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euf_seq_plugin: fix identity elimination after merge, activate loop merging, integrate sgraph improvements (#9414)

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* Initial plan

* Initial plan

* Fix identity elimination after merge and activate loop merging in euf_seq_plugin

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Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Apply three ZIPT code review improvements to euf_seq_plugin

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Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Address code review: improve loop-merge defensive code and test variable names

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Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Refactor: extract saturating_add helper, simplify hash-check condition

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Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>
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Copilot 2026-04-29 11:12:00 -07:00 • committed by GitHub
parent f461369ab8
commit 42582c6835
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3 changed files with 134 additions and 5 deletions
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65
src/test/euf_seq_plugin.cpp
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@ -227,6 +227,69 @@ static void test_sgraph_egraph_sync() {
SASSERT(nx->get_root() != ny->get_root());
}
// test seq_plugin: identity elimination fires after a post-registration merge
// When b ~ "" is learned AFTER concat(a, b) is registered, the plugin must
// re-check identity rules and conclude concat(a, b) ~ a.
static void test_seq_plugin_identity_after_merge() {
std::cout << "test_seq_plugin_identity_after_merge\n";
ast_manager m;
reg_decl_plugins(m);
euf::egraph eg(m);
euf::sgraph sg(m, eg);
euf::egraph& g = sg.get_egraph();
seq_util seq(m);
sort_ref str_sort(seq.str.mk_string_sort(), m);
expr_ref a(m.mk_const("a", str_sort), m);
expr_ref b(m.mk_const("b", str_sort), m);
expr_ref empty(seq.str.mk_empty(str_sort), m);
expr_ref ab(seq.str.mk_concat(a, b), m);
// Register concat(a, b) first — at this point b is not yet empty.
auto* nab = get_node(g, seq, ab);
auto* na = g.find(a);
auto* nb = g.find(b);
auto* nempty = get_node(g, seq, empty);
g.propagate();
// Now learn b ~ "" via a merge.
g.merge(nb, nempty, nullptr);
g.propagate();
// After propagation, concat(a, b) should be equivalent to a.
SASSERT(nab->get_root() == na->get_root());
std::cout << g << "\n";
}
// test seq_plugin: loop merging — concat(r{lo1,hi1}, r{lo2,hi2}) = r{lo1+lo2, hi1+hi2}
static void test_seq_plugin_loop_merge() {
std::cout << "test_seq_plugin_loop_merge\n";
ast_manager m;
reg_decl_plugins(m);
euf::egraph eg(m);
euf::sgraph sg(m, eg);
euf::egraph& g = sg.get_egraph();
seq_util seq(m);
sort_ref str_sort(seq.str.mk_string_sort(), m);
expr_ref x(m.mk_const("x", str_sort), m);
expr_ref r(seq.re.mk_to_re(x), m);
// r{2,3} and r{1,2} — bounds are chosen so the merged form r{3,5} is a distinct loop.
expr_ref first_loop(seq.re.mk_loop_proper(r, 2, 3), m);
expr_ref second_loop(seq.re.mk_loop_proper(r, 1, 2), m);
expr_ref expected_merged_loop(seq.re.mk_loop_proper(r, 3, 5), m);
// concat(r{2,3}, r{1,2})
expr_ref concat_loops(seq.re.mk_concat(first_loop, second_loop), m);
auto* nc = get_node(g, seq, concat_loops);
auto* nl35 = get_node(g, seq, expected_merged_loop);
g.propagate();
// After propagation, concat(r{2,3}, r{1,2}) should be equivalent to r{3,5}.
SASSERT(nc->get_root() == nl35->get_root());
std::cout << g << "\n";
}
void tst_euf_seq_plugin() {
s_var = 0; test_sgraph_basic();
s_var = 0; test_sgraph_backtrack();
@ -235,4 +298,6 @@ void tst_euf_seq_plugin() {
s_var = 0; test_seq_plugin_star_merge();
s_var = 0; test_seq_plugin_nullable_absorb();
s_var = 0; test_sgraph_egraph_sync();
s_var = 0; test_seq_plugin_identity_after_merge();
s_var = 0; test_seq_plugin_loop_merge();
}