Commit 6e8170e3 authored by Alexandre Duret-Lutz's avatar Alexandre Duret-Lutz

degen: do not mark initial trivial SCCs as accepting

Doing so is not wrong, but it's superfluous, and the extra accepting
state will cause additional work in emptiness checks based on NDFS.
Report from Jan Strejček.

* src/tgbaalgos/degen.cc: Here.
* src/tgbatest/degenid.test: Add a test case.
parent 54a8ce50
......@@ -72,6 +72,7 @@ namespace spot
acc_cond::mark_t common = a_->acc().all_sets();
acc_cond::mark_t union_ = 0U;
bool has_acc_self_loop = false;
bool seen = false;
for (auto& t: a_->out(s))
{
// Ignore transitions that leave the SCC of s.
......@@ -85,7 +86,10 @@ namespace spot
// an accepting self-loop?
has_acc_self_loop |= (t.dst == s) && a_->acc().accepting(t.acc);
seen = true;
}
if (!seen)
common = 0U;
cache_[s] = std::make_tuple(common, union_, has_acc_self_loop);
}
......
......@@ -222,3 +222,35 @@ EOF
run 0 ../../bin/dstar2tgba in.dra -BD --stats=%s > out.stat
test 6 = "`cat out.stat`"
# Only one state should be accepting. In spot 1.2.x an initial state
# in a trivial SCC was marked as accepting: this is superfluous.
../../bin/ltl2tgba -BH 'a & GFb & GFc' > out
cat out
cat >expected<<EOF
HOA: v1
name: "a & G(Fb & Fc)"
States: 4
Start: 0
AP: 3 "a" "b" "c"
acc-name: Buchi
Acceptance: 1 Inf(0)
properties: trans-labels explicit-labels state-acc deterministic
properties: stutter-invariant
--BODY--
State: 0
[0] 1
State: 1 {0}
[1&2] 1
[!1&2] 2
[!2] 3
State: 2
[1] 1
[!1] 2
State: 3
[1&2] 1
[!1&2] 2
[!2] 3
--END--
EOF
diff out expected
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