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C++: Fix performance of bbEntryReachesLocally

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This predicate was fast with the queries and engine from 1.18. With the
queries from `master` it got a bad join order in the
`UninitializedLocal.ql` query, which made it take 2m34s on Wireshark.
This commit decomposes `bbEntryReachesLocally` into two predicates that
together take only 4s.
This commit is contained in:
Jonas Jensen
2018-11-29 15:09:53 +01:00
parent f4ec168666
commit 62d478eab3
1 changed files with 10 additions and 2 deletions
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12
cpp/ql/src/semmle/code/cpp/controlflow/LocalScopeVariableReachability.qll
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@@ -96,10 +96,18 @@ abstract class LocalScopeVariableReachability extends string {
private predicate bbEntryReachesLocally(BasicBlock bb, SemanticStackVariable v, ControlFlowNode node) {
exists(int n |
node = bb.getNode(n) and isSink(node, v) |
not exists(int m | m < n | isBarrier(bb.getNode(m), v))
node = bb.getNode(n) and
isSink(node, v)
|
not exists(this.firstBarrierIndexIn(bb, v))
or
n <= this.firstBarrierIndexIn(bb, v)
)
}
private int firstBarrierIndexIn(BasicBlock bb, SemanticStackVariable v) {
result = min(int m | isBarrier(bb.getNode(m), v))
}
}
/**