diff --git a/cmake/compiler_warnings.cmake b/cmake/compiler_warnings.cmake
index 339c2e6f5..d631ee11a 100644
--- a/cmake/compiler_warnings.cmake
+++ b/cmake/compiler_warnings.cmake
@@ -30,6 +30,8 @@ set(MSVC_WARNINGS "/W3")
 set(GCC_AND_CLANG_WARNINGS_AS_ERRORS
   # https://clang.llvm.org/docs/DiagnosticsReference.html#wodr
   "-Werror=odr"
+  # https://clang.llvm.org/docs/DiagnosticsReference.html#wreturn-type
+  "-Werror=return-type"
 )
 set(GCC_WARNINGS_AS_ERRORS
   ""
diff --git a/src/ast/euf/euf_egraph.h b/src/ast/euf/euf_egraph.h
index f2eedc21d..dd6c9b9da 100644
--- a/src/ast/euf/euf_egraph.h
+++ b/src/ast/euf/euf_egraph.h
@@ -192,8 +192,8 @@ namespace euf {
         enode_vector           m_empty_enodes;
         unsigned               m_num_scopes = 0;
         bool                   m_inconsistent = false;
-        enode                  *m_n1 = nullptr;
-        enode                  *m_n2 = nullptr;
+        enode*                 m_n1 = nullptr;
+        enode*                 m_n2 = nullptr;
         justification          m_justification;
         unsigned               m_new_th_eqs_qhead = 0;
         svector<th_eq>         m_new_th_eqs;
@@ -205,11 +205,11 @@ namespace euf {
         uint64_t               m_congruence_timestamp = 0;
 
         std::vector<std::function<void(enode*,enode*)>> m_on_merge;
-        std::function<void(enode*, enode*)>    m_on_propagate_literal;
-        std::function<void(enode*)>            m_on_make;
-        std::function<void(expr*,expr*,expr*)> m_used_eq;
-        std::function<void(app*,app*)>         m_used_cc;  
-        std::function<void(std::ostream&, void*)>   m_display_justification;
+        std::function<void(enode*,enode*)>              m_on_propagate_literal;
+        std::function<void(enode*)>                     m_on_make;
+        std::function<void(expr*,expr*,expr*)>          m_used_eq;
+        std::function<void(app*,app*)>                  m_used_cc;
+        std::function<void(std::ostream&,void*)>        m_display_justification;
 
         void push_eq(enode* r1, enode* n1, unsigned r2_num_parents) {
             m_updates.push_back(update_record(r1, n1, r2_num_parents));
@@ -279,7 +279,6 @@ namespace euf {
         void merge(enode* n1, enode* n2, void* reason) { merge(n1, n2, justification::external(reason)); }        
         void new_diseq(enode* n);
 
-
         /**
            \brief propagate set of merges. 
            This call may detect an inconsistency. Then inconsistent() is true.
@@ -326,13 +325,13 @@ namespace euf {
         void set_relevant(enode* n);
         void set_default_relevant(bool b) { m_default_relevant = b; }
 
