From 0daf444cec13f884cd6451a62720611b1815468c Mon Sep 17 00:00:00 2001
From: Jakob Rath <git@jakobrath.eu>
Date: Wed, 4 Jan 2023 11:59:14 +0100
Subject: [PATCH] Actually revert boolean decisions

---
 src/math/polysat/solver.cpp | 12 ++++++++----
 src/math/polysat/solver.h   |  3 +--
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/math/polysat/solver.cpp b/src/math/polysat/solver.cpp
index 60f8f9c12..a00f6a831 100644
--- a/src/math/polysat/solver.cpp
+++ b/src/math/polysat/solver.cpp
@@ -603,6 +603,9 @@ namespace polysat {
                 size_t undefs = count_if(cl, [&](sat::literal lit) { return !m_bvars.is_assigned(lit); });
                 if (undefs >= 2)
                     m_lemmas.push_back(&cl);
+                else {
+                    SASSERT_EQ(undefs, 0);  // if !is_true && undefs == 1 then we missed a propagation.
+                }
             }
         }
 #endif
@@ -883,12 +886,13 @@ namespace polysat {
 
     void solver::revert_decision(pvar v) {
         unsigned max_jump_level = get_level(v) - 1;
-        backjump_and_learn(max_jump_level);
+        backjump_and_learn(max_jump_level, false);
     }
 
     void solver::revert_bool_decision(sat::literal const lit) {
         unsigned max_jump_level = m_bvars.level(lit) - 1;
-        backjump_and_learn(max_jump_level);
+        backjump_and_learn(max_jump_level, true);
+        SASSERT(m_level < max_jump_level || m_bvars.is_false(lit));
     }
 
     std::optional<lemma_score> solver::compute_lemma_score(clause const& lemma) {
@@ -938,7 +942,7 @@ namespace polysat {
         return {{jump_level, branching_factor}};
     }
 
-    void solver::backjump_and_learn(unsigned max_jump_level) {
+    void solver::backjump_and_learn(unsigned max_jump_level, bool force_fallback_lemma) {
         sat::literal_vector narrow_queue = m_conflict.take_narrow_queue();
         clause_ref_vector lemmas = m_conflict.take_lemmas();
 
@@ -963,7 +967,7 @@ namespace polysat {
 
         for (clause* lemma : lemmas)
             appraise_lemma(lemma);
-        if (!best_lemma || best_score.jump_level() > max_jump_level) {
+        if (force_fallback_lemma || !best_lemma || best_score.jump_level() > max_jump_level) {
             // No (good) lemma has been found, so build the fallback lemma from the conflict state.
             lemmas.push_back(m_conflict.build_lemma());
             appraise_lemma(lemmas.back());
diff --git a/src/math/polysat/solver.h b/src/math/polysat/solver.h
index c327c23e8..ef05f12e9 100644
--- a/src/math/polysat/solver.h
+++ b/src/math/polysat/solver.h
@@ -275,8 +275,7 @@ namespace polysat {
         void resolve_conflict();
         void revert_decision(pvar v);
         void revert_bool_decision(sat::literal lit);
-        void backjump_and_learn(unsigned jump_level, clause& lemma);
-        void backjump_and_learn(unsigned max_jump_level);
+        void backjump_and_learn(unsigned max_jump_level, bool force_fallback_lemma);
         std::optional<lemma_score> compute_lemma_score(clause const& lemma);
 
         // activity of variables based on standard VSIDS