https://bugs.freedesktop.org/show_bug.cgi?id=84232
Priority: medium Bug ID: 84232 Assignee: dri-devel@lists.freedesktop.org Summary: PHINode containing itself causes segfault in LLVM when compiling Blender OpenCL kernel with R600 backend Severity: normal Classification: Unclassified OS: All Reporter: vitalif@yourcmc.ru Hardware: Other Status: NEW Version: XOrg CVS Component: DRM/Radeon Product: DRI
Created attachment 106717 --> https://bugs.freedesktop.org/attachment.cgi?id=106717&action=edit Blender output with R600_DEBUG=compute,fs,vs,gs,ps,cs
I'm trying to run Blender using Mesa OpenCL implementation on a radeonsi card. First the kernel didn't want to compile, but that was caused by a bug in it (they were using . instead of -> in 1 place), and after fixing this bug I've got the kernel to compile...
...But after that, LLVM started to crash during translation of IR into shader code with R600 backend.
I've done some investigation and figured out that the crash is caused by a PHINode containing itself. SIAnnotateControlFlow::handleLoopCondition() can't handle such situation - it recurses into itself, calls Phi->eraseFromParent() inside the inner execution, returns into outer one, gets zeroed out object and crashes when trying to do something with its members... for example when trying to erase it again.
I've tried to understand the semantics of such PHINodes from reading the code and got a suspicion that the rest of LLVM code just ignores PHINodes equal to their parent, so I've tried to fix the bug by making handleLoopCondition() skip IncomingValues equal to the Phi itself, but the bug didn't go away! Surprisingly, PHINode may not just contain itself directly, but it also may contain itself inside another PHINode, i.e. Phi->getIncomingValue(0)->getIncomingValue(0) == Phi, which results in the same problem with SIAnnotateControlFlow...
I'll attach Blender output with R600_DEBUG = trace everything and a stack trace of the crash.
The bug reproduced with llvm 3.5 and snapshot of 3.6; blender is 2.71; Mesa is from OIBAF's repository.
sudo -E CYCLES_OPENCL_TEST=1 R600_DEBUG=compute,fs,vs,gs,ps,cs blender cup\ of\ coffee\ 5.blend &> kernel-llvm.log