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translate, simplify: limit containment checks of n-ary operators

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Fixes #521.

* spot/tl/simplify.cc, spot/tl/simplify.hh,
spot/twaalgos/translate.cc, spot/twaalgos/translate.hh: Add an option
to limit automata-based implication checks of n-ary operators when too
many operands are used.  Defaults to 16.
* bin/spot-x.cc, NEWS, doc/tl/tl.tex: Document it.
* tests/core/bdd.test: Disable the limit for this test.
This commit is contained in:
Alexandre Duret-Lutz 2022-11-15 17:27:10 +01:00
parent f2c65ea557
commit 843c4cdb91
8 changed files with 33 additions and 11 deletions
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5
NEWS
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@ -6,6 +6,11 @@ New in spot 2.11.2.dev (not yet released)
slower than necessary because the translator was configured to
favor determinism unnecessarily. (Issue #521.)
- Automata-based implication checks for f&g and f|g could be
very slow when those n-ary operator had two many arguments.
They have been limited to 16 operands, but this value can be changed
with option -x tls-max-ops=N. (Issue #521 too.)
New in spot 2.11.2 (2022-10-26)
Command-line tools:

3
bin/spot-x.cc
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@ -47,6 +47,9 @@ depends on the --low, --medium, or --high settings.") },
{ DOC("tls-max-states",
"Maximum number of states of automata involved in automata-based \
implication checks for formula simplifications. Defaults to 64.") },
{ DOC("tls-max-ops",
"Maximum number of operands in n-ary opertors (or, and) on which \
implication-based simplifications are attempted. Defaults to 16.") },
{ nullptr, 0, nullptr, 0, "Translation options:", 0 },
{ DOC("ltl-split", "Set to 0 to disable the translation of automata \
as product or sum of subformulas.") },

6
doc/tl/tl.tex
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@ -1926,6 +1926,12 @@ Many of the above rules were collected from the
literature~\cite{somenzi.00.cav,tauriainen.03.tr,babiak.12.tacas} and
sometimes generalized to support operators such as $\M$ and $\W$.
The first six rules, about n-ary operators $\AND$ and $\OR$, are
implemented for $n$ operands by testing each operand against all
other. To prevent the complexity to escalate, this is only performed
with up to 16 operands. That value can be changed in
``\verb|tl_simplifier_options::containment_max_ops|''.
The following rules mix implication-based checks with formulas that
are pure eventualities ($e$) or that are purely universal ($u$).

10
spot/tl/simplify.cc
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@ -2507,8 +2507,11 @@ namespace spot
unsigned mos = mo.size();
if ((opt_.synt_impl | opt_.containment_checks)
&& mo.is(op::Or, op::And))
&& mo.is(op::Or, op::And)
&& (opt_.containment_max_ops == 0
|| opt_.containment_max_ops >= mos))
{
bool is_and = mo.is(op::And);
// Do not merge these two loops, as rewritings from the
// second loop could prevent rewritings from the first one
// to trigger.
@ -2520,7 +2523,6 @@ namespace spot
// if fo => !fi, then fi & fo = false
// if !fi => fo, then fi | fo = true
// if !fo => fi, then fi | fo = true
bool is_and = mo.is(op::And);
if (c_->implication_neg(fi, fo, is_and)
|| c_->implication_neg(fo, fi, is_and))
return recurse(is_and ? formula::ff() : formula::tt());
@ -2531,8 +2533,8 @@ namespace spot
formula fo = mo.all_but(i);
// if fi => fo, then fi | fo = fo
// if fo => fi, then fi & fo = fo
if ((mo.is(op::Or) && c_->implication(fi, fo))
|| (mo.is(op::And) && c_->implication(fo, fi)))
if (((!is_and) && c_->implication(fi, fo))
|| (is_and && c_->implication(fo, fi)))
{
// We are about to pick fo, but hold on!
// Maybe we actually have fi <=> fo, in

5
spot/tl/simplify.hh
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@ -1,5 +1,5 @@
// -*- coding: utf-8 -*-
// Copyright (C) 2011-2017, 2019, 2020 Laboratoire de Recherche et Developpement
// Copyright (C) 2011-2022 Laboratoire de Recherche et Developpement
// de l'Epita (LRDE).
//
// This file is part of Spot, a model checking library.
@ -96,6 +96,9 @@ namespace spot
// If greater than 0, bound the number of states used by automata
// in containment checks.
unsigned containment_max_states = 0;
// If greater than 0, maximal number of terms in a multop to perform
// containment checks on this multop.
unsigned containment_max_ops = 16;
};
// fwd declaration to hide technical details.

5
spot/twaalgos/translate.cc
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@ -62,8 +62,8 @@ namespace spot
gf_guarantee_set_ = true;
}
ltl_split_ = opt->get("ltl-split", 1);
int tls_max_states = opt->get("tls-max-states", 64);
tls_max_states_ = std::max(0, tls_max_states);
tls_max_states_ = std::max(0, opt->get("tls-max-states", 64));
tls_max_ops_ = std::max(0, opt->get("tls-max-ops", 16));
exprop_ = opt->get("exprop", -1);
branchpost_ = opt->get("branch-post", -1);
}
@ -72,6 +72,7 @@ namespace spot
{
tl_simplifier_options options(false, false, false);
options.containment_max_states = tls_max_states_;
options.containment_max_ops = tls_max_ops_;
switch (level_)
{
case High:

3
spot/twaalgos/translate.hh
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@ -155,7 +155,8 @@ namespace spot
bool gf_guarantee_set_ = false;
bool ltl_split_;
int branchpost_ = -1;
unsigned tls_max_states_ = 0;
unsigned tls_max_states_ = 64;
unsigned tls_max_ops_ = 16;
int exprop_;
const option_map* opt_;
};

7
tests/core/bdd.test
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@ -24,20 +24,21 @@ set -e
# Make sure that setting the SPOT_BDD_TRACE envvar actually does
# something.
genltl --kr-n=3 |
SPOT_BDD_TRACE=1 ltl2tgba -x tls-max-states=0 -D >out 2>err
SPOT_BDD_TRACE=1 ltl2tgba -x tls-max-states=0,tls-max-ops=0 -D >out 2>err
cat err
grep spot: out && exit 1
grep 'spot: BDD package initialized' err
# This value below, which is the number of time we need to garbage
# collect might change if we improve the tool or change the way BuDDy
# is initialized.
test 2 = `grep -c 'spot: BDD GC' err`
test 15 = `grep -c 'spot: BDD GC' err`
# Minimal size for this automaton.
# See also https://www.lrde.epita.fr/dload/spot/mochart10-fixes.pdf
test "2240,4214" = `autfilt --stats=%s,%e out`
# With the default value of tls-max-states, no GC is needed
genltl --kr-n=3 | SPOT_BDD_TRACE=1 ltl2tgba -D --stats=%s,%e >out 2>err
genltl --kr-n=3 |
SPOT_BDD_TRACE=1 ltl2tgba -D -x tls-max-ops=0 --stats=%s,%e >out 2>err
cat err
grep 'spot: BDD package initialized' err
test 0 = `grep -c 'spot: BDD GC' err`