-        void set_on_merge(std::function<void(enode* root,enode* other)>& on_merge) { m_on_merge.push_back(on_merge); }
-        void set_on_propagate(std::function<void(enode* lit,enode* ante)>& on_propagate) { m_on_propagate_literal = on_propagate; }
-        void set_on_make(std::function<void(enode* n)>& on_make) { m_on_make = on_make; }
-        void set_used_eq(std::function<void(expr*,expr*,expr*)>& used_eq) { m_used_eq = used_eq; }
-        void set_used_cc(std::function<void(app*,app*)>& used_cc) { m_used_cc = used_cc; }
-        void set_display_justification(std::function<void (std::ostream&, void*)> & d) { m_display_justification = d; }
-        
+        void set_on_merge(std::function<void(enode* root,enode* other)> on_merge) { m_on_merge.push_back(std::move(on_merge)); }
+        void set_on_propagate(std::function<void(enode* lit,enode* ante)> on_propagate) { m_on_propagate_literal = std::move(on_propagate); }
+        void set_on_make(std::function<void(enode* n)> on_make) { m_on_make = std::move(on_make); }
+        void set_used_eq(std::function<void(expr*,expr*,expr*)> used_eq) { m_used_eq = std::move(used_eq); }
+        void set_used_cc(std::function<void(app*,app*)> used_cc) { m_used_cc = std::move(used_cc); }
+        void set_display_justification(std::function<void(std::ostream&, void*)> d) { m_display_justification = std::move(d); }
+
         void begin_explain();
         void end_explain();
         bool uses_congruence() const { return m_uses_congruence; }
diff --git a/src/test/pdd.cpp b/src/test/pdd.cpp
index 0c9b0f85c..740ae4f2b 100644
--- a/src/test/pdd.cpp
+++ b/src/test/pdd.cpp
@@ -153,12 +153,49 @@ public:
         pdd b = m.mk_var(1);
         pdd c = m.mk_var(2);
         pdd d = m.mk_var(3);
-        pdd p = (a + b)*(c + 3*d) + 2;
-        std::cout << p << "\n";
-        for (auto const& m : p) {
-            std::cout << m << "\n";
-        }
+
+        auto const check = [](unsigned const expected_num_monomials, pdd const& p) {
+            unsigned count = 0;
+            std::cout << p << "\n";
+            for (auto const& m : p) {
+                std::cout << "  " << m << "\n";
+                ++count;
+            }
+            VERIFY_EQ(expected_num_monomials, count);
+        };
+
+        check(9, (a + b + 2)*(c + 3*d + 5) + 2);
+        check(5, (a + b)*(c + 3*d) + 2);
+        check(1, a);
+        check(2, a + 5);
+        check(1, m.mk_val(5));
+        check(0, m.mk_val(0));
     }
+
+    static void linear_iterator() {
+        std::cout << "test linear iterator\n";
+        pdd_manager m(4);
+        pdd a = m.mk_var(0);
+        pdd b = m.mk_var(1);
+        pdd c = m.mk_var(2);
+        pdd d = m.mk_var(3);
+        pdd p = (a + b + 2)*(c + 3*d + 5) + 2;
+        std::cout << p << "\n";
+        for (auto const& m : p.linear_monomials())
+            std::cout << "  " << m << "\n";
+        std::cout << a << "\n";
+        for (auto const& m : a.linear_monomials())
+            std::cout << "  " << m << "\n";
+        pdd one = m.mk_val(5);
+        std::cout << one << "\n";
+        for (auto const& m : one.linear_monomials())
+            std::cout << "  " << m << "\n";
+        pdd zero = m.mk_val(0);
+        std::cout << zero << "\n";
+        for (auto const& m : zero.linear_monomials())
+            std::cout << "  " << m << "\n";
+    }
+
     static void order() {
         std::cout << "order\n";
         pdd_manager m(4);
@@ -693,6 +730,7 @@ void tst_pdd() {
     dd::test::canonize();
     dd::test::reset();
     dd::test::iterator();
+    dd::test::linear_iterator();
     dd::test::order();
     dd::test::order_lm();
     dd::test::mod4_operations();
diff --git a/src/test/rational.cpp b/src/test/rational.cpp
index 711958de5..8fe565c62 100644
--- a/src/test/rational.cpp
+++ b/src/test/rational.cpp
@@ -466,6 +466,28 @@ static void tst12() {
         std::cout << i << ": " << r.get_bit(i) << "\n";
 }
 
+static void tst13() {
+    std::cout << "test13\n";
+    rational const step = rational(1) / rational(3);
+    for (rational r; r < 5000; r += step) {
+        {
+            unsigned k = r.prev_power_of_two();
+            if (r >= 1) {
+                VERIFY(rational::power_of_two(k) <= r);
+                VERIFY(r < rational::power_of_two(k + 1));
+            }
+            else {
+                VERIFY_EQ(k, 0);
+            }
+        }
+        {
+            unsigned k = r.next_power_of_two();
+            VERIFY(r <= rational::power_of_two(k));
+            VERIFY(k == 0 || rational::power_of_two(k - 1) < r);
+        }
+    }
+}
+
 
 void tst_rational() {
     TRACE("rational", tout << "starting rational test...\n";);
@@ -492,4 +514,5 @@ void tst_rational() {
     tst10(true);
     tst10(false);
     tst12();
+    tst13();
 }
diff --git a/src/util/dlist.h b/src/util/dlist.h
index 07aefa97e..4c0e51e58 100644
--- a/src/util/dlist.h
+++ b/src/util/dlist.h
@@ -188,14 +188,14 @@ class dll_iterator {
     dll_iterator(T const* elem, bool first): m_elem(elem), m_first(first) { }
 
 public:
-    static dll_iterator mk_begin(T const* elem) {
-        // Setting first==(bool)elem makes this also work for elem==nullptr;
+    static dll_iterator mk_begin(T const* list) {
+        // Setting first==(bool)list makes this also work for list==nullptr;
         // but we can't implement top-level begin/end for pointers because it clashes with the definition for arrays.
-        return {elem, (bool)elem};
+        return {list, (bool)list};
     }
 
