JDK-8290892 introduces a targeted unit test and a stress mode (-XX:+StressReachabilityFences) where ReachabilityFence (RF) nodes are aggressively inserted during byte code parsing.

One shortcoming of StressReachabilityFences mode is that it stresses RF machinery, but doesn't check any RF invariants.

Consider introducing RF validation pass which ensures reachability edges are correctly placed in the IR graph according to initial RF node placement.