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parser: improve unreachable state removal

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Currently states are added to the reachable set when they are popped
from the workqueue. This however can result in states being
added to the work queue multiple times and reprocessed.

Eg. If state 2 has the transitions, and 9 is not in the reachable set
  a -> 9
  b -> 9
  c -> 9
  d -> 9
  e -> 3

then 9 will get pushed onto the work 4 times. Even worse other states
on the workqueue may also add state 9 to the workqueue because it has
not been added to the reachable set.

Instead add states to the reachable set when they are added to the
workqueue. The first encounter with a state will result in it being
reachable and all other encounters will see that it already in the set
and not add it to the workqueue.

Signed-off-by: John Johansen <john.johansen@canonical.com>
This commit is contained in:
John Johansen 2025-01-01 16:17:58 -08:00
parent 40e9b2a961
commit 4fb3dbc7b3
1 changed files with 11 additions and 4 deletions
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15
parser/libapparmor_re/hfa.cc
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@ -546,6 +546,14 @@ void DFA::dump_uniq_perms(const char *s)
//TODO: add prompt
}
// make sure work_queue and reachable insertion are always done together
static void push_reachable(set<State *> &reachable, list<State *> &work_queue,
State *state)
{
work_queue.push_back(state);
reachable.insert(state);
}
/* Remove dead or unreachable states */
void DFA::remove_unreachable(optflags const &opts)
{
@ -553,19 +561,18 @@ void DFA::remove_unreachable(optflags const &opts)
/* find the set of reachable states */
reachable.insert(nonmatching);
work_queue.push_back(start);
push_reachable(reachable, work_queue, start);
while (!work_queue.empty()) {
State *from = work_queue.front();
work_queue.pop_front();
reachable.insert(from);
if (from->otherwise != nonmatching &&
reachable.find(from->otherwise) == reachable.end())
work_queue.push_back(from->otherwise);
push_reachable(reachable, work_queue, from->otherwise);
for (StateTrans::iterator j = from->trans.begin(); j != from->trans.end(); j++) {
if (reachable.find(j->second) == reachable.end())
work_queue.push_back(j->second);
push_reachable(reachable, work_queue, j->second);
}
}