https://bugs.llvm.org/show_bug.cgi?id=43720
Bug ID: 43720
Summary: [JumpThreading] Hangs when called with complex
switch/state machines as generated by coroutines
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Created attachment 22690
--> https://bugs.llvm.org/attachment.cgi?id=22690&action=edit
A dirty workaround for the bug reported
In ProcessThreadableEdges, it is possible for PredsToFactor to be empty for its
call to "ThreadEdge".
This seemingly spins the whole thing in an infinite loop, where:
if (PredBBs.size() == 1)
PredBB = PredBBs[0];
else {
LLVM_DEBUG(dbgs() << " Factoring out " << PredBBs.size()
<< " common predecessors.\n");
PredBB = SplitBlockPreds(BB, PredBBs, ".thr_comm");
}
Writes "Factors out 0 common predecessors", which seems to be a nop, leading to
the same 0-edge being threaded again, and again, and again.
Perhaps someone who knows the code better than I can see if it is _always_ an
error to pass an empty PredBBs to ThreadEdge, in which case it should be
asserted in ThreadEdge, and/or how it's possible to end up with an empty
PredBBs in the first place.
Workaround attached.
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