d0c80, flags=...) at kernel/qeventdispatcher_unix.cpp:940
#34 0x0000003ea526c5d6 in QEventDispatcherX11::processEvents (this=0x19d0c80, flags=...) at kernel/qeventdispatcher_x11.cpp:152
#35 0x0000003b9ed82edf in QEventLoop::processEvents (this=this@entry=0x7fff543653b0, flags=...) at kernel/qeventloop.cpp:149
#36 0x0000003b9ed8322d in QEventLoop::exec (this=this@entry=0x7fff543653b0, flags=...) at kernel/qeventloop.cpp:204
#37 0x0000003b9ed88749 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1221
#38 0x0000003ea51c83fc in QApplication::exec () at kernel/qapplication.cpp:3823
#39 0x00000039fc87e411 in kdemain (argc=3, argv=0x7fff543656b8) at /usr/src/debug/kde-workspace-4.11.7/kwin/main.cpp:597
#40 0x0000003b94021d65 in __libc_start_main (main=0x4009d0 <main(int, char**)>, argc=3, argv=0x7fff543656b8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fff543656a8) at libc-start.c:285
#41 0x0000000000400a01 in _start ()

That backtrace actually looks more like the "normal" ones
Can you say whether the other backtrace occurs reproducibly with deactivated "suspend ... fullscreen ..."? (or the crash location in the driver is "random")