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LibRegex: Don't repeat the same fork again

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If some state has already been tried, skip over it as it would never
lead to a match regardless.
This fixes performance/memory issues in cases like
/(a+)+b/.exec("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
or
/(a|a?)+b/...

Fixes #2622.
This commit is contained in:
Ali Mohammad Pur
2025-01-15 15:22:01 +01:00
committed by Andreas Kling
parent 7ceeb85ba7
commit cce000d57c
Notes: github-actions[bot] 2025-01-17 09:35:15 +00:00 
Author: https://github.com/alimpfard
Commit: https://github.com/LadybirdBrowser/ladybird/commit/cce000d57c5
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3261
3 changed files with 66 additions and 9 deletions
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30
Libraries/LibRegex/RegexMatcher.cpp
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@@ -468,6 +468,7 @@ bool Matcher<Parser>::execute(MatchInput const& input, MatchState& state, size_t
}
BumpAllocatedLinkedList<MatchState> states_to_try_next;
HashTable<u64> seen_state_hashes;
#if REGEX_DEBUG
size_t recursion_level = 0;
#endif
@@ -545,17 +546,34 @@ bool Matcher<Parser>::execute(MatchInput const& input, MatchState& state, size_t
continue;
case ExecutionResult::Succeeded:
return true;
case ExecutionResult::Failed:
if (!states_to_try_next.is_empty()) {
case ExecutionResult::Failed: {
bool found = false;
while (!states_to_try_next.is_empty()) {
state = states_to_try_next.take_last();
if (auto hash = state.u64_hash(); seen_state_hashes.set(hash) != HashSetResult::InsertedNewEntry) {
dbgln_if(REGEX_DEBUG, "Already seen state, skipping: {}", hash);
continue;
}
found = true;
break;
}
if (found)
continue;
}
return false;
}
case ExecutionResult::Failed_ExecuteLowPrioForks: {
if (states_to_try_next.is_empty()) {
return false;
bool found = false;
while (!states_to_try_next.is_empty()) {
state = states_to_try_next.take_last();
if (auto hash = state.u64_hash(); seen_state_hashes.set(hash) != HashSetResult::InsertedNewEntry) {
dbgln_if(REGEX_DEBUG, "Already seen state, skipping: {}", hash);
continue;
}
found = true;
break;
}
state = states_to_try_next.take_last();
if (!found)
return false;
#if REGEX_DEBUG
++recursion_level;
#endif