Shared: fix a bug in stateful outbarriers #15507
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Fixes a bug in the handling of stateful out-barriers.
These were initially placed at the very last pruning step, since they aren't relevant for pruning in practice.
However,
subpathsis computed in a way that isn't affected by the pruning, whereasedgesis affected. This can result in a tuplesubpaths(arg, par, ret, res)whereedges*(par, ret)does not hold.This means we get a spurious
arg -> resedge, which can result in a spurious alert. And this alert is missing its data flow path, because no path can be materialised forpar -> ret.The solution I've opted for is just to check the out-barrier when we generate the steps that feed into
pathStep. I've verified (for one query) that when stateful out-barriers aren't in use, the DIL is unaffected.