-    static dll_iterator mk_end(T const* elem) {
-        return {elem, false};
+    static dll_iterator mk_end(T const* list) {
+        return {list, false};
     }
 
     using value_type = T;
@@ -232,18 +232,17 @@ public:
     dll_iterator<T> end() const { return dll_iterator<T>::mk_end(m_list); }
 };
 
-
 template < typename T
          , typename U = std::enable_if_t<std::is_base_of_v<dll_base<T>, T>>  // should only match if T actually inherits from dll_base<T>
          >
-dll_iterator<T> begin(T const& elem) {
-    return dll_iterator<T>::mk_begin(&elem);
+dll_iterator<T> begin(T const& list) {
+    return dll_iterator<T>::mk_begin(&list);
 }
 
 template < typename T
          , typename U = std::enable_if_t<std::is_base_of_v<dll_base<T>, T>>  // should only match if T actually inherits from dll_base<T>
          >
-dll_iterator<T> end(T const& elem)
+dll_iterator<T> end(T const& list)
 {
-    return dll_iterator<T>::mk_end(&elem);
+    return dll_iterator<T>::mk_end(&list);
 }
diff --git a/src/util/sat_literal.h b/src/util/sat_literal.h
index aeb23bddd..58088e628 100644
--- a/src/util/sat_literal.h
+++ b/src/util/sat_literal.h
@@ -30,7 +30,7 @@ namespace sat {
 
     typedef svector<bool_var> bool_var_vector;
 
-    const bool_var null_bool_var  = UINT_MAX >> 1;
+    inline constexpr bool_var null_bool_var = UINT_MAX >> 1;
 
     /**
        \brief The literal b is represented by the value 2*b, and
@@ -39,9 +39,7 @@ namespace sat {
     class literal {
         unsigned  m_val;
     public:
-        literal():m_val(null_bool_var << 1) {
-            SASSERT(var() == null_bool_var && !sign());
-        }
+        constexpr literal(): m_val(null_bool_var << 1) { }
 
         explicit literal(bool_var v, bool _sign = false):
             m_val((v << 1) + static_cast<unsigned>(_sign)) {
@@ -49,11 +47,11 @@ namespace sat {
             SASSERT(sign() == _sign);
         }
 
-        bool_var var() const {
+        constexpr bool_var var() const {
             return m_val >> 1;
         }
 
-        bool sign() const {
+        constexpr bool sign() const {
             return m_val & 1ul;
         }
 
@@ -86,7 +84,10 @@ namespace sat {
         friend bool operator!=(literal const & l1, literal const & l2);
     };
 
-    const literal null_literal;
+    inline constexpr literal null_literal;
+    static_assert(null_literal.var() == null_bool_var);
+    static_assert(!null_literal.sign());
+
     using literal_hash = obj_hash<literal>;
 
     inline literal to_literal(unsigned x) { literal l; l.m_val = x; return l; }
diff --git a/src/util/tbv.cpp b/src/util/tbv.cpp
index 017ca0eb7..5048267ad 100644
--- a/src/util/tbv.cpp
+++ b/src/util/tbv.cpp
@@ -142,12 +142,8 @@ void tbv_manager::set(tbv& dst, rational const& r, unsigned hi, unsigned lo) {
         set(dst, r.get_uint64(), hi, lo);
         return;
     }
-    for (unsigned i = 0; i < hi - lo + 1; ++i) {
-        if (bitwise_and(r, rational::power_of_two(i)).is_zero())
-            set(dst, lo + i, BIT_0);
-        else
-            set(dst, lo + i, BIT_1);
-    }
+    for (unsigned i = 0; i < hi - lo + 1; ++i)
+        set(dst, lo + i, r.get_bit(i) ? BIT_1 : BIT_0);
 }
 
 void tbv_manager::set(tbv& dst, tbv const& other, unsigned hi, unsigned lo) {