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add comments, fix a bug in early return for min-term version of expansion

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2026-04-21 16:49:29 +02:00
parent 3beeadfe51
commit 40122b494c
1 changed files with 20 additions and 15 deletions
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35
src/smt/seq/seq_nielsen.cpp
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@ -935,7 +935,7 @@ namespace seq {
// pass 3: power simplification (mirrors ZIPT's LcpCompression +
// SimplifyPowerElim + SimplifyPowerSingle)
for (str_eq& eq : m_str_eq) {
SASSERT(eq.m_lhs && eq.m_rhs);
SASSERT(eq.well_formed());
if (eq.is_trivial())
continue;
@ -971,7 +971,7 @@ namespace seq {
// - If p ≤ c: pow_side := rest_pow, other_side := w^(c-p) · rest_other
// - If c ≤ p: pow_side := w^(p-c) · rest_pow, other_side := rest_other
// - If p = c: both reduce completely (handled by both conditions above).
SASSERT(eq.m_lhs && eq.m_rhs);
SASSERT(eq.well_formed());
bool comm_changed = false;
for (int side = 0; side < 2 && !comm_changed; ++side) {
euf::snode*& pow_side = side == 0 ? eq.m_lhs : eq.m_rhs;
@ -1047,7 +1047,7 @@ namespace seq {
// power of the same base, cancel the common power prefix.
// (Subsumed by 3c for many cases, but handles same-base-power
// pairs that CommPower may miss when both leading tokens are powers.)
SASSERT(eq.m_lhs && eq.m_rhs);
SASSERT(eq.well_formed());
for (unsigned od = 0; od < 2 && !changed; ++od) {
bool fwd = (od == 0);
euf::snode* lh = dir_token(eq.m_lhs, fwd);
@ -1117,7 +1117,7 @@ namespace seq {
// consume concrete characters from str_mem via Brzozowski derivatives
// in both directions (left-to-right, then right-to-left), mirroring ZIPT.
for (str_mem& mem : m_str_mem) {
SASSERT(mem.m_str && mem.m_regex);
SASSERT(mem.well_formed());
if (mem.is_primitive())
continue;
for (unsigned od = 0; od < 2; ++od) {
@ -1145,7 +1145,7 @@ namespace seq {
// consume symbolic characters via uniform derivatives
for (str_mem& mem : m_str_mem) {
SASSERT(mem.m_str && mem.m_regex);
SASSERT(mem.well_formed());
if (mem.is_primitive())
continue;
while (mem.m_str && !mem.m_str->is_empty()) {
@ -1198,7 +1198,7 @@ namespace seq {
// expensive exploration. Mirrors ZIPT NielsenNode.CheckRegexWidening.
SASSERT(m_graph.m_seq_regex);
for (str_mem const& mem : m_str_mem) {
SASSERT(mem.m_str && mem.m_regex);
SASSERT(mem.well_formed());
if (mem.is_primitive())
continue;
dep_tracker dep = mem.m_dep;
@ -2462,7 +2462,7 @@ namespace seq {
str_mem const*& mem_out,
bool& fwd) const {
for (str_mem const& mem : node->str_mems()) {
SASSERT(mem.m_str && mem.m_regex && !mem.is_trivial(node));
SASSERT(mem.well_formed() && !mem.is_trivial(node));
for (unsigned od = 0; od < 2; ++od) {
bool local_fwd = (od == 0);
@ -2938,7 +2938,7 @@ namespace seq {
};
for (str_mem const& mem : node->str_mems()) {
SASSERT(mem.m_str && mem.m_regex);
SASSERT(mem.well_formed());
if (mem.is_primitive() || !mem.m_regex->is_classical())
continue;
@ -3008,8 +3008,8 @@ namespace seq {
}
bool nielsen_graph::fire_gpower_intro(
nielsen_node* node, str_eq const& eq,
euf::snode* var, euf::snode_vector const& ground_prefix_orig, bool fwd) {
nielsen_node* node, str_eq const& eq,
euf::snode* var, euf::snode_vector const& ground_prefix_orig, bool fwd) {
// Compress repeated patterns in the ground prefix (mirrors ZIPT's LcpCompressionFull).
// E.g., [a,b,a,b] has minimal period 2 → use [a,b] as the power base.
@ -3161,7 +3161,7 @@ namespace seq {
auto const& eqs = node->str_eqs();
for (unsigned eq_idx = 0; eq_idx < eqs.size(); ++eq_idx) {
str_eq const& eq = eqs[eq_idx];
SASSERT(eq.m_lhs && eq.m_rhs);
SASSERT(eq.well_formed());
if (eq.is_trivial())
continue;
@ -3298,7 +3298,7 @@ namespace seq {
bool nielsen_graph::apply_regex_if_split(nielsen_node *node) {
for (str_mem const &mem : node->str_mems()) {
SASSERT(mem.m_str && mem.m_regex);
SASSERT(mem.well_formed());
expr *r_expr = mem.m_regex->get_expr();
expr_ref c(m), th(m), el(m);
@ -3380,7 +3380,7 @@ namespace seq {
bool nielsen_graph::apply_regex_var_split(nielsen_node* node) {
for (str_mem const& mem : node->str_mems()) {
SASSERT(mem.m_str && mem.m_regex);
SASSERT(mem.well_formed());
if (mem.is_primitive())
continue;
euf::snode* first = mem.m_str->first();
@ -3439,9 +3439,14 @@ namespace seq {
fresh_char = m_sg.mk(char_expr);
}
else {
th_rewriter rw(m);
// for variables at mod_count 0 and other terms, use symbolic (str.len expr)
return get_or_create_char_var(first);
// NSB rewview:
// it really is seq.nth (length-of-prefix that was chopped of for first)
// assume len(x) contains the expression for the current length of x,
// then the suffix where the current x is located is at str.len(x) - len(x)
// (seq.nth x (- (str.len x) len(x))
//
fresh_char = m_sg.mk(get_or_create_char_var(first));
}
euf::snode* replacement = m_sg.mk_concat(fresh_char, first);