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reintroduce performance improvement - but sound this time

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Erik Krogh Kristensen
2020-12-16 16:04:51 +01:00
parent 4392f0270c
commit c58f67b189
1 changed files with 24 additions and 2 deletions
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26
javascript/ql/src/Performance/ReDoS.ql
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@@ -118,9 +118,23 @@ newtype TStatePair =
MkStatePair(State q1, State q2) { MkStatePair(State q1, State q2) {
isFork(q1, _, _, _, _) and q2 = q1 isFork(q1, _, _, _, _) and q2 = q1
or or
step(_, _, _, q1, q2) (step(_, _, _, q1, q2) or step(_, _, _, q2, q1)) and
rankState(q1) <= rankState(q2)
} }
/**
* Gets a unique number for a `state`.
* Is used to create an ordering of states, where states with the same `toString()` will be ordered differently.
*/
int rankState(State state) {
state =
rank[result](State s, Location l |
l = s.getRepr().getLocation()
|
s order by l.getStartLine(), l.getStartColumn(), s.toString()
)
}
class StatePair extends TStatePair { class StatePair extends TStatePair {
State q1; State q1;
State q2; State q2;
@@ -190,12 +204,20 @@ predicate isFork(State q, InputSymbol s1, InputSymbol s2, State r1, State r2) {
stateInsideBacktracking(r2) stateInsideBacktracking(r2)
} }
/**
* Gets the state pair `(q1, q2)` or `(q2, q1)`; note that only
* one or the other is defined.
*/
StatePair mkStatePair(State q1, State q2) {
result = MkStatePair(q1, q2) or result = MkStatePair(q2, q1)
}
/** /**
* Holds if there are transitions from the components of `q` to the corresponding * Holds if there are transitions from the components of `q` to the corresponding
* components of `r` labelled with `s1` and `s2`, respectively. * components of `r` labelled with `s1` and `s2`, respectively.
*/ */
predicate step(StatePair q, InputSymbol s1, InputSymbol s2, StatePair r) { predicate step(StatePair q, InputSymbol s1, InputSymbol s2, StatePair r) {
exists(State r1, State r2 | step(q, s1, s2, r1, r2) and r = MkStatePair(r1, r2)) exists(State r1, State r2 | step(q, s1, s2, r1, r2) and r = mkStatePair(r1, r2))
} }
/** /**