[4.0] SimplifyCFG: fix hang caused by infinite loop in CFG #11654
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Explanation: This fixes a compiler hang. It can happen for control flows which contain branches to non-single-cycle empty infinite loops.
Scope of Issue: This can only happen if the source already contains an infinite loop. But as I have seen before, such situations can implicitly occur if the source contains an assert which is optimized away in the optimized build.
Risk: Low. The change just adds an additional bail-out condition which checks for infinite loops in the CFG.
Reviewed By: Roman
Testing: There is a regression test for it
Jira/Radar: SR-5764, rdar://problem/34